Social and environmental impact of palm oil

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Social_and_environmental_impact_of_palm_oil 

Palm oil, produced from the oil palm, is a basic source of income for many farmers in South East Asia, Central and West Africa, and Central America. It is locally used as cooking oil, exported for use in much commercial food and personal care products and is converted into biofuel. It produces up to 10 times more oil per unit area than soybeans, rapeseed or sunflowers.

Oil palms produce 38% of the world's vegetable-oil output on 5% of the world's vegetable-oil farmland. Palm oil plantations, typically monoculture crops are under increasing scrutiny for their effects on the environment, including loss of carbon-sequestering, biodiverse forest land. There is also concern over displacement and disruption of human and animal populations due to palm oil cultivation.

Statistics

Oil palms (Elaeis guineensis)

An estimated 1.5 million small farmers grow the crop in Indonesia, along with about 500,000 people directly employed in the sector in Malaysia, plus those connected with related industries.

As of 2006, the cumulative land area of palm oil plantations is approximately 11,000,000 hectares (42,000 sq mi). In 2005 the Malaysian Palm Oil Association, responsible for about half of the world's crop, estimated that they manage about half a billion perennial carbon-sequestering palm trees. Demand for palm oil has been rising and is expected to climb further.

Between 1967 and 2000 the area under cultivation in Indonesia expanded from less than 2,000 square kilometres (770 sq mi) to more than 30,000 square kilometres (12,000 sq mi). Deforestation in Indonesia for palm oil (and illegal logging) is so rapid that a 2007 United Nations Environment Programme (UNEP) report said that most of the country's forest might be destroyed by 2022. The rate of forest loss has declined in the past decade.

Global production is forecast at a record 46.9m tonnes in 2010, up from 45.3m in 2009, with Indonesia providing most of the increase.

Social issues

Oil palm is a valuable economic crop and provides a source of employment. It allows small landholders to participate in the cash economy and often results in improvements to local infrastructure and greater access to services such as schools and health facilities. In some areas, the cultivation of oil palm has replaced traditional practices, often due to the higher income potential of palm oil. The modernisation of cultivation practices has led to issues including food insecurity. This issue stems from the intensive use of land which leads to soil degradation. As a result, the ability for locals to produce their own food has dwindled and they are having to look for food in other areas as they can no longer rely exclusively on their land.

However, in some cases, land has been developed by oil palm plantations without consultation or compensation of the Indigenous Peoples occupying the land. This has occurred in Papua New Guinea, Colombia, and Indonesia. In the Sarawak state of Malaysian Borneo, there has been debate over whether there was an appropriate level of consultation with the Long Teran Kanan community prior to the development of local land for palm oil plantations. Appropriation of native lands has led to conflict between the plantations and local residents in each of these countries.

According to a 2008 report by NGOs including Friends of the Earth, palm oil companies have also reportedly used force to acquire land from Indigenous communities in Indonesia. Additionally, some Indonesian oil palm plantations are dependent on imported labor or undocumented immigrants, which has raised concerns about the working conditions and social impacts of these practices. Issues regarding the exploitation of child labor have also been a major concern.

Deforestation

Habitat loss

The production of palm oil requires intensive deforestation and this has led to a gradual loss of flora and fauna in the areas where land is cleared for the cultivation of palm oil. Tropical rainforests in countries including Malaysia and Indonesia have been the most ideal countries to have large palm oil plantations as they provide the most suitable climate with ample rainfall and sunshine throughout the year. Between the years 1990 and 2005, the total land in Malaysia used for palm oil cultivation increased by 2.4 million ha and reached 4.2 million ha. During that period, over 1.1 million ha of tropical rainforest was lost. The diverse biodiversity that each rainforest possesses has been diminishing at a rapid rate as fauna is often very fragile and easily affected by deforestation. Animal wildlife has been most affected in areas where significant amounts of land, for commercial palm oil purposes, have been cleared to allow the trees to be planted. Animals have been forced to relocate and have increasingly come into contact with humans as they have started to roam around the surrounding villages in search for food. Some animals have not been able to adapt and relocate elsewhere, leading to their populations decreasing significantly and this has disrupted the symbiotic relationships that the flora and fauna have with their habitat. Deforestation negatively affects biodiversity when forests are converted into plantations and leaves relatively low species richness in primary forests compared to undisturbed forests. One species of particular concern is the critically endangered Bornean orangutan. A notable study in 2018 showed that from 1999 to 2015, over 100,000 orangutans were lost due to unsustainable natural resource exploitation (including the palm oil industry). This number was obtained by tracking the number of nests over this 16 year study period. Results show that nests declined from 22.5 nests per kilometer at the start of the study, to 10.1 nests per kilometer by the end of the study. On the other hand E. guineensis cultivation also helps to push species invasions further, e.g. Anoplolepis gracilipes in southeast Asia. Biodiversity suffers in almost all taxa – Room 1975 and Fayle et al 2010 find so for ants, Danielsen and Heegaard 1995 for bats and primates, Liow et al 2001 for bees, Chung et al 2000 for beetles, Peh et al 2006 for birds, Davis and Philips 2005 for dung beetles, Hassall et al 2006 for isopods, Glor et al 2001 for lizards, Chang et al 1997 for mosquitoes, Chey 2006 for moths, and Bernard et al 2009 for small mammals. Almost all taxa also suffer loss of abundance but there are exceptions, species which increase abundance but still lose species richness – Davis and Philips 2005 find so in dung beetles, Hassall et al 2006 in isopods, Glor et al 2001 in lizards and Danielsen and Heegaard 1995 in bats. The very unusual exception is bees, which Liow et al 2001 find lose abundance but gain species diversity in oil palm.

Soil degradation

The process of removing existing flora and planting palm oil trees is detrimental for the quality of the soil in the ground. When the existing flora is removed to make way for the new plants, the soil surrounding it is often eroded away. When palm oil trees are planted, large amounts of fertilisers and pesticides are used to ensure rapid growth and the health of each tree. Younger palm oil trees absorb more valuable nutrients from the soil which degrades the quality of the soil. As the nutrients are absorbed by the young trees, there is a depletion in nutrients and consequently, there is a lower level of remaining nutrients for other trees. This problem is also another cause for the increased use of fertilisers during the palm oil production process. Distances between adjacent palm oil trees in plantations have also been designed to be very close in order to optimise use of the limited space available. This has further impacted soil quality because as the trees grow, they require more minerals and water from the soil. Due to the close distances between trees, there is a limited supply of nutrients that the trees can depend on which leads to the plantation workers supplying the trees with higher amounts of fertilisers, pesticides and water. This process further harms the state of the soil and makes it challenging for existing flora and fauna to survive in the area. Tuma et al 2019 find replacement of forest with oil palm plantations reduces the number of bioturbator species, although not the actual volume of bioturbation performed.

In tropical countries such as Malaysia and Indonesia, where a majority of palm oil plantations are located, there are continual rain showers and sun exposure throughout the day. Palm oil plantations that are geographically located close to rivers have exacerbated impacts on surrounding local communities. This is due to the increased use of fertilisers and pesticides which has led to higher amounts of both being washed away by the frequent rain into rivers. This is an issue because rivers are central to the daily lives of local villagers. They use water from the river for personal consumption and also use the river as a source of food, which makes them vulnerable to the residue from fertilisers and pesticides. The untreated water that the local villagers are exposed to can potentially cause detrimental health effects, including diseases such as cholera, E. coli and lead poisoning.

The damage from soil erosion and poor soil quality has also affected the livelihoods of many local villagers that live close to these palm oil plantations as they can no longer depend solely on their land for the cultivation of food and timber. Local villagers are now inclined to find new sources of food and materials for shelter. As a result, local villagers have been indirectly forced to move out and relocate depending on the extent of the loss of the plants and animals native to the area. This has led to economic complications as governments now need to reallocate their resources to support these typically marginalised communities.

Other environmental issues

A satellite image showing deforestation in Malaysian Borneo to allow the plantation of oil palm

 

The remaining distribution of the Sumatran orangutan in Indonesia

 

A Sumatran orangutan at Bukit Lawang, Indonesia

In Indonesia, rising demand for palm oil and timber has led to the clearing of tropical forest land in Indonesian national parks. According to a 2007 report published by UNEP, at the rate of deforestation at that time, an estimated 98 percent of Indonesian forest would be destroyed by 2022 due to legal and illegal logging, forest fires and the development of palm oil plantations.

Malaysia, the second largest producer of palm oil has pledged to conserve a minimum of 50 percent of its total land area as forests. As of 2010, 58 percent of Malaysia was forested.

Palm oil cultivation has been criticised for:

• Greenhouse gas emissions. Deforestation in tropical areas accounts for an estimated 10 percent of manmade CO
  ₂ emissions, and is a driver toward dangerous climate change.
• Habitat destruction, leading to the demise of critically endangered species (e.g. the Sumatran elephant, Sumatran tiger, the Sumatran rhinoceros, and the Sumatran orangutan).
• Reduced biodiversity, including damage to biodiversity hotspots.
• Cultivating crops on land that belongs to indigenous people in the Sarawak and Kalimantan states on the island of Borneo and the Malaysian state of Sabah.
• The increase in outbreaks of zoonotic diseases is linked with deforestation in tropical countries.

Water pollution

Main article: Water pollution

In some states where oil palm is established, lax enforcement of environmental legislation leads to encroachment of plantations into riparian strips, and release of pollutants such as palm oil mill effluent (POME) into the environment. POME is a waste product created during the final stages of palm oil extraction. The process of waste management can be highly difficult and costly. As a result, one common method of disposal involves discharge into nearby water reservoirs. POME contains high nutrient concentrations and can foster the growth of algae blooms, which deplete oxygen levels and can have negative implications for aquatic life, and consequently alter ecosystems.

More environment-friendly practices have been developed. Among those approaches is anaerobic treatment of POME, which might allow for biogas (methane) production and electricity generation, but it is very difficult to maintain optimum growth conditions for the anaerobic organisms that break down acetate to methane (primarily Methanosaeta concilii, a species of Archaea).

Greenhouse gas emissions

Damage to peatland, partly due to palm oil production, is claimed to contribute to environmental degradation, including four percent of global greenhouse gas emissions and eight percent of all global emissions caused annually by burning fossil fuels, due to the clearing of large areas of rainforest for palm oil plantations. Many Indonesian and Malaysian rainforests lie atop peat bogs that store great quantities of carbon. Forest removal and bog drainage to make way for plantations releases this carbon. A study reveals that the conversion of peatlands contributes between 16.6 and 27.9 percent of total greenhouse gas emissions from Malaysia and Indonesia combined. The process of draining peatlands and the growth of young palms results in 50 percent greater greenhouse gas emissions when compared to mature plantations. This is a growing concern among ecologists and environmentalists as more tropical peatlands are being converted into plantations due to land shortage, in order to meet the increasing demand for palm oil.

Researchers are looking for possible, more environmentally friendly, solutions and ways to help the situation and have suggested that if enough land is conserved and there remain large enough areas of primary forest reserves, the effects of the palm oil industry may not have as much of an impact on wildlife and biodiversity. Environmental groups like Greenpeace, the Roundtable on Sustainable Palm Oil, and Amnesty International are also taking part in advocating bans on unsustainable palm oil crops and the companies that purchase these exports.

Environmental groups such as Greenpeace claim that this deforestation produces far more emissions than biofuels remove. Greenpeace identified Indonesian peatlands—unique tropical forests whose dense soil can be burned to release carbon emissions—which are being destroyed to make way for palm oil plantations. Greenpeace argues the peatlands represent massive carbon sinks, and they claim the destruction already accounts for four percent of annual global CO₂ emissions. However, according to the Tropical Peat Research Laboratory, at least one measurement has shown that oil palm plantations are carbon sinks because oil palms convert carbon dioxide into oxygen just as other trees do, and, as reported in Malaysia's Second National Communication to the United Nations Framework Convention on Climate Change, oil palm plantations contribute to Malaysia's net carbon sink.

Greenpeace recorded peatland destruction in the Indonesian province of Riau on the island of Sumatra, home to 25 percent of Indonesia's palm oil plantations. Greenpeace claims this would have devastating consequences for Riau's peatlands, which have already been degraded by industrial development and store a massive 14.6 billion tonnes of carbon, roughly one year's greenhouse gas emissions.

Environmentalists and conservationists have been called upon to team up with palm oil companies to purchase small tracts of existing palm plantation, so they can use the profits to create privately owned nature reserves. It has been suggested that this is a more productive strategy than the current confrontational approach that threatens the livelihoods of millions of smallholders.

Haze

Main article: Southeast Asian haze

 

A 2005 air pollution crisis in Kuala Lumpur. Southeast Asian haze is a recurrent issue linked to land clearing for palm oil and pulpwood.

Haze, a form of air pollution, is a major recurrent issue across Southeast Asia, partly linked to burning of rainforest and peat swamp forest to clear land for palm oil plantations.

National differences

A palm oil plantation in Indonesia

Indonesia and Malaysia

Main articles: Palm oil production in Indonesia and Palm oil production in Malaysia

In the two countries responsible for over 80% of world oil palm production, Indonesia and Malaysia, smallholders account for 35–40% of the total area of planted oil palm and as much as 33% of the output. Elsewhere, as in West African countries that produce mainly for domestic and regional markets, smallholders produce up to 90% of the annual harvest.

As a result of Malaysia's commitment to retain natural forest cover on at least 50% of the nation's land, the growth of new palm oil plantations has slowed in recent years. According to Malaysia's Plantation Industries and Commodities Minister Bernard Dompok, significant expansion of palm oil is no longer possible, therefore Malaysian farmers are now focusing on increasing production without expansion.

In January 2008, the CEO of the Malaysian Palm Oil Council wrote a letter to the Wall Street Journal stating that Malaysia was aware of the need to pursue a sustainable palm oil industry. Since then the Malaysian government, along with palm oil companies, have increased production of certified sustainable palm oil (CSPO). Malaysia has been recognized by the Roundtable on Sustainable Palm Oil as the largest producer of CSPO, producing 50% of the world's supply, and accounting for 40% of CSPO growers worldwide. Indonesia produces 35% of the world's CSPO.

In Indonesia, the Indigenous Peoples' Alliance of the Archipelago (AMAN) under the direction of Mina Susana Setra has fought for policies that find balance between economic need and indigenous people's rights. 99% of the palm oil concessions in the country concern land that is occupied by indigenous people. In 2012, AMAN led an advocacy team which won a Constitutional Court case recognizing customary land rights; however, implementation of programs that protect indigenous rights, the environment and developers have failed to come to fruition except in limited cases.

Africa

In Africa, the situation is very different compared to Indonesia or Malaysia. In its Human Development Report 2007-2008, the United Nations Development Program says production of palm oil in West Africa is largely sustainable, mainly because it is undertaken on a smallholder level without resorting to diversity-damaging monoculture. The United Nations Food and Agriculture program is encouraging small farmers across Africa to grow palm oil, because the crop offers opportunities to improve livelihoods and incomes for the poor.

Increasing demand

Food and cosmetics companies, including ADM, Unilever, Cargill, Procter & Gamble, Nestlé, Kraft and Burger King, are driving the demand for new palm oil supplies, demand was partly driven by a need for a replacement for high trans fat content oils.

Although palm oil is used in the production of biofuels and proposals have been made to use it in large installations, a 2012 report by the International Food Policy Research Institute concluded that the increase in palm oil production is related to food demands, not biofuel demands.

Biodiesel

Biodiesel made from palm oil grown on sustainable non-forest land and from established plantations reduces greenhouse gas emissions. According to Greenpeace, clearing peatland to plant oil palms releases large amounts of greenhouse gasses, and that biodiesel produced from oil palms grown on this land may not result in a net reduction of greenhouse gas emissions. However, research by Malaysia's Tropical Peat Research Unit has found that oil palm plantations developed on peatland produce lower carbon dioxide emissions than forest peat swamp. However, it has been suggested that this research unit was commissioned by politicians who have interests in the palm oil industry.

In 2011, eight of Malaysia's Federal Land Development Authority (FELDA) plantations were certified under the International Sustainability and Carbon Certification System (ISCC), becoming part of Asia's first ISCC certified supply and production chain for palm biodiesel. This certification system complies with the European Union's Renewable Energy Directive (RED). In 2012, the European Commission approved the RSPO's biofuel certification scheme allowing certified sustainable palm oil biofuel to be sold in Europe.

Sustainability

In Borneo, the forest (F), is being replaced by oil palm plantations (G). These changes are irreversible for all practical purposes (H).

At least 17.4% of palm oil fruit produced globally in 2016 complied with voluntary sustainability standards such as the Roundtable on Sustainable Palm Oil, Rainforest Alliance, and organic.

The Roundtable on Sustainable Palm Oil (RSPO), founded in 2004, works to promote the production of sustainably sourced palm oil through involvement with growers, processors, food companies, investors and NGOs. Beginning in 2008, palm oil that meets RSPO introduced standards has been designated "certified sustainable palm oil" (CSPO). Within two years of implementation, CSPO-designated palm oil comprised 7 percent of the global palm oil market. As of October 2012, 12 percent of palm oil has been certified by the RSPO. However, in the first year of CSPO certification only 30 percent of sustainable oil was marketed as CSPO.

In The Economist in 2010, the RSPO was criticized for not setting standards for greenhouse-gas emissions for plantations and because its members account for only 40 percent of palm oil production. In a 2007 report, Greenpeace was critical of RSPO-member food companies saying that they are "dependent on suppliers that are actively engaged in deforestation and the conversion of peatlands".

Following a contribution of $1 billion from Norway, in May 2010, Indonesia announced a two-year suspension on new agreements to clear natural forests and peatlands. Additionally, Indonesia announced plans to create its own organization similar to the RSPO, which, as a government certification system, will introduce mandatory regulation for all Indonesian palm oil producers.

In 2011, Malaysia began developing a national certification, the "Malaysia sustainable palm oil" (MSPO) certification, to improve involvement in sustainable palm oil production nationwide. The certification program, aimed at small and medium-sized producers, is expected to be launched in 2014. Malaysia has initiated its own environmental assessment on oil palm industry based on Life Cycle Assessment (LCA) approaches. LCA has been applied to assess the environmental impact of production of oil palm seedlings, oil palm fresh fruit bunches, crude palm oil, crude palm kernel oil and refined palm oil. The assessment on downstream industries such as bio-diesel, was also conducted.

In July 2020 scientists show via detailed analysis of satellite images that certified "sustainable" palm oil production resulted in deforestation of tropical forests of Sumatra and Borneo and endangered mammals' habitat degradation in the past 30 years.

Carbon credit programs

Oil palm producers are eligible to take part in Clean Development Mechanism (CDM) programs in which developed nations invest in clean energy projects in developing nations to earn carbon credits to offset their own greenhouse gas emissions and to reduce greenhouse gas emissions worldwide.

Investors have been cautious about investing in palm oil biofuel projects because of the impact the expansion of oil palm plantations has had on tropical rain forests, but according to the South East Asian CDM development company YTL-SV Carbon, many CDM projects in the palm oil sector focus on improving use of waste products to reduce gas emissions and do not contribute to the establishment of new oil palm plantations.

SPOTT: ESG policy transparency assessments

Basics of environmental sustainability

Palm oil output has been gradually increasing since the end of the twentieth century, with a 15-fold rise between 1980 and 2014. (IUCN, 2021). Aside from the main producing countries of Indonesia and Malaysia, Latin American countries are beginning to play a larger role in the global palm oil industry.

SPOTT is a free, online platform that evaluates commodity producers, processors, and traders on their public disclosure on environmental, social, and governance (ESG) issues.

SPOTT evaluates the public disclosure of 100 palm oil producers, processors, and traders in terms of their organization, policies, and practices relating to environmental, social, and governance (ESG) issues. To track their growth over time, each company is given a percentage score.

For palm oil, timber and pulp, and natural rubber companies, SPOTT assessments follow three complete frameworks of best practice indicators. Each framework includes precise scoring criteria for over 100 indicators that are grouped into ten categories.

The SPOTT indicators were created by ZSL in consultation with technical consultants to ensure that they are closely matched with related programs such as the United Nations Sustainable Development Goals.

Policies and pledges made by the company may not be carried out effectively on the ground. Although the media monitor on each company's page may provide some insight, independent due diligence should include measures to analyze implementation levels.

Use of sustainable oil by corporations

The World Wildlife Foundation (WWF) publishes an annual report on the use of sustainable palm oil by major corporations. In the 2011 report, 31 of the 132 companies surveyed received a top score for their use of sustainable palm oil. This represents an increase from 2009, the first year the report was issued, where no companies received top scores.

The WWF reports that 87 companies have committed to using only sustainable palm oil by 2015, including Unilever and Nestlé, both of which committed to exclusively using sustainable palm oil following demonstrations and urgings from environmental organizations in the late 2000s. However, according to the WWF, the overall growth in the use of sustainable palm oil is too slow.

Retailers who have made commitments to offering products containing sustainable oil, including Walmart and Carrefour, have attributed the slow rate of growth in the availability of sustainable palm oil to a lack of consumer interest and awareness in products made with sustainable palm oil. These companies have expressed concern about the potential impact of low consumer demand on the cost and future availability of sustainable palm oil.

Persuading governments

It may be possible to persuade governments of nations that produce competing products to enact protectionist legislation against the products of deforestation, an approach that was presented in a report by the National Farmers Union (United States) and Avoided Deforestation Partners. The 2010 report estimates that protecting the 13,000,000 hectares (50,000 sq mi) of mostly tropical forest that are lost annually worldwide would boost American agricultural revenue by $190–270 billion between 2012 and 2030. However, several conservation groups, including Conservation International, Environmental Defense Fund, National Wildlife Federation, and The Nature Conservancy, presented a rebuttal to the report, stating that it was "based on the assumption, totally unfounded, that deforestation in tropical countries can be easily interrupted, and its conclusions are therefore also unrealistic."

Photocatalytic water splitting

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Photocatalytic_water_splitting

Photocatalytic water splitting is a process that uses photocatalysis for the dissociation of water (H₂O) into hydrogen (H
₂) and oxygen (O
₂). Only light energy (photons), water, and a catalyst(s) are needed, since this is what naturally occurs in natural photosynthetic oxygen production and CO₂ fixation.

Hydrogen fuel production using water and light (photocatalytic water splitting), instead of petroleum, is an important renewable energy strategy.

Concepts

2 mol H₂O is split into 1 mol O
₂ and 2 mol H
₂ using light in the process shown below.

${\displaystyle \begin{array}{c}E>1.23\text{eV}\\ 2{\text{H}}_2^{}\text{O}\stackrel{-\rightharpoonup }{\leftharpoondown -}2{\text{H}}_2^{}+{\text{O}}_2^{}\\ (E\text{: photon energy.})\end{array}}$

The process of water-splitting is a highly endothermic process (ΔH > 0). Water splitting occurs naturally in photosynthesis when the energy of four photons is absorbed and converted into chemical energy through a complex biochemical pathway (Dolai's or Kok's S-state diagrams).

O–H bond homolysis in water requires energy of 6.5 - 6.9 eV (UV photon). Infrared light has sufficient energy to mediate water splitting because it technically has enough energy for the net reaction. However, it does not have enough energy to mediate the elementary reactions leading to the various intermediates involved in water splitting (this is why there is still water on Earth). Nature overcomes this challenge by absorbing four visible photons. In the laboratory, this challenge is typically overcome by coupling the hydrogen production reaction with a sacrificial reductant other than water.

Materials used in photocatalytic water splitting fulfill the band requirements and typically have dopants and/or co-catalysts added to optimize their performance. A sample semiconductor with the proper band structure is titanium dioxide (TiO
₂) and is typically used with a co-catalyst such as platinum (Pt) to increase the rate of H
₂ production. A major problem in photocatalytic water splitting is photocatalyst decomposition and corrosion.

Method of evaluation

Photocatalysts must conform to several key principles in order to be considered effective at water splitting. A key principle is that H
₂ and O
₂ evolution should occur in a stoichiometric 2:1 ratio; significant deviation could be due to a flaw in the experimental setup and/or a side reaction, neither of which indicate a reliable photocatalyst for water splitting. The prime measure of photocatalyst effectiveness is quantum yield (QY), which is:

QY (%) = (Photochemical reaction rate) / (Photon absorption rate) × 100%

To assist in comparison, the rate of gas evolution can also be used. A photocatalyst that has a high quantum yield and gives a high rate of gas evolution is a better catalyst.

The other important factor for a photocatalyst is the range of light that is effective for operation. For example, a photocatalyst is more desirable to use visible photons than UV photons.

Photocatalysts

The solar-to-hydrogen (STH) efficiency of photocatalytic water splitting, however, has remained very low. Here we have developed a strategy to achieve a high STH efficiency of 9.2 per cent using pure water, concentrated solar light and an indium gallium nitride photocatalyst. The success of this strategy originates from the synergistic effects of promoting forward hydrogen–oxygen evolution and inhibiting the reverse hydrogen–oxygen recombination by operating at an optimal reaction temperature (about 70 degrees Celsius), which can be directly achieved by harvesting the previously wasted infrared light in sunlight. Moreover, this temperature-dependent strategy also leads to an STH efficiency of about 7 per cent from widely available tap water and sea water and an STH efficiency of 6.2 per cent in a large-scale photocatalytic water-splitting system with a natural solar light capacity of 257 watts. Our study offers a practical approach to produce hydrogen fuel efficiently from natural solar light and water, overcoming the efficiency bottleneck of solar hydrogen production.

NaTaO
₃:La

NaTaO
₃:La yielded the highest water splitting rate of photocatalysts without using sacrificial reagents. This ultraviolet-based photocatalyst was reported to show water splitting rates of 9.7 mmol/h and a quantum yield of 56%. The nanostep structure of the material promotes water splitting as edges functioned as H
₂ production sites and the grooves functioned as O
₂ production sites. Addition of NiO particles as co-catalysts assisted in H
₂ production; this step used an impregnation method with an aqueous solution of Ni(NO
₃)
₂•6H
₂O and evaporated the solution in the presence of the photocatalyst. NaTaO
₃ has a conduction band higher than that of NiO, so photo-generated electrons are more easily transferred to the conduction band of NiO for H
₂ evolution.

K
₃Ta
₃B
₂O
₁₂

K
₃Ta
₃B
₂O
₁₂ is another catalyst solely activated by UV and above light. It does not have the performance or quantum yield of NaTaO
₃:La. However, it can split water without the assistance of co-catalysts and gives a quantum yield of 6.5%, along with a water splitting rate of 1.21 mmol/h. This ability is due to the pillared structure of the photocatalyst, which involves TaO
₆ pillars connected by BO
₃ triangle units. Loading with NiO did not assist the photocatalyst due to the highly active H
₂ evolution sites.

(Ga
_.82Zn
_.18)(N
_.82O
_.18)

(Ga
_.82Zn
_.18)(N
_.82O
_.18) had the highest quantum yield in visible light for visible light-based photocatalysts that do not utilize sacrificial reagents as of October 2008. The photocatalyst featured a quantum yield of 5.9% and a water splitting rate of 0.4 mmol/h. Tuning the catalyst was done by increasing calcination temperatures for the final step in synthesizing the catalyst. Temperatures up to 600 °C helped to reduce the number of defects, while temperatures above 700 °C destroyed the local structure around zinc atoms and were thus undesirable. The treatment ultimately reduced the amount of surface Zn and O defects, which normally function as recombination sites, thus limiting photocatalytic activity. The catalyst was then loaded with Rh
_2-yCr
_yO
₃ at a rate of 2.5 wt% Rh and 2 wt% Cr for better performance.

Molecular catalysts

Proton reduction catalysts based on earth-abundant elements carry out one side of the water-splitting half-reaction.

A mole of octahedral nickel(II) complex, [Ni(bztpen)]²⁺ (bztpen = N-benzyl-N,N’,N’-tris(pyridine-2-ylmethyl)ethylenediamine) produced 308,000 moles of hydrogen over 60 hours of electrolysis with an applied potential of -1.25 V vs. standard hydrogen electrode.

Cobalt-based photocatalysts have been reported, including tris(bipyridine) cobalt(II), compounds of cobalt ligated to certain cyclic polyamines, and some cobaloximes.

In 2014 researchers announced an approach that connected a chromophore to part of a larger organic ring that surrounded a cobalt atom. The process is less efficient than a platinum catalyst although cobalt is less expensive, potentially reducing costs. The process uses one of two supramolecular assemblies based on Co(II)-templated coordination of Ru(bpy)+32 (bpy = 2,2′-bipyridyl) analogues as photosensitizers and electron donors to a cobaloxime macrocycle. The Co(II) centers of both assemblies are high spin, in contrast to most previously described cobaloximes. Transient absorption optical spectroscopies indicate that charge recombination occurs through multiple ligand states within the photosensitizer modules.

Bismuth vanadate

Bismuth vanadate is a visible-light-driven photocatalyst with a bandgap of 2.4 eV. BV have demonstrated efficiencies of 5.2% for flat thin films and 8.2% for core-shell WO₃@BiVO₄ nanorods with thin absorbers.

Bismuth oxides

Bismuth oxides are characterized by visible light absorption properties, just like vanadates.

Tungsten diselenide (WSe₂)

Tungsten diselenide has photocatalytic properties that might be a key to more efficient electrolysis.

III-V semiconductor systems

Systems based on III-V semiconductors, such as InGaP, enable solar-to-hydrogen efficiencies of up to 14%. Challenges include long-term stability and cost.

2D semiconductor systems

2-dimensional semiconductors such as MoS
₂ are actively researched as potential photocatalysts.

Aluminum‐based metal-organic frameworks (MOF)

An aluminum‐based metal-organic framework (MOF) made from 2‐aminoterephthalate can be modified by incorporating Ni²⁺ cations into the pores through coordination with the amino groups. Molybdenum disulfide

Porous organic polymers (POPs)

Organic semiconductor photocatalysts, in particular porous organic polymers (POPs), attracted attention due to their low cost, low toxicity, and tunable light absorption vs inorganic counterparts. They display hHigh porosity, low density, diverse composition, facile functionalization, high chemical/thermal stability, as well as high surface areas. Efficient conversion of hydrophobic polymers into hydrophilic polymer nano-dots (Pdots) increased polymer-water interfacial contact, which significantly improved performance.

Ansa-Titanocene(III/IV) Triflate Complexes

Beweries, et. al., developed a light-driven "losed cycle of water splitting using ansa-titanocene(III/IV) triflate complexes".

Indium gallium nitride

An Indium gallium nitride (InxGa1-xN) photocatalyst achieved a solar-to-hydrogen efficiency of 9.2% from pure water and concentrated sunlight. The effiency is due to the synergistic effects of promoting hydrogen–oxygen evolution and inhibiting recombination by operating at an optimal reaction temperature (~70 degrees C), powered by harvesting previously wasted infrared light. An STH efficiency of about 7% was realized from tap water and seawater and efficiency of 6.2% in a larger-scale system with a solar light capacity of 257 watts.

Sacrificial reagents

Cd
_1-xZn
_xS

Solid solutions Cd
_1-xZn
_xS with different Zn concentration (0.2 < x < 0.35) have been investigated in the production of hydrogen from aqueous solutions containing ${\displaystyle {\text{SO}}_3^{2-}/{\text{S}}^{2-}}$ as sacrificial reagents under visible light. Textural, structural and surface catalyst properties were determined by N
₂ adsorption isotherms, UV–vis spectroscopy, SEM and XRD and related to the activity results in hydrogen production from water splitting under visible light. It was reported that the crystallinity and energy band structure of the Cd
_1-xZn
_xS solid solutions depend on their Zn atomic concentration. The hydrogen production rate increased gradually as Zn concentration on photocatalysts increased from 0.2 to 0.3. The subsequent increase in the Zn fraction up to 0.35 reduced production. Variation in photoactivity was analyzed for changes in crystallinity, level of the conduction band and light absorption ability of Cd
_1-xZn
_xS solid solutions derived from their Zn atomic concentration.

Solar fuel

From Wikipedia, the free encyclopedia

A solar fuel is a synthetic chemical fuel produced from photovoltaic solar energy. Solar fuels can be produced through photochemical (i.e. activation of certain chemical reactions by photons), photobiological (i.e., artificial photosynthesis), and electrochemical reactions (i.e. using the electricity from solar panels to drive a chemical reaction).

Solar fuels can also be produced by thermochemical reactions (i.e., through the use of solar heat supplied by concentrated solar thermal energy to drive a chemical reaction).

Light is used as an energy source, with solar energy being transduced to chemical energy, typically by reducing protons to hydrogen, or carbon dioxide to organic compounds.

A solar fuel can be produced and stored for later use, when sunlight is not available, making it an alternative to fossil fuels and batteries. Examples of such fuels are hydrogen, ammonia, and hydrazine. Diverse photocatalysts are being developed to carry these reactions in a sustainable, environmentally friendly way.

Overview

The world's dependence on the declining reserves of fossil fuels poses not only environmental problems but also geopolitical ones. Solar fuels, in particular hydrogen, are viewed as an alternative source of energy for replacing fossil fuels especially where storage is essential. Electricity can be produced directly from sunlight through photovoltaics, but this form of energy is rather inefficient to store compared to hydrogen. A solar fuel can be produced when and where sunlight is available, and stored and transported for later usage. This makes it much more convenient, because it can be used in situations where direct sunlight is not available.

The most widely researched solar fuels are hydrogen, because the only product of using this fuel is water, and products of photochemical carbon dioxide reduction, which are more conventional fuels like methane and propane. Upcoming research also involves ammonia and related substances (i.e. hydrazine). These can address the challenges that come with hydrogen, by being a more compact and safer way of storing hydrogen. Direct ammonia fuel cells are also being researched.

Solar fuels can be produced via direct or indirect processes. Direct processes harness the energy in sunlight to produce a fuel without intermediary energy conversions. Solar thermochemistry uses the heat of the sun directly to heat a receiver adjacent to the solar reactor where the thermochemical process is performed. In contrast, indirect processes have solar energy converted to another form of energy first (such as biomass or electricity) that can then be used to produce a fuel. Indirect processes have been easier to implement but have the disadvantage of being less efficient than the direct method. Therefore, direct methods should be considered more interesting than their less efficient counterparts. New research therefore focusses more on this direct conversion, but also in fuels that can be used immediately to balance the power grid.

Hydrogen production

See also: Hydrogen production

Photoelectrochemical

See also: Photoelectrolysis of water

 

A sample of a photoelectric cell in a lab environment. Catalysts are added to the cell, which is submerged in water and illuminated by simulated sunlight. The bubbles seen are oxygen (forming on the front of the cell) and hydrogen (forming on the back of the cell).

In a solar photoelectrochemical process, hydrogen can be produced by electrolysis. To use sunlight in this process, a photoelectrochemical cell can be used, where one photosensitized electrode converts light into an electric current that is then used for water splitting. One such type of cell is the dye-sensitized solar cell. This is an indirect process, since it produces electricity that then is used to form hydrogen. Another indirect process using sunlight is conversion of biomass to biofuel using photosynthetic organisms; however, most of the energy harvested by photosynthesis is used in life-sustaining processes and therefore lost for energy use.

A semiconductor can also be used as the photosensitizer. When a semiconductor is hit by a photon with an energy higher than the bandgap, an electron is excited to the conduction band and a hole is created in the valence band. Due to band bending, the electrons and holes move to the surface, where these charges are used to split the water molecules. Many different materials have been tested, but none so far have shown the requirements for practical application.

Photochemical

See also: Photocatalytic water splitting

In a photochemical process, the sunlight is directly used to split water into hydrogen and oxygen. Because the absorption spectrum of water does not overlap with the emission spectrum of the sun, direct dissociation of water cannot take place; a photosensitizer needs to be used. Several such catalysts have been developed as proof of concept, but not yet scaled up for commercial use; nevertheless, their relative simplicity gives the advantage of potential lower cost and increased energy conversion efficiency. One such proof of concept is the "artificial leaf" developed by Nocera and coworkers: a combination of metal oxide-based catalysts and a semiconductor solar cell produces hydrogen upon illumination, with oxygen as the only byproduct.

Photobiological

In a photobiological process, the hydrogen is produced using photosynthetic microorganisms (green microalgae and cyanobacteria) in photobioreactors. Some of these organisms produce hydrogen upon switching culture conditions; for example, Chlamydomonas reinhardtii produces hydrogen anaerobically under sulfur deprivation, that is, when cells are moved from one growth medium to another that does not contain sulfur, and are grown without access to atmospheric oxygen. Another approach was to abolish activity of the hydrogen-oxidizing (uptake) hydrogenase enzyme in the diazotrophic cyanobacterium Nostoc punctiforme, so that it would not consume hydrogen that is naturally produced by the nitrogenase enzyme in nitrogen-fixing conditions. This N. punctiforme mutant could then produce hydrogen when illuminated with visible light.

Another mutant Cyanobacteria, Synechocystis, is using genes of the bacteria Rubrivivax gelatinosus CBS to produce hydrogen. The CBS bacteria produce hydrogen through the oxidation of carbon monoxide. Researchers are working to implement these genes into the Synechocystis. If these genes can be applied, it will take some effort to overcome the problems of oxygen inhibition in the production of hydrogen, but it is estimated that this process can potentially yield as much as 10% solar energy capture. This makes photobiological research a very exciting and promising branch of the hydrogen production explorations. Still the problems of overcoming the short-term nature of algal hydrogen production are many and research is in the early stages. However, this research provides a viable way to industrialize these renewable and environmental friendly processes.

Thermochemical

See also: Thermochemical cycle

In the solar thermochemical process, water is split into hydrogen and oxygen using direct solar heat, rather than electricity, inside a high temperature solar reactor which receives highly concentrated solar flux from a solar field of heliostats that focus the highly concentrated sunlight into the reactor.

The two most promising routes are the two step cerium oxide cycle and the copper chlorine hybrid cycle. For the cerium oxide cycle the first step is to strip the CeO₃ into Ce₂O₃ at more than 1400 °C. After the thermal reduction step to reduce the metal oxide, hydrogen is then produced through hydrolysis at around 800 °C. The copper chloride cycle requires a lower temperature (~500°C), which makes this process more efficient, but the cycle contains more steps and is also more complex than the cerium oxide cycle.

Because hydrogen manufacture requires continuous performance, the solar thermochemical process includes thermal energy storage. Another thermochemical method uses solar reforming of methane, a process that replicates traditional fossil fuel reforming process but substitutes solar heat.

In a November 2021 publication in Nature, Aldo Steinfeld of Swiss technological university ETH Zurich reported an artificial photosynthesis where carbon dioxide and water vapour absorbed from the air are passed over a cerium oxide catalyst heated by concentrated solar power to produce hydrogen and carbon monoxide, transformed through the Fischer-Tropsch process into complex hydrocarbons forming methanol, a liquid fuel. Scaling could produce the 414 billion L (414 million m³) of aviation fuel used in 2019 with a surface of 45,000 km² (17,000 sq mi): 0.5% of the Sahara Desert. One author, Philipp Furler, leads specialist Synhelion, which in 2022 was building a solar fuel production facility at Jülich, west of Cologne, before another one in Spain. Swiss airlines, part of the Lufthansa Group, should become its first customer in 2023.

Carbon dioxide reduction

See also: Electrochemical reduction of carbon dioxide, Photoelectrochemical reduction of carbon dioxide, Photochemical reduction of carbon dioxide, and Biofuel

Carbon dioxide (CO₂) can be reduced to carbon monoxide (CO) and other more reduced compounds, such as methane, using the appropriate photocatalysts. One early example was the use of Tris(bipyridine)ruthenium(II) chloride (Ru(bipy)₃Cl₂) and cobalt chloride (CoCl₂) for CO₂ reduction to CO. In recent years many new catalysts have been found to reduce CO₂ into CO, after which the CO could be used to make hydrocarbons using for example the Fischer-Tropsch process. The most promising system for the solar-powered reduction of CO₂ is the combination of a photovoltaic cell with an electrochemical cell (PV+EC).

For the photovoltaic cell the highly efficient GaInP/GaAs/Ge solar cell has been used, but many other series-connected and/or tandem (multi-junction) PV architectures can be employed to deliver the required voltage and current density to drive the CO₂ reduction reactions and provide reasonable product outflow. The solar cells/panels can be placed in direct contact with the electrolyzer(s), which can bring advantages in terms of system compactness and thermal management of both technologies, or separately for instance by placing the PV outdoors exposed to sunlight and the EC systems protected indoors.

The currently best performing electrochemical cell is the gas diffusion electrode (GED) flow cell. In which the CO₂ reacts on Ag nanoparticles to produce CO. Solar to CO efficiencies of up to 19% have been reached, with minimal loss in activity after 20h. 

CO can also be produced without a catalyst using microwave plasma driven dissociation of CO₂. This process is relatively efficient, with an electricity to CO efficiency of up to 50%, but with low conversion around 10%. These low conversions are not ideal, because CO and CO₂ are hard to separate at large scale in a efficient manner. The big upside of this process is that it can be turned off and on quite rapidly and does not use scarce materials. The (weakly ionised) plasma is produced using microwaves, these microwaves can accelerate the free electrons in the plasma. These electrons interact with the CO₂ which vibrationally excite the CO₂, this leads to dissociation of the CO₂ to CO. The excitation and dissociation happens fast enough that only a little bit of the energy is converted to heat, which keeps the efficiency high. The dissociation also produces an oxygen radical, which reacts with CO₂ to CO and O₂. 

Also in this case, the use of microorganisms has been explored. Using genetic engineering and synthetic biology techniques, parts of or whole biofuel-producing metabolic pathways can be introduced in photosynthetic organisms. One example is the production of 1-butanol in Synechococcus elongatus using enzymes from Clostridium acetobutylicum, Escherichia coli and Treponema denticola. One example of a large-scale research facility exploring this type of biofuel production is the AlgaePARC in the Wageningen University and Research Centre, Netherlands.

Ammonia and hydrazine production

Hydrogen rich substances as ammonia and hydrazine are great for storing hydrogen. This is due to their energy density, for ammonia at least 1.3 times that of liquid hydrogen. Hydrazine is almost twice as dense in energy compared to liquid hydrogen, however a downside is that dilution is required in the use of direct hydrazine fuel cells, which lowers the overall power one can get from this fuel cell. Besides the high volumetric density, ammonia and hydrous hydrazine have a low flammability, which makes it superior to hydrogen by lowering the storage and transportation costs.

Ammonia

Direct ammonia fuel cells are researched for this exact reason and new studies presented a new integrated solar-based ammonia synthesis and fuel cell. The solar base follows from excess solar power that is used to synthesize ammonia. This is done by using an ammonia electrolytic cell (AEC) in combination with a proton exchange membrane (PEM) fuel cell. When a dip in solar power occurs, a direct ammonia fuel cell kicks into action providing the lacking energy. This recent research (2020) is a clear example of efficient use of energy, which is essentially done by temporary storage and use of ammonia as a fuel. Storage of energy in ammonia does not degrade over time, which is the case with batteries and flywheels. This provides long-term energy storage. This compact form of energy has the additional advantage that excess energy can easily be transported to other locations. This needs to be done with high safety measures due to the toxicity of ammonia for humans. Further research needs to be done to complement this system with wind energy and hydro-power plants to create a hybrid system to limit the interruptions in power supply. It is necessary to also investigate on the economic performance of the proposed system. Some scientists envision a new ammonia economy that is almost the same as the oil industry, but with the enormous advantage of inexhaustible carbon-free power. This so called green ammonia is considered as a potential fuel for super large ships. South Korean shipbuilder DSME plans on commercializing these ships by 2025.

Hydrazine

Another way of storing energy is with the use of hydrazine. This molecule is related to ammonia and has the potential to be equally as useful as ammonia. It can be created from ammonia and hydrogen peroxide or via chlorine based oxidations. This makes it an even denser energy storing fuel. The downside of hydrazine is that it is very toxic and that it will react with oxygen quite violently. This makes it an ideal fuel for oxygen low area's such as space. Recent launched Iridium NEXT satellites have hydrazine as their source of energy. However toxic, this fuel has great potential, because safety measures can be increased sufficiently to safely transport and convert hydrazine back into hydrogen and ammonia. Researchers discovered a way to decompose hydrazine with a photo catalysis system that works over the entire visible-light region. This means that sunlight can not only be used to produce hydrazine, but also to produce hydrogen from this fuel. The decomposition of hydrazine is done with a p-n bilayer consisting of fullerene (C₆₀), also known as "buckeyballs" which is a n-type semiconductor and zinc phthalocyanine (ZnPc) which is a p-type semiconductor creating an organic photo catalysis system. This system uses visible light irradiation to excite electrons to the n-type semiconductor creating an electric current. The holes created in the p-type semiconductor are forced in the direction of the so called Nafion part of the device, which oxidizes hydrazine to nitrogen gas and dissolved hydrogen ions. This was done in the first compartment of the fuel cell. The hydrogen ions travel through a salt bridge to another compartment to be reduced to hydrogen gas by the electrons, gained by the interaction with light, from the first compartment. Thus creating hydrogen, which can be used in fuel cells. This promising studies shows that hydrazine is a solar fuel that has great potential to become very useful in the energy transition.

A different approach to hydrazine are the direct fuel cells. The concepts for these cells have been developed since the 1960s. Recent studies provide much better direct hydrazine fuel cells, for example with the use of hydrogen peroxide as an oxidant. Making the anode basic and the cathode acidic increased the power density a lot, showing high peaks of around 1 W/cm² at a temperature of 80 degrees Celsius. As mentioned earlier the main weakness of direct hydrazine fuel cells is the high toxicity of hydrazine and its derivatives. However hydrous hydrazine, which is a water-like liquid retains the high hydrogen density and can be stored and transported safely using the existing fuel infrastructure. Researchers also aim for self-powered fuel cells involving hydrazine. These fuel cells make use of hydrazine in two ways, namely as the fuel for a direct fuel cell and as the splitting target. This means that one only needs hydrazine to produce hydrogen with this fuel cell, so no external power is needed. This is done with the use of iron doped cobalt sulfide nanosheets. The doping with iron decreases the free-energy changes of hydrogen adsorption and hydrazine dehydrogenation. This method has a 20 hour stability and 98% Faradaic efficiency, which is comparable with the best reported claims of self-powered hydrogen generating cells.

Other applications

• Electrolysis of water for hydrogen production combined with solar photovoltaics using alkaline, PEM, and SOEC electrolyzers; This basic use of solar light generated electric power to separate water into hydrogen and oxygen has proven a little bit more efficient than for example hydrogen capture by steam reforming. The alkaline production technology of hydrogen has low costs and is considered mature. This has a consequence that the yield per unit of time is significantly higher than when using PEM technology. However, PEM technology has no corrosion issues and is more efficient, whereas alkaline production technology has the disadvantage of corrosion and worse efficiency. In addition to that, PEM technology has a fast start-up and simple maintenance. Though, in bulk production the alkaline hydrogen production technology is superior.
• Heliogen claims success in the use of solar heliostats used to direct sunlight to a tower, to reach temperatures over 1000°C in the production of hydrogen. Temperatures above 2500°C can thermochemically split water into hydrogen and oxygen without the use of electricity. This can be done using the heat of nuclear power plants or by adaptive solar mirror fields to redirect the sunlight to reach high temperatures needed for these thermochemical processes. However, this way of producing hydrogen is in its infancy and it has not yet been proven that this production hydrogen is profitable and efficient, because it has to compete with other, mature technologies.