Parallel water photo-oxidation reaction pathways in hematite photoanodes: implications for solar fuel production
Parallel water photo-oxidation reaction pathways in hematite photoanodes: implications for solar fuel production
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DOI：
10.1039/d1ee03953a
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发表时间：
2022-04-29
影响因子：
32.5
通讯作者：
Rothschild, Avner
中科院分区：
文献类型：
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作者：
Tsyganok, Anton;Monroy-Castillero, Paulino;Rothschild, Avner
稳定金属氧化物光阳极上的水光氧化对太阳能燃料生产提出了严峻的挑战。该反应被广泛认为以四个逐步的氢氧化物耦合空穴转移步骤的顺序途径进行，产生氧化的表面中间体，捕获空穴，同时其吸附物改变形式（例如，从-OH到=O再到-OOH，再回到-OH）以保持电荷中性。在这里，我们研究了水光氧化条件下赤铁矿光阳极极化后的动电位放电特性。关闭八号后，一些氧化中间体会自发放电，而另一些则保持氧化状态一段时间。在阴极电位扫描（在黑暗中）期间，亚稳态中间体以双峰波放电。自从关闭八号系统以来，经过长时间的延迟后，相对峰值高度被发现发生逆转。这一意想不到的观察结果表明放电以平行路径进行，这表明导致水光氧化的逆反应也是如此。互补光电化学阻抗谱测量显示出独特的电荷转移特征，支持水光氧化反应中平行路径的普遍存在。通过微观动力学模型，我们得出了一个标准，解释了为什么在我们的测量中观察到的峰值反转只能从平行路径中出现。平行路径的盛行从根本上拓宽了水光氧化反应机制的现有范式，并且可能激发新的策略来降低该反应的高过电势，从而提高太阳能燃料生产的效率。
Water photo-oxidation on stable metal-oxide photoanodes presents a critical challenge for solar fuel production. This reaction is widely considered to proceed in a sequential pathway with four stepwise hydroxide-coupled hole transfer steps, resulting in oxidized surface intermediates that trap holes while their adsorbates change forms (e.g., from -OH to =O to -OOH and back to -OH) so as to maintain charge neutrality. Here we study the potentiodynamic discharge characteristics of hematite photoanodes following polarization under water photo-oxidation conditions. Upon turning the Eight off, some of the oxidized intermediates discharge spontaneously whereas others remain oxidized for a while. The metastable intermediates discharge in a double-peak wave during cathodic potential sweep (in the dark). The relative peak heights were found to reverse after Long time delays since turning the Eight off. This unexpected observation indicates that the discharge proceeds in parallel pathways, suggesting the same for the reverse reaction that Leads to water photo-oxidation. Complementary photoelectrochemical impedance spectroscopy measurements display distinct charge transfer features, supporting the prevalence of parallel pathways in the water photo-oxidation reaction. Through a micro-kinetic model, we derive a criterion that explains why peak reversal, as observed in our measurements, can emerge only from parallel pathways. The prevalence of parallel pathways fundamentally broadens the current paradigm of the water photo-oxidation reaction mechanism, and it may inspire new strategies to reduce the high overpotential of this reaction so as to enhance the efficiency of solar fuel production.