CO2 Electroreduction on Borated Copper Surfaces: Boron Active Sites, not Copper

Boron-doped copper has recently emerged as an active and stable catalyst for the electrochemical reduction of CO2 to value-added C2 products. Here, we develop a realistic model of CO electroreduction on surface borides of copper under operational conditions, taking into account the effects of electrode potential, electrolyte environment, and pH. We study the possible reconstruction of the electrocatalyst surface using grand canonical DFT and global optimization to obtain a potential-dependent grand canonical ensemble description of metastable, hydrogen-covered catalyst surfaces. Two key surface configurations, low H-coverage (LC, -0.6 VSHE) and high H-coverage (HC, -0.8 VSHE) dominate this ensemble, with the former being kinetically persistent and C2 selective under strongly reducing conditions. Nonmetallic boron sites on the surface copper boride are found to bind CO more strongly than copper sites, and mechanistic investigation of CO electroreduction pathways presents a surprisingly unconventional case of boron-centered reactivity in contrast to typical copper-centered reactivity. Neighboring boron sites present along boron chains on the surface copper boride are found to facilitate C–C coupling, thereby driving the high C2 selectivity of this electrocatalyst.