Proton-exchange membrane fuel cell

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https://en.wikipedia.org/wiki/Proton-exchange_membrane_fuel_cell 

 

Diagram of a PEM fuel cell

Proton-exchange membrane fuel cells (PEMFC), also known as polymer electrolyte membrane (PEM) fuel cells, are a type of fuel cell being developed mainly for transport applications, as well as for stationary fuel-cell applications and portable fuel-cell applications. Their distinguishing features include lower temperature/pressure ranges (50 to 100 °C) and a special proton-conducting polymer electrolyte membrane. PEMFCs generate electricity and operate on the opposite principle to PEM electrolysis, which consumes electricity. They are a leading candidate to replace the aging alkaline fuel-cell technology, which was used in the Space Shuttle.

Science

PEMFCs are built out of membrane electrode assemblies (MEA) which include the electrodes, electrolyte, catalyst, and gas diffusion layers. An ink of catalyst, carbon, and electrode are sprayed or painted onto the solid electrolyte and carbon paper is hot pressed on either side to protect the inside of the cell and also act as electrodes. The pivotal part of the cell is the triple phase boundary (TPB) where the electrolyte, catalyst, and reactants mix and thus where the cell reactions actually occur. Importantly, the membrane must not be electrically conductive so the half reactions do not mix. Operating temperatures above 100 °C are desired so the water byproduct becomes steam and water management becomes less critical in cell design.

Reactions

Further information: Fuel cell

A proton exchange membrane fuel cell transforms the chemical energy liberated during the electrochemical reaction of hydrogen and oxygen to electrical energy, as opposed to the direct combustion of hydrogen and oxygen gases to produce thermal energy.

A stream of hydrogen is delivered to the anode side of the MEA. At the anode side it is catalytically split into protons and electrons. This oxidation half-cell reaction or hydrogen oxidation reaction (HOR) is represented by:

At the anode:

${\displaystyle \mathrm {H} _{2}\rightarrow \mathrm {2H} ^{+}+\mathrm {2e} ^{-}}$

${\displaystyle E^{\circ }=0\,\mathrm {V} \,\,\,{\frac {\mathrm {d} E^{\circ }}{\mathrm {d} T}}=0\,\mathrm {mV\,K^{-1}} }$

${\displaystyle \left(1\right)}$

The newly formed protons permeate through the polymer electrolyte membrane to the cathode side. The electrons travel along an external load circuit to the cathode side of the MEA, thus creating the current output of the fuel cell. Meanwhile, a stream of oxygen is delivered to the cathode side of the MEA. At the cathode side oxygen molecules react with the protons permeating through the polymer electrolyte membrane and the electrons arriving through the external circuit to form water molecules. This reduction half-cell reaction or oxygen reduction reaction (ORR) is represented by:

At the cathode:

${\displaystyle {\frac {1}{2}}\mathrm {O} _{2}+{2\mathrm {H} }^{+}+\mathrm {2e} ^{-}\rightarrow \mathrm {H} _{2}\mathrm {O} }$

${\displaystyle E^{\circ }=1.2291\,\mathrm {V} \,\,\,{\frac {\mathrm {d} E^{\circ }}{\mathrm {d} T}}=-0.8456\,\mathrm {mV\,K^{-1}} }$

${\displaystyle \left(2\right)}$

Overall reaction:

${\displaystyle \mathrm {H} _{2}+{\frac {1}{2}}\mathrm {O} _{2}\rightarrow \mathrm {H} _{2}\mathrm {O} }$

${\displaystyle E^{\circ }=1.2291\,\mathrm {V} \,\,\,{\frac {\mathrm {d} E^{\circ }}{\mathrm {d} T}}=-0.8456\,\mathrm {mV\,K^{-1}} }$

${\displaystyle \left(3\right)}$

The reversible reaction is expressed in the equation and shows the reincorporation of the hydrogen protons and electrons together with the oxygen molecule and the formation of one water molecule. The potentials in each case are given with respect to the standard hydrogen electrode.

Polymer electrolyte membrane

Main article: Polymer electrolyte membrane

SEM micrograph of a PEMFC MEA cross-section with a non-precious metal catalyst cathode and Pt/C anode. False colors applied for clarity.

 

MEA fabrication methods for PEMFC

To function, the membrane must conduct hydrogen ions (protons) but not electrons as this would in effect "short circuit" the fuel cell. The membrane must also not allow either gas to pass to the other side of the cell, a problem known as gas crossover. Finally, the membrane must be resistant to the reducing environment at the cathode as well as the harsh oxidative environment at the anode.

Splitting of the hydrogen molecule is relatively easy by using a platinum catalyst. Unfortunately however, splitting the oxygen molecule is more difficult, and this causes significant electric losses. An appropriate catalyst material for this process has not been discovered, and platinum is the best option.

Strengths

The PEMFC is a prime candidate for vehicle and other mobile applications of all sizes down to mobile phones, because of its compactness.

Weaknesses

Fuel Cells based on PEM still have many issues:

1. Water management

Water management is crucial to performance: if water is evaporated too slowly, it will flood the membrane and the accumulation of water inside of field flow plate will impede the flow of oxygen into the fuel cell, but if water evaporates too fast, the membrane will dry and the resistance across it increases. Both cases will cause damage to stability and power output. Water management is a very difficult subject in PEM systems, primarily because water in the membrane is attracted toward the cathode of the cell through polarization.

A wide variety of solutions for managing the water exist including integration of an electroosmotic pump.

Another innovative method to resolve the water recirculation problem is the 3D fine mesh flow field design used in the Toyota Mirai, 2014. Conventional design of FC stack recirculates water from the air outlet to the air inlet through a humidifier with a straight channel and porous metal flow fields. The flow field is a structure made up of a rib and channels. However, the rib partially covers the gas diffusion layer (GDL) and the resultant gas-transport distance is longer than the inter-channel distance. Furthermore, the contact pressure between the GDL and the rib also compresses the GDL, making its thickness non-uniform across the rib and channel. The large width and non-uniform thickness of the rib will increase potential for water vapor to accumulate and the oxygen will be compromised. As a result, oxygen will be impeded to diffuse into catalyst layer, leading to nonuniform power generation in the FC.

This new design enabled the first FC stack functions without a humidifying system meanwhile overcoming water recirculation issues and achieving high power output stability. The 3D micro lattice allows more pathways for gas flow; therefore, it promotes airflow toward membrane electrode and gas diffusion layer assembly (MEGA) and promotes O2 diffusion to the catalyst layer. Unlike conventional flow fields, the 3D micro-lattices in the complex field, which act as baffles and induce frequent micro-scale interfacial flux between the GDL and flow-fields^[53]. Due to this repeating micro-scale convective flow, oxygen transport to catalyst layer (CL) and liquid water removal from GDL is significantly enhanced. The generated water is quickly drawn out through the flow field, preventing accumulation within the pores. As a result, the power generation from this flow field is uniform across the cross-section and self-humidification is enabled.

2. Vulnerability of the Catalyst

The platinum catalyst on the membrane is easily poisoned by carbon monoxide, which is often present in product gases formed by methane reforming (no more than one part per million is usually acceptable). This generally necessitates the use of the water gas shift reaction to eliminate CO from product gases and form more hydrogen. Additionally, the membrane is sensitive to the presences of metal ions, which may impair proton conduction mechanisms and can be introduced by corrosion of metallic bipolar plates, metallic components in the fuel cell system or from contaminants in the fuel/oxidant.

PEM systems that use reformed methanol were proposed, as in Daimler Chrysler Necar 5; reforming methanol, i.e. making it react to obtain hydrogen, is however a very complicated process, that also requires purification from the carbon monoxide the reaction produces. A platinum-ruthenium catalyst is necessary as some carbon monoxide will unavoidably reach the membrane. The level should not exceed 10 parts per million. Furthermore, the start-up times of such a reformer reactor are of about half an hour. Alternatively, methanol, and some other biofuels can be fed to a PEM fuel cell directly without being reformed, thus making a direct methanol fuel cell (DMFC). These devices operate with limited success.

3. Limitation of Operating Temperature

The most commonly used membrane is Nafion by Chemours, which relies on liquid water humidification of the membrane to transport protons. This implies that it is not feasible to use temperatures above 80 to 90 °C, since the membrane would dry. Other, more recent membrane types, based on polybenzimidazole (PBI) or phosphoric acid, can reach up to 220 °C without using any water management (see also High Temperature Proton Exchange Membrane fuel cell, HT-PEMFC): higher temperature allow for better efficiencies, power densities, ease of cooling (because of larger allowable temperature differences), reduced sensitivity to carbon monoxide poisoning and better controllability (because of absence of water management issues in the membrane); however, these recent types are not as common. PBI can be doped with phosphoric or sulfuric acid and the conductivity scales with amount of doping and temperature. At high temperatures, it is difficult to keep Nafion hydrated, but this acid doped material does not use water as a medium for proton conduction. It also exhibits better mechanical properties, higher strength, than Nafion and is cheaper. However, acid leaching is a considerable issue and processing, mixing with catalyst to form ink, has proved tricky. Aromatic polymers, such as PEEK, are far cheaper than Teflon (PTFE and backbone of Nafion) and their polar character leads to hydration that is less temperature dependent than Nafion. However, PEEK is far less ionically conductive than Nafion and thus is a less favorable electrolyte choice. Recently, protic ionic liquids and protic organic ionic plastic crystals have been shown as promising alternative electrolyte materials for high temperature (100–200 °C) PEMFCs.

Electrodes

An electrode typically consists of carbon support, Pt particles, Nafion ionomer, and/or Teflon binder. The carbon support functions as an electrical conductor; the Pt particles are reaction sites; the ionomer provides paths for proton conduction, and the Teflon binder increases the hydrophobicity of the electrode to minimize potential flooding. In order to enable the electrochemical reactions at the electrodes, protons, electrons and the reactant gases (hydrogen or oxygen) must gain access to the surface of the catalyst in the electrodes, while the product water, which can be in either liquid or gaseous phase, or both phases, must be able to permeate from the catalyst to the gas outlet. These properties are typically realized by porous composites of polymer electrolyte binder (ionomer) and catalyst nanoparticles supported on carbon particles. Typically platinum is used as the catalyst for the electrochemical reactions at the anode and cathode, while nanoparticles realize high surface to weight ratios (as further described below) reducing the amount of the costly platinum. The polymer electrolyte binder provides the ionic conductivity, while the carbon support of the catalyst improves the electric conductivity and enables low platinum metal loading. The electric conductivity in the composite electrodes is typically more than 40 times higher as the proton conductivity.

Gas diffusion layer

The GDL electrically connects the catalyst and current collector. It must be porous, electrically conductive, and thin. The reactants must be able to reach the catalyst, but conductivity and porosity can act as opposing forces. Optimally, the GDL should be composed of about one third Nafion or 15% PTFE. The carbon particles used in the GDL can be larger than those employed in the catalyst because surface area is not the most important variable in this layer. GDL should be around 15–35 µm thick to balance needed porosity with mechanical strength. Often, an intermediate porous layer is added between the GDL and catalyst layer to ease the transitions between the large pores in the GDL and small porosity in the catalyst layer. Since a primary function of the GDL is to help remove water, a product, flooding can occur when water effectively blocks the GDL. This limits the reactants ability to access the catalyst and significantly decreases performance. Teflon can be coated onto the GDL to limit the possibility of flooding. Several microscopic variables are analyzed in the GDLS such as: porosity, tortuosity and permeability. These variables have incidence over the behavior of the fuel cells.

Efficiency

The maximal theoretical efficiency applying the Gibbs free energy equation ΔG = −237.13 kJ/mol and using the heating value of Hydrogen (ΔH = −285.84 kJ/mol) is 83% at 298 K.

${\displaystyle \eta ={\frac {\Delta G}{\Delta H}}=1-{\frac {T\Delta S}{\Delta H}}}$

The practical efficiency of a PEMs is in the range of 50–60% . Main factors that create losses are:

• Activation losses
• Ohmic losses
• Mass transport losses

Metal-organic frameworks

Metal-organic frameworks (MOFs) are a relatively new class of porous, highly crystalline materials that consist of metal nodes connected by organic linkers. Due to the simplicity of manipulating or substituting the metal centers and ligands, there are a virtually limitless number of possible combinations, which is attractive from a design standpoint. MOFs exhibit many unique properties due to their tunable pore sizes, thermal stability, high volume capacities, large surface areas, and desirable electrochemical characteristics. Among their many diverse uses, MOFs are promising candidates for clean energy applications such as hydrogen storage, gas separations, supercapacitors, Li-ion batteries, solar cells, and fuel cells. Within the field of fuel cell research, MOFs are being studied as potential electrolyte materials and electrode catalysts that could someday replace traditional polymer membranes and Pt catalysts, respectively.

As electrolyte materials, the inclusion of MOFs seems at first counter-intuitive. Fuel cell membranes generally have low porosity to prevent fuel crossover and loss of voltage between the anode and cathode. Additionally, membranes tend to have low crystallinity because the transport of ions is more favorable in disordered materials. On the other hand, pores can be filled with additional ion carriers that ultimately enhance the ionic conductivity of the system and high crystallinity makes the design process less complex.

The general requirements of a good electrolyte for PEMFCs are: high proton conductivity (>10⁻² S/cm for practical applications) to enable proton transport between electrodes, good chemical and thermal stability under fuel cell operating conditions (environmental humidity, variable temperatures, resistance to poisonous species, etc.), low cost, ability to be processed into thin-films, and overall compatibility with other cell components. While polymeric materials are currently the preferred choice of proton-conducting membrane, they require humidification for adequate performance and can sometimes physically degrade due to hydrations effects, thereby causing losses of efficiency. As mentioned, Nafion is also limited by a dehydration temperature of < 100 °C, which can lead to slower reaction kinetics, poor cost efficiency, and CO poisoning of Pt electrode catalysts. Conversely, MOFs have shown encouraging proton conductivities in both low and high temperature regimes as well as over a wide range of humidity conditions. Below 100 °C and under hydration, the presence of hydrogen bonding and solvent water molecules aid in proton transport, whereas anhydrous conditions are suitable for temperatures above 100 °C. MOFs also have the distinct advantage of exhibiting proton conductivity by the framework itself in addition to the inclusion of charge carries (i.e., water, acids, etc.) into their pores.

A low temperature example is work by Kitagawa, et al. who used a two-dimensional oxalate-bridged anionic layer framework as the host and introduced ammonium cations and adipic acid molecules into the pores to increase proton concentration. The result was one of the first instances of a MOF showing “superprotonic” conductivity (8 × 10⁻³ S/cm) at 25 °C and 98% relative humidity (RH). They later found that increasing the hydrophilic nature of the cations introduced into the pores could enhance proton conductivity even more. In this low temperature regime that is dependent on degree of hydration, it has also been shown that proton conductivity is heavily dependent on humidity levels.

A high temperature anhydrous example is PCMOF2, which consists of sodium ions coordinated to a trisulfonated benzene derivative. To improve performance and allow for higher operating temperatures, water can be replaced as the proton carrier by less volatile imidazole or triazole molecules within the pores. The maximum temperature achieved was 150 °C with an optimum conductivity of 5 × 10⁻⁴ S/cm, which is lower than other current electrolyte membranes. However, this model holds promise for its temperature regime, anhydrous conditions, and ability to control the quantity of guest molecules within the pores, all of which allowed for the tunability of proton conductivity. Additionally, the triazole-loaded PCMOF2 was incorporated into a H₂/air membrane-electrode assembly and achieved an open circuit voltage of 1.18 V at 100 °C that was stable for 72 hours and managed to remain gas tight throughout testing. This was the first instance that proved MOFs could actually be implemented into functioning fuel cells, and the moderate potential difference showed that fuel crossover due to porosity was not an issue.

To date, the highest proton conductivity achieved for a MOF electrolyte is 4.2 × 10⁻² S/cm at 25 °C under humid conditions (98% RH), which is competitive with Nafion. Some recent experiments have even successfully produced thin-film MOF membranes instead of the traditional bulk samples or single crystals, which is crucial for their industrial applicability. Once MOFs are able to consistently achieve sufficient conductivity levels, mechanical strength, water stability, and simple processing, they have the potential to play an important role in PEMFCs in the near future.

MOFs have also been targeted as potential replacements of platinum group metal (PGM) materials for electrode catalysts, although this research is still in the early stages of development. In PEMFCs, the oxygen reduction reaction (ORR) at the Pt cathode is significantly slower than the fuel oxidation reaction at the anode, and thus non-PGM and metal-free catalysts are being investigated as alternatives. The high volumetric density, large pore surface areas, and openness of metal-ion sites in MOFs make them ideal candidates for catalyst precursors. Despite promising catalytic abilities, the durability of these proposed MOF-based catalysts is currently less than desirable and the ORR mechanism in this context is still not completely understood.

Catalyst research

Much of the current research on catalysts for PEM fuel cells can be classified as having one of the following main objectives:

1. to obtain higher catalytic activity than the standard carbon-supported platinum particle catalysts used in current PEM fuel cells
2. to reduce the poisoning of PEM fuel cell catalysts by impurity gases
3. to reduce the cost of the fuel cell due to use of platinum-based catalysts
4. to enhance the ORR activity of platinum group metal-free electrocatalysts

Examples of these approaches are given in the following sections.

Increasing catalytic activity

As mentioned above, platinum is by far the most effective element used for PEM fuel cell catalysts, and nearly all current PEM fuel cells use platinum particles on porous carbon supports to catalyze both hydrogen oxidation and oxygen reduction. However, due to their high cost, current Pt/C catalysts are not feasible for commercialization. The U.S. Department of Energy estimates that platinum-based catalysts will need to use roughly four times less platinum than is used in current PEM fuel cell designs in order to represent a realistic alternative to internal combustion engines. Consequently, one main goal of catalyst design for PEM fuel cells is to increase the catalytic activity of platinum by a factor of four so that only one-fourth as much of the precious metal is necessary to achieve similar performance.

One method of increasing the performance of platinum catalysts is to optimize the size and shape of the platinum particles. Decreasing the particles’ size alone increases the total surface area of catalyst available to participate in reactions per volume of platinum used, but recent studies have demonstrated additional ways to make further improvements to catalytic performance. For example, one study reports that high-index facets of platinum nanoparticles (that is Miller indexes with large integers, such as Pt (730)) provide a greater density of reactive sites for oxygen reduction than typical platinum nanoparticles.

Since the most common and effective catalyst, platinum, is extremely expensive, alternative processing is necessary to maximize surface area and minimize loading. Deposition of nanosized Pt particles onto carbon powder (Pt/C) provides a large Pt surface area while the carbon allows for electrical connection between the catalyst and the rest of the cell. Platinum is so effective because it has high activity and bonds to the hydrogen just strongly enough to facilitate electron transfer but not inhibit the hydrogen from continuing to move around the cell. However, platinum is less active in the cathode oxygen reduction reaction. This necessitates the use of more platinum, increasing the cell's expense and thus feasibility. Many potential catalyst choices are ruled out because of the extreme acidity of the cell.

The most effective ways of achieving the nanoscale Pt on carbon powder, which is currently the best option, are through vacuum deposition, sputtering, and electrodeposition. The platinum particles are deposited onto carbon paper that is permeated with PTFE. However, there is an optimal thinness to this catalyst layer, which limits the lower cost limit. Below 4 nm, Pt will form islands on the paper, limiting its activity. Above this thickness, the Pt will coat the carbon and be an effective catalyst. To further complicate things, Nafion cannot be infiltrated beyond 10 um, so using more Pt than this is an unnecessary expense. Thus the amount and shape of the catalyst is limited by the constraints of other materials.

A second method of increasing the catalytic activity of platinum is to alloy it with other metals. For example, it was recently shown that the Pt₃Ni(111) surface has a higher oxygen reduction activity than pure Pt(111) by a factor of ten. The authors attribute this dramatic performance increase to modifications to the electronic structure of the surface, reducing its tendency to bond to oxygen-containing ionic species present in PEM fuel cells and hence increasing the number of available sites for oxygen adsorption and reduction.

Further efficiencies can be realized using an Ultrasonic nozzle to apply the platinum catalyst to the electrolyte layer or to carbon paper under atmospheric conditions resulting in high efficiency spray. Studies have shown that due to the uniform size of the droplets created by this type of spray, due to the high transfer efficiency of the technology, due to the non-clogging nature of the nozzle and finally due to the fact that the ultrasonic energy de-agglomerates the suspension just before atomization, fuel cells MEA's manufactured this way have a greater homogeneity in the final MEA, and the gas flow through the cell is more uniform, maximizing the efficiency of the platinum in the MEA. Recent studies using inkjet printing to deposit the catalyst over the membrane have also shown high catalyst utilization due to the reduced thickness of the deposited catalyst layers.

Very recently, a new class of ORR electrocatalysts have been introduced in the case of Pt-M (M-Fe and Co) systems with an ordered intermetallic core encapsulated within a Pt-rich shell. These intermetallic core-shell (IMCS) nanocatalysts were found to exhibit an enhanced activity and most importantly, an extended durability compared to many previous designs. While the observed enhancement in the activities is ascribed to a strained lattice, the authors report that their findings on the degradation kinetics establish that the extended catalytic durability is attributable to a sustained atomic order.

Reducing poisoning

The other popular approach to improving catalyst performance is to reduce its sensitivity to impurities in the fuel source, especially carbon monoxide (CO). Presently, pure hydrogen gas is becoming economical to mass-produce by electrolysis. However, at the moment hydrogen gas is produced by steam reforming light hydrocarbons, a process which produces a mixture of gases that also contains CO (1–3%), CO₂ (19–25%), and N₂ (25%). Even tens of parts per million of CO can poison a pure platinum catalyst, so increasing platinum's resistance to CO is an active area of research.

For example, one study reported that cube-shaped platinum nanoparticles with (100) facets displayed a fourfold increase in oxygen reduction activity compared to randomly faceted platinum nanoparticles of similar size. The authors concluded that the (111) facets of the randomly shaped nanoparticles bonded more strongly to sulfate ions than the (100) facets, reducing the number of catalytic sites open to oxygen molecules. The nanocubes they synthesized, in contrast, had almost exclusively (100) facets, which are known to interact with sulfate more weakly. As a result, a greater fraction of the surface area of those particles was available for the reduction of oxygen, boosting the catalyst's oxygen reduction activity.

In addition, researchers have been investigating ways of reducing the CO content of hydrogen fuel before it enters a fuel cell as a possible way to avoid poisoning the catalysts. One recent study revealed that ruthenium-platinum core–shell nanoparticles are particularly effective at oxidizing CO to form CO₂, a much less harmful fuel contaminant. The mechanism that produces this effect is conceptually similar to that described for Pt₃Ni above: the ruthenium core of the particle alters the electronic structure of the platinum surface, rendering it better able to catalyze the oxidation of CO.

Lowering cost

The challenge for the viability of PEM fuel cells today still remains in their cost and stability. The high cost can in large part be attributed to the use of the precious metal of platinum in the catalyst layer of PEM cells. The electrocatalyst currently accounts for nearly half of the fuel cell stack cost. Although the Pt loading of PEM fuel cells has been reduced by two orders of magnitude over the past decade, further reduction is necessary to make the technology economically viable for commercialization. Whereas some research efforts aim to address this issue by improving the electrocatalytic activity of Pt-based catalysts, an alternative is to eliminate the use of Pt altogether by developing a non-platinum-group-metal (non-PGM) cathode catalyst whose performance rivals that of Pt-based technologies. The U.S. Department of Energy has been setting milestones for the development of fuel cells, targeting a durability of 5000 hours and a non-PGM catalyst ORR volumetric activity of 300 A cm⁻³.

Promising alternatives to Pt-based catalysts are Metal/Nitrogen/ Carbon-catalysts (M/N/C-catalysts). To achieve high power density, or output of power over surface area of the cell, a volumetric activity of at least 1/10 that of Pt-based catalysts must be met, along with good mass transport properties. While M/N/C-catalysts still demonstrate poorer volumetric activities than Pt-based catalysts, the reduced costs of such catalysts allows for greater loading to compensate. However, increasing the loading of M/N/C-catalysts also renders the catalytic layer thicker, impairing its mass transport properties. In other words, H₂, O₂, protons, and electrons have greater difficulty in migrating through the catalytic layer, decreasing the voltage output of the cell. While high microporosity of the M/N/C catalytic network results in high volumetric activity, improved mass transport properties are instead associated to macroporosity of the network. These M/N/C materials are synthesized using high temperature pyrolysis and other high temperature treatments of precursors containing the metal, nitrogen, and carbon.

Recently, researchers have developed a Fe/N/C catalyst derived from iron (II) acetate (FeAc), phenanthroline (Phen), and a metal-organic-framework (MOF) host. The MOF is a Zn(II) zeolitic imidazolate framework (ZIF) called ZIF-8, which demonstrates a high microporous surface area and high nitrogen content conducive to ORR activity. The power density of the FeAc/Phen/ZIF-8-catalyst was found to be 0.75 W cm⁻² at 0.6 V. This value is a significant improvement over the maximal 0.37 W cm⁻² power density of previous M/N/C-catalysts and is much closer to matching the typical value of 1.0–1.2 W cm⁻² for Pt-based catalysts with a Pt loading of 0.3 mg cm⁻². The catalyst also demonstrated a volumetric activity of 230 A·cm⁻³, the highest value for non-PGM catalysts to date, approaching the U.S. Department of Energy milestone.

While the power density achieved by the novel FeAc/Phen/ZIF-8-catalyst is promising, its durability remains inadequate for commercial application. It is reported that the best durability exhibited by this catalyst still had a 15% drop in current density over 100 hours in H₂/air. Hence while the Fe-based non-PGM catalysts rival Pt-based catalysts in their electrocatalytic activity, there is still much work to be done in understanding their degradation mechanisms and improving their durability.

Applications

The major application of PEM fuel cells focuses on transportation primarily because of their potential impact on the environment, e.g. the control of emission of the green house gases (GHG). Other applications include distributed/stationary and portable power generation. Most major motor companies work solely on PEM fuel cells due to their high power density and excellent dynamic characteristics as compared with other types of fuel cells. Due to their light weight, PEMFCs are most suited for transportation applications. PEMFCs for buses, which use compressed hydrogen for fuel, can operate at up to 40% efficiency. Generally PEMFCs are implemented on buses over smaller cars because of the available volume to house the system and store the fuel. Technical issues for transportation involve incorporation of PEMs into current vehicle technology and updating energy systems. Full fuel cell vehicles are not advantageous if hydrogen is sourced from fossil fuels; however, they become beneficial when implemented as hybrids. There is potential for PEMFCs to be used for stationary power generation, where they provide 5 kW at 30% efficiency; however, they run into competition with other types of fuel cells, mainly SOFCs and MCFCs. Whereas PEMFCs generally require high purity hydrogen for operation, other fuel cell types can run on methane and are thus more flexible systems. Therefore, PEMFCs are best for small scale systems until economically scalable pure hydrogen is available. Furthermore, PEMFCs have the possibility of replacing batteries for portable electronics, though integration of the hydrogen supply is a technical challenge particularly without a convenient location to store it within the device.

History

Before the invention of PEM fuel cells, existing fuel cell types such as solid-oxide fuel cells were only applied in extreme conditions. Such fuel cells also required very expensive materials and could only be used for stationary applications due to their size. These issues were addressed by the PEM fuel cell. The PEM fuel cell was invented in the early 1960s by Willard Thomas Grubb and Leonard Niedrach of General Electric. Initially, sulfonated polystyrene membranes were used for electrolytes, but they were replaced in 1966 by Nafion ionomer, which proved to be superior in performance and durability to sulfonated polystyrene.

PEM fuel cells were used in the NASA Gemini series of spacecraft, but they were replaced by Alkaline fuel cells in the Apollo program and in the Space shuttle. General Electric continued working on PEM cells and in the mid-1970s developed PEM water electrolysis technology for undersea life support, leading to the US Navy Oxygen Generating Plant. The British Royal Navy adopted this technology in early 1980s for their submarine fleet. In the late 1980s and early 1990s, Los Alamos National Lab and Texas A&M University experimented with ways to reduce the amount of platinum required for PEM cells.

Parallel with Pratt and Whitney Aircraft, General Electric developed the first proton exchange membrane fuel cells (PEMFCs) for the Gemini space missions in the early 1960s. The first mission to use PEMFCs was Gemini V. However, the Apollo space missions and subsequent Apollo-Soyuz, Skylab and Space Shuttle missions used fuel cells based on Bacon's design, developed by Pratt and Whitney Aircraft.

Extremely expensive materials were used and the fuel cells required very pure hydrogen and oxygen. Early fuel cells tended to require inconveniently high operating temperatures that were a problem in many applications. However, fuel cells were seen to be desirable due to the large amounts of fuel available (hydrogen and oxygen).

Despite their success in space programs, fuel cell systems were limited to space missions and other special applications, where high cost could be tolerated. It was not until the late 1980s and early 1990s that fuel cells became a real option for wider application base. Several pivotal innovations, such as low platinum catalyst loading and thin film electrodes, drove the cost of fuel cells down, making development of PEMFC systems more realistic. However, there is significant debate as to whether hydrogen fuel cells will be a realistic technology for use in automobiles or other vehicles. (See hydrogen economy.) A large part of PEMFC production is for the Toyota Mirai. The US Department of Energy estimates a 2016 price at $53/kW if 500,000 units per year were made.

Low-carbon economy

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Low-carbon_economy 

Environmental economics
Concepts
Bright green environmentalism Circular economy Eco commerce Ecological economics Environmental enterprise Environmental finance Fiscal environmentalism Green accounting Green economy Green growth Green job Green recovery Green trading Natural resource economics Sustainable design Sustainable development Sustainable tourism
Policies
Environmental pricing reform Environmental tariff Free public transport Pigovian tax
Dynamics
Green paradox Green politics Marginal abatement cost Pollution haven hypothesis
Climate change
Climate change mitigation Carbon footprint Green New Deal Food miles
Carbon pricing
Carbon price Carbon tax Carbon emission trading Carbon credit Carbon fee and dividend Carbon finance Carbon offset Climate finance Ecotax Emissions trading Personal carbon trading Social cost of carbon
Energy transition
Sustainable energy 2000-watt society Carbon leakage Carbon neutrality Carbon-neutral fuel Feed-in tariff Low-carbon economy Net metering Renewable energy commercialization

Wind Turbine with Workers - Boryspil - Ukraine

A low-carbon economy (LCE) or decarbonised economy is an economy based on energy sources that produce low levels of greenhouse gas (GHG) emissions. GHG emissions due to anthropogenic (human) activity are the dominant cause of observed climate change since the mid-20th century. Continued emission of greenhouse gases may cause long-lasting changes around the world, increasing the likelihood of severe, pervasive, and irreversible effects for people and ecosystems.

Shifting to a low-carbon economy on a global scale could bring substantial benefits both for developed and developing countries. Many countries around the world are designing and implementing low-emission development strategies (LEDS). These strategies seek to achieve social, economic, and environmental development goals while reducing long-term greenhouse gas emissions and increasing resilience to the effects of climate change.

Globally implemented low-carbon economies are therefore proposed as a precursor to the more advanced, zero-carbon economy. The GeGaLo index of geopolitical gains and losses assesses how the geopolitical position of 156 countries may change if the world fully transitions to renewable energy resources. Former fossil fuel exporters are expected to lose power, while the positions of former fossil fuel importers and countries rich in renewable energy resources is expected to strengthen.

Rationale and aims

Nations may seek to become low-carbon or decarbonised economies as a part of a national climate change mitigation strategy. A comprehensive strategy to mitigate climate change is through carbon neutrality.

The aim of an LCE is to integrate all aspects of itself from its manufacturing, agriculture, transportation, and power generation, etc. around technologies that produce energy and materials with little GHG emission, and, thus, around populations, buildings, machines, and devices that use those energies and materials efficiently, and, dispose of or recycle its wastes so as to have a minimal output of GHGs. Furthermore, it has been proposed that to make the transition to an LCE economically viable we would have to attribute a cost (per unit output) to GHGs through means such as emissions trading and/or a carbon tax.

Some nations are presently low carbon: societies that are not heavily industrialized or populated. In order to avoid climate change on a global level, all nations considered carbon-intensive societies and societies that are heavily populated might have to become zero-carbon societies and economies. EU emission trading system allows companies to buy international carbon credits, thus the companies can channel clean technologies to promote other countries to adopt low-carbon developments.

Benefits

Low-carbon economies present multiple benefits to ecosystem resilience, trade, employment, health, energy security, and industrial competitiveness.

Ecosystem resilience

A view of southern Central Park in New York, NY.

Low emission development strategies for the land use sector can prioritize the protection of carbon-rich ecosystems to not only reduce emissions, but also to protect biodiversity and safeguard local livelihoods to reduce rural poverty - all of which can lead to more climate resilient systems, according to a report by the Low Emission Development Strategies Global Partnership (LEDS GP). REDD+ and blue carbon initiatives are among the measures available to conserve, sustainably manage, and restore these carbon rich ecosystems, which are crucial for natural carbon storage and sequestration, and for building climate resilient communities.

Economic benefits

Job creation

Transitioning to a low-carbon, environmentally and socially sustainable economies can become a strong driver of job creation, job upgrading, social justice, and poverty eradication if properly managed with the full engagement of governments, workers, and employers’ organizations.

Estimates from the International Labour Organization’s Global Economic Linkages model suggest that unmitigated climate change, with associated negative impacts on enterprises and workers, will have negative effects on output in many industries, with drops in output of 2.4% by 2030 and 7.2% by 2050.

Transitioning to a low-carbon economy will cause shifts in the volume, composition, and quality of employment across sectors and will affect the level and distribution of income. Research indicates that eight sectors employing around 1.5 billion workers, approximately half the global workforce, will undergo major changes: agriculture, forestry, fishing, energy, resource intensive manufacturing, recycling, buildings, and transport.

Business competitiveness

Low emission industrial development and resource efficiency can offer many opportunities to increase the competitiveness of economies and companies. According to the Low Emission Development Strategies Global Partnership (LEDS GP), there is often a clear business case for switching to lower emission technologies, with payback periods ranging largely from 0.5–5 years, leveraging financial investment.

Improved trade policy

Trade and trade policies can contribute to low-carbon economies by enabling more efficient use of resources and international exchange of climate-friendly goods and services. Removing tariffs and nontariff barriers to trade in clean energy and energy efficiency technologies are one such measure. In a sector where finished products consist of many components that cross borders numerous times - a typical wind turbine, for example, contains up to 8,000 components - even small tariff cuts would reduce costs. This would make the technologies more affordable and competitive in the global market, particularly when combined with a phasing out of fossil fuel subsidies.

Energy policy

Renewable energy and energy efficiency

See also: Renewable energy commercialization

 

Worldwide installed wind power capacity 1997–2020 [MW], history and predictions. Data source: WWEA

 

Solar array at Nellis Solar Power Plant. These panels track the sun in one axis.

Recent advances in technology and policy will allow renewable energy and energy efficiency to play major roles in displacing fossil fuels, meeting global energy demand while reducing carbon dioxide emissions. Renewable energy technologies are being rapidly commercialized and, in conjunction with efficiency gains, can achieve far greater emissions reductions than either could independently.

Renewable energy is energy that comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable (naturally replenished). In 2015, about 19% of global final energy consumption came from renewables. During the five years from the end of 2004 through 2009, worldwide renewable energy capacity grew at rates of 10–60 percent annually for many technologies. For wind power and many other renewable technologies, growth accelerated in 2009 relative to the previous four years. More wind power capacity was added during 2009 than any other renewable technology. However, grid-connected photovoltaics increased the fastest of all renewables technologies, with a 60 percent annual average growth rate for the five-year period.

Energy for power, heat, cooling, and mobility is the key ingredient for development and growth, with energy security a prerequisite economic growth, making it arguably the most important driver for energy policy. Scaling up renewable energy as part of a low emission development strategy can diversify a country's energy mixes and reduces dependence on imports. In the process of decarbonizing heat and transport through electrification, potential changes to electricity peak demand need to be anticipated whilst switching to alternative technologies such as heat pumps for electric vehicles.

Installing local renewable capacities can also lower geopolitical risks and exposure to fuel price volatility, and improve the balance of trade for importing countries (noting that only a handful of countries export oil and gas). Renewable energy offers lower financial and economic risk for businesses through a more stable and predictable cost base for energy supply.

Energy efficiency gains in recent decades have been significant, but there is still much more that can be achieved. With a concerted effort and strong policies in place, future energy efficiency improvements are likely to be very large. Heat is one of many forms of "energy wastage" that could be captured to significantly increase useful energy without burning more fossil fuels.

Sustainable biofuels

Main article: Sustainable biofuel

Biofuels, in the form of liquid fuels derived from plant materials, are entering the market, driven by factors such as oil price spikes and the need for increased energy security. However, many of the biofuels that are currently being supplied have been criticised for their adverse impacts on the natural environment, food security, and land use.

The challenge is to support biofuel development, including the development of new cellulosic technologies, with responsible policies and economic instruments to help ensure that biofuel commercialization is sustainable. Responsible commercialization of biofuels represents an opportunity to enhance sustainable economic prospects in Africa, Latin America and Asia.

Biofuels have a limited ability to replace fossil fuels and should not be regarded as a ‘silver bullet’ to deal with transport emissions. However, they offer the prospect of increased market competition and oil price moderation. A healthy supply of alternative energy sources will help to combat gasoline price spikes and reduce dependency on fossil fuels, especially in the transport sector. Using transportation fuels more efficiently is also an integral part of a sustainable transport strategy.

Nuclear power

Nuclear power has been offered as the primary means to achieve a LCE. In terms of large industrialized nations, mainland France, due primarily to 75% of its electricity being produced by nuclear power, has the lowest carbon dioxide production per unit of GDP in the world and it is the largest exporter of electricity in the world, earning it approximately €3 billion annually in sales.

Concern is often expressed with the matter of spent nuclear fuel storage and security; although the physical issues are not large, the political difficulties are significant. The liquid fluoride thorium reactor (LFTR) has been suggested as a solution to the concerns posed by conventional nuclear.

France reprocesses their spent nuclear fuel at the La Hague site since 1976 and has also treated spent nuclear fuel from France, Japan, Germany, Belgium, Switzerland, Italy, Spain, and the Netherlands.

Some researchers have determined that achieving substantial decarbonization and combating climate change would be much more difficult without increasing nuclear power. Nuclear power is a reliable form of energy that is available 24/7, relatively safe, and can be expanded on a large scale. Nuclear power plants can replace fossil fuel-based power plants — shifting to a low carbon economy.

As of 2021, the expansion of nuclear energy as a method of achieving a low-carbon economy has varying degrees of support. Agencies and organizations that believe decarbonization is not possible without some nuclear power expansion include the United Nations Economic Commission for Europe, the International Energy Agency (IEA), the International Atomic Energy Agency, and the Energy Impact Center (EIC). Both IEA and EIC believe that widespread decarbonization must occur by 2040 in order mitigate the adverse effects of climate change and that nuclear power must play a role. The latter organization suggests that net-negative carbon emissions are possible using nuclear power to fuel carbon capture technology.

Smart grid

One proposal from Karlsruhe University developed as a virtual power station is the use of solar and wind energy for base load with hydro and biogas for make up or peak load. Hydro and biogas are used as grid energy storage. This requires the development of a smart intelligent grid hopefully including local power networks than use energy near the site of production, thereby reducing the existing 5% grid loss.

Decarbonisation technologies

There are five technologies commonly identified in decarbonisation:

1. Electrifying heat as furnaces are powered by electricity rather than burning fuels. Green energy must still be used.
2. The use of hydrogen as a furnace steam, a chemical feedstock, or a reactant in chemical processes.
3. The use of biomass as a source of energy or feedstock. In other words, replacing coal with bio coal or gas with bio-gas. One example is charcoal, which is made by converting wood into coal and has a CO₂ footprint of zero.
4. Carbon capture and storage. This is where greenhouse gases are isolated from other natural gases, compressed, and injected into the earth to avoid being emitted into the atmosphere.
5. Carbon capture and usage. The aim of this method is to turn industrial gases into something valuable, such as ethanol or raw materials for the chemical industry.

Decarbonisation plans that get to zero CO₂ emissions

A comprehensive decarbonisation plan describes how to generate enough green energy to replace coal, oil, and natural gas; and takes into consideration factors such as increasing GDP, increasing standard of living, and increasing efficiencies. Each year the world consumes 583 exajoules (EJ) of heat energy. This corresponds to 56,000 TWh of electricity when heat is converted to electricity via a 35% efficient turbine. To decarbonise, the world needs to generate this energy without emitting CO₂. To get a sense of how large this is, one can look at how many Hoover Dams, London Arrays and nuclear reactors corresponds to this amount of energy:

• 22,600 London Arrays, a wind farm with 175 large windmills
• 13,500 Hoover Dams, a large hydroelectric dam in Nevada (based on average production between 1999 and 2008)
• 21-times more than the world's current installed base of 400 GWe of nuclear power

Below are example global decarbonization plans:

• Chapter 11 of How to Avoid a Climate Disaster, by Bill Gates
• Power Electronics' Plan To Get to Zero CO₂ Emissions
• A Global Decarbonization Plan, by the Manhattan 2 Project

Below are example plans that decarbonize the United States:

• The Net-Zero America Project, by Princeton University
• Getting To Zero, by the Center for Climate and Energy Solutions
• America's Zero Carbon Action Plan, by the Sustainable Development Solutions Network
• "Energy Decarb" scenario within DOE's 2021 Solar Futures Study.

Tools that create decarbonization plans are in various stages of development:

• C-Roads Climate Policy Simulator
• Power Electronics' Develop Your Own Decarbonization Plan

Carbon-neutral hydrocarbons

Main article: Carbon-neutral fuel

Carbon capture and storage

Global proposed vs. implemented annual CO₂ sequestration. More than 75% of proposed gas processing projects have been implemented, with corresponding figures for other industrial projects and power plant projects being about 60% and 10%, respectively.

Carbon capture and storage (CCS) or carbon capture and sequestration is the process of capturing carbon dioxide (CO₂) before it enters the atmosphere, transporting it, and storing it (carbon sequestration) for centuries or millennia. Usually the CO₂ is captured from large point sources, such as coal-fired power plant, a chemical plant or biomass power plant, and then stored in an underground geological formation. The aim is to prevent the release of CO₂ from heavy industry with the intent of mitigating the effects of climate change. Although CO₂ has been injected into geological formations for several decades for various purposes, including enhanced oil recovery, the long-term storage of CO₂ is a relatively new concept. Carbon capture and utilization (CCU) and CCS are sometimes discussed collectively as carbon capture, utilization, and sequestration (CCUS). This is because CCS is a relatively expensive process yielding a product with an intrinsic low value (i.e. CO₂). Hence, carbon capture makes economically more sense when being combined with a utilization process where the cheap CO₂ can be used to produce high-value chemicals to offset the high costs of capture operations.

CO₂ can be captured directly from an industrial source, such as a cement kiln, using a variety of technologies; including absorption, adsorption, chemical looping, membrane gas separation or gas hydration. As of 2020, about one thousandth of global CO₂ emissions are captured by CCS. Most projects are industrial.

Storage of the CO₂ is envisaged either in deep geological formations, or in the form of mineral carbonates. Pyrogenic carbon capture and storage (PyCCS) is also being researched. Geological formations are currently considered the most promising sequestration sites. The US National Energy Technology Laboratory (NETL) reported that North America has enough storage capacity for more than 900 years worth of CO₂ at current production rates. A general problem is that long-term predictions about submarine or underground storage security are very difficult and uncertain, and there is still the risk that some CO₂ might leak into the atmosphere. Opponents point out that many CCS projects have failed to deliver on promised emissions reductions. Additionally, opponents argue that rather than focusing on carbon removal, carbon capture and storage is a justification for indefinite fossil fuel usage disguised as marginal emission reductions. One of the most well-known failures is the FutureGen program, partnerships between the US federal government and coal energy production companies which were intended to demonstrate ″clean coal″, but never succeeded in producing any carbon-free electricity from coal.

Combined heat and power

Combined Heat and Power (CHP) is a technology which by allowing the more efficient use of fuel will at least reduce carbon emissions; should the fuel be biomass or biogas or hydrogen used as an energy store then in principle it can be a zero carbon option. CHP can also be used with a nuclear reactor as the energy source; there are examples of such installations in the far North of the Russian Federation.

Decarbonisation activity by sector

Primary sector

Agriculture

See also: Low carbon diet

Most of the agricultural facilities in the developed world are mechanized due to rural electrification. Rural electrification has produced significant productivity gains, but it also uses a lot of energy. For this and other reasons (such as transport costs) in a low-carbon society, rural areas would need available supplies of renewably produced electricity.

Irrigation can be one of the main components of an agricultural facility's energy consumption. In parts of California, it can be up to 90%. In the low carbon economy, irrigation equipment will be maintained and continuously updated and farms will use less irrigation water.

Livestock operations can also use a lot of energy depending on how they are run. Feedlots use animal feed made from corn, soybeans, and other crops. Energy must be expended to produce these crops, process, and transport them. Free-range animals find their own vegetation to feed on. The farmer may expend energy to take care of that vegetation, but not nearly as much as the farmer growing cereal and oil-seed crops.

Many livestock operations currently use a lot of energy to water their livestock. In the low-carbon economy, such operations will use more water conservation methods such as rainwater collection, water cisterns, etc., and they will also pump/distribute that water with on-site renewable energy sources (most likely wind and solar).

Due to rural electrification, most agricultural facilities in the developed world use a lot of electricity. In a low-carbon economy, farms will be run and equipped to allow for greater energy efficiency. Changes in the dairy industry include heat recovery, solar hearing, and use of biodigesters:

Replacing livestock with plant-based alternatives is another way of reducing our carbon emissions. The carbon footprint of livestock is large - it provides just 18% of total calories but takes up 83% of farmland.

Forestry

Main article: Wood economy

Protecting forests provides integrated benefits to all, ranging from increased food production, safeguarded local livelihoods, protected biodiversity and ecosystems provided by forests, and reduced rural poverty. Adopting low emission strategies for both agricultural and forest production also mitigates some of the effects of climate change.

In the low-carbon economy, forestry operations will be focused on low-impact practices and regrowth. Forest managers will make sure that they do not disturb soil-based carbon reserves too much. Specialized tree farms will be the main source of material for many products. Quick maturing tree varieties will be grown on short rotations in order to maximize output.

Mining

Flaring and venting of natural gas in oil wells is a significant source of greenhouse gas emissions. Its contribution to greenhouse gases has declined by three-quarters in absolute terms since a peak in the 1970s of approximately 110 million metric tons/year, and in 2004 accounted for about 1/2 of one percent of all anthropogenic carbon dioxide emissions.

The World Bank estimates that 134 billion cubic meters of natural gas are flared or vented annually (2010 datum), an amount equivalent to the combined annual gas consumption of Germany and France or enough to supply the entire world with gas for 16 days. This flaring is highly concentrated: 10 countries account for 70% of emissions, and twenty for 85%.

Secondary sector

A factory in Sweden releases pollution into the air.

Basic metals processing

• high efficiency electric motors
• induction furnaces
• heat recovery

Nonmetallic product processing

• variable speed drives
• injection molding - replace hydraulic with electric servo motors

Wood processing

• high efficiency motors
• high efficiency fans
• dehumidifier driers

Paper and pulp making

• variable speed drives
• high efficiency motors

Food processing

• high efficiency boilers
• heat recovery e.g. refrigeration
• solar hot water for pre-heating
• bio fuels e.g. tallow, wood

Tertiary sector

Building and Construction

In 2018, building construction and operations accounted for 39% of global greenhouse gas emissions. The construction industry has seen marked advances in building performance and energy efficiency over recent decades, but there continues to be a large need for additional improvement in order to decarbonize this sector. International and government organizations have taken actions to promote the decarbonization of buildings, including the United Nations Framework Convention on Climate Change (UNFCCC) signed in 1992, the Kyoto Protocol signed in 1997, and many countries' Nationally Determined Contributions (NDC) of the Paris Climate Agreement which was signed in 2016.

The largest contributor to building sector emissions (49% of total) is the production of electricity for use in buildings. To decarbonize the building sector, the production of electrical energy will need to reduce its dependence on fossil fuels such as coal and natural gas, and instead shift to carbon-free alternatives like solar, wind, and nuclear. Currently many countries are heavily dependent on fossil fuels for electricity generation. In 2018, 61% of US electricity generation was produced by fossil fuel power plants (23% by coal and 38% by natural gas).

Of global building sector GHG emissions, 28% are produced during the manufacturing process of building materials such as steel, cement (a key component of concrete), and glass. The conventional process inherently related to the production of steel and cement results in large amounts of CO₂ emitted. For example, the production of steel in 2018 was responsible for 7 to 9% of the global CO₂ emissions. However, these industries lend themselves very well for carbon capture and storage and carbon capture and utilization technology as the CO₂ is available in large concentration in an exhaust gas, which is considered a so-called point source. GHG emissions which are produced during the mining, processing, manufacturing, transportation and installation of building materials are referred to as the embodied carbon of a material. The embodied carbon of a construction project can be reduced by using low-carbon materials for building structures and finishes, reducing demolition, and reusing buildings and construction materials whenever possible.

The remaining 23% of global building sector GHG emissions are produced directly on site during building operations. These emissions are produced by fossil fuels such as natural gas which are burned on site to generate hot water, provide space heating, and supply cooking appliances. These pieces of equipment will need to be replaced by carbon-free alternatives such as heat pumps and induction cooktops to decarbonize the building sector.

Retail

Retail operations in the low-carbon economy will have several new features. One will be high-efficiency lighting such as compact fluorescent, halogen, and eventually LED light sources. Many retail stores will also feature roof-top solar panel arrays. These make sense because solar panels produce the most energy during the daytime and during the summer. These are the same times that electricity is the most expensive and also the same times that stores use the most electricity.

Transportation

Elements of Low-Carbon Urban Development

Sustainable, low-carbon transport systems are based on minimizing travel and shifting to more environmentally (as well as socially and economically) sustainable mobility, improving transport technologies, fuels and institutions. Decarbonisation of mobility by means of:

• More energy efficiency and alternative propulsion:
  • Increased focus on fuel efficient vehicle shapes and configurations, with more vehicle electrification, particularly through battery electric vehicles (BEV) or all-electric vehicles
  • More alternative and flex-fuel vehicles (based on local conditions and availability)
  • Driver training for more fuel efficiency.
  • Low-carbon biofuels cellulosic (biodiesel, bioethanol, biobutanol)
  • Petroleum fuel surcharges will be a more significant part of consumer costs.
• Less international movement of physical objects, despite more overall trade (as measure by value of goods)
• Greater use of marine and electric rail transport, less use of air and truck transport.
• Increased non-motorised transport (i.e. walking and cycling) and public transport usage, less reliance on private motor vehicles.
• More pipeline capacity for common fluid commodities such as water, ethanol, butanol, natural gas, petroleum, and hydrogen (in addition to gasoline and diesel).

Sustainable transport has many co-benefits that can accelerate local sustainable development. According to a series of reports by the Low Emission Development Strategies Global Partnership (LEDS GP), low carbon transport can help create jobs, improve commuter safety through investment in bicycle lanes and pedestrian pathways, make access to employment and social opportunities more affordable and efficient. It also offers a practical opportunity to save people's time and household income as well as government budgets, making investment in sustainable transport a 'win-win' opportunity.

Health services

There have been some moves to investigate the ways and extent to which health systems contribute to greenhouse gas emissions and how they may need to change to become part of a low-carbon world. The Sustainable Development Unit of the NHS in the UK is one of the first official bodies to have been set up in this area, whilst organisations such as the Campaign for Greener Healthcare are also producing influential changes at a clinical level. This work includes

• Quantification of where the health services emissions stem from.
• Information on the environmental impacts of alternative models of treatment and service provision

Some of the suggested changes needed are:

• Greater efficiency and lower ecological impact of energy, buildings, and procurement choices (e.g., in-patient meals, pharmaceuticals, and medical equipment).
• A shift from focusing solely on cure to prevention, through the promotion of healthier, lower-carbon lifestyles, e.g. diets lower in red meat and dairy products, walking or cycling wherever possible, better town planning to encourage more outdoor lifestyles.
• Improving public transport and liftsharing options for transport to and from hospitals and clinics.

Tourism

Low-carbon tourism includes travels with low energy consumption, and low CO₂ and pollution emissions. Change of personal behavior to more low-carbon oriented activities is mostly influenced by both individual awareness and attitudes, as well as external social aspect, such as culture and environment. Studies indicate that educational level and occupation influence an individual perception of low-carbon tourism.

Actions taken by countries

A good overview of the history of international efforts towards a low-carbon economy, from its initial seed at the inaugural UN Conference on the Human Environment in Stockholm in 1972, has been given by David Runnals. On the international scene, the most prominent early step in the direction of a low-carbon economy was the signing of the Kyoto Protocol, which came into force in 2005, under which most industrialized countries committed to reduce their carbon emissions. Europe is the leading geopolitical continent in defining and mobilising decarbonisation policies. For instance, the UITP - an organisation advocating sustainable mobility and public transport - has an EU office, but less well developed contacts with, for example, the US. The European Union Committee of the UITP wants to promote decarbonisation of urban mobility in Europe. However, the 2014 Global Green Economy Index™ (GGEI) ranks 60 nations on their green economic performance, finding that the Nordic countries and Switzerland have the best combined performance around climate change and green economy.

China

Main article: Renewable energy in China

In China, the city of Dongtan is to be built to produce zero net greenhouse gas emissions.

The Chinese State Council announced in 2009 it aimed to cut China's carbon dioxide emissions per unit of GDP by 40%-45% in 2020 from 2005 levels. However carbon dioxide emissions were still increasing by 10% a year by 2013 and China was emitting more carbon dioxide than the next two biggest countries combined (U.S.A. and India). Total carbon dioxide emissions were projected to increase until 2030.

Costa Rica

Costa Rica sources much of its energy needs from renewables and is undertaking reforestation projects. In 2007, the Costa Rican government announced the commitment for Costa Rica to become the first carbon neutral country by 2021.

Iceland

Main article: Renewable energy in Iceland

Iceland began utilising renewable energy early in the 20th century and so since has been a low-carbon economy. However, since dramatic economic growth, Iceland's emissions have increased significantly per capita. As of 2009, Iceland energy is sourced from mostly geothermal energy and hydropower, renewable energy in Iceland and, since 1999, has provided over 70% of the nation's primary energy and 99.9% of Iceland's electricity. As a result of this, Iceland's carbon emissions per capita are 62% lower than those of the United States despite using more primary energy per capita, due to the fact that it is renewable and low-cost. Iceland seeks carbon neutrality and expects to use 100% renewable energy by 2050 by generating hydrogen fuel from renewable energy sources.

Peru

The Economic Commission for Latin America and the Caribbean (ECLAC) estimates that economic losses related to climate change for Peru could reach over 15% of national gross domestic product (GDP) by 2100. Being a large country with a long coastline, snow-capped mountains and sizeable forests, Peru's varying ecosystems are extremely vulnerable to climate change. Several mountain glaciers have already begun to retreat, leading to water scarcity in some areas. In the period between 1990 and 2015, Peru experienced a 99% increase in per capita carbon emissions from fossil fuel and cement production, marking one of the largest increases amongst South American countries.

Peru brought in a National Strategy on Climate Change in 2003. It is a detailed accounting of 11 strategic focuses that prioritize scientific research, mitigation of climate change effects on the poor, and creating Clean Development Mechanism (CDM) mitigation and adaptation policies.

In 2010, the Peruvian Ministry of Environment published a Plan of Action for Adaptation and Mitigation of Climate Change. The Plan categorises existing and future programmes into seven action groups, including: reporting mechanisms on GHG emissions, mitigation, adaptation, research and development of technology of systems, financing and management, and public education. It also contains detailed budget information and analysis relating to climate change.

In 2014, Peru hosted the Twentieth Conference of the Parties of the United Nations Framework Convention on Climate Change (UNFCCC COP20) negotiations. At the same time, Peru enacted a new climate law which provides for the creation of a national greenhouse gas inventory system called INFOCARBONO. According to the Low Emission Development Strategies Global Partnership (LEDS GP), INFOCARBONO is a major transformation of the country's greenhouse gas management system. Previously, the system was under the sole control of the Peruvian Ministry of the Environment. The new framework makes each relevant ministry responsible for their own share of greenhouse gas management.

United Kingdom

Main article: Greenhouse gas emissions by the United Kingdom

In the United Kingdom, the Climate Change Act 2008 outlining a framework for the transition to a low-carbon economy became law on November 26, 2008. It was the world's first long-term legislation to reduce carbon emissions. This act requires an 80% cut in the UK's carbon emissions by 2050 (compared to 1990 levels), with an intermediate target of between 26% and 32% by 2020. Thus, the UK became the first country to set such a long-range and significant carbon reduction target into law.

A meeting at the Royal Society on 17–18 November 2008 concluded that an integrated approach, making best use of all available technologies, is required to move toward a low-carbon future. It was suggested by participants that it would be possible to move to a low-carbon economy within a few decades, but that 'urgent and sustained action is needed on several fronts'.

In June 2012, the UK coalition government announced the introduction of mandatory carbon reporting, requiring around 1,100 of the UK's largest listed companies to report their greenhouse gas emissions every year. Deputy Prime Minister Nick Clegg confirmed that emission reporting rules would come into effect from April 2013 in his piece for The Guardian.

In July 2014, the UK Energy Savings Opportunity Scheme (ESOS) came into force. This requires all large businesses in the UK to undertake mandatory assessments looking at energy use and energy efficiency opportunities at least once every four years.

The low carbon economy has been described as a "UK success story", accounting for more than £120 billion in annual sales and employing almost 1 million people. A 2013 report suggests that over a third of the UK's economic growth in 2011/12 was likely to have come from green business. This data is complementary to the strong correlation between GDP per capita and national rates of energy consumption.