Hydration-effect Boosted Active Hydrogen Facilitates Neutral Ammonia Electrosynthesis from Nitrate Reduction

Abstract

Electrocatalytic nitrate reduction to ammonia (NO₃RR) in a neutral medium is a green and effective strategy for treating nitrate pollution meanwhile producing ammonia. However, the insufficient active hydrogen (H^*) on the catalyst surface resulting from the sluggish Volmer step (H₂O → H⁺ + OH⁻), and the competitive hydrogen evolution reaction (HER) caused by H^* coupling severely restrict the enhancement of NO₃RR activity. Herein, a hydration-effect boosted H^*-rich strategy facilitating neutral ammonia electrosynthesis from nitrate reduction is proposed. The introduction of the hydration-effect-promoting element aluminum into the copper-based catalyst forming CuAlO₂, which adjusts the electron density distribution in the catalyst system, and the resulting hydration-effect significantly promotes the H^* generation in a neutral medium. Moreover, the rapid charge transfer at the CuO/CuAlO₂ interface facilitates the reaction kinetics and the H^* diffusion. More importantly, the introduction of Al weakens the overly strong adsorption of intermediates by CuO, thereby accelerating the hydrogenation process and suppressing HER. Thus, under neutral conditions, CuO/CuAlO₂ reached a Faradaic efficiency and an ammonia yield as high as 97.81 ± 1.94% and 10.21 ± 0.64 mg h⁻¹ cm⁻² at −1.0 V versus RHE toward NO₃RR.