Electrochemical nitrate reduction to NH3 by faceted Cu2O nanostructures in acidic medium

Abstract

In this work, we have thoroughly studied the electrochemical nitrate reduction reaction (NO₃RR) by cubic, octahedral and truncated octahedral Cu₂O nanocrystals (NCs) for the production of NH₃. Electrochemical NO₃RR is generally carried out in an alkaline medium due to the enhanced hydrogen evolution reaction (HER) in acidic conditions. Interestingly, the faceted Cu₂O NCs were found to show efficient activity for the formation of NH₃ in an acidic medium over neutral and alkaline media. Octahedral Cu₂O NCs showed higher faradaic efficiency (FE) of 84.56% at −0.6 V vs. RHE with an NH₃ production rate of 11.5 mg h⁻¹ cm⁻² in acidic medium. However, in an alkaline medium, under the same conditions, the octahedral Cu₂O NCs showed 45.9% FE for NH₃ with a production rate of 15 mg h⁻¹ cm⁻². However, FE for NH₃ was found to be higher (80%) in a neutral medium, and the production rate was quite low (1.5 mg h⁻¹ cm⁻²). The higher activity in the acidic medium is attributed exclusively due to the presence of Cu(I), which could act as the active catalyst for electrochemical NO₃RR.