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

In-situ reconstructed Co(OH) 2 /Co 3 O 4 heterostructure on Co 3 O 4 boosted adsorption and activation of nitrate to nitrite and the formed Co(OH) 2 promoted the dissociation of water to active hydrogen for hydrogenation of nitrogen species to ammonia, unveiling origin of the improvement of NO 3 RR performance for enhanced energy supply in zinc-nitrate battery. 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 (NO 3 RR) to ammonia. In-situ characterizations can precisely track reaction process and unveil the origin of activity enhancement. Here, in-situ reconstruction of pre-catalyst Co 3 O 4 fabricates a stable heterojunction Co(OH) 2 /Co 3 O 4 to boost NO 3 RR to ammonia. In-situ generated heterojunction accelerates the transformation of *NO 3 to *NO 2 , 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 NO 3 RR to NH 3 and achieving a high Faradaic efficiency (FE) about 96.2% and a high NH 3 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 Co 3 O 4 markedly decreased the energy barrier of *NO 3 → *NO 2 and accelerated the hydrogenation step of *NH → *NH 2 → *NH 3 . Co(OH) 2 /Co 3 O 4 heterostructure-based Zn-NO 3 − 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 NO 3 RR 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.