Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Department of Chemistry, Ministry of Education, Fudan University, Shanghai 200433, China.
J Am Chem Soc. 2010 Sep 22;132(37):13008-15. doi: 10.1021/ja105340b.
Due to its high overpotential and low efficiency, the conversion of water to O(2) using solar energy remains a bottleneck for photocatalytic water splitting. Here the microscopic mechanisms of the oxygen evolution reaction (OER) on differently structured anatase surfaces in aqueous surroundings, namely, (101), (001), and (102), are determined and compared systematically by combining first-principles density functional theory calculations and a parallel periodic continuum solvation model. We show that OER involves the sequential removal of protons from surface oxidative species, forming surface peroxo and superoxo intermediates. The initiating step, the first proton removal, dictates the high overpotential. Only at an overpotential of 0.7 V (1.93 V vs SHE) does this rate-controlling step become surmountable at room temperature: the free energy change of the step is 0.69, 0.63, and 0.61 eV for (101), (102), and (001) surfaces, respectively. We therefore conclude that (i) OER is not sensitive to the local surface structure of anatase and (ii) visible light (<∼590 nm) is, in principle, capable of driving the photocatatlytic OER on anatase kinetically. By co-doping high-valent elements into the anatase subsurface, we demonstrate that the high overpotential of the OER can be significantly reduced, with extra occupied levels above the valence band.
由于其高过电位和低效率，利用太阳能将水转化为 O(2)仍然是光催化水分解的一个瓶颈。在这里，通过结合第一性原理密度泛函理论计算和并行周期性连续体溶剂化模型，系统地确定并比较了在水相环境中不同结构锐钛矿表面上氧析出反应（OER）的微观机制，即（101）、（001）和（102）。我们表明，OER 涉及从表面氧化物种中顺序去除质子，形成表面过氧和超氧中间体。引发步骤，即第一个质子的去除，决定了高过电位。只有在 0.7 V（1.93 V 相对于 SHE）的过电位下，室温下这个控制步骤才变得可以克服：步骤的自由能变化分别为（101）、（102）和（001）表面的 0.69、0.63 和 0.61 eV。因此，我们得出结论：（i）OER 对锐钛矿的局部表面结构不敏感；（ii）可见光（<∼590nm）原则上能够在动力学上驱动锐钛矿的光催化 OER。通过将高价元素共掺杂到锐钛矿亚表面，我们证明了 OER 的高过电位可以通过价带上方的额外占据能级显著降低。
