Coupled cation and pH effects in the hydrogen evolution reaction: An electrostati perspective

Cation effects on the hydrogen evolution reaction (HER) have been recognized for nearly a century, yet their physical origins, particularly their strong coupling with pH, remain debated. Experiments show pronounced and often inverted trends in HER activity with cation identity and concentration, which vary with pH, electrode material, and applied potential. Despite extensive research, no unified framework has reconciled these observations. In this Perspective, we revisit these trends from an electrostatic point of view. Using Butler–Volmer–Frumkin theory, we show that inverted cation trends between acidic and alkaline electrolytes arise naturally from the opposite roles of Frumkin corrections in proton- versus water-mediated Volmer steps. Multiple inversions observed under alkaline conditions further expose the limitations of single-factor, primarily atomistic, explanations, while a recent electrostatic framework accounting for local potential and electric field effects offers a coherent picture of many trends. These considerations highlight interfacial electrostatics as a critical factor and motivate integrated approaches bridging continuum and atomistic descriptions.