Underappreciated Role of Low-Energy Facets in Nitrogen Electroreduction

Abstract

Electrocatalytic nitrogen reduction reaction (NRR) is a promising route to replace the energy-intensive Haber–Bosch process. However, weak nitrogen-surface interaction impedes the reaction efficiency and demands better understanding of the catalyst surface chemistry. Here, we expand the design rules for NRR to include the low-energy smooth surfaces, in contrast to conventional wisdom favoring irregular or high-index facets, grain boundaries, and edge sites. Our Ni3S4 catalyst with low-energy facets achieves a 6.8 ± 3.3% Faradaic efficiency (FE) for NRR, compared to 1.9 ± 3.6% for a control of the same crystal structure and composition but with a more disordered surface. First-principles calculations reveal that the synthetic conditions allow choosing whether Ni-rich or S-rich surfaces would be more stable, which affects the coordination of the active Ni site and its reactivity. In addition, the combination of Lewis acid and Lewis base sites allows separating the adsorption of different reactants, resulting in a suppression of the competing hydrogen evolution reaction.