Oxygen reduction and evolution at single-metal active sites: Comparison between functionalized graphitic materials and protoporphyrins
Oxygen reduction and evolution at single-metal active sites: Comparison between functionalized graphitic materials and protoporphyrins
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DOI：
10.1016/j.susc.2012.08.005
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发表时间：
2013-01-01
期刊：
影响因子：
1.9
通讯作者：
Koper, M. T. M.
中科院分区：
文献类型：
--
作者：
Calle-Vallejo, F.;Martinez, J. I.;Koper, M. T. M.
低温燃料电池和电解槽等清洁技术在全球的推广严格取决于它们的技术可靠性和经济承受能力。目前，这两个条件都很难满足，主要是因为同一个原因：氧电极，它有很大的过电位，而且是由贵重材料制成的。一种可能的解决方案是使用具有单一金属活性中心的非贵金属电催化剂。在吸附中间体密度泛函理论计算和热力学分析的基础上，我们比较了功能化石墨化材料和气相卟啉与后过渡金属的氧还原(ORR)和放氧(OER)活性。我们发现，这两种材料的活性趋势大致相同，具有7-9基团过渡金属的活性中心可能是良好的ORR和OER电催化剂。然而，自旋分析表明，在固体电催化剂中，金属原子的可能氧化态具有更大的灵活性，而在卟啉中，金属原子的氧化态必须是+2。这些观察表明，这些材料的催化活性主要是由于最近邻相互作用。基于此，我们认为这类电催化剂可以通过仔细选择活性中心附近的载体和配体性质和/或其附近的分支来改进，以便在吸附过程中电荷来回转移，并形成选择性氢键。(C)2012爱思唯尔B.V.保留所有权利。
A worldwide spread of clean technologies such as low-temperature fuel cells and electrolyzers depends strictly on their technical reliability and economic affordability. Currently, both conditions are hardly fulfilled mainly due to the same reason: the oxygen electrode, which has large overpotentials and is made of precious materials. A possible solution is the use of non-noble electrocatalysts with single-metal active sites. Here, on the basis of DFT calculations of adsorbed intermediates and a thermodynamic analysis, we compare the oxygen reduction (ORR) and evolution (OER) activities of functionalized graphitic materials and gas-phase porphyrins with late transition metals. We find that both kinds of materials follow approximately the same activity trends, and active sites with transition metals from groups 7 to 9 may be good ORR and OER electrocatalysts. However, spin analyses show more flexibility in the possible oxidation states of the metal atoms in solid electrocatalysts, while in porphyrins they must be +2. These observations reveal that the catalytic activity of these materials is mainly due to nearest-neighbor interactions. Based on this, we propose that this class of electrocatalysts may be improved by careful selections of the support and the ligand properties close to the active sites and/or the ramifications near them, so that charge is transferred back and forth during adsorption and selective hydrogen bonds are formed. (c) 2012 Elsevier B.V. All rights reserved.