Electrocatalytic Nitrate Reduction to Hydroxylamine: Breaking the Activity-Selectivity Trade-Off by Designer...

Electrocatalytic nitrate reduction reaction (NitRR) offers a promising route for hydroxylamine (NH₂OH) 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 NH₂OH production via NitRR with high performance. Experimental and theoretical investigations have unraveled the synergy of dual active sites in promoting NO₃ ^- to NH₂OH conversion. The electron-sufficient Ni^(2-δ)+ site weakens the binding of *NH₂OH intermediate and minimizes its excessive reduction to undesired NH₃ 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 NH₂OH formation is increased. The concurrently enhanced selectivity and activity result in a high Faradaic efficiency of 92.3% and an unprecedented NH₂OH 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 NH₂OH production with a high solar-to-NH₂OH efficiency of 17.74%. Our work offers advanced electrocatalysts and new insights for sustainable NH₂OH electrosynthesis.