Competition between CO2 Reduction and H2 Evolution on Transition-Metal Electrocatalysts

The well-known hydrogen evolution reaction (HER) volcano plot describes the relationship between H binding energy and the corresponding hydrogen evolution catalytic activity, which depends on the species of metal. Under CO2/CO reduction conditions or in cases where CO impurities enter electrodes, the catalyst may exist under a high coverage of coadsorbed CO. We present DFT calculations that suggest that coadsorbed CO during hydrogen evolution will weaken the binding strength between H and the catalyst surface. For metals on the right-hand side (too weak of hydrogen binding) this should lead to a suppression of the HER, as has been reported for metals such as Cu and Pt. However, for metals on the left-hand side of the volcano (too strong of hydrogen binding), this may actually enhance the kinetics of the hydrogen evolution reaction, although this effect will be countered by a decreased availability of sites for HER, which are blocked by CO. We performed experiments in Ar and CO2 environments of two represe...