Enabling kinetics matching in electrocatalytic ammonia synthesis by leveraging spatially-confined Cu/Fe2O3 heterointerfaces to maximize *H supply and utilization

In electrochemical nitrate reduction reaction (NITRR), the generation of active hydrogen (*H) and its poor utilization in conversion of various nitrate intermediates often cause mismatched kinetics, resulting in low ammonia yield rate (YR NH3 ) and Faraday efficiency (FE NH3 ). Herein, we construct a spatially-confined Cu/Fe 2 O 3 heterointerfaces within porous carbon fiber, featuring oxygen vacancy-rich iron oxide nanoparticles (∼14.7 nm) interface-coupled well-dispersed Cu nanocrystals. The interfacial metallic copper sites with optimized interfacial electron transfer accelerate the consumption of NO 2 – through supplying the most abundant active *H to equilibrate NITRR kinetics. The easy desorption of generated NH 3 from active sites facilitates the accelerated reaction cycles by rapidly exposing the spent active sites. Correspondingly, this catalyst achieves nearly 100 % nitrate conversion, with a YR NH3 of 81.3 mg h −1 mg cat -1 , FE NH3 of 98.11 %, and 100 % NH 3 selectivity without any nitrite accumulation, outperforming most state-to-art catalysts as reported. Impressively, when nitrite acts as reactant, ammonia synthesis through nitrite reduction reaches YR NH3 of 99 mg h −1 mg cat -1 and FE NH3 of 99.44 % outperforming all the same series reported. Moreover, active *H quenching and isotope labeling experiments uncover the generation of the most abundant active *H species and their high utilization among the reported results. Density function theory (DFT) calculations further indicate the interfacial Cu/Fe 2 O 3 regulates the d-band center of the catalyst, optimizing the adsorption of nitrate and further lowering the reaction energy barrier of the decisive step (*NO→*NOH).