Photoelectrochemical Nitrogen Reduction to Ammonia on Cupric and Cuprous Oxide Photocathodes

Photoelectrochemical N₂ reduction enables the production of NH₃ under ambient conditions using water as the hydrogen source. Furthermore, by utilizing solar energy, photoelectrochemical N₂ reduction can significantly reduce the energy input required for N₂ reduction. In this study, photoelectrochemical N₂ production was investigated using CuO and Cu₂O photocathodes that are known to be poorly catalytic for water reduction, the major reaction competing with N₂ reduction. When tested under simulated solar illumination with isotopically labeled ¹⁵N₂ in 0.1 M KOH solution, the CuO and Cu₂O photocathodes produced ¹⁵NH₃ with a Faradaic efficiency of 17% and 20% at 0.6 V and 0.4 V vs. RHE, respectively. These potentials are significantly more positive than the thermodynamic reduction potential of N₂, which demonstrates how the use of photoexcited electrons in the CuO and Cu₂O photocathodes can reduce the energy input required for NH₃ production. Here, the use of photoexcited electrons in these photocathodes for N₂ reduction, water reduction, and photocorrosion was carefully examined.