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Solar hydrogen: Photoanodes made of alpha-SnWO4 promise high efficiencies

Date:
January 26, 2021
Source:
Helmholtz-Zentrum Berlin für Materialien und Energie
Summary:
Photoanodes made of metal oxides are considered to be a viable solution for the production of hydrogen with sunlight. Alpha-SnWO4 has optimal electronic properties for photoelectrochemical water splitting with sunlight, but corrodes easily. Protective layers of nickel oxide prevent corrosion, but reduce the photovoltage and limit the efficiency. Now a team has investigated at BESSY II what happens at the interface between the photoanode and the protective layer.
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Photoanodes made of metal oxides are considered to be a viable solution for the production of hydrogen with sunlight. α-SnWO4has optimal electronic properties for photoelectrochemical water splitting with sunlight, but corrodes easily. Protective layers of nickel oxide prevent corrosion, but reduce the photovoltage and limit the efficiency. Now a team at HZB has investigated at BESSY II what happens at the interface between the photoanode and the protective layer. Combined with theoretical methods, the measurement data reveal the presence of an oxide layer that impairs the efficiency of the photoanode.

Hydrogen is an important factor in a sustainable energy system. The gas stores energy in chemical form and can be used in many ways: as a fuel, a feedstock for other fuels and chemicals or even to generate electricity in fuel cells. One solution to produce hydrogen in a climate-neutral way is the electrochemical splitting of water with the help of sunlight. This requires photoelectrodes that provide a photovoltage and photocurrent when exposed to light and at the same time do not corrode in water. Metal oxide compounds have promising prerequisites for this. For example, solar water splitting devices using bismuth vanadate (BiVO4) photoelectrodes achieve already today ~8 % solar-to-hydrogen efficiency, which is close to the material's theoretical maximum of 9 %.

Theoretical limit is 20 % in α-SnWO4

To achieve efficiencies beyond 9 %, new materials with a smaller band gap are needed. The metal oxide α-SnWO4has a band gap of 1.9 eV, which is perfectly suited for photoelectrochemical water splitting. Theoretically, a photoanode made of this material could convert ~20 % of the irradiated sunlight into chemical energy (stored in the form of hydrogen). Unfortunately, the compound degrades very quickly in an aqueous environment.

Protection against corrosion comes with a price

Thin layers of nickel oxide (NiOx) can protect the α-SnWO4photoanode from corrosion, but were found to also significantly reduce the photovoltage. To understand why this is the case, a team led by Dr. Fatwa Abdi at the HZB Institute for Solar Fuels has analysed the α-SnWO4/NiOxinterface in detail at BESSY II.

Interface explored at BESSY II

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"We studied samples with different thicknesses of NiOxwith hard X-ray photoelectron spectroscopy (HAXPES) at BESSY II and interpreted the measured data with results from calculations and simulations," says Patrick Schnell, the first author of the study and a PhD student in the HI-SCORE International Research School at HZB. "These results indicate that a thin oxide layer forms at the interface, which reduces the photovoltage," explains Abdi.

Outlook: better protection layers

Overall, the study provides new, fundamental insights into the complex nature of interfaces in metal oxide-based photoelectrodes. "These insights are very helpful for the development of low-cost, scalable metal oxide photoelectrodes," says Abdi. α-SnWO4is particularly promising in this regard. "We are currently working on an alternative deposition process for NiOxon α-SnWO4that does not lead to the formation of an interfacial oxide layer, which is likely to be SnO2. If this is successful, we expect that the photoelectrochemical performance of α -SnWO4will increase significantly."

Story Source:

Materialsprovided byHelmholtz-Zentrum Berlin für Materialien und Energie.注:内容可能be edited for style and length.


Journal Reference:

  1. Patrick Schnell, Moritz Kölbach, Markus Schleuning, Keisuke Obata, Rowshanak Irani, Ibbi Y. Ahmet, Moussab Harb, David E. Starr, Roel van de Krol, Fatwa F. Abdi.Photovoltag界面氧化形成限制e of α‐SnWO 4 /NiO x Photoanodes Prepared by Pulsed Laser Deposition.Advanced Energy Materials, 2021; 2003183 DOI:10.1002/aenm.202003183

Cite This Page:

Helmholtz-Zentrum Berlin für Materialien und Energie. "Solar hydrogen: Photoanodes made of alpha-SnWO4 promise high efficiencies." ScienceDaily. ScienceDaily, 26 January 2021. .
Helmholtz-Zentrum Berlin für Materialien und Energie. (2021, January 26). Solar hydrogen: Photoanodes made of alpha-SnWO4 promise high efficiencies.ScienceDaily. Retrieved August 7, 2023 from www.koonmotors.com/releases/2021/01/210126134041.htm
Helmholtz-Zentrum Berlin für Materialien und Energie. "Solar hydrogen: Photoanodes made of alpha-SnWO4 promise high efficiencies." ScienceDaily. www.koonmotors.com/releases/2021/01/210126134041.htm (accessed August 7, 2023).

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