Surface Dynamic Redox Modulation of CuFe Achieving Near-Unity Selectivity in Solar-Integrated Nitrate-to-Ammonia Conversion.

Electrocatalytic nitrate reduction (NO₃ ⁻RR) provides a sustainable pathway for NH₃ production under ambient conditions. Although operation in neutral media is more practically relevant, the reaction generally suffers from sluggish kinetics and unfavorable hydrogenation steps, which collectively limit NH₃ selectivity. Here, we develop a graphene-encapsulated CuFe alloy catalyst (CuFe-G) that enables highly efficient NO₃ ⁻RR via a dynamically generated CuFeδ+ surface active layer. The synergistic alloy interface drives the spontaneous conversion of NO₃ ⁻ to NO₂ ⁻, while in Situ surface redox dynamics create an active CuFeδ+ layer that optimizes *NO adsorption and accelerates hydrogenation kinetics. In parallel, encapsulation of the dynamic CuFeδ+ species within multilayer graphene constructs a mechanically robust and highly conductive interface that stabilizes the active sites and facilitates rapid charge transport. As a result, CuFe-G delivers a peak NH₃ Faradaic efficiency of 99.63% at -1.0 V vs. RHE, together with an NH₃ yield rate of 8.03 mg h⁻¹ mgcat ⁻¹. When integrated into a CuFe-G‖RuO₂ electrolyzer, the system further achieves a current density of 400 mA cm⁻² at 2.6 V and maintains a solar-to-ammonia efficiency of 4.1% under fluctuating illumination. This work therefore establishes a dynamically redox-regulated catalytic platform for sustainable, solar-driven nitrate-to-ammonia conversion.