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Published January 31, 2024 | Published
Journal Article Open

Molecular Additives Improve the Selectivity of CO₂ Photoelectrochemical Reduction over Gold Nanoparticles on Gallium Nitride


Photoelectrochemical CO2 reduction (CO2R) is an appealing solution for converting carbon dioxide into higher-value products. However, CO2R in aqueous electrolytes suffers from poor selectivity due to the competitive hydrogen evolution reaction that is dominant on semiconductor surfaces in aqueous electrolytes. We demonstrate that functionalizing gold/p-type gallium nitride devices with a film derived from diphenyliodonium triflate suppresses hydrogen generation from 90% to 18%. As a result, we observe increases in the Faradaic efficiency and partial current density for carbon monoxide of 50% and 3-fold, respectively. Furthermore, we demonstrate through optical absorption measurements that the molecular film employed herein, regardless of thickness, does not affect the photocathode’s light absorption. Altogether, this study provides a rigorous platform for elucidating the catalytic structure–property relationships to enable engineering of active, stable, and selective materials for photoelectrochemical CO2R.

Copyright and License

© 2024 American Chemical Society.


This material is based on work performed by the Liquid Sunlight Alliance, which is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Fuels from Sunlight Hub, under Grant DE-SC0021266. Part of this work was carried out at the Molecular Materials Research Center in the Beckman Institute of the California Institute of Technology. The Resnick Sustainability Institute is acknowledged for support of enabling facilities at Caltech. The authors thank Yungchieh Lai for performing ICP-MS measurements and Azhar Carim for helping collect cross-sectional SEM data. A.A. acknowledges support from the Kavli Nanoscience Institute Postdoctoral Fellowship.

Conflict of Interest

The authors declare no competing financial interest.


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Additional details

January 31, 2024
January 31, 2024