Manipulating the interactions between N-intermediates and one-dimensional conjugated coordination polymers to boost electroreduction of nitrate to ammonia

Abstract

Electrocatalytic reduction of nitrate to ammonia (NITRR) is a promising strategy to remove nitrate pollutants and generate ammonia under mild conditions. However, the low conversion rate of nitrate and insufficient ammonia production rate severely limits the development of NITRR. Manipulating the adsorption of N-intermediates on the surface of catalyst greatly affects the activity and the selectivity of catalytic reaction. Herein, four one-dimensional π-d conjugated coordination polymers (1D CCPs) are synthesized and applied to NITRR. The selectivity and activity of NITRR are well improved by metal ion substitutions, which regulate the adsorption towards generated intermediates. The ammonia production rate reaches 2.28 mg h^–1 cm^–2 over Cu-BTA in 2 h, comparable to recent works at low nitrate concentrations, and the conversion rate of nitrate up to 96.74% in four hours with 79.46% ammonia selectivity. Density functional theory calculations reveal that Cu-BTA had electron-richer Cu center, causing the enhanced free energy of *NO and the attenuation of N=O bond. Therefore, the ΔG required for converting *NO to *NHO is reduced and the further hydrogenation is promoted. Additionally, the adsorption energies toward NH₃ are also effectively reduced by metal ions substitution, accelerating the desorption of generated and adsorbed NH₃, making the turnover of catalysts more frequent.