Tuning mobility of intermediate and electron transfer to enhance electrochemical reduction of nitrate to ammonia on Cu2O/Cu interface

Abstract Compared to traditional haber-bosch process for synthetic ammonia, electrochemical reduction of nitrate to ammonia (ERNA) offers a promising and sustainable technology to generate ammonia at ambient temperature. However, the performance of ERNA is impeded by lacking of sound strategy for designing high-performance electrocatalyst. Here, a Cu based electrode with Cu2O/Cu interface was prepared by pulse electrodeposition and electroreduction, achieving the fast rate constant of 0.14 min-1 for reducing nitrate with a high ammonia yield rate of 2.17 mg cm-2 h-1 (faradaic efficiency: 84.36%) and ammonia selectivity of 94.4% at -0.25 V vs. RHE. Particularly, density functional theory (DFT) calculations for the adsorption energy indicated that Cu2O/Cu interface alleviated adsorption energy of NO2− from -2.02 eV (pure Cu) to -1.59 eV, improving surface diffusion of adsorbed NO2− . And DFT calculations for electronic structure implied that Cu2O/Cu interface upshifted the d band center of Cu (-2.25 eV vs. -2.48 eV of pure Cu), boosting electron transfer to NO3− . Additionally, in-situ infrared spectroscopic analysis confirmed vital intermediates of NO2− and NH2OH on Cu2O/Cu to identify reaction pathway and Gibbs free energy diagram clarified this interface decreased reaction barrier of crucial step (reducing *NO2 to *NO) from 0.31 eV (pure Cu) to -0.77 eV for the enhancement of ERNA. Thereby, these findings demonstrated that Cu2O/Cu interface tunes mobility of NO2− and electron transfer to NO3− on Cu based electrocatalyst is an efficient method to promote performance of ERNA with high efficiency and rate.