Nickel Hydroxide Catalyzed Bias-free Photoelectrochemical NH<sub>3</sub> Production via Nitrate Reduction.

Jin, Wonjoo; Go, Hyunju; Jeong, Juyeon; Park, Jeonghwan; Tayyebi, Ahmad; Yu, Je Min; Kim, Seungchul; Choi, Keunsu et al. · Adv Mater · 2025

basic_science · Level V

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Abstract

The photoelectrochemical nitrate reduction reaction (PEC NO<sub>3</sub>RR) potentially converts nitrate, a major water pollutant, into NH<sub>3</sub>, which is an eco-friendly, next-generation energy source. However, achieving high efficiency in the PEC NO<sub>3</sub>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<sub>3</sub>RR is successfully implemented that demonstrated a high NH<sub>3</sub> production rate of 2468 µg cm<sup>-2</sup> h<sup>-1</sup> (at -0.1 V vs RHE) using a c-Si photocathode with Ni foil as the catalyst. Conducting the PEC NO<sub>3</sub>RR under alkaline conditions can lead to the self-activation of the Ni surface with Ni(OH)<sub>2</sub>. Ni(OH)<sub>2</sub> can suppress the competitive HER and facilitate NO<sub>3</sub>RR, enhancing NH<sub>3</sub> production efficiency. Furthermore, a PEC NO<sub>3</sub>RR system is developed that operates without external voltage and achieved bias-free record-high solar to NH<sub>3</sub> conversion efficiency of 3.8% and an NH<sub>3</sub> production rate of 554 µg cm<sup>-2</sup> h<sup>-1</sup>.