Activity and Selectivity Trends in Electrocatalytic\nNitrate Reduction on Transition Metals

Abstract

Electrocatalytic\nreduction is a promising approach to remediate\nnitrate (NO₃^–), one of the world’s\nmost widespread water pollutants. In the present work, we elucidate\nactivity and selectivity trends of transition metals for electrocatalytic\nnitrate reduction to benign or value-added products such as N₂ and NH₃. Using density functional theory (DFT)\ncalculations, we find that the adsorption strengths of oxygen and\nnitrogen atoms act as descriptors for the overall activity and selectivity\nof nitrate reduction electrocatalysts. Nitrate reduction rates, volcano\nplots, surface species coverages, and the degree of rate control were\npredicted for transition metal electrocatalysts as a function of applied\npotential using DFT-based microkinetic modeling. Our microkinetic\nmodel rationalizes a number of experimental observations including\nthe activity trends of pure metals and our in situ X-ray absorption\nspectroscopy measurements of competitive adsorption between hydrogen\nand nitrate on Pt/C. We also predict that Fe₃Ru, Fe₃Ni, Fe₃Cu, and Pt₃Ru are promising catalysts\nfor nitrate electroreduction toward N₂ with relatively\nhigh activity and selectivity. Ultimately, this work gives insight\ninto nitrate reduction on transition metal surfaces and can guide\nthe design of improved electrocatalysts for nitrate remediation.