Uncovering the active sites of Cu oxides nanowires during low-concentration nitrate electrochemical reduction to ammonia

Identifying the true active sites is essential for the development of efficient catalysts for the electrochemical reduction of neutral, dilute nitrate to ammonia, because electrocatalysts often undergo structural transformations during operation conditions, potentially forming new active phases. In this work, copper oxides nanowires with varying Cu valence states were fabricated by in-situ electrochemical reduction of the pre-catalysts (denoted as P-CuO 200, CuO 300, and CuO 400 ) for the electrochemical reduction of neutral, dilute nitrate (5 mM) to ammonia. In-situ and ex-situ characterizations indicated that the surface CuO of these pre-catalysts was partially or fully reduced to Cu 2 O or metallic Cu during activation process. The Cu 2 O species were further transformed into oxide-derived copper (OD-Cu), serving as the true active sites. Among them, the CuO 300 (OD-Cu/Cu 2 O) catalyst with the highest Cu 2 O content, achieved a Faradaic efficiency of 90.8%, a nitrate conversion of 98.3%, and an ammonia yield of 3.3 mg h −1  cm −2 at −0.4 V vs. RHE, outperforming most reported Cu-based materials. Computational results confirmed that OD-Cu facilitated *NO 2 adsorption and protonation, lowering the energy barrier. This study bridges the critical gap between pre-catalyst structures and dynamically formed active sites, providing valuable guidance for the rational design of Cu-based catalysts. Download: Download high-res image (101KB) Download: Download full-size image