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Mechanistic Insight into the Oxygen Reduction Reaction on the Mn–N4/C Single-Atom Catalyst: The Role of the Solvent Environment
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2020-03-19 , DOI: 10.1021/acs.jpcc.0c00352 Hao Cao 1 , Guang-Jie Xia 1 , Jie-Wei Chen 1 , Hui-Min Yan 1 , Zhen Huang 1 , Yang-Gang Wang 1
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2020-03-19 , DOI: 10.1021/acs.jpcc.0c00352 Hao Cao 1 , Guang-Jie Xia 1 , Jie-Wei Chen 1 , Hui-Min Yan 1 , Zhen Huang 1 , Yang-Gang Wang 1
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The design of platinum group metal (PGM)-free catalysts is crucial to the application of energy conversion due to their excellent catalytic capability. Recently, M–Nx (M = Mn, Fe, Co, etc.) single-atom catalysts embedded in graphene have been extensively studied with respect to catalyzing the oxygen reduction reaction (ORR). Although the ORR is operated in the liquid phase, few mechanistic studies have taken the solvation effect into consideration. In the present work, we have performed ab initio molecular dynamics (AIMD) simulations as well as density functional theory (DFT) calculations to investigate the influence of the solvation effect on the mechanisms of ORR on MnN4–graphene by using explicit water molecules. It is found that the solvent environment can effectively promote the charge transfer from the substrate to O2, leading to the transformation from superoxide species to peroxide species. This also makes the ORR preferably proceed via a dissociative pathway, where O2 can be easily adsorbed on the single Mn site in the form of a “side-on” type, leading to the probable rupture of the O–O bond before being protonated. Furthermore, the solvent water molecules also raise the reactivity of protonation steps for *O and *OH intermediates by the elongation of the Mn–O bond with the assistance of the surrounding hydrogen bonds. Finally, on the basis of the calculated free-energy pathway, the liquid-phase model gives a more correct estimation for the overpotential than the gas-phase model, which is consistent with the experimental observation. The present work provides detailed information for understanding the reaction mechanisms of ORR at the surface–liquid interface on the M–Nx/C single-atom catalyst.
中文翻译：
Mn–N 4 / C单原子催化剂上氧还原反应的机理研究：溶剂环境的作用
无铂族金属（PGM）的催化剂由于其出色的催化能力，对于能量转换的应用至关重要。近年来，已经广泛研究了嵌入石墨烯中的M–N x（M = Mn，Fe，Co等）单原子催化剂，以催化氧还原反应（ORR）。尽管ORR在液相中操作，但很少有机理研究将溶剂化作用纳入考虑。在目前的工作中，我们已经执行了从头算分子动力学（AIMD）模拟以及密度泛函理论（DFT）计算，以研究溶剂化效应对ORR对MnN 4机理的影响。–通过使用显性水分子的石墨烯。发现溶剂环境可以有效地促进电荷从底物转移到O 2，从而导致从超氧化物种向过氧化物种的转变。这也使得ORR优选通过解离途径进行，其中O 2可以很容易地以“侧开”型形式吸附在单个Mn部位，导致质子化之前O-O键可能断裂。此外，溶剂水分子还通过在周围氢键的帮助下延长Mn-O键，提高了* O和* OH中间体的质子化步骤的反应性。最后，在计算出的自由能路径的基础上，液相模型对超电势的估计要比气相模型更正确，这与实验观察相符。本工作为了解ORR在M–Nx / C单原子催化剂的表面-液体界面的反应机理提供了详细的信息。
更新日期：2020-03-20
中文翻译：
Mn–N 4 / C单原子催化剂上氧还原反应的机理研究：溶剂环境的作用
无铂族金属（PGM）的催化剂由于其出色的催化能力，对于能量转换的应用至关重要。近年来，已经广泛研究了嵌入石墨烯中的M–N x（M = Mn，Fe，Co等）单原子催化剂，以催化氧还原反应（ORR）。尽管ORR在液相中操作，但很少有机理研究将溶剂化作用纳入考虑。在目前的工作中，我们已经执行了从头算分子动力学（AIMD）模拟以及密度泛函理论（DFT）计算，以研究溶剂化效应对ORR对MnN 4机理的影响。–通过使用显性水分子的石墨烯。发现溶剂环境可以有效地促进电荷从底物转移到O 2，从而导致从超氧化物种向过氧化物种的转变。这也使得ORR优选通过解离途径进行，其中O 2可以很容易地以“侧开”型形式吸附在单个Mn部位，导致质子化之前O-O键可能断裂。此外，溶剂水分子还通过在周围氢键的帮助下延长Mn-O键，提高了* O和* OH中间体的质子化步骤的反应性。最后，在计算出的自由能路径的基础上，液相模型对超电势的估计要比气相模型更正确，这与实验观察相符。本工作为了解ORR在M–Nx / C单原子催化剂的表面-液体界面的反应机理提供了详细的信息。
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