Artificial Cu-Ni catalyst towards highly efficient nitrate-to-ammonia conversion

Abstract

Accelerated industrialization disrupts the global nitrogen cycle, resulting in alarmingly increased nitrate in groundwater. Electrocatalytic nitrate reduction (ECNR) with high automation can effectively convert nitrate to ammonia, simultaneously achieving nitrate removal and decentralized ammonia fabrication. However, realizing highly efficient nitrate reduction toward ammonia has proven challenging due to the complex reaction steps and sluggish kinetics. Here we report that Cu-Ni alloys enable stable and highly efficient nitrate-to-ammonia conversion, and the reduction of nitrate and the selectivity for ammonium can reach 83.87% and 93.6% in 4 h, respectively. The best reaction condition is obtained by adjusting pH and applied potential (Eh) according to the sequential proton-electron transfer theory. The introduction of Ni is identified to be conducive to the upshifted d-band center of the catalyst, enhancing the adsorption of nitrate and the corresponding intermediates. The reaction intermediates and mechanistic pathways of the nitrate-to-ammonia process are elucidated by rotating disk electrode (RDE) and in-situ Fourier-transform infrared spectroscopy. This work provides a new idea for the synergistic mechanism of bimetallic denitrification and puts forward a reaction path of nitrate on bimetallic catalysts for ammonia production from nitrate. [Figure not available: see fulltext.].