MOFs-derived hollow cage composed of ultra-small CuO/Co₃O₄ hetero-nanograins for efficient nitrate reduction

The meticulous design of heterogeneous interfaces presents a promising approach for enhancing the electrocatalytic activity of Cu-based materials in nitrate reduction reactions. Herein, we developed a self-templated metal–organic frameworks transformation strategy to synthesize hollow multi-metallic oxide materials with well-defined interfaces. By utilizing novel hollow Cu–Co bimetallic Prussian blue analogs as precursors, a hollow cage composed of ultra-small CuO/Co₃O₄ hetero-nanograins was successfully constructed. It was discovered that this structure greatly enhanced the electrocatalytic activity for the conversion of NO₃⁻ to NH₃, achieving a remarkably high Faradaic efficiency (FE) for NH₃ (with a maximum FE of 90.68%) at low overpotential ranges. Furthermore, electrochemical experiments and in situ spectroscopy provided evidence that electrochemically induced reconstruction led to the formation of synergistic sites between Cu and Co₃O₄. This enabled the sequential reduction of nitrate and nitrite on adjacent metal/metal oxide phases, resulting in the rapid generation of NH₃.