The alkaline water electrolysis is plagued by sluggish kinetics in cathodic hydrogen evolution reaction (HER) even on the platinum catalysts. The electrode/electrolyte interface in alkaline HER is also far more complex and controversial than the acidic case, due to presence of near-surface alkali metal (AM) cations, surface adsorbates, and different interfacial water structures that they lead to.<br/>Herein, we conduct a density functional theory (DFT) study with explicit solvation, including static calculations, grand canonical DFT calculations, ab initio molecular dynamic (AIMD) simulation, and micro-solvation cluster calculations, to gain molecular level insights into the surface adsorption properties, solvation structure, and the dynamics at the Pt/water interface in presence of cations and surface OHad species, or at different pH values. Electrochemical impedance spectroscopy (EIS) and electrical transport spectroscopy (ETS) are also performed by experimental collaborators to probe the surface species and interfacial capacitance.<br/>Our integrated studies suggest that the AM cations play an indirect role in modifying HER kinetics: Smaller cations destabilize surface OHad to a lesser extent in the potential window of HER, leading to a higher OHad coverage on Pt surface. The highly polar surface OHad weakens the O-H in nearby water molecules, which can promote alkaline Volmer kinetics and hence boost the HER activity. Different pH, however, influences the activity by favoring different configurations of the contact water layer, resulting in a non-linear switch in HER kinetics at the pH of c.a. 10.

Unriddling the cationic and pH effect in alkaline hydrogen evolution reaction on Pt

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