H_2O在Pt电极上解离反应的理论研究

水解离生成氧气的反应（OER：H2O→1/2O2＋2H＋＋2e-）是阳极最重要的反应之一,且广泛应用于能量存储/转化的各种设备中。但是由于该反应需要很高的过电势,其在电解工业（如氯碱工业）中造成大量的能量损失,所以人们一直在努力寻找对于氧气析出反应有更高效率的阳极材料。人们熟知在一定的电势条件下,水会解离成氧化物种（如OH和O）吸附于电极表面,并且随着电势的增加,吸附的氧化物种会进一步耦合成氧气。研究了H2O在Pt电极上的解离反应。通过计算,获得了氧气析出过程中密堆积的Pt（111）表面和台阶Pt（211）表面的相图。结果显示台阶面能够更好的吸附氧化物种（O和OH）,且在相同电势条件下比平台（111）表面的氧覆盖度高。在金属表面发生氧覆盖的同时,我们发现在电势低于1.4 V时表面氧化形成次表层的氧的过程在热力学上已经能够发生。如计算结果所示,Pt电极上的H2O解离反应是表面敏感反应,并且在高电势条件下易于氧化腐蚀。

Water dissociation on Pt Anode from First Principles

Electrochemical reactions catalyzed by metal electrode,despite its huge importance in chemistry,are poorly understood at the atomic level.As a prototype reaction in electrochemistry,oxygen evolution on Pt anode is systematically investigated in this work by combining periodic density functional theory calculations with a new theoretical approach to mimic the electrochemical environment.The surface phase diagrams for both the closed-packed Pt（111）and stepped（211）are determined,which demonstrates that stepped surface sites can better accumulate oxidative species and thus reach to a higher local O coverage compared to Pt（111）at a given potential.Above 1.4 V,oxygen evolution on Pt is accompanied by the surface oxidation on terraces and the dissociation of H2O becomes the rate-determining step.The strong structure-sensitivity of oxygen coupling reaction rationalizes why Pt is not a good anode material for oxygen evolution.The general implications on searching for better anode catalysts are also presented.