The electrochemical reduction of CO 2 is known to be influenced by the identity of the alkali metal cation in the electrolyte; however, a satisfactory explanation for this phenomenon has not been developed. Here we present the results of experimental and theoretical studies aimed at elucidating the effects of electrolyte cation size on the intrinsic activity and selectivity of metal catalysts for the reduction of CO 2 . Experiments were conducted under conditions where the influence of electrolyte polarization is minimal in order to show that cation size affects the intrinsic rates of formation of certain reaction products, most notably for HCOO The observed trends in activity with cation size are attributed to an increase in the concentration of cations at the outer Helmholtz plane with increasing cation size.

We synthesize vertically oriented core-shell nanowires with substoichiometric MoO(3) cores of ∼20-50 nm and conformal MoS(2) shells of ∼2-5 nm. The core-shell architecture, produced by low-temperature sulfidization, is designed to utilize the best properties of each component material while mitigating their deficiencies. The substoichiometric MoO(3) core provides a high aspect ratio foundation and enables facile charge transport, while the conformal MoS(2) shell provides excellent catalytic activity and protection against corrosion in strong acids.

Field-sensitive electrochemical reactions are controlled by electrode charging which is sensitive to the size of the electrolyte containing cations.