Key Role of Cations in Stabilizing Hydrogen Radicals for CO 2 -to-CO Conversion via a Reverse Water-Gas Shift Reaction.

Electrochemically converting CO 2 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 2 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 2 -to-CO conversion and partial current density on Au catalysts. Unexpectedly, K + with a higher proton transport performs the best for CO 2 -to-CO conversion. We thus revisit the roles of alkali cations and find that hydrated K + can stabilize hydrogen radicals benefiting CO 2 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 2 via a reverse water-gas shift route under electrochemical conditions.