Surface Charge Universally Predicts the Presence of Cation Effects in Electrocatalysis

The identity of spectator cations in the electrolyte has an important influence on the rates of many electrocatalytic reactions, But these effects are not always observed. Recently, we found that the surface charge of the catalyst, quantified by the potential of zero total charge (PZTC), predicts when cation effects will be observed for the oxygen reduction reaction (ORR). Here, we demonstrate the universality of this descriptor to rationalize the observation or absence of cation effects across a range of reactions (the hydrogen evolution reaction, the ORR, methanol oxidation, ethylene glycol oxidation, and glycerol oxidation) and metal surfaces (Pt, Pd, Ag, and Au). We argue that when the reaction's operating potential is negative of the metal's PZTC, electrolyte cations accumulate at the catalyst surface and influence reaction rates. When reactions occur positive of the PZTC, cation effects are not observed.