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Abstract：
Electrocatalytic 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 pKa [Formula: see text] 4.3. Quantum mechanics (QM) and reactive dynamics using a reactive force field (ReaxFF) molecular dynamics (RMD) calculations confirm the enrichment of hydroniums (H3O[Formula: see text]) near Pt surface and predict a surface hydronium pKa of 2.5 to 4.4, corroborating the experimental results. Importantly, the observed Pt-surface hydronium pKa 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.
摘要：
电催化析氢反应（HER）对于绿色氢生成至关重要，并且表现出难以理解的独特的pH依赖性动力学。对电化学界面的分子水平理解对于开发更有效的电化学过程至关重要。在这里，我们利用专门的表面特异性电传输光谱（ETS）方法来探测Pt-地表水质子化状态，并通过实验确定表面水合pKa[公式：见正文]4.3。使用反应力场（ReaxFF）的量子力学（QM）和反应动力学分子动力学（RMD）计算证实了Pt表面附近的水合氢（H3O[公式：见正文]）的富集，并预测表面水合氢pKa为2.5至4.4，证实了实验结果。重要的是,观察到的Pt表面水合pKa与pH依赖性HER动力学密切相关，在较低pH下的质子化表面状态有利于快速塔菲尔动力学，塔菲尔斜率为每十年30mV，在较高pH下的去质子化表面状态遵循Volmer-step限制动力学，塔菲尔斜率为每十年120mV，提供对pH依赖性HER动力学的稳健和精确的解释。这些见解可能有助于设计用于可再生能源转换的改进的电催化剂。
