Abstract

The oxygen reduction reaction (ORR) is a highly important reaction in electrochemistry. The following short review details recent advances in novel non-precious metal catalysts containing transition metal macrocycles for use in the ORR. Unbound, many of these electrodes were found to generate high levels of side products such as O₂⁻ and H₂O₂ via 2-electron processes, and for this reason, it is aimed to create systems which would favor a 4-electron process which would completely convert oxygen to H₂O. The 4-electron reduction of O₂ releases the most energy in a fuel cell. Novel catalytic materials containing metal macrocycles were created mimicking the structure of enzyme metal centers, the metal in the macrocycle bound to a fifth axial ligand. These structures were observed to exhibit improved catalytic activity, and in the case of cobalt, phthalocyanine systems were observed to move away from the inefficient 2-electron process towards the more complete 4-electron process in alkaline media. Both experimental results (XPS, EPR, cyclic voltammetry and polarization curves) and theoretical models were gathered for various pentacoordinate systems and various electronic effects of the axial ligand on metal center were proposed. Penta-coordinate macrocycles are an important tool for further manipulating and tuning the electronic behavior of transition metal centers for catalysis of the ORR.

中文翻译：

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五配位过渡金属大环作为氧还原反应的电催化剂

摘要

氧还原反应（ORR）是电化学中非常重要的反应。以下简短评论详细介绍了用于ORR的新型新型非贵金属催化剂，其中包含过渡金属大环化合物。未结合的，许多这些电极被发现产生高水平的副产物如O ₂ ^-和H ₂ ö ₂通过2-电子过程，并且因为这个原因，它的目的是建立这将有利于一个4-电子处理系统这将氧完全转化成H ₂ O.的O-四电子还原₂释放燃料电池中最大的能量。创造了包含金属大环的新型催化材料，其模仿了酶金属中心的结构，大环中的金属与第五个轴向配体结合。观察到这些结构表现出改善的催化活性，并且在钴的情况下，观察到酞菁体系在碱性介质中从低效的2-电子过程向更完整的4-电子过程移动。收集了各种五坐标系统的实验结果（XPS，EPR，循环伏安法和极化曲线）和理论模型，并提出了轴向配体对金属中心的各种电子效应。