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Published November 9, 2018 | Supplemental Material
Journal Article Open

Bi-containing n-FeWO_4 Thin Films Provide the Largest Photovoltage and Highest Stability for a sub-2 eV Band Gap Photoanode

Abstract

Photoelectrocatalysis of the oxygen evolution reaction remains a primary challenge for development of tandem-absorber solar fuel generators due to the lack of a photoanode with broad solar spectrum utilization, a large photovoltage, and stable operation. Bismuth vanadate with a 2.4–2.5 eV band gap has shown the most promise becauses its photoactivity down to 0.4 V vs RHE is sufficiently low to couple to a lower-gap photocathode for fuel synthesis. Through development of photoanodes based on the FeWO_4 structure, in particular, Fe-rich variants with addition of about 6% Bi, we demonstrate the same 0.4 V vs RHE turn-on voltage with a 2 eV band gap metal oxide, enabling a 2-fold increase in the device efficiency limit. Combinatorial exploration of materials composition and processing facilitated synthesis of n-type variants of this typical p-type semiconductor that exhibit much higher photoactivity than previous implementations of FeWO_4 in solar photochemistry. The photoanodes are particularly promising for solar fuel applications given their stable operation in acid and base.

Additional Information

© 2018 American Chemical Society. Received: August 17, 2018; Accepted: October 12, 2018; Published: October 12, 2018. This material is based upon work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993. Computational work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. DOE under Contract DE-AC02-05CH11231. Seebeck and resistivity characterization were supported by the U.S. Department of Energy under Contract No. DE-AC36-08GO28308 with Alliance for Sustainable Energy, LLC, the Manager and Operator of the National Renewable Energy Laboratory, with funding provided by the Office of Science, Office of Basic Energy Sciences, as part of the Energy Frontier Research Center "Center for Next Generation of Materials Design: Incorporating Metastability". We thank Dr. Mitsutaro Umehara for assistance with collection of cross-sectional SEM images. Author Contributions: L.Z. and A.S. contributed equally. The authors declare no competing financial interest.

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