(52i) Influence of Alkali Metal Cations on the Hydrogen Evolution Reaction in Acidic and Basic Electrolytes

Electrocatalytic water splitting is an attractive method for storing renewable electricity in the form of chemical bonds. However, widespread implementation of this technology requires improvements in the activity of electrocatalysts for the cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER). One approach for improving catalytic performance is to modify the environment surrounding the active site, rather than the active site structure itself. For instance, choice of electrolyte cation is known to influence rates of HER on metal electrodes, but a clear explanation of this behavior is lacking. Here, we present experimental and theoretical studies aimed at elucidating the role of alkali metal cations in alkaline and acidic electrolytes for the HER on polycrystalline noble metal (Cu, Ag, Au) and reactive metal (Pd, Pt, Ir) electrodes. We found that HER activity in alkaline electrolytes increases with alkali metal cation size on noble metals (Cs⁺ > K⁺ > Na⁺ > Li⁺) and decreases with alkali metal cation size on reactive metals (Li⁺ > Na⁺ > K⁺ > Cs⁺). In acidic electrolytes, there was no systematic trend with alkali metal cation size for HER for all metals. Density functional theory calculations show that the observed activity trends in alkaline conditions are due to interactions between solvated alkali cations and hydroxide generated from water dissociation. In acidic conditions, hydrogen binding energy is unaffected by the presence of cations, explaining the lack of a systematic trend in HER activity. This study describes the role of the electrochemical environment on HER performance, helping guide the rational design of more efficient electrocatalysts.