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

Abstract The photoelectrochemical nitrate reduction reaction (PEC NO 3 RR) potentially converts nitrate, a major water pollutant, into NH 3 , which is an eco‐friendly, next‐generation energy source. However, achieving high efficiency in the PEC NO 3 RR has been challenging because of the need for high applied voltage and competition with the hydrogen evolution reaction (HER). In this study, a PEC NO 3 RR is successfully implemented that demonstrated a high NH 3 production rate of 2468 µg cm −2 h −1 (at −0.1 V vs RHE) using a c‐ Si photocathode with Ni foil as the catalyst. Conducting the PEC NO 3 RR 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 NO 3 RR, enhancing NH 3 production efficiency. Furthermore, a PEC NO 3 RR system is developed that operates without external voltage and achieved bias‐free record‐high solar to NH 3 conversion efficiency of 3.8% and an NH 3 production rate of 554 µg cm −2 h −1 .