Evidence that Crystal Facet Orientation Dictates Oxygen Evolution Intermediates on Rutile Manganese Oxide
Evidence that Crystal Facet Orientation Dictates Oxygen Evolution Intermediates on Rutile Manganese Oxide
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DOI：
10.1002/adfm.201706319
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发表时间：
2018-06-13
影响因子：
19
通讯作者：
Nakamura, Ryuhei
中科院分区：
文献类型：
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作者：
Kakizaki, Hirotaka;Ooka, Hideshi;Nakamura, Ryuhei
阐明区分光系统II的放氧中心与其无机对应物的机制对于开发有效的放氧反应（OER）催化剂至关重要。以前的研究表明，在中性条件下MnO2催化剂的较大过电位可能是由于Mn 3+中间体对电荷分离的不稳定性。在这里，通过监测的表面中间体的电化学OER在金红石MnO 2与不同的小面取向，中间物种的稳定性和晶体刻面之间的相关性被明确确认为第一次。发现Mn 3+中间体在亚稳（101）表面上的覆盖率比（110）表面高11倍，导致（101）表面的上级OER活性。OER活性的差异可能是由于Mn 3+的表面电子态的差异，其中Mn 2+和Mn 4+的层间电荷平衡产生两种Mn 3+物种在（101）面上是有利的。考虑到OER酶在Kok循环期间稳定地容纳Mn3+的事实，具有亚稳态表面的金红石MnO2催化剂的增强的OER活性突出了不仅模拟目标天然酶的晶体结构而且模拟其电子结构的重要性。
Elucidating the mechanism that differentiates the oxygen-evolving center of photosystem II with its inorganic counterpart is crucial to develop efficient catalysts for the oxygen evolution reaction (OER). Previous studies have suggested that the larger overpotential for MnO2 catalysts under neutral conditions may result from the instability of the Mn3+ intermediate to charge disproportionation. Here, by monitoring the surface intermediates of electrochemical OER on rutile MnO2 with different facet orientations, a correlation between the stability of the intermediate species and crystal facets is confirmed explicitly for the first time. The coverage of the Mn3+ intermediate is found to be 11-fold higher on the metastable (101) surfaces compared to (110) surfaces, leading to the superior OER activity of (101) surfaces. The difference in OER activity may result from the difference in surface electronic states of Mn3+, where interlayer charge comproportionation of Mn2+ and Mn4+ to generate two Mn3+ species is favored on (101) facets. Considering the fact that the OER enzyme accommodates Mn3+ stably during the Kok cycle, the enhanced OER activity of the rutile MnO2 catalyst with a metastable surface highlights the importance of mimicking not only the crystal structure but also the electronic structure of the targeted natural enzyme.