Anodic Oxidation-Induced Interfacial Regulation of Nanoporous Co₂P/CoOOH for Electrocatalytic Nitrate Reduction to Ammonia

The rechargeable Zn-nitrate battery presents a promising strategy for renewable energy conversion, ammonia production, and sewage treatment. Despite achieving excellent performance with transition metal-based electrocatalysts, the structure evolution of the electrocatalyst during Zn-nitrate battery charging/discharging and the corresponding reaction mechanism on nitrate reduction reaction (NO₃RR) are still unclear. Inspired by the structural reconstruction in the charging process, nanoporous Co₂P/CoOOH prepared by dealloying and anodic oxidation is reported as an electrocatalyst for NO₃RR, achieving remarkable catalytic performance (ammonia yield rate: 1.93 mmol h^-1 cm^-2, Faradaic efficiency: 94.18%) with a high cathodic energy efficiency of 34.51%. Additionally, the assembled rechargeable Zn-nitrate battery delivers a power density of 31.99 mW cm^-2 with a high charge-discharge stability. In-situ spectroscopy investigation reveals the generation of a Co₂P/Co₃O₄ heterosturcture through a synergetic redox reaction involving the cobalt species and nitrate ions during NO₃RR, which enhances the approach of potassium-ionized water and improves ammonia generation kinetics by regulating the NO₂^- and *NH₂ generation. Density functional theoretical calculation further illustrates that Co₂P/Co₃O₄ heterostructure optimizes the adsorption of the *NO intermediate and enables an energetically favorable rate-limiting *NOH formation step. The unique structural evolution and nitrate activation mode of cobalt-based heterostructure would provide new insights on designing efficient electrocatalysts for nitrate reduction and rechargeable Zn-nitrate battery.