Nickel Hydroxide Catalyzed Bias-free Photoelectrochemical NH3 Production via Nitrate Reduction

Abstract

The photoelectrochemical nitrate reduction reaction (PEC NO3RR) potentially converts nitrate, a major water pollutant, into NH3, which is an eco-friendly, next-generation energy source. However, achieving high efficiency in the PEC NO3RR has been challenging because of the need for high applied voltage and competition with the hydrogen evolution reaction (HER). In this study, a PEC NO3RR is successfully implemented that demonstrated a high NH3 production rate of 2468 mu g cm-2 h-1 (at -0.1 V vs RHE) using a c-Si photocathode with Ni foil as the catalyst. Conducting the PEC NO3RR under alkaline conditions can lead to the self-activation of the Ni surface with Ni(OH)2. Ni(OH)2 can suppress the competitive HER and facilitate NO3RR, enhancing NH3 production efficiency. Furthermore, a PEC NO3RR system is developed that operates without external voltage and achieved bias-free record-high solar to NH3 conversion efficiency of 3.8% and an NH3 production rate of 554 mu g cm-2 h-1.