More Hydrogen from Hot Water Splitting

A higher electrolyte temperature increases the activity of a thin-film electrode for solar hydrogen generation by 40 percent.

The Science

Solar hydrogen generation is a promising technology for using sunlight to convert water into hydrogen fuel. This technology could be both efficient and economical. One approach uses materials called metal oxides, including one that combines the elements bismuth and vanadium. To make hydrogen, cells made of these materials, called photoelectrodes, are immersed in an electrolyte. When exposed to sunlight, the cells and electrolyte react to split water into hydrogen and oxygen. Cells made of bismuth and vandate have the advantages of low costs and high stability. However, researchers know little about how temperature affects their performance. In this study, scientists demonstrated that higher temperatures in the electrolyte surrounding cells increase the activity of a bismuth-vanadate electrode by 40%. This results in increased hydrogen production.

The Impact

This work provides insights on the effect of operating temperature on solar water splitting. It adds to researchers’ knowledge of metal oxide cells and how they perform in solar fuel technology. In addition, it provides a new understanding of how electrolytes affect the surfaces of metal-oxide cells during water splitting. These new insights allow for further development of materials to facilitate solar hydrogen generation. This work will help the technology reach new levels of efficiency and aid in bringing these solutions to the marketplace.

Summary

Photoelectrochemical (PEC) water splitting is typically carried out and studied at room temperature. This work, conducted at the Center for Functional Nanomaterials, a Department of Energy Office of Science user facility operated by Brookhaven National Laboratory, investigates the effect of temperature on PEC water splitting using a bismuth vanadate (BiVO₄) photoanode as a model system. The systematic electrochemical study demonstrates that the PEC activity is boosted at elevated electrolyte temperatures and indicates that thermal energy plays a main role in improving charge carrier separation in the bulk of BiVO₄. The researchers observed irreversible surface reconstruction after PEC reactions at elevated temperature in the presence of hole scavengers, with regularly spaced stripes emerging on BiVO₄ grains. The surface-reconstructed photoelectrode exhibits as much as a 40% improvement in photocurrent density and a favorable shift (~0.25 V) of photocurrent onset. This work provides insights on the influence of temperature on the photoelectrode in solar water splitting and reveals the effect of hole scavengers in photoelectrochemical measurements.

Contact

Funding

This research used resources of the Materials Synthesis & Characterization, Electron Microscopy, and Proximal Probes Facilities of the Center for Functional Nanomaterials, a Department of Energy Office of Science user facility operated by Brookhaven National Laboratory.

Publications

Zhou, C., Zhang, L., Tong, X., and Liu, M., Temperature Effect on Photoelectrochemical Water Splitting: A Model Study Based on BiVO4 Photoanodes. ACS Applied Materials & Interfaces 13, 61227 (2021). [DOI: https://doi.org/10.1021/acsami.1c19623]

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Program: BES , SUF

Performer: University , DOE Laboratory , CFN