Key Role of Cations in Stabilizing Hydrogen Radicals for CO-to-CO Conversion via a Reverse Water-Gas Shift Reaction.

Electrochemically converting CO into valuable chemicals and fuels in acidic media is argued as a promising energy- and carbon-efficient route. Although several key roles of alkali cations have been unveiled, the alkali cation trends for CO reduction remain largely elusive. With decreasing cation size from Cs to Li, here we show that the apparent proton diffusion coefficient in 3.0 M Li is tens-fold lower than in 3.0 M K and 3.0 M Cs acidic electrolytes. Although Li has the strongest inhibition ability for proton transport, it acts the worst for both the CO-to-CO conversion and partial current density on Au catalysts. Unexpectedly, K with a higher proton transport performs the best for CO-to-CO conversion. We thus revisit the roles of alkali cations and find that hydrated K can stabilize hydrogen radicals benefiting CO conversion at the electrode interface while for Li this is not the case. This study proposes that cation-stabilized atomic hydrogen assists in activating CO via a reverse water-gas shift route under electrochemical conditions.