%AZhong, Guangyan%ACheng, Tao%AShah, Aamir%AWan, Chengzhang%AHuang, Zhihong%AWang, Sibo%ALeng, Tianle%AHuang, Yu%AGoddard, William%ADuan, Xiangfeng%BJournal Name: Proceedings of the National Academy of Sciences; Journal Volume: 119; Journal Issue: 39 %D2022%I %JJournal Name: Proceedings of the National Academy of Sciences; Journal Volume: 119; Journal Issue: 39 %K %MOSTI ID: 10385692 %PMedium: X %TDetermining the hydronium pKα at platinum surfaces and the effect on pH-dependent hydrogen evolution reaction kinetics %XElectrocatalytic hydrogen evolution reaction (HER) is critical for green hydrogen generation and exhibits distinct pH-dependent kinetics that have been elusive to understand. A molecular-level understanding of the electrochemical interfaces is essential for developing more efficient electrochemical processes. Here we exploit an exclusively surface-specific electrical transport spectroscopy (ETS) approach to probe the Pt-surface water protonation status and experimentally determine the surface hydronium pK a = 4.3. Quantum mechanics (QM) and reactive dynamics using a reactive force field (ReaxFF) molecular dynamics (RMD) calculations confirm the enrichment of hydroniums (H 3 O + * ) near Pt surface and predict a surface hydronium pK a of 2.5 to 4.4, corroborating the experimental results. Importantly, the observed Pt-surface hydronium pK a correlates well with the pH-dependent HER kinetics, with the protonated surface state at lower pH favoring fast Tafel kinetics with a Tafel slope of 30 mV per decade and the deprotonated surface state at higher pH following Volmer-step limited kinetics with a much higher Tafel slope of 120 mV per decade, offering a robust and precise interpretation of the pH-dependent HER kinetics. These insights may help design improved electrocatalysts for renewable energy conversion. %0Journal Article