Mechanistic Insights into the Suppression of Proton Intercalation and the Hydrogen Evolution Reaction through...

The hydrogen evolution reaction (HER) is an inevitable parasitic process that limits the efficiency and selectivity of electrochemical hydrogenation reactions using water as the hydrogen source. Although introducing oxygen vacancies and heteroatom dopants into transition-metal oxides is widely employed to enhance hydrogenation activity, such modifications often inadvertently promote HER. Here, we demonstrate a counterintuitive suppression of proton intercalation and HER in metalloid phosphorus (P)-doped WO₃ catalysts, with progressively stronger suppression at higher P-doping levels. Electrochemical impedance spectroscopy, Mott-Schottky analysis, and hydrogen bond dissociation free energy (H-BDFE) measurement reveal that, despite enhanced electronic conductivity, improved interfacial charge transfer, and decreased H-BDFE, phosphorus doping significantly increases the adsorption resistance associated with W-H* intermediate formation and reduces H* surface coverage, thereby suppressing HER kinetics. Density functional theory calculations further show that even though the W d-band center was downshifted toward its Fermi level, P-doping broadens the distribution of hydrogen binding strengths across oxygen sites of the WO₃ catalysts, such that many sites bind hydrogen too weakly to support efficient proton intercalation. These insights reveal an alternative HER suppression mechanism whereby heteroatom doping enables local control of proton intercalation and hydrogen adsorption kinetics beyond conventional d-band tuning, proton/electron supply, or charge-transport limitations.