In situ evolved phase and heterostructure boosting nitrate to ammonia synthesis for enhanced energy supply in Zn-NO3− battery

Abstract

Revealing the dynamic reconfiguration of catalysts and the evolution of active species during catalysis, elucidating and regulating the reconfiguration mechanism are paramount to the development of high-performance electrochemical nitrate reduction (NO₃RR) to ammonia. In-situ characterizations can precisely track reaction process and unveil the origin of activity enhancement. Here, in-situ reconstruction of pre-catalyst Co₃O₄ fabricates a stable heterojunction Co(OH)₂/Co₃O₄ to boost NO₃RR to ammonia. In-situ generated heterojunction accelerates the transformation of *NO₃ to *NO₂, while Co(OH)₂ promotes the dissociation of water to active *H species for the hydrogenation of *N species, and thereby improving the deoxygenation and hydrogenation ability of NO₃RR to NH₃ and achieving a high Faradaic efficiency (FE) about 96.2% and a high NH₃ production rate of 218.5 μmol h⁻¹ mg_cat⁻¹ at −0.3 V. Density functional theory (DFT) calculations verified that in-situ formed active species Co(OH)₂ on Co₃O₄ markedly decreased the energy barrier of *NO₃ → *NO₂ and accelerated the hydrogenation step of *NH → *NH₂ → *NH₃. Co(OH)₂/Co₃O₄ heterostructure-based Zn-NO₃⁻ cell achieves excellent energy supply (1.22 V), a high ammonia yield rate (48.9 µmol h⁻¹ cm⁻²), and a high FE (91%). The establishment of the structure–activity relationship during NO₃RR provides guidance for designing advanced electrode materials, and the in-situ evolution of species on the electrode surface unveils the intrinsic nature of improved catalytic performance.