The use of renewable electricity to drive chemical reactions is an approach to storing the energy from intermittent sources (solar, wind) in the form of chemical bonds. Combining photoabsorber and electrocatalytic components into integrated devices, we developed copper oxide-based photocathodes for proton reduction to hydrogen (1,2), as well as carbon dioxide reduction to carbon monoxide (3), in demonstrations of efficient solar-to-fuels conversion.

Recently, oxide-derived copper emerged as an intriguing electrocatalyst for the conversion of carbon dioxide into hydrocarbon products. In an effort to modify the product selectivity of copper oxide nanowire arrays, we used atomic layer deposition to apply conformal layers of tin oxide to the electrode surface. This copper-tin-oxide hybrid exhibited nearly unity selectivity for carbon monoxide as CO₂ reduction product, deviating significantly from the behavior expected for copper or tin alone, neither of which typically produce CO at high selectivity. This result suggests sub-monolayer composition modification of electrode surfaces can be a powerful strategy for tuning electrocatalyst selectivity.

1. J. Luo, L. Steier, M.-K. Son, M. Schreier, M. T. Mayer and M. Grätzel, Nano Letters, 2016, 16, 1848–1857.
2. P. Dias, M. Schreier, S. D. Tilley, J. Luo, J. Azevedo, L. Andrade, D. Bi, A. Hagfeldt, A. Mendes, M. Grätzel and M. T. Mayer, Adv. Energy Mater., 2015, 5, 1501537.
3. M. Schreier, J. Luo, P. Gao, T. Moehl, M. T. Mayer and M. Grätzel, J. Am. Chem. Soc., 2016, 138, 1938–1946.
4. M. Schreier, F. Héroguel, L. Steier, S. Ahmad, J. S. Luterbacher, M. T. Mayer, J. Luo and M. Grätzel, Nature Energy, 2017, 2, 17087.