Electrocatalytic Nitrate Reduction to Hydroxylamine: Breaking the Activity‐Selectivity Trade‐Off by Designer Bifunctional Metal‐Organic Frameworks

Abstract

ABSTRACT Electrocatalytic nitrate reduction reaction (NitRR) offers a promising route for hydroxylamine (NH 2 OH) synthesis under ambient conditions. However, the inherent activity‐selectivity trade‐off limits the overall performance. To overcome this challenge, a bimetallic NiMg‐MOF‐74 electrocatalyst is designed for NH 2 OH production via NitRR with high performance. Experimental and theoretical investigations have unraveled the synergy of dual active sites in promoting NO 3 − to NH 2 OH conversion. The electron‐sufficient Ni (2‐δ)+ site weakens the binding of *NH 2 OH intermediate and minimizes its excessive reduction to undesired NH 3 byproduct. Moreover, the electron‐deficient Mg (2+δ)+ site with higher charge density than Ni (2‐δ)+ facilitates hydration and hydrogenation steps of N─O species over proximal Ni (2‐δ)+ site, thus the overall activity for NH 2 OH formation is increased. The concurrently enhanced selectivity and activity result in a high Faradaic efficiency of 92.3% and an unprecedented NH 2 OH yield rate of 55.1 mg h −1 cm −2 in a flow reactor, which can be directly utilized for the preparation of value‐added oxime compounds. Further, the coupling of NitRR with photovoltaics in one system enables bias‐free NH 2 OH production with a high solar‐to‐NH 2 OH efficiency of 17.74%. Our work offers advanced electrocatalysts and new insights for sustainable NH 2 OH electrosynthesis.