Quantitative Understanding of the Sluggish Kinetics of Hydrogen Reactions in Alkaline Media Based on a Microscopic Hamiltonian Model for the Volmer Step
Quantitative Understanding of the Sluggish Kinetics of Hydrogen Reactions in Alkaline Media Based on a Microscopic Hamiltonian Model for the Volmer Step
复制标题
基于 Volmer 步骤的微观哈密顿模型定量理解碱性介质中氢反应的缓慢动力学
DOI：
10.1021/acs.jpcc.9b03639
复制
发表时间：
2019-07-18
影响因子：
3.7
通讯作者：
Chen, Shengli
中科院分区：
文献类型：
--
作者：
Huang, Jun;Li, Peng;Chen, Shengli
碱性介质中析氢/氧化反应的迟缓动力学一直是碱性膜燃料电池的技术障碍，也是基础电催化领域的一个热门科学难题。人们的注意力主要集中在热力学起源上，而对微观动力学的了解较少，对关键因素的定量解释仍然缺乏。为了填补这一空白，建立了碱性Volmer步骤的微观哈密顿模型，碱性Volmer步骤是氢反应的基本步骤，包括电子相互作用、键断裂、溶剂重组和双层静电效应。该模型给出了一个简单而又信息丰富的碱性Volmer步骤活化势垒的解析公式，量化了各种因素的贡献；粗略地说，四分之一的H-OH键能进入活化能。这个模型解释说，在荷电越高的界面上看到的更大的活化能并不是因为它更难重组溶剂，而是因为它在将OH-带入双分子层时消耗了更多的功，即更大的功项。以前用来提高碱性介质中氢反应活性的策略在一个连贯的框架内是合理的。
The sluggish kinetics of hydrogen evolution/oxidation reactions in alkaline media remains a technical barrier for alkaline membrane fuel cells and a scientific puzzle under heated discussion in fundamental electrocatalysis. Much attention has been centered around thermodynamic origins, whereas microscopic kinetics is less understood and a quantitative account of key factors is yet missing. To fill in this gap, a microscopic Hamiltonian model is developed for the alkaline Volmer step, an elementary step of hydrogen reactions, encompassing electronic interactions, bond breaking, solvent reorganization, and double-layer electrostatic effects. The model gives out a simple yet informative analytical formula for the activation barrier of the alkaline Volmer step, quantifying the contributions of various factors; roughly speaking, one quarter of the H-OH bond energy enters into the activation energy. This model elucidates that the larger activation energy seen at a more charged interface is not because it is more difficult to reorganize the solvents but rather because it consumes more work in bringing OH- to the double layer, namely, a larger work term. Previous strategies used to boost the activity of hydrogen reactions in alkaline media are rationalized in a coherent framework.