Enzyme-Mimicking Metal–Phosphide Tandem Catalytic Centers for Efficient Electrochemical Nitrate-to-Ammonia Conversion and Zinc–Nitrate Battery

Achieving spatially coupled and functionally complementary active sites in synthetic catalysts remains a significant challenge. Inspired by the enzymatic cascade involving nitrate reductase and nitrite reductase, we report a nanozyme comprising iron clusters and iron-doped nickel phosphide nanoparticles on CeO₂ nanorods (Fe–Fe_xNi_2−xP/CeO₂) in proximity for efficient electrocatalytic nitrate-to-ammonia conversion and Zn–NO₃⁻ battery. The Fe clusters serve as nitrate reductase mimics, promoting the deoxygenation step of NO₃⁻ to NO₂⁻, while the adjacent Fe_xNi_2−xP nanoparticles serve as nitrite reductase mimics, accelerating the subsequent hydrogenation steps to NH₃. The CeO₂ nanorods stabilize the dual active sites and function as proton reservoirs to suppress the hydrogen evolution reaction. Thus, the nanozyme delivers exceptional performance in NH₃ electrosynthesis, achieving a high yield rate of 43.5 mg h⁻¹ cm⁻² with a Faradaic efficiency (FE) of 91.2% at –0.7 V versus RHE in an H-type cell and an industrial-level current density of 800 mA cm⁻² for over 100 h under flow-cell conditions (FE_NH3 > 90%) at the same potential. When employed Fe–Fe_xNi_2−xP/CeO₂ as a cathode in a rechargeable Zn–NO₃⁻ battery, it enables simultaneous NH₃ production and power generation, delivering a peak power density of 21.1 mW cm⁻² and an NH₃ yield rate of 1.9 mg h⁻¹ cm⁻².