Photoelectrolysis of water

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Photoelectrolysis of water, also known as photoelectrochemical water splitting , occurs in a photoelectrochemical cell when light is used as the energy source for the electrolysis of water, producing dihydrogen which can be used as a fuel. This process is one route to a "hydrogen economy", in which hydrogen fuel is produced efficiently and inexpensively from natural sources without using fossil fuels. [1] [2] In contrast, steam reforming usually or always uses a fossil fuel to obtain hydrogen. Photoelectrolysis is sometimes known colloquially as the hydrogen holy grail for its potential to yield a viable alternative to petroleum as a source of energy; such an energy source would supposedly come without the sociopolitically undesirable effects of extracting and using petroleum.

Mechanism

The PEC cell primarily consists of three components: the photoelectrode the electrolyte and a counter electrode. The semiconductor crucial to this process, absorbs sunlight, initiating electron excitation and subsequent water molecule splitting into hydrogen and oxygen.

Photoanode Reaction (Oxygen Evolution): H2O → 2H++1 2O2+ 2e−

Photocathode Reaction (Hydrogen Evolution): 2H++ 2e− → H2

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41598 2017 11971

These half-reactions show the fundamental chemistry involved in photoelectrolysis, where the photoanode facilitates oxygen evolution and the photocathode supports hydrogen evolution.

Current Research and Technological Advances

Recent advancements have focused on enhancing the semiconductor materials and cell design to improve the solar-to-hydrogen (STH) conversion efficiency, currently between 8%-14%, with a theoretical maximum around 42%. [3] Innovations include:

Semiconductor Materials: Research emphasizes the importance of semiconductors with smaller band gaps (under 2.1 eV) which are more effective at utilizing broader light spectra, thus improving efficiency. [4]

Cocatalysts: The use of transition metal-based cocatalysts has been pivotal in enhancing charge separation and reducing overpotential, thereby improving the overall efficiency of the water-splitting reaction. [5]

Nanoporous Materials: These materials have been utilized to increase the surface area for electron transport, significantly boosting the efficiency of photoelectrochemical systems. [6]

Advantages: Utilizing sunlight, photoelectrolysis serves as a renewable method for hydrogen production, offering scalability and adaptability across different geographical conditions.

Challenges: The primary hurdles include the still-developing efficiency of the process and the intermittent nature of solar energy, which can affect consistent hydrogen production. Additionally, finding durable and efficient materials for long-term operation remains a challenge. [7] [8]

Role in the Hydrogen Economy

As part of a sustainable hydrogen economy, photoelectrolysis presents a promising avenue for clean hydrogen production. Although currently more expensive than traditional methods like steam methane reforming, the potential for technological advancements could make it more economically viable. [9]

Conclusion and Future Prospects

The ongoing development in materials science and cell design is likely to enhance the viability of photoelectrolysis, making it a key player in the future landscape of renewable energy technologies. Continued research and investment in overcoming existing challenges will be crucial to harness the full potential of this technology.

Devices based on hydrogenase have also been investigated. [10]

See also

Related Research Articles

<span class="mw-page-title-main">Electrolysis</span> Technique in chemistry and manufacturing

In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from naturally occurring sources such as ores using an electrolytic cell. The voltage that is needed for electrolysis to occur is called the decomposition potential. The word "lysis" means to separate or break, so in terms, electrolysis would mean "breakdown via electricity."

In photochemistry, photohydrogen is hydrogen produced with the help of artificial or natural light. This is how the leaf of a tree splits water molecules into protons, electrons and oxygen. Photohydrogen may also be produced by the photodissociation of water by ultraviolet light.

A "photoelectrochemical cell" is one of two distinct classes of device. The first produces electrical energy similarly to a dye-sensitized photovoltaic cell, which meets the standard definition of a photovoltaic cell. The second is a photoelectrolytic cell, that is, a device which uses light incident on a photosensitizer, semiconductor, or aqueous metal immersed in an electrolytic solution to directly cause a chemical reaction, for example to produce hydrogen via the electrolysis of water.

Artificial photosynthesis is a chemical process that biomimics the natural process of photosynthesis. The term artificial photosynthesis is used loosely, referring to any scheme for capturing and then storing energy from sunlight by producing a fuel, specifically a solar fuel. An advantage of artificial photosynthesis would be that the solar energy could converted and stored. By contrast, using photovoltaic cells, sunlight is converted into electricity and then converted again into chemical energy for storage, with some necessary losses of energy associated with the second conversion. The byproducts of these reactions are environmentally friendly. Artificially photosynthesized fuel would be a carbon-neutral source of energy, but it has never been demonstrated in any practical sense. The economics of artificial photosynthesis are noncompetitive.

<span class="mw-page-title-main">Water splitting</span> Chemical reaction

Water splitting is the chemical reaction in which water is broken down into oxygen and hydrogen:

<span class="mw-page-title-main">Electrolysis of water</span> Electricity-induced chemical reaction

Electrolysis of water is using electricity to split water into oxygen and hydrogen gas by electrolysis. Hydrogen gas released in this way can be used as hydrogen fuel, but must be kept apart from the oxygen as the mixture would be extremely explosive. Separately pressurised into convenient 'tanks' or 'gas bottles', hydrogen can be used for oxyhydrogen welding and other applications, as the hydrogen / oxygen flame can reach approximately 2,800°C.

Hydrogen gas is produced by several industrial methods. Nearly all of the world's current supply of hydrogen is created from fossil fuels. Most hydrogen is gray hydrogen made through steam methane reforming. In this process, hydrogen is produced from a chemical reaction between steam and methane, the main component of natural gas. Producing one tonne of hydrogen through this process emits 6.6–9.3 tonnes of carbon dioxide. When carbon capture and storage is used to remove a large fraction of these emissions, the product is known as blue hydrogen.

<span class="mw-page-title-main">Biohydrogen</span> Hydrogen that is produced biologically

Biohydrogen is H2 that is produced biologically. Interest is high in this technology because H2 is a clean fuel and can be readily produced from certain kinds of biomass, including biological waste. Furthermore some photosynthetic microorganisms are capable to produce H2 directly from water splitting using light as energy source.

<span class="mw-page-title-main">Solid oxide electrolyzer cell</span> Type of fuel cell

A solid oxide electrolyzer cell (SOEC) is a solid oxide fuel cell that runs in regenerative mode to achieve the electrolysis of water by using a solid oxide, or ceramic, electrolyte to produce hydrogen gas and oxygen. The production of pure hydrogen is compelling because it is a clean fuel that can be stored, making it a potential alternative to batteries, methane, and other energy sources. Electrolysis is currently the most promising method of hydrogen production from water due to high efficiency of conversion and relatively low required energy input when compared to thermochemical and photocatalytic methods.

Photocatalytic water splitting is a process that uses photocatalysis for the dissociation of water (H2O) into hydrogen (H
2
) and oxygen (O
2
). The inputs are light energy (photons), water, and a catalyst(s). The process is inspired by Photosynthesis, which converts water and carbon dioxide into oxygen and carbohydrates. Water splitting using solar radiation has not been commercialized. Photocatalytic water splitting is done by dispersing photocatalyst particles in water or depositing them on a substrate, unlike Photoelectrochemical cell, which are assembled into a cell with a photoelectrode. Hydrogen fuel production using water and light (photocatalytic water splitting), instead of petroleum, is an important renewable energy strategy.

Electromethanogenesis is a form of electrofuel production where methane is produced by direct biological conversion of electrical current and carbon dioxide.

Photoelectrochemistry is a subfield of study within physical chemistry concerned with the interaction of light with electrochemical systems. It is an active domain of investigation. One of the pioneers of this field of electrochemistry was the German electrochemist Heinz Gerischer. The interest in this domain is high in the context of development of renewable energy conversion and storage technology.

Photoelectrochemical reduction of carbon dioxide, also known as photoelectrolysis of carbon dioxide, is a chemical process whereby carbon dioxide is reduced to carbon monoxide or hydrocarbons by the energy of incident light. This process requires catalysts, most of which are semiconducting materials. The feasibility of this chemical reaction was first theorised by Giacomo Luigi Ciamician, an Italian photochemist. Already in 1912 he stated that "[b]y using suitable catalyzers, it should be possible to transform the mixture of water and carbon dioxide into oxygen and methane, or to cause other endo-energetic processes."

Solar–hydrogen energy cycle is an energy cycle where a solar powered electrolyzer is used to convert water to hydrogen and oxygen. Hydrogen and oxygen produced thus are stored to be used by a fuel cell to produce electricity when no sunlight is available.

A solar fuel is a synthetic chemical fuel produced from solar energy. Solar fuels can be produced through photochemical, photobiological, and electrochemical reactions.

<span class="mw-page-title-main">Bismuth vanadate</span> Chemical compound

Bismuth vanadate is the inorganic compound with the formula BiVO4. It is a bright yellow solid. It is widely studied as visible light photo-catalyst with a narrow band gap of less than 2.4 eV. It is a representative of "complex inorganic colored pigments," or CICPs. More specifically, bismuth vanadate is a mixed-metal oxide. Bismuth vanadate is also known under the Colour Index International as C.I. Pigment Yellow 184. It occurs naturally as the rare minerals pucherite, clinobisvanite, and dreyerite.

<span class="mw-page-title-main">Proton exchange membrane electrolysis</span> Technology for splitting water molecules

Proton exchange membrane(PEM) electrolysis is the electrolysis of water in a cell equipped with a solid polymer electrolyte (SPE) that is responsible for the conduction of protons, separation of product gases, and electrical insulation of the electrodes. The PEM electrolyzer was introduced to overcome the issues of partial load, low current density, and low pressure operation currently plaguing the alkaline electrolyzer. It involves a proton-exchange membrane.

<span class="mw-page-title-main">Kevin Sivula</span> American molecular engineer

Kevin Sivula is a highly cited American chemical engineer and researcher in the field of solar cells. He is a professor of molecular engineering at EPFL and the head of the Laboratory for Molecular Engineering of Optoelectronic Nanomaterials at EPFL's School of Basic Sciences.

Kyoung-Shin Choi (Korean: 최경신) is a professor of chemistry at the University of Wisconsin-Madison. Choi's research focuses on the electrochemical synthesis of electrode materials, for use in electrochemical and photoelectrochemical devices.

Hydrogen evolution reaction (HER) is a chemical reaction that yields H2. The conversion of protons to H2 requires reducing equivalents and usually a catalyst. In nature, HER is catalyzed by hydrogenase enzymes. Commercial electrolyzers typically employ supported platinum as the catalyst at the anode of the electrolyzer. HER is useful for producing hydrogen gas, providing a clean-burning fuel. HER, however, can also be an unwelcome side reaction that competes with other reductions such as nitrogen fixation, or electrochemical reduction of carbon dioxide or chrome plating.

References

  1. Crabtree, G. W.; Dresselhaus, M. S.; Buchanan, M. V. (2004). "The Hydrogen Economy". Physics Today. 57 (12): 39–44. Bibcode:2004PhT....57l..39C. doi: 10.1063/1.1878333 . S2CID   28286456.
  2. Ropero-Vega, J.L.; Pedraza-Avella, J.A.; Niño-Gómez, M.E. (September 2015). "Hydrogen production by photoelectrolysis of aqueous solutions of phenol using mixed oxide semiconductor films of Bi–Nb–M–O (M=Al, Fe, Ga, In) as photoanodes". Catalysis Today. 252: 150–156. doi:10.1016/j.cattod.2014.11.007.
  3. Dincer, ibrahim (2017). sustainable hydrogen production. doi:10.1016/C2014-0-00658-2. ISBN   978-0-12-801563-6.
  4. "Recent Advances on Small Band Gap Semiconductor Materials (≤2.1 eV) for Solar Water Splitting." Catalysts, 13, 728". doi: 10.3390/catal13040728 .{{cite journal}}: Cite journal requires |journal= (help)
  5. Kumar (2022). ". Recent trends in photoelectrochemical water splitting: the role of cocatalysts". NPG Asia Materials. 14: 88. Bibcode:2022npjAM..14...88K. doi: 10.1038/s41427-022-00436-x .
  6. Sharma. "A review on the design of nanostructure-based materials for photoelectrochemical hydrogen generation from wastewater: Bibliometric analysis mechanisms prospective and challenges". International Journal of Hydrogen Energy. doi:10.1016/j.ijhydene.2023.01.056.
  7. Gosh. "Towards Hydrogen Infrastructure".{{cite journal}}: Cite journal requires |journal= (help)
  8. Rajaitha. "Multifunctional materials for photo-electrochemical water splitting".{{cite journal}}: Cite journal requires |journal= (help)
  9. Huang (2023). "Hydrogen Production by Photoelectrolysis". Tripod.
  10. Parkin, Alison (2014). "Chapter 5. Understanding and Harnessing Hydrogenases, Biological Dihydrogen Catalysts". In Peter M.H. Kroneck and Martha E. Sosa Torres (ed.). The Metal-Driven Biogeochemistry of Gaseous Compounds in the Environment. Metal Ions in Life Sciences. Vol. 14. Springer. pp. 99–124. doi:10.1007/978-94-017-9269-1_5. ISBN   978-94-017-9268-4. PMID   25416392.