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arXiv 1605.00550physics.chem-phcond-mat.mtrl-sci
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台阶结合水的部分氧化导致金属电极台阶边缘的反常pH效应

Partial oxidation of Step-Bound Water Leads to Anomalous pH Effects on Metal Electrode Step-Edges

Kathleen Schwarz, Bingjun Xu, Yushan Yan, Ravishankar Sundararaman

摘要:

设计用于燃料电池和电解槽等应用的更好的多相催化剂需要从机理上理解电催化反应及其活性对操作条件(如pH)的依赖性。迄今为止,对铂表面电化学性质的意外pH依赖性的令人满意的解释仍然难以捉摸,先前的解释诉诸于多种物质的复杂共吸附,并导致有限的预测能力。这种知识差距表明,这些催化剂的基本性质尚未被理解,限制了系统的改进。在这里,我们使用密度泛函理论(DFT)分析吸附时的电荷和自由能的变化,以建立水吸附在铂阶边缘在很宽的电压范围内,包括双层区域,吸附时约0.2个电子的损失。我们将展示如何解释这种尚未报道的净表面电荷的变化,由于这种水的异常pH值的变化的氢欠电位沉积(Hupd)和零总电荷(PZTC)在已发表的实验数据中观察到的电位。水的这种部分氧化不限于铂金属台阶边缘,并且我们报道了水在常用催化金属(包括铜、银、铱和钯)的金属台阶边缘上的电荷,说明水的这种部分氧化广泛地影响金属电极的反应性。

英文摘要:

The design of better heterogeneous catalysts for applications such as fuel cells and electrolyzers requires a mechanistic understanding of electrocatalytic reactions and the dependence of their activity on operating conditions such as pH. A satisfactory explanation for the unexpected pH dependence of electrochemical properties of platinum surfaces has so far remained elusive, with previous explanations resorting to complex co-adsorption of multiple species and resulting in limited predictive power. This knowledge gap suggests that the fundamental properties of these catalysts are not yet understood, limiting systematic improvement. Here, we analyze the change in charge and free energies upon adsorption using density-functional theory (DFT) to establish that water adsorbs on platinum step edges across a wide voltage range, including the double-layer region, with a loss of approximately 0.2 electrons upon adsorption. We show how this as-yet unreported change in net surface charge due to this water explains the anomalous pH variations of the hydrogen underpotential deposition (Hupd) and the potentials of zero total charge (PZTC) observed in published experimental data. This partial oxidation of water is not limited to platinum metal step edges, and we report the charge of the water on metal step edges of commonly used catalytic metals, including copper, silver, iridium, and palladium, illustrating that this partial oxidation of water broadly influences the reactivity of metal electrodes.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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