Photoelectrochemical Nitrogen Reduction to Ammonia on Cupric and Cuprous Oxide Photocathodes

Photoelectrochemical N 2 reduction enables the production of NH 3 under ambient conditions using water as the hydrogen source. Furthermore, by utilizing solar energy, photoelectrochemical N 2 reduction can significantly reduce the amount of energy required for N 2 reduction. In this study, photoelectrochemical N 2 reduction was investigated using CuO and Cu 2 O photocathodes that are known to be poorly catalytic for water reduction, the major reaction competing with N 2 reduction. When tested under simulated solar illumination with isotopically labeled 15 N 2 in a 0.1 M KOH solution, the CuO and Cu 2 O photocathodes produced 15 NH 3 with Faradaic efficiencies of 17% and 20% at 0.6 and 0.4 V vs the reversible hydrogen electrode, respectively. These potentials are significantly more positive than the thermodynamic reduction potential of N 2, which demonstrates how the use of photoexcited electrons in the CuO and Cu 2 O photocathodes can reduce the amount of energy required for NH 3 production. The use of photoexcited electrons in these photocathodes for N 2 reduction, water reduction, and photocorrosion was carefully examined.