Søren B. Scott

R.

CO electroreduction activity on oxide-derived Cu (OD-Cu) was found to correlate with metastable surface features that bind CO strongly. OD-Cu electrodes prepared by H2 reduction of Cu2O precursors reduce CO to acetate and ethanol with nearly 50% Faradaic efficiency at moderate overpotential. Temperature-programmed desorption of CO on OD-Cu revealed the presence of surface sites with strong CO binding that are distinct from the terraces and stepped sites found on polycrystalline Cu foil. After annealing at 350 °C, the surface-area corrected current density for CO reduction is 44-fold lower and the Faradaic efficiency is less than 5%. These changes are accompanied by a reduction in the proportion of strong CO binding sites. We propose that the active sites for CO reduction on OD-Cu surfaces are strong CO binding sites that are supported by grain boundaries. Uncovering these sites is a first step toward understanding the surface chemistry necessary for efficient CO electroreduction.

Abstract Understanding what controls the reaction rate on iridium-based catalysts is central to designing better electrocatalysts for the water oxidation reaction in proton exchange membrane electrolysers. Here we quantify the densities of redox-active centres and probe their binding strengths on amorphous IrO x and rutile IrO 2 using operando time-resolved optical spectroscopy. We establish a quantitative experimental correlation between the intrinsic reaction rate and the active-state energetics. We find that adsorbed oxygen species, *O, formed at water oxidation potentials, exhibit repulsive adsorbate–adsorbate interactions. Increasing their coverage weakens their binding, thereby promoting O–O bond formation, which is the rate-determining step. These analyses suggest that although amorphous IrO x exhibits a higher geometric current density, the intrinsic reaction rates per active state on IrO x and IrO 2 are comparable at given potentials. Finally, we present a modified volcano plot that elucidates how the intrinsic water oxidation kinetics can be increased by optimizing both the binding energy and the interaction strength between the catalytically active states.