Explanation of Dramatic pH-Dependence of Hydrogen Binding on Noble Metal Electrode: Greatly Weakened Water Adsorption at High pH
Explanation of Dramatic pH-Dependence of Hydrogen Binding on Noble Metal Electrode: Greatly Weakened Water Adsorption at High pH
复制标题
DOI：
10.1021/jacs.8b04006
复制
发表时间：
2018-06-27
影响因子：
15
通讯作者：
Goddard, William A., III
中科院分区：
文献类型：
--
作者：
Cheng, Tao;Wang, Lu;Goddard, William A., III
氢氧化反应（HOR）和析氢反应（HER）在碱性电解质中比在酸性电解质中慢2个数量级，但没有提供解释。理解这一显著的pH依赖性HOR/HER性能的第一步是解释pH依赖性氢与电极的结合，这是实验观察到的一种令人困惑的行为。本文采用量子力学分子动力学（QMMD）方法，考虑溶剂和外加电压（U）的影响，对水/Pt（100）界面在欠电位吸附氢（H-UPD）条件下的反应进行了原位模拟。我们发现，当U变得更负时，电极倾向于排斥水，这反过来又增加了氢键。我们预测了0.13 eV的增加，从pH = 0.2到pH = 12.8的氢结合的斜率为10 meV/pH，这是接近8至12 meV/pH的实验观察。因此，我们得出结论，水吸附的变化是pH依赖性的氢结合的贵金属的主要原因。对表面水在修饰电化学反应中的关键作用的新认识为设计针对碱性电解质的HER/HOR催化剂提供了指导。
Hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) are both 2 orders slower in alkaline electrolyte than in acidic electrolyte, but no explanation has been provided. The first step toward understanding this dramatic pH-dependent HOR/HER performance is to explain the pH-dependent hydrogen binding to the electrode, a perplexing behavior observed experimentally. In this work, we carried out Quantum Mechanics Molecular Dynamics (QMMD) with explicit considerations of solvent and applied voltage (U) to in situ simulate water/Pt(100) interface in the condition of under-potential adsorption of hydrogen (H-UPD). We found that as U is made more negative, the electrode tends to repel water, which in turn increases the hydrogen binding. We predicted a 0.13 eV increase in hydrogen binding from pH = 0.2 to pH = 12.8 with a slope of 10 meV/pH, which is close to the experimental observation of 8 to 12 meV/pH. Thus, we conclude that the changes in water adsorption are the major causes of pH-dependent hydrogen binding on a noble metal. The new insight of critical role of surface water in modifying electrochemical reactions provides a guideline in designing HER/HOR catalyst targeting for the alkaline electrolyte.