Water oxidation is the key kinetic bottleneck of photoelectrochemical devices for fuel synthesis. Despite advances in the identification of intermediates, elucidating the catalytic mechanism of this multi-redox reaction on metal-oxide photoanodes remains a significant experimental and theoretical challenge. Here, we report an experimental analysis of water oxidation kinetics on four widely studied metal oxides, focusing particularly on haematite. We observe that haematite is able to access a reaction mechanism that is third order in surface-hole density, which is assigned to equilibration between three surface holes and M(OH)-O-M(OH) sites. This reaction exhibits low activation energy (Ea ≈ 60 meV). Density functional theory is used to determine the energetics of charge accumulation and O-O bond formation on a model haematite (110) surface. The proposed mechanism shows parallels with the function of the oxygen evolving complex of photosystem II, and provides new insights into the mechanism of heterogeneous water oxidation on a metal oxide surface.

中文翻译：

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原位光谱电化学和 DFT 揭示赤铁矿光阳极的多孔水氧化催化作用。

水氧化是燃料合成光电化学装置的关键动力学瓶颈。尽管在中间体鉴定方面取得了进展，但阐明金属氧化物光阳极上这种多重氧化还原反应的催化机制仍然是一项重大的实验和理论挑战。在这里，我们报告了四种广泛研究的金属氧化物的水氧化动力学实验分析，特别关注赤铁矿。我们观察到赤铁矿能够获得表面孔密度三阶的反应机制，这被指定为三个表面孔和 M(OH)-OM(OH) 位点之间的平衡。该反应表现出低活化能（Ea ≈ 60 meV）。密度泛函理论用于确定模型赤铁矿 (110) 表面上电荷积累和 OO 键形成的能量。