Photoelectrochemical Nitrate and Nitrite Reduction Using Cu₂O Photocathodes

Nitrate in wastewater streams causes eutrophication, and nitrate removal is of great importance for environmental protection. Electrochemical nitrate reduction has the advantage of directly converting nitrate to benign or useful chemicals, but it typically requires a considerable overpotential. In this study, photoelectrochemical nitrate reduction is investigated using a Cu2O photocathode, where photoexcited electrons in the conduction band inherently have an overpotential of >1.6 V for nitrate reduction. The Cu2O photocathode is found to reduce nitrate to nitrite selectively with a high Faradaic efficiency (>85%). More importantly, as the surface of Cu2O is particularly catalytic for nitrate reduction, nitrate reduction on Cu2O kinetically suppresses photocorrosion of Cu2O without the need for additional catalyst or protection layers. In addition to nitrate reduction, nitrite reduction on Cu2O is examined to compare the effects of nitrate and nitrite reduction kinetics on the photocurrent generation and photocorrosion of Cu2O photocathodes.