Electrolyte Engineering toward Efficient Hydrogen Production Electrocatalysis with Oxygen-Crossover Regulation under Densely Buffered Near-Neutral pH Conditions

This study tackles the core issues associated with near-neutral pH water splitting, particularly regarding electrolyte engineering in the electrocatalysis and product crossover. The hydrogen evolution reaction (HER) was investigated on Pt, Ni, and NiMo catalysts in various concentrations of cations and anions to describe their performances by quantifying kinetics and mass transport. The choice of electrolyte in terms of its identity and activity drastically altered the HER performance. Electrolyte properties (activity coefficient, kinematic viscosity, and diffusion coefficient) accurately described the mass-transport contribution, which was easily isolated when a highly active Pt catalyst was used. The HER rate on the Pt was maximized by tuning the solute concentration (typically 1.5 to 2.0 M). Moreover, the kinematic viscosity and oxygen solubility under such densely buffered conditions governed the oxygen mass-transport flux in the electrolyte, which, in turn, tuned the crossover flux. At near-neutral pH, as high as 90% selectivity toward the HER was achieved even under an oxygen-saturated condition, where only a 40 mV overpotential was needed to achieve 10 mA cm –2 for the HER. This information can be regarded as an important milestone for achieving a highly efficient water splitting system at near-neutral pH.