While the term was defined originally to mean "methods and
attitudes typical of or attributed to natural scientists", some
scholars, as well as political and religious
leaders, have also adopted it as a pejorative term with the meaning "an
exaggerated trust in the efficacy of the methods of natural science
applied to all areas of investigation (as in philosophy, the social sciences, and the humanities)".
Overview
Francis Bacon has been viewed by some scholars as an early proponent of scientism, but this is a modern assertion as Bacon was a devout Anglican, writing in his Essays, "a little philosophy inclineth man's mind to atheism, but depth in philosophy bringeth men's minds about to religion."
More generally, scientism is often interpreted as science applied "in excess". This use of the term scientism has two senses:
The improper use of science or scientific claims. This usage applies equally in contexts where science might not apply, such as when the topic is perceived as beyond the scope of scientific inquiry, and in contexts where there is insufficient empirical evidence to justify a scientific conclusion. It includes an excessive deference to the claims of scientists or an uncritical eagerness to accept any result described as scientific. This can be a counterargument to appeals to scientific authority.
It can also address attempts to apply natural science methods and
claims of certainty to the social sciences, which Friedrich Hayek
described in The Counter-Revolution of Science
(1952) as being impossible, because those methods attempt to eliminate
the "human factor", while social sciences (including his own topic of economics) mainly concern the study of human action.
"The belief that the methods of natural science, or the categories
and things recognized in natural science, form the only proper elements
in any philosophical or other inquiry", or that "science, and only science, describes the world as it is in itself, independent of perspective" with a concomitant "elimination of the psychological [and spiritual] dimensions of experience".Tom Sorell provides this definition: "Scientism is a matter of putting
too high a value on natural science in comparison with other branches of
learning or culture." Philosophers such as Alexander Rosenberg have also adopted "scientism" as a name for the opinion that science is the only reliable source of knowledge.
It is also sometimes used to describe the universal applicability of the scientific method, and the opinion that empirical science constitutes the most authoritative worldview or the most valuable part of human learning, sometimes to the complete exclusion of other opinions, such as historical,
philosophical, economic or cultural opinions. It has been defined as
"the view that the characteristic inductive methods of the natural
sciences are the only source of genuine factual knowledge and, in particular, that they alone can yield true knowledge about man and society". The term scientism is also used by historians, philosophers, and cultural critics to highlight the possible dangers of lapses towards excessive reductionism with respect to all topics of human knowledge.
For social theorists practising the tradition of Max Weber, such as Jürgen Habermas and Max Horkheimer, the concept of scientism relates significantly to the philosophy of positivism, but also to the cultural rationalization for modern Western civilization.Ernesto Sabato, physicist and essayist, wrote in his 1951 essay Hombres y engranajes ("Man and mechanism") of the "superstition of science" as the most contradictory of all superstitions, since this would be the "superstition that one should not be superstitious". He wrote: "science had become a new magic and the man in the street believed in it the more the less he understood it".
Definitions
Reviewing the references to scientism in the works of contemporary scholars in 2003, Gregory R. Peterson detected two main general themes:
It is used to criticize a totalizing opinion of science as if it were capable of describing all reality and knowledge, or as if it were the only true method to acquire knowledge about reality and the nature of things;
It is used, often pejoratively,
to denote violations by which the theories and methods of one
(scientific) discipline are applied inappropriately to another
(scientific or non-scientific) discipline and its domain. An example of
this second usage is to term as scientism any attempt to claim science
as the only or primary source of human values (a traditional domain of ethics) or as the source of meaning and purpose (a traditional domain of religion and related worldviews).
The term scientism was popularized by F. A. Hayek, who defined it in 1942 as the "slavish imitation of the method and language of Science".
MathematicianAlexander Grothendieck, in his 1971 essay "The New Universal Church", characterized scientism as a religion-like ideology that advocates scientific reductionism, scientific authoritarianism, political technocracy and technological salvation, while denying the epistemological validity of feelings and experiences such as love, emotion, beauty and fulfillment.
He predicted that "in coming years, the chief political dividing line
will fall less and less among the traditional division between 'right' and 'left', but increasingly between the adherents of scientism, who advocate 'technological progress
at any price', and their opponents, i.e., roughly speaking, those who
regard the enhancement of life, in all its richness and variety, as
being the supreme value".
E. F. Schumacher, in his A Guide for the Perplexed (1977), criticized scientism as an impoverished world view confined solely to what can be counted, measured and weighed. "The architects of the modern worldview, notably Galileo and Descartes,
assumed that those things that could be weighed, measured, and counted
were more true than those that could not be quantified. If it couldn't
be counted, in other words, it didn't count."
In 1979, Karl Popper defined scientism as "the aping of what is widely mistaken for the method of science".
In 2003, Mikael Stenmark proposed the expression scientific expansionism as a synonym of scientism. In the Encyclopedia of Science and Religion, he wrote that, while the doctrines
that are described as scientism have many possible forms and varying
degrees of ambition, they share the idea that the boundaries of science
(that is, typically the natural sciences) could and should be expanded
so that something that has not been previously considered as a subject
pertinent to science can now be understood as part of science (usually
with science becoming the sole or the main arbiter regarding this area
or dimension).
According to Stenmark, the strongest form of scientism states that
science does not have any boundaries and that all human problems and all
aspects of human endeavor, with due time, will be dealt with and solved
by science alone. This idea has also been termed the myth of progress.
Intellectual historian T. J. Jackson Lears
argued in 2013 that there has been a recent reemergence of
"nineteenth-century positivist faith that a reified 'science' has
discovered (or is about to discover) all the important truths about
human life. Precise measurement and rigorous calculation, in this view,
are the basis for finally settling enduring metaphysical and moral controversies." Lears specifically identified Harvard psychologist Steven Pinker's work as falling in this category. Philosophers John N. Gray and Thomas Nagel have made similar criticisms against popular works by moral psychologist Jonathan Haidt, atheist author Sam Harris, and writer Malcolm Gladwell.
Strong and weak scientism
There are various ways of classifying kinds of scientism. Some authors distinguish between strong and weak scientism, as follows:
Strong scientism: "of all the knowledge we have, scientific knowledge is the only 'real knowledge'" (Moti Mizrahi), or, "the view that some proposition or theory is true and/or rational to believe if and only if it is a scientific proposition or theory" (J. P. Moreland), or, "only science yields epistemically credible data" (Michael W. Austin)
Weak scientism: "of all the knowledge we have, scientific knowledge is the best knowledge" (Moti Mizrahi), or, "science is the most valuable, most serious, and most authoritative sector of human learning"(J. P. Moreland), or, "scientific knowledge claims are the most credible knowledge claims" (Michael W. Austin)
Relevance to debates about science and religion
Both religious and non-religious scholars have applied the term scientism to individuals associated with New Atheism. TheologianJohn Haught argued that philosopher Daniel Dennett and other New Atheists subscribe to a belief system of scientific naturalism,
which includes the dogma that "only nature, including humans and our
creations, is real: that God does not exist; and that science alone can
give us complete and reliable knowledge of reality."
Haught argued that this belief system is self-refuting since it
requires its adherents to assent to beliefs that violate its own stated
requirements for knowledge.
Christian philosopher Peter Williams argued in 2013 that it is only by
conflating science with scientism that New Atheists feel qualified to
"pontificate on metaphysical issues". Daniel Dennett responded to religious criticism of his 2006 book Breaking the Spell: Religion as a Natural Phenomenon
by saying that accusations of scientism "[are] an all-purpose,
wild-card smear ... When someone puts forward a scientific theory that
[religious critics] really don't like, they just try to discredit it as
'scientism'. But when it comes to facts, and explanations of facts, science is the only game in town".
Non-religious scholars have also associated New Atheist thought with scientism and/or with positivism. Atheist philosopher Thomas Nagel argued that philosopher Sam Harris conflated all empirical knowledge with scientific knowledge. Marxist literary critic Terry Eagleton argued that Christopher Hitchens
possessed an "old-fashioned scientistic notion of what counts as
evidence" that reduces knowledge to what can and cannot be proven by
scientific procedure. Agnostic philosopher Anthony Kenny has also criticized New Atheist philosopher Alexander Rosenberg's The Atheist's Guide to Reality for resurrecting a self-refuting epistemology of logical positivism and reducing all knowledge of the universe to the discipline of physics.
Michael Shermer, founder of The Skeptics Society, discussed resemblances between scientism and traditional religions, indicating the cult of personality that develops for some scientists. He defined scientism as a worldview that encompasses natural explanations, eschews supernatural and paranormal speculations, and embraces empiricism and reason.
The Iranian scholar Seyyed Hossein Nasr has stated that in the Western world, many will accept the ideology of modern science, not as "simple ordinary science", but as a replacement for religion.
Gregory R. Peterson wrote that "for many theologians and philosophers, scientism is among the greatest of intellectual sins". Genetic biologist Austin L. Hughes wrote in the conservative journal The New Atlantis
that scientism has much in common with superstition: "the stubborn
insistence that something ... has powers which no evidence supports."
Repeating common criticisms of logical positivism and verificationism, philosopher of religionKeith Ward has said that scientism is philosophically inconsistent or even self-refuting, as the truth of the two statements "no statements are true unless they can be proven scientifically (or logically)"
and "no statements are true unless they can be shown empirically to be
true" cannot themselves be proven scientifically, logically, or
empirically.
Philosopher Paul Feyerabend, who was an enthusiastic proponent of scientism during his youth, later came to characterize science as "an essentially anarchic enterprise"
and argued emphatically that science merits no exclusive monopoly of
"dealing in knowledge" and that scientists have never operated within a
distinct and narrowly self-defined tradition. In his essay Against Method he depicted the process of contemporary scientific education as a mild form of indoctrination,
intended for "making the history of science duller, simpler, more
uniform, more 'objective' and more easily accessible to treatment by
strict and unchanging rules".
[S]cience can stand on its own feet and does not need any help from rationalists, secular humanists, Marxists
and similar religious movements; and ... non-scientific cultures,
procedures and assumptions can also stand on their own feet and should
be allowed to do so ... Science must be protected from ideologies; and
societies, especially democratic societies, must be protected from
science ... In a democracy scientific institutions, research programmes,
and suggestions must therefore be subjected to public control, there
must be a separation of state and science just as there is a separation
between state and religious institutions, and science should be taught
as one view among many and not as the one and only road to truth and
reality.
Physicist and philosopher Mario Bunge used the term scientism with a favorable rather than pejorative sense in numerous books published during several decades, and in articles with titles such as "In Defense of Realism and Scientism" and "In Defense of Scientism". Bunge said that scientism should not be equated with inappropriate reductionism, and he dismissed critics of science such as Hayek and Habermas as dogmatists and obscurantists:
To innovate in the young sciences
it is necessary to adopt scientism. This is the methodological thesis
that the best way of exploring reality is to adopt the scientific
method, which may be boiled down to the rule "Check your guesses."
Scientism has been explicitly opposed by dogmatists and obscurantists of
all stripes, such as the neoliberal ideologist Friedrich von Hayek and
the "critical theorist" Jürgen Habermas, a ponderous writer who managed
to amalgamate Hegel, Marx, and Freud, and decreed that "science is the
ideology of late capitalism."
In 2018, philosophers Maarten Boudry and Massimo Pigliucci co-edited a book titled Science Unlimited? The Challenges of Scientism in which a number of chapters by philosophers and scientists defended scientism. In his chapter "Two Cheers for Scientism", Taner Edis wrote:
It is defensible to claim that
scientific, philosophical, and humanistic forms of knowledge are
continuous, and that a broadly naturalistic description of our world
centered on natural science is correct ... At the very least, such views
are legitimate—they may be mistaken, but not because of an
elementary error, a confusion of science with ideology, or an offhand
dismissal of the humanities. Those of us who argue for such a view are
entitled to have two cheers for an ambitious conception of science; and
if that is scientism, so be it.
Thomas M. Lessl argued that religious themes persist in what he terms scientism, the public rhetoric of science.
There are two methods of describing this idea of scientism: the
epistemological method (the assumption that the scientific method trumps
other ways of knowing) and the ontological
method (that the rational mind represents the world and both operate in
knowable ways). According to Lessl, the ontological method is an
attempt to "resolve the conflict between rationalism and skepticism".
Lessl also argued that without scientism, there would not be a
scientific culture.
In the introduction to his collected works on the sociology of religion, Max Weber
asked why "the scientific, the artistic, the political, or the economic
development [elsewhere] ... did not enter upon that path of
rationalization which is peculiar to the Occident?" According to the German social theorist Jürgen Habermas, "For Weber, the intrinsic (that is, not merely contingent) relationship between modernity and what he called 'Occidental rationalism' was still self-evident." Weber described a process of rationalisation, disenchantment and the "disintegration of religious world views" that resulted in modern secular societies and capitalism.
"Modernization" was introduced as a
technical term only in the 1950s. It is the mark of a theoretical
approach that takes up Weber's problem but elaborates it with the tools
of social-scientific functionalism ...
The theory of modernization performs two abstractions on Weber's
concept of "modernity". It dissociates "modernity" from its modern
European origins and stylizes it into a spatio-temporally neutral model
for processes of social development in general. Furthermore, it breaks
the internal connections between modernity and the historical context of
Western rationalism,
so that processes of modernization ... [are] no longer burdened with
the idea of a completion of modernity, that is to say, of a goal state
after which "postmodern"
developments would have to set in. ... Indeed it is precisely
modernization research that has contributed to the currency of the
expression "postmodern" even among social scientists.
Habermas is critical of pure instrumental rationality,
arguing that the "Social Life–World" of subjective experiencing is
better suited to literary expression, whereas the sciences deal with
"intersubjectively accessible experiences" that can be generalized in a formal language, while the literary arts "must generate an intersubjectivity of mutual understanding in each concrete case".Habermas quoted writer Aldous Huxley in support of this duality of literature and science:
The world with which literature
deals is the world in which human beings are born and live and finally
die; the world in which they love and hate, in which they experience
triumph and humiliation, hope and despair; the world of sufferings and
enjoyments, of madness and common sense, of silliness, cunning and
wisdom; the world of social pressures and individual impulses, of reason
against passion, of instincts and conventions, of shared language and
unsharable feelings and sensations...
Several methods exist for storing hydrogen.
These include mechanical approaches such as using high pressures and
low temperatures, or employing chemical compounds that release H2
upon demand. While large amounts of hydrogen are produced by various
industries, it is mostly consumed at the site of production, notably for
the synthesis of ammonia. For many years hydrogen has been stored as compressed gas or cryogenic
liquid, and transported as such in cylinders, tubes, and cryogenic
tanks for use in industry or as propellant in space programs. The
overarching challenge is the very low boiling point of H2: it boils around 20.268 K (−252.882 °C or −423.188 °F). Achieving such low temperatures requires expending significant energy.
Although molecular hydrogen has very high energy density on a mass basis, partly because of its low molecular weight,
as a gas at ambient conditions it has very low energy density by
volume. If it is to be used as fuel stored on board a vehicle, pure
hydrogen gas must be stored in an energy-dense form to provide
sufficient driving range. Because hydrogen is the smallest molecule, it
easily escapes from containers. Its effective 100-year global warming potential (GWP100) is estimated to be 11.6 ± 2.8.
Established technologies
Net storage density of hydrogen
Compressed hydrogen
Compressed hydrogen
is a storage form whereby hydrogen gas is kept under pressures to
increase the storage density. Compressed hydrogen in hydrogen tanks at
350 bar (5,000 psi) and 700 bar (10,000 psi) are used for hydrogen tank
systems in vehicles, based on type IV carbon-composite technology. Car manufacturers including Honda and Nissan have been developing this solution.
Liquefied hydrogen
Liquid hydrogen tanks for cars, producing for example the BMW Hydrogen 7. Japan has a liquid hydrogen (LH2) storage site in Kobe port. Hydrogen is liquefied by reducing its temperature to −253 °C, similar to liquefied natural gas
(LNG) which is stored at −162 °C. A potential efficiency loss of only
12.79% can be achieved, or 4.26 kW⋅h/kg out of 33.3 kW⋅h/kg.
Chemical storage
Hydrogen
gravimetric capacity of proposed storage materials for hydrogen fuel as
a function of hydrogen release temperature. The targets have since been
lowered.
Chemical storage could offer high storage performance due to the high
storage densities. For example, supercritical hydrogen at 30 °C and 500
bar only has a density of 15.0 mol/L while methanol has a hydrogen density of 49.5 mol H2/L methanol and saturated dimethyl ether at 30 °C and 7 bar has a density of 42.1 mol H2/L dimethyl ether.
Regeneration of storage material is problematic. A large number of chemical storage systems have been investigated. H2 release can be induced by hydrolysis reactions or catalyzed dehydrogenation reactions. Illustrative storage compounds are hydrocarbons, boron hydrides, ammonia, and alane etc.
A most promising chemical approach is electrochemical hydrogen storage,
as the release of hydrogen can be controlled by the applied
electricity. Most of the materials listed below can be directly used for electrochemical hydrogen storage.
Nanomaterials, particularly those produced by ball mill and severe plastic deformation, offer an alternative that overcomes the two major barriers of bulk materials, rate of sorption and activation. High-entropy alloy
materials such as TiZrCrMnFeNi also show advantages of fast and
reversible hydrogen storage at room temperature with good storage
capacity for stationary applications.
Enhancement of sorption kinetics and storage capacity can be improved through nanomaterial-based catalyst doping, as shown in the work of the Clean Energy Research Center in the University of South Florida. This research group studied LiBH4 doped with nickelnanoparticles
and analyzed the weight loss and release temperature of the different
species. They observed that an increasing amount of nanocatalyst lowers
the release temperature by approximately 20 °C and increases the weight
loss of the material by 2-3%. The optimum amount of Ni particles was
found to be 3 mol%, for which the temperature was within the limits
established (around 100 °C) and the weight loss was notably greater than
the undoped species.
The rate of hydrogen sorption improves at the nanoscale due to the short diffusion distance in comparison to bulk materials. They also have favorable surface-area-to-volume ratio.
The release temperature of a material is defined as the temperature at which the desorption
process begins. The energy or temperature to induce release affects the
cost of any chemical storage strategy. If the hydrogen is bound too
weakly, the pressure needed for regeneration is high, thereby cancelling
any energy savings. The target for onboard hydrogen fuel systems is
roughly <100 °C for release and <700 bar for recharge (20–60
kJ/mol H2). A modified van 't Hoff equation,
relates temperature and partial pressure of hydrogen during the
desorption process. The modifications to the standard equation are
related to size effects at the nanoscale.
Where pH2 is the partial pressure of hydrogen, ΔH is the enthalpy of the sorption process (exothermic), ΔS is the change in entropy, R is the ideal gas constant, T is the temperature in Kelvin, Vm is the molar volume of the metal, r is the radius of the nanoparticle and γ is the surface free energy of the particle.
From the above relation we see that the enthalpy and entropy
change of desorption processes depend on the radius of the nanoparticle.
Moreover, a new term is included that takes into account the specific
surface area of the particle and it can be mathematically proven that a
decrease in particle radius leads to a decrease in the release
temperature for a given partial pressure.
Hydrogenation of CO2
Current approach to reduce CO2
includes capturing and storing from facilities across the world.
However, storage poses technical and economic barriers preventing global
scale application. To utilize CO2 at the point source, CO2
hydrogenation is a realistic and practical approach. Conventional
hydrogenation reduces unsaturated organic compounds by addition of H2. One method of CO2 hydrogenation is via the methanol pathway. Methanol can be used to produce long chain hydrocarbons. Some barriers of CO2 hydrogenation includes purification of captured CO2, H2 source from splitting water and energy inputs for hydrogenation. To overcome these barriers, we can further develop green H2 technology and encourage catalyst research at industrial and academic level. For industrial applications, CO2 is often converted to methanol. Until now, much progress has been made for CO2 to C1 molecules. However, CO2 to high value molecules still face many roadblocks and the future of CO2 hydrogenation depends on the advancement of catalytic technologies.
Again the persistent problems are the % weight of H2 that they carry and the reversibility of the storage process.
Some are easy-to-fuel liquids at ambient temperature and pressure,
whereas others are solids which could be turned into pellets. These
materials have good energy density, although their specific energy is often worse than the leading hydrocarbon fuels.
An alternative method for lowering dissociation temperatures is doping with activators. This strategy has been used for aluminium hydride, but the complex synthesis makes the approach unattractive.
Reversible hydrogen storage is exhibited by frustrated Lewis pair, which produces a borohydride.
The phosphino-borane on the left accepts one equivalent of hydrogen
at one atmosphere and 25 °C and expels it again by heating to 100 °C.
The storage capacity is 0.25 wt%.
Recent advances in metal hydrides
1. Nano-engineered magnesium-based hydrides
Traditional MgH2
stores 7.6 wt% hydrogen, but its high desorption temperature
(>300 °C) limits applications. Mg-Ti-V nanocomposites can reduce the
desorption temperature to below 200 °C, which improved usability in fuel
cell vehicles (FCVs). Carbon-coordinated MgH2 exhibits 80% of improvement on cycling stability over 1000 cycles.
2. Complex hydrides for high-capacity storage
LiBH4 + MgH2 composites stored about 11 wt% of hydrogen, which is one of the highest capacities reported. And ammonia borane (H₃NBH₃) releases 12 wt% hydrogen at moderate temperatures (~100–150 °C), making it a promising on-board storage candidate.
Hydrogen can be produced using aluminium by reacting it with water. It was previously believed that, to react with water, aluminium must be stripped of its natural oxide layer using caustic substances, alloys, or mixing with gallium (which produces aluminium nanoparticles that allow 90% of the aluminium to react). It has since been demonstrated that efficient reaction is possible by increasing the temperature and pressure of the reaction. The byproduct of the reaction to create hydrogen is aluminium oxide, which can be recycled back into aluminium with the Hall–Héroult process,
making the reaction theoretically renewable. Although this requires
electrolysis, which consumes a large amount of energy, the energy is
then stored in the aluminium (and released when the aluminium is reacted
with water).
Magnesium
Mg-based
hydrogen storage materials can be generally fell into three categories,
i.e., pure Mg, Mg-based alloys, and Mg-based composites. Particularly,
more than 300 sorts of Mg-based hydrogen storage alloys have been
receiving extensive attention
because of the relatively better overall performance. Nonetheless, the
inferior hydrogen absorption/desorption kinetics rooting in the overly
undue thermodynamic stability of metal hydride make the Mg-based
hydrogen storage alloys currently not appropriate for the real
applications, and therefore, massive attempts have been dedicated to
overcoming these shortages. Some sample preparation methods, such as
smelting, powder sintering, diffusion, mechanical alloying, the
hydriding combustion synthesis method, surface treatment, and heat
treatment, etc., have been broadly employed for altering the dynamic
performance and cycle life of Mg-based hydrogen storage alloys. Besides,
some intrinsic modification strategies, including alloying, nanostructuring, doping by catalytic additives, and acquiring nanocomposites with other hydrides, etc., have been mainly explored for intrinsically boosting the performance of Mg-based hydrogen storage alloys. Like aluminium, magnesium also reacts with water to produce hydrogen.
Of the primary hydrogen storage alloys progressed formerly, Mg
and Mg-based hydrogen storage materials are believed to provide the
remarkable possibility of the practical application, on account of the
advantages as following: 1) the resource of Mg is plentiful and
economical. Mg element exists abundantly and accounts for ≈2.35% of the
earth's crust with the rank of the eighth; 2) low density of merely 1.74
g cm-3; 3) superior hydrogen storage capacity. The theoretical hydrogen
storage amounts of the pure Mg is 7.6 wt % (weight percent), and the Mg2Ni is 3.6 wt%, respectively.
Alanates-based systems
Lithium alanate (LiAlH4) was synthesized for the first time in 1947 by dissolution of lithium hydride in an ether solution of aluminium chloride. LiAlH4 has a theoretical gravimetric capacity of 10.5 wt %H2 and dehydrogenates in the following three steps: 3LiAlH4 ↔ Li3AlH6 + 3H2 + 2Al (423–448 K; 5.3 wt %H2; ∆H = −10 kJ·mol−1 H2); Li3AlH6 ↔ 3LiH + Al + 1.5H2 (453–493 K; 2.6 wt %H2; ∆H = 25 kJ·mol−1 H2); 3LiH + 3Al ↔ 3LiAl + 3/2H2 (>673 K; 2.6 wt %H2; ∆H = 140 kJ·mol−1 H2).
The first two steps lead to a total amount of hydrogen released equal
to 7.9 wt %, which could be attractive for practical applications, but
the working temperatures and the desorption kinetics are still far from
the practical targets. Several strategies have been applied in the last
few years to overcome these limits, such as ball-milling and catalysts
additions.
Potassium Alanate (KAlH4) was first prepared by Ashby et al.
by one-step synthesis in toluene, tetrahydrofuran, and diglyme.
Concerning the hydrogen absorption and desorption properties, this
alanate was only scarcely studied. Morioka et al., by temperature programmed desorption (TPD) analyses, proposed the following dehydrogenation mechanism: 3KAlH4 →K3AlH6 + 2Al + 3H2 (573 K, ∆H = 55 kJ·mol−1 H2; 2.9 wt %H2), K3AlH6 → 3KH + Al + 3/2H2 (613 K, ∆H = 70 kJ·mol−1 H2; 1.4 wt %H2), 3KH → 3K + 3/2H2 (703 K, 1.4 wt %H2).
These reactions were demonstrated reversible without catalysts addition
at relatively low hydrogen pressure and temperatures. The addition of
TiCl3 was found to decrease the working temperature of the first
dehydrogenation step of 50 K, but no variations were recorded for the last two reaction steps.
Unsaturated organic compounds can store huge amounts of hydrogen. These Liquid Organic Hydrogen Carriers
(LOHC) are hydrogenated for storage and dehydrogenated again when the
energy/hydrogen is needed. Using LOHCs, relatively high gravimetric
storage densities can be reached (about 6 wt-%) and the overall energy efficiency is higher than for other chemical storage options such as producing methane from the hydrogen. Both hydrogenation and dehydrogenation of LOHCs requires catalysts.
It was demonstrated that replacing hydrocarbons by hetero-atoms, like
N, O etc. improves reversible de/hydrogenation properties.
Cycloalkanes
Research
on LOHC was concentrated on cycloalkanes at an early stage, with its
relatively high hydrogen capacity (6-8 wt %) and production of COx-free hydrogen. Heterocyclic aromatic compounds (or N-Heterocycles) are also appropriate for this task. A compound featuring in LOHC research is N-Ethylcarbazole [de] (NEC) but many others do exist. Dibenzyltoluene,
which is already used as a heat transfer fluid in industry, was
identified as potential LOHC. With a wide liquid range between -39 °C
(melting point) and 390 °C (boiling point) and a hydrogen storage
density of 6.2 wt% dibenzyltoluene is ideally suited as LOHC material. Formic acid has been suggested as a promising hydrogen storage material with a 4.4wt% hydrogen capacity.
Cycloalkanes reported as LOHC include cyclohexane,
methyl-cyclohexane and decalin. The dehydrogenation of cycloalkanes is
highly endothermic (63-69 kJ/mol H2), which means this process requires high temperature.
Dehydrogenation of decalin is the most thermodynamically favored among
the three cycloalkanes, and methyl-cyclohexane is second because of the
presence of the methyl group.
Research on catalyst development for dehydrogenation of cycloalkanes
has been carried out for decades. Nickel (Ni), Molybdenum (Mo) and
Platinum (Pt) based catalysts are highly investigated for
dehydrogenation. However, coking is still a big challenge for catalyst's
long-term stability.
N-Heterocycles
The temperature required for hydrogenation and dehydrogenation drops significantly for heterocycles vs simple carbocycles.
Among all the N-heterocycles, the saturated-unsaturated pair of
dodecahydro-N-ethylcarbazole (12H-NEC) and NEC has been considered as a
promising candidate for hydrogen storage with a fairly large hydrogen
content (5.8wt%).
The figure on the top right shows dehydrogenation and hydrogenation of
the 12H-NEC and NEC pair. The standard catalyst for NEC to 12H-NEC is Ru
and Rh based. The selectivity of hydrogenation can reach 97% at 7 MPa
and 130 °C-150 °C.
Although N-Heterocyles can optimize the unfavorable thermodynamic
properties of cycloalkanes, a lot of issues remain unsolved, such as
high cost, high toxicity and kinetic barriers etc.
The imidazolium ionic liquids such
alkyl(aryl)-3-methylimidazolium N-bis(trifluoromethanesulfonyl)imidate
salts can reversibly add 6–12 hydrogen atoms in the presence of
classical Pd/C or Ir0 nanoparticle catalysts and can be used as
alternative materials for on-board hydrogen-storage devices. These salts
can hold up to 30 g L−1 of hydrogen at atmospheric pressure.
Formic acid
Formic acid is a highly effective hydrogen storage material, although its H2density
is low. Carbon monoxide free hydrogen has been generated in a very wide
pressure range (1–600 bar). A homogeneous catalytic system based on
water-soluble ruthenium catalysts selectively decompose HCOOH into H2 and CO2 in aqueous solution.
This catalytic system overcomes the limitations of other catalysts
(e.g. poor stability, limited catalytic lifetimes, formation of CO) for
the decomposition of formic acid making it a viable hydrogen storage
material.
And the co-product of this decomposition, carbon dioxide, can be used
as hydrogen vector by hydrogenating it back to formic acid in a second
step. The catalytic hydrogenation of CO2 has long been studied and efficient procedures have been developed.Formic acid contains 53 g L−1
hydrogen at room temperature and atmospheric pressure. By weight, pure
formic acid stores 4.3 wt% hydrogen. Pure formic acid is a liquid with a
flash point 69 °C (cf. gasoline −40 °C, ethanol 13 °C). 85% formic acid
is not flammable.
Ammonia (NH3) releases H2
in an appropriate catalytic reformer. Ammonia provides high hydrogen
storage densities as a liquid with mild pressurization and cryogenic
constraints: It can also be stored as a liquid at room temperature and
pressure when mixed with water. Ammonia is the second most commonly
produced chemical in the world and a large infrastructure for making,
transporting, and distributing ammonia exists. Ammonia can be reformed
to produce hydrogen with no harmful waste, or can mix with existing
fuels and under the right conditions burn efficiently. Since there is no
carbon in ammonia, no carbon by-products are produced; thereby making
this possibility a "carbon neutral" option for the future. Pure ammonia
burns poorly at the atmospheric pressures found in natural gas fired
water heaters and stoves. Under compression in an automobile engine it
is a suitable fuel for slightly modified gasoline engines. Ammonia is a
suitable alternative fuel because it has 18.6 MJ/kg energy density at
NTP and carbon-free combustion byproducts.
Ammonia has several challenges to widespread adaption as a
hydrogen storage material. Ammonia is a toxic gas with a potent odor at
standard temperature and pressure.
Additionally, advances in the efficiency and scalability of ammonia
decomposition are needed for commercial viability, as fuel cell
membranes are highly sensitive to residual ammonia and current
decomposition techniques have low yield rates. A variety of transition metals can be used to catalyze the ammonia decomposition reaction, the most effective being ruthenium. This catalysis works through chemisorption, where the adsorption energy of N2 is less than the reaction energy of dissociation.
Hydrogen purification can be achieved in several ways. Hydrogen can be
separated from unreacted ammonia using a permeable, hydrogen-selective
membrane. It can also be purified through the adsorption of ammonia, which can be selectively trapped due to its polarity.
In September 2005 chemists from the Technical University of Denmark announced a method of storing hydrogen in the form of ammonia saturated into a salt tablet. They claim it will be an inexpensive and safe storage method.
Positive attributes of Ammonia
High theoretical energy density
Wide spread availability
Large scale commercial production
Benign decomposition pathway to H2 and N2
Negative attributes of Ammonia
Toxicity
Corrosive
High decomposition temperature leading to efficiency loss
Hydrazine
Hydrazine breaks down in the cell to form nitrogen and hydrogen/
Silicon hydrides and germanium hydrides are also candidates of hydrogen
storage materials, as they can subject to energetically favored
reaction to form covalently bonded dimers with loss of a hydrogen
molecule.
Prior to 1980, several compounds were investigated for hydrogen
storage including complex borohydrides, or aluminohydrides, and ammonium
salts. These hydrides have an upper theoretical hydrogen yield limited
to about 8.5% by weight. Amongst the compounds that contain only B, N,
and H (both positive and negative ions), representative examples
include: amine boranes, boron hydride ammoniates, hydrazine-borane
complexes, and ammonium octahydrotriborates or tetrahydroborates. Of
these, amine boranes (and especially ammonia borane)
have been extensively investigated as hydrogen carriers. During the
1970s and 1980s, the U.S. Army and Navy funded efforts aimed at
developing hydrogen/deuterium gas-generating compounds for use in the
HF/DF and HCl chemical lasers,
and gas dynamic lasers. Earlier hydrogen gas-generating formulations
used amine boranes and their derivatives. Ignition of the amine
borane(s) forms boron nitride (BN) and hydrogen gas. In addition to ammonia borane
(H3BNH3), other gas-generators include diborane diammoniate, H2B(NH3)2BH4.
Physical storage
In
this case hydrogen remains in physical forms, i.e., as gas,
supercritical fluid, adsorbate, or molecular inclusions. Theoretical
limitations and experimental results are considered
concerning the volumetric and gravimetric capacity of glass
microvessels, microporous, and nanoporous media, as well as safety and
refilling-time demands. Because hydrogen is the smallest molecule, it
easily escapes from containers and during transfer from container to
container. While it does not directly contribute to radiative forcing,
hydrogen is estimated to have an effective 100-year global warming
potential of 11.6 ± 2.8 due to its impact on processes such as atmospheric methane oxidation and tropospheric ozone production.
Zeolites
Zeolites are microporous and highly crystalline aluminosilicate materials. As they exhibit cage and tunnel structures, they offer the potential for the encapsulation of non-polar gases such as H2. In this system, hydrogen is physisorbed
on the surface of the zeolite pores through a mechanism of adsorption
that involves hydrogen being forced into the pores under pressure and
low temperature. Therefore, similar to other porous materials, its hydrogen storage capacity depends on the BET surface area,
pore volume, the interaction of molecular hydrogen with the internal
surfaces of the micropores, and working conditions such as pressure and
temperature.
Research shows that the channel diameter is also one of the
parameters determining this capacity, especially at high pressure. In
this case, an effective material should exhibit a large pore volume and a
channel diameter close to the kinetic diameter of the hydrogen molecule (dH=2.89 Å).
Table below shows the hydrogen uptake of several zeolites at liquid nitrogen temperature (77K):
H2 uptake of several high surface area zeolites
Zeolite
Framework Type (IZA Code)
Pressure (bar)
H2 Uptake (wt%)
BET Surface Area (m2/g)
NaY (Si/Al = 2.4)
FAU
0.57
0.37
HY (Si/Al = 2.7)
FAU
0.95
0.56
MCM-41
1
0.58
1017
H-ZSM-5 (Si/Al = 40)
MFI
0.92
0.71
418
H-SAPO-34
CHA
0.92
1.09
547
H-CHA (Si/Al = 2.1)
CHA
0.92
1.10
490
H-SSZ-13 (Si/Al = 11.6)
CHA
0.92
1.28
638
NaA
LTA
0.93
1.21
LiX (Si/Al = 1.4)
FAU
0.60
0.88
NaX (Si/Al = 1.05)
FAU
0.61
1.22
CaX (Si/Al = 1.4)
FAU
1.01
1.25
669
Li-LSX (Si/Al = 1.0)
FAU
1.01
1.50
717
Na-LSX (Si/Al = 1.0)
FAU
1.01
1.46
642
K-LSX (Si/Al = 1.0)
FAU
1.01
1.33
570
Porous or layered carbon
Activated carbons are highly porous amorphous carbon materials with high apparent surface area. Hydrogen physisorption can be increased in these materials by increasing the apparent surface area and optimizing pore diameter to around 7 Å.
These materials are of particular interest due to the fact that they
can be made from waste materials, such as cigarette butts which have
shown great potential as precursor materials for high-capacity hydrogen
storage materials.
Graphene can store hydrogen efficiently. The H2 adds to the double bonds giving graphane. The hydrogen is released upon heating to 450 °C.
Carbon nanotubes
Hydrogen carriers based on nanostructured carbon (such as carbon buckyballs and nanotubes)
have been proposed. However, hydrogen content amounts up to ≈3.0-7.0
wt% at 77K which is far from the value set by US Department of Energy (6
wt% at nearly ambient conditions).
To realize carbon materials as effective hydrogen storage technologies, carbon nanotubes (CNTs) have been doped with MgH2. The metal hydride has proven to have a theoretical storage capacity (7.6 wt%) that fulfills the United States Department of Energy
requirement of 6 wt%, but has limited practical applications due to its
high release temperature. The proposed mechanism involves the creation
of fast diffusion channels by CNTs within the MgH2 lattice. Fullerene
substances are other carbonaceous nanomaterials that have been tested
for hydrogen storage in this center. Fullerene molecules are composed of
a C60 close-caged structure, that allows for hydrogenation of the double bonded carbons leading to a theoretical C60H60isomer with a hydrogen content of 7.7 wt%. However, the release temperature in these systems is high (600 °C).
Metal–organic frameworks
Metal–organic frameworks
represent another class of synthetic porous materials that store
hydrogen and energy at the molecular level. MOFs are highly crystalline
inorganic-organic hybrid structures that contain metal clusters or ions
(secondary building units) as nodes and organic ligands as linkers. When
guest molecules (solvent) occupying the pores are removed during
solvent exchange and heating under vacuum, porous structure of MOFs can
be achieved without destabilizing the frame and hydrogen molecules will
be adsorbed onto the surface of the pores by physisorption. Compared to
traditional zeolites and porous carbon materials, MOFs have very high
number of pores and surface area which allow higher hydrogen uptake in a
given volume. Thus, research interests on hydrogen storage in MOFs have
been growing since 2003 when the first MOF-based hydrogen storage was
introduced. Since there are infinite geometric and chemical variations
of MOFs based on different combinations of SBUs and linkers, many
researches explore what combination will provide the maximum hydrogen
uptake by varying materials of metal ions and linkers.
Factors influencing hydrogen storage ability
Temperature,
pressure and composition of MOFs can influence their hydrogen storage
ability. The adsorption capacity of MOFs is lower at higher temperature
and higher at lower temperatures. With the rising of temperature,
physisorption decreases and chemisorption increases. For MOF-519 and MOF-520, the isosteric heat of adsorption decreased with pressure increase. For MOF-5, both gravimetric and volumetric hydrogen uptake increased with increase in pressure.
The total capacity may not be consistent with the usable capacity under
pressure swing conditions. For instance, MOF-5 and IRMOF-20, which have
the highest total volumetric capacity, show the least usable volumetric
capacity.
Absorption capacity can be increased by modification of structure. For
example, the hydrogen uptake of PCN-68 is higher than PCN-61.
Porous aromatic frameworks (PAF-1), which is known as a high surface
area material, can achieve a higher surface area by doping.
Modification of MOFs
There
are many different ways to modify MOFs, such as MOF catalysts, MOF
hybrids, MOF with metal centers and doping. MOF catalysts have high
surface area, porosity and hydrogen storage capacity. However, the
active metal centers are low. MOF hybrids have enhanced surface area,
porosity, loading capacity and hydrogen storage capacity. Nevertheless,
they are not stable and lack active centers. Doping in MOFs can increase
hydrogen storage capacity, but there might be steric effect and inert
metals have inadequate stability. There might be formation of
interconnected pores and low corrosion resistance in MOFs with metal
centers, while they might have good binding energy and enhanced
stability. These advantages and disadvantages for different kinds of
modified MOFs show that MOF hybrids are more promising because of the
good controllability in selection of materials for high surface area,
porosity and stability.
In 2006, chemists achieved hydrogen storage concentrations of up to 7.5 wt% in MOF-74 at a low temperature of 77 K. In 2009, researchers reached 10 wt% at 77 bar (1,117 psi) and 77 K with MOF NOTT-112.
Most articles about hydrogen storage in MOFs report hydrogen uptake
capacity at a temperature of 77K and a pressure of 1 bar because these
conditions are commonly available and the binding energy between
hydrogen and the MOF at this temperature is large compared to the
thermal vibration energy. Varying several factors such as surface area,
pore size, catenation, ligand structure, and sample purity can result in
different amounts of hydrogen uptake in MOFs.
In 2020, researchers reported that NU-1501-Al, an ultraporous
metal–organic framework (MOF) based on metal trinuclear clusters,
yielded "impressive gravimetric and volumetric storage performances for
hydrogen and methane", with a hydrogen delivery capacity of 14.0% w/w,
46.2 g/litre.
Cryo-compressed
Cryo-compressed
storage of hydrogen is the only technology that meets 2015 DOE targets
for volumetric and gravimetric efficiency (see "CcH2" on slide 6 in).
Furthermore, another study has shown that cryo-compression
exhibits interesting cost advantages: ownership cost (price per mile)
and storage system cost (price per vehicle) are actually the lowest when
compared to any other technology (see third row in slide 13 of).
Like liquid storage, cryo-compressed uses cold hydrogen (20.3 K
and slightly above) in order to reach a high energy density. However,
the main difference is that, when the hydrogen would warm-up due to heat
transfer with the environment ("boil off"), the tank is allowed to go
to pressures much higher (up to 350 bars versus a couple of bars for
liquid storage). As a consequence, it takes more time before the
hydrogen has to vent, and in most driving situations, enough hydrogen is
used by the car to keep the pressure well below the venting limit.
Consequently, it has been demonstrated that a high driving range
could be achieved with a cryo-compressed tank : more than 650 miles
(1,050 km) were driven with a full tank mounted on a hydrogen-fueled
engine of Toyota Prius. Research is still underway to study and demonstrate the full potential of the technology.
As of 2010, the BMW Group has started a thorough component and
system level validation of cryo-compressed vehicle storage on its way to
a commercial product.
Cryo-supercritical
Clathrate hydrates
H2 caged in a clathrate hydrate was first reported in 2002, but requires very high pressures to be stable. In 2004, researchers showed solid H2-containing hydrates could be formed at ambient temperature and tens of bars by adding small amounts of promoting substances such as THF. These clathrates have a theoretical maximum hydrogen densities of around 5 wt% and 40 kg/m3.
Glass capillary arrays
A
team of Russian, Israeli and German scientists have collaboratively
developed an innovative technology based on glass capillary arrays for
the safe infusion, storage and controlled release of hydrogen in mobile
applications. The C.En technology has achieved the United States Department of Energy (DOE) 2010 targets for on-board hydrogen storage systems.
DOE 2015 targets can be achieved using flexible glass capillaries and cryo-compressed method of hydrogen storage.
Glass microspheres
Hollow glass microspheres
(HGM) can be utilized for controlled storage and release of hydrogen.
HGMs with a diameter of 1 to 100 μm, a density of 1.0 to 2.0 gm/cc and a
porous wall with openings of 10 to 1000 angstroms
are considered for hydrogen storage. The advantages of HGMs for
hydrogen storage are that they are nontoxic, light, cheap, recyclable,
reversible, easily handled at atmospheric conditions, capable of being
stored in a tank, and the hydrogen within is non-explosive.
Each of these HGMs is capable of containing hydrogen up to 150 MPa
without the heaviness and bulk of a large pressurized tank. All of these
qualities are favorable in vehicular applications. Beyond these
advantages, HGMs are seen as a possible hydrogen solution due to
hydrogen diffusivity
having a large temperature dependence. At room temperature, the
diffusivity is very low, and the hydrogen is trapped in the HGM. The
disadvantage of HGMs is that to fill and outgas
hydrogen effectively the temperature must be at least 300 °C which
significantly increases the operational cost of HGM in hydrogen storage. The high temperature can be partly attributed to glass being an insulator and having a low thermal conductivity; this hinders hydrogen diffusivity, and subsequently a higher temperature is required to achieve the desired storage capacity.
To make this technology more economically viable for commercial use, research is being done to increase the efficiency of hydrogen diffusion through the HGMs. One study done by Dalai et al. sought to increase the thermal conductivity of the HGM through doping the glass with cobalt. In doing so they increased the thermal conductivity from 0.0072 to 0.198 W/m-K at 10 wt% Co. Increases in hydrogen adsorption though were only seen up to 2 wt% Co (0.103 W/m-K) as the metal oxide
began to cover pores in the glass shell. This study concluded with a
hydrogen storage capacity of 3.31 wt% with 2 wt% Co at 200 °C and 10
bar.
A study done by Rapp and Shelby sought to increase the hydrogen
release rate through photo-induced outgassing in doped HGMs in
comparison to conventional heating methods. The glass was doped with optically active metals to interact with the high-intensity infrared light. The study found that 0.5 wt% Fe3O4 doped 7070 borosilicate glass
had hydrogen release increase proportionally to the infrared lamp
intensity. In addition to the improvements to diffusivity by infrared
alone, reactions between the hydrogen and iron-doped glass increased the
Fe2+/Fe3+ ratio which increased infrared absorption therefore further increasing the hydrogen yield.
As of 2020, the progress made in studying HGMs has increased its
efficiency but it still falls short of Department of Energy targets for
this technology. The operation temperatures for both hydrogen adsorption
and release are the largest barrier to commercialization.
Stationary hydrogen storage
Unlike
mobile applications, hydrogen density is not a huge problem for
stationary applications. As for mobile applications, stationary
applications can use established technology:
'Available storage technologies, their capacity and discharge time.'
Underground hydrogen storage is the practice of hydrogen storage in caverns, salt domes and depleted oil and gas fields. Large quantities of gaseous hydrogen have been stored in caverns by ICI for many years without any difficulties. The storage of large quantities of liquid hydrogen underground can function as grid energy storage. The round-trip efficiency is approximately 40% (vs. 75–80% for pumped-hydro (PHES)), and the cost is slightly higher than pumped hydro, if only a limited number of hours of storage is required.
Another study referenced by a European staff working paper found that
for large scale storage, the cheapest option is hydrogen at €140/MWh for
2,000 hours of storage using an electrolyser, salt cavern storage and
combined-cycle power plant. The European project Hyunder
indicated in 2013 that for the storage of wind and solar energy an
additional 85 caverns are required as it cannot be covered by PHES and CAES systems.
A German case study on storage of hydrogen in salt caverns found that
if the German power surplus (7% of total variable renewable generation
by 2025 and 20% by 2050) would be converted to hydrogen and stored
underground, these quantities would require some 15 caverns of 500,000
cubic metres each by 2025 and some 60 caverns by 2050 – corresponding to
approximately one third of the number of gas caverns currently operated
in Germany.
In the US, Sandia Labs are conducting research into the storage of
hydrogen in depleted oil and gas fields, which could easily absorb large
amounts of renewably produced hydrogen as there are some 2.7 million
depleted wells in existence.
Underground hydrogen storage is the practice of hydrogen storage in caverns, salt domes and depleted oil/gas fields. Large quantities of gaseous hydrogen have been stored in caverns for many years. The storage of large quantities of hydrogen underground in solution-mined salt domes, aquifers, excavated rock caverns, or mines can function as grid energy storage, essential for the hydrogen economy. By using a turboexpander the electricity needs for compressed storage on 200 bar amounts to 2.1% of the energy content.
Salt caverns
The
Chevron Phillips Clemens Terminal in Texas has stored hydrogen since
the 1980s in a solution-mined salt cavern. The cavern roof is about
2,800 feet (850 m) underground. The cavern is a cylinder with a diameter
of 160 feet (49 m), a height of 1,000 feet (300 m), and a usable
hydrogen capacity of 1,066 million cubic feet (30.2×106 m3), or 2,520 metric tons (2,480 long tons; 2,780 short tons).
Salt caverns are artificially created by injecting water from the
surface into a well in the rock salt, where rock salt is a
polycrystalline material made of NaCl, halite. Locations such as salt
domes or bedded salt are usually picked for salt caverns' creation. Salt
caverns can reach a maximum depth of 2000 m and a maximum volume
capacity of 1,000,000 m3. The frequency of injection and withdrawal
cycles ranges between 10 and 12 cycles per year. The leak rate is around
1%.
Due to the physiochemical properties of the rock salt, salt
caverns exhibit multiple advantages. Key characteristics are low water
content, low porosity and permeability, and its chemical inertia towards
hydrogen.
Permeability is a key parameter in underground hydrogen storage, which
affects its ability to seal. Though studies have found dilatancy and
extensional fracture can cause significant permeability increase, rock
salt crystal's recrystallization, which is a grain boundaries healing
process, may contribute to its mechanical stiffness and permeability
recovery.
Its plastic properties prevent the formation and spread of fractures
and protect it from losing its tightness, which is particularly
important for hydrogen storage.
Some of the disadvantages of salt caverns include lower storage
capacity, large amount of water needed, and the effect of corrosion.
Cushion gas is needed to avoid creep due to pressure drop when
withdrawing gas from the reservoir. Though the need for cushion gas is
relatively small, around 20%, the operational cost can still add up when
working with a larger storage capacity. Cost is another big concern,
where the cost of construction and operation are still high.
Though people have experience with storing natural gas, storing
hydrogen is a lot more complex. Factors such as hydrogen diffusivity in
solids cause restrictions in salt cavern storage. Microbial activity is
under extensive research worldwide because of its impact on hydrogen
loss. As a result of methanogenic bacteria's bacterial metabolism,
carbon dioxide and hydrogen are consumed and methane is produced, which
leads to the loss of hydrogen stored in the salt caverns.
Development
Sandia National Laboratories released in 2011 a life-cycle cost analysis framework for geologic storage of hydrogen.
ETI released in 2015 a report The role of hydrogen storage in a clean responsive power system noting that the UK has sufficient salt bed resources to provide tens of GWe.
RAG Austria AG
finished a hydrogen storage project in a depleted oil and gas field in
Austria in 2017, and is conducting its second project "Underground Sun
Conversion".
A cavern sized 800 m tall and 50 m diameter can hold hydrogen equivalent to 150 GWh.
Power to gas
Power to gas is a technology which converts electrical power to a gas fuel. There are two methods: the first is to use the electricity for water splitting and inject the resulting hydrogen into the natural gas grid; the second, less efficient method is used to convert carbon dioxide and hydrogen to methane, (see natural gas) using electrolysis and the Sabatier reaction.
A third option is to combine the hydrogen via electrolysis with a
source of carbon (either carbon dioxide or carbon monoxide from biogas, from industrial processes or via direct air-captured carbon dioxide) via biomethanation, where biomethanogens (archaea) consume carbon dioxide and hydrogen and produce methane within an anaerobic
environment. This process is highly efficient, as the archaea are
self-replicating and only require low-grade (60 °C) heat to perform the
reaction.
Another process has also been achieved by SoCalGas
to convert the carbon dioxide in raw biogas to methane in a single
electrochemical step, representing a simpler method of converting excess
renewable electricity into storable natural gas.
The UK has completed surveys and is preparing to start injecting
hydrogen into the gas grid as the grid previously carried 'town gas'
which is a 50% hydrogen-methane gas formed from coal. Auditors KPMG
found that converting the UK to hydrogen gas could be £150bn to £200bn
cheaper than rewiring British homes to use electric heating powered by
lower-carbon sources.
Excess power or off peak power generated by wind generators or
solar arrays can then be used for load balancing in the energy grid.
Using the existing natural gas system for hydrogen, Fuel cell maker Hydrogenics and natural gas distributor Enbridge have teamed up to develop such a power to gas system in Canada.
Pipeline storage of hydrogen where a natural gas network is used for the storage of hydrogen. Before switching to natural gas, the German gas networks were operated using towngas,
which for the most part (60-65%) consisted of hydrogen. The storage
capacity of the German natural gas network is more than 200,000 GW·h
which is enough for several months of energy requirement. By comparison,
the capacity of all German pumped storage power plants amounts to only
about 40 GW·h. The transport of energy through a gas network is done
with much less loss (<0.1%) than in a power network (8%). The use of
the existing natural gas pipelines for hydrogen was studied by NaturalHy.
Automotive onboard hydrogen storage
Portability is one of the biggest challenges in the automotive industry, where high density storage systems are problematic due to safety concerns.
High-pressure tanks weigh much more than the hydrogen they can hold. For example, in the 2014 Toyota Mirai, a full tank contains only 5.7% hydrogen, the rest of the weight being the tank.
System densities are often around half those of the working material, thus while a material may store 6 wt% H2,
a working system using that material may only achieve 3 wt% when the
weight of tanks, temperature and pressure control equipment, etc., is
considered.
Fuel cells and storage
Due
to its clean-burning characteristics, hydrogen is a clean fuel
alternative for the automotive industry. Hydrogen-based fuel could
significantly reduce the emissions of greenhouse gases such as CO2, SO2 and NOx. Three problems for the use of hydrogen fuel cells
(HFC) are efficiency, size, and safe onboard storage of the gas. Other
major disadvantages of this emerging technology involve cost,
operability and durability issues, which still need to be improved from
the existing systems. To address these challenges, the use of
nanomaterials has been proposed as an alternative option to the
traditional hydrogen storage systems. The use of nanomaterials could
provide a higher density system and increase the driving range towards
the target set by the DOE at 300 miles. Carbonaceous materials such as carbon nanotube
and metal hydrides are the main focus of research. They are currently
being considered for onboard storage systems due to their versatility,
multi-functionality, mechanical properties and low cost with respect to
other alternatives.
Other advantages of nanomaterials in fuel cells
The
introduction of nanomaterials in onboard hydrogen storage systems may
be a major turning point in the automotive industry. However, storage is
not the only aspect of the fuel cell to which nanomaterials may
contribute. Different studies have shown that the transport and catalytic properties of Nafion membranes used in HFCs can be enhanced with TiO2/SnO2 nanoparticles. The increased performance is caused by an improvement in hydrogen splitting kinetics due to catalytic activity of the nanoparticles. Furthermore, this system exhibits faster transport of protons across the cell which makes HFCs with nanoparticle composite membranes a promising alternative.
Increasing gas pressure improves the energy density by volume making
for smaller container tanks. The standard material for holding
pressurised hydrogen in tube trailers is steel (there is no hydrogen embrittlement
problem with hydrogen gas). Tanks made of carbon and glass fibres
reinforcing plastic as fitted in Toyota Marai and Kenworth trucks are
required to meet safety standards. Few materials are suitable for tanks
as hydrogen being a small molecule tends to diffuse through many
polymeric materials. The most common on board hydrogen storage in 2020
vehicles was hydrogen at pressure 700bar = 70MPa. The energy cost of
compressing hydrogen to this pressure is significant.
Pressurized gas pipelines are always made of steel and operate at much lower pressures than tube trailers.
Alternatively, higher volumetric energy density liquid hydrogen or slush hydrogen may be used. However, liquid hydrogen is cryogenic and boils at 20.268 K (−252.882 °C or −423.188 °F). Cryogenic storage cuts weight but requires large liquification energies. The liquefaction process, involving pressurizing and cooling steps, is energy intensive.
The liquefied hydrogen has lower energy density by volume than gasoline
by approximately a factor of four, because of the low density of liquid
hydrogen – there are actually more oxidizable hydrogen atoms in a litre
of gasoline (116 grams) than there are in a litre of pure liquid
hydrogen (71 grams). Like any other liquid at cryogenic temperatures, the liquid hydrogen storage tanks must also be well insulated to minimize boil off.
Japan has a liquid hydrogen (LH2) storage facility at a terminal
in Kobe, and was expected to receive the first shipment of liquid
hydrogen via LH2 carrier in 2020.
Hydrogen is liquified by reducing its temperature to −253 °C, similar
to liquified natural gas (LNG) which is stored at −162 °C. A potential
efficiency loss of 12.79% can be achieved, or 4.26 kWh/kg out of
33.3 kWh/kg.
The Hydrogen Storage Materials research field is vast, having tens of thousands of published papers.
According to Papers in the 2000 to 2015 period collected from Web of
Science and processed in VantagePoint bibliometric software, a
scientometric review of research in hydrogen storage materials was
constituted. According to the literature, hydrogen energy went through a
hype-cycle type of development in the 2000s. Research in Hydrogen
Storage Materials grew at increasing rates from 2000 to 2010.
Afterwards, growth continued but at decreasing rates, and a plateau was
reached in 2015. Looking at individual country output, there is a
division between countries that after 2010 inflected to a constant or
slightly declining production, such as the European Union countries, the
US and Japan, and those whose production continued growing until 2015,
such as China and South Korea. The countries with most publications were
China, the EU and the United States, followed by Japan. China kept the
leading position throughout the entire period, and had a higher share of
hydrogen storage materials publications in its total research output.
Among materials classes, Metal-Organic Frameworks were the most
researched materials, followed by Simple Hydrides. Three typical
behaviors were identified:
New materials, researched mainly after 2004, such as MOFs and Borohydrides;
Classic materials, present through the entire period with growing number of papers, such as Simple Hydrides, and
Materials with stagnant or declining research through the end of the period, such as AB5 alloys and Carbon Nanotubes.
However, current physisorption technologies are still far from being commercialized. The experimental studies are executed for small samples less than 100 g.
The described technologies require high pressure and/or low
temperatures as a rule. Therefore, at their current state of the art
these techniques are not considered as a separate novel technology but
as a type of valuable add-on to current compression and liquefaction methods.
Physisorption processes are reversible since no activation energy
is involved and the interaction energy is very low. In materials such
as metal–organic frameworks,
porous carbons, zeolites, clathrates, and organic polymers, hydrogen is
physisorbed on the surface of the pores. In these classes of materials,
the hydrogen storage capacity mainly depends on the surface area and
pore volume. The main limitation of use of these sorbents as H2storage
materials is weak van der Waals interaction energy between hydrogen and
the surface of the sorbents. Therefore, many of the physisorption based
materials have high storage capacities at liquid nitrogen temperature
and high pressures, but their capacities become very low at ambient
temperature and pressure.
LOHC, liquid organic hydrogen storage systems is a promising technique for future hydrogen storage. LOHC are organic compounds that can absorb and release hydrogen through chemical reactions.
These compounds are characterized by the fact that they can be loaded
and un-loaded with considerable amounts of hydrogen in a cyclic process.
In principle, every unsaturated compound (organic molecules with C-C double or triple bonds) can take up hydrogen during hydrogenation.
This technique ensures that the release of compounds into the
atmosphere are entirely avoided in hydrogen storage. Therefore, LOHCs is
an attractive way to provide wind and solar energy for mobility
applications in the form of liquid energy carrying molecules of similar
energy storage densities and manageability as today's fossil fuels.
