Activity and Selectivity Trends in Electrocatalytic Nitrate Reduction on Transition Metals

Electrocatalytic reduction is a promising approach to remediate nitrate (NO3–), one of the world's most widespread water pollutants. In the present work, we elucidate activity and selectivity trends of transition metals for electrocatalytic nitrate reduction to benign or value-added products such as N2 and NH3. Using density functional theory (DFT) calculations, we find that the adsorption strengths of oxygen and nitrogen atoms act as descriptors for the overall activity and selectivity of nitrate reduction electrocatalysts. Nitrate reduction rates, volcano plots, surface species coverages, and the degree of rate control were predicted for transition metal electrocatalysts as a function of applied potential using DFT-based microkinetic modeling. Our microkinetic model rationalizes a number of experimental observations including the activity trends of pure metals and our in situ X-ray absorption spectroscopy measurements of competitive adsorption between hydrogen and nitrate on Pt/C. We also predict that Fe3Ru, Fe3Ni, Fe3Cu, and Pt3Ru are promising catalysts for nitrate electroreduction toward N2 with relatively high activity and selectivity. Ultimately, this work gives insight into nitrate reduction on transition metal surfaces and can guide the design of improved electrocatalysts for nitrate remediation.