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 amount of energy required for N2 reduction. In this study, photoelectrochemical N2 reduction 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 a 0.1 M KOH solution, the CuO and Cu2O photocathodes produced 15NH3 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 N2, which demonstrates how the use of photoexcited electrons in the CuO and Cu2O photocathodes can reduce the amount of energy required for NH3 production. The use of photoexcited electrons in these photocathodes for N2 reduction, water reduction, and photocorrosion was carefully examined.