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首页> 外文期刊>Electrocatalysis >A Carbon-Free Ag-Co3O4 Composite as a Bifunctional Catalyst for Oxygen Reduction and Evolution: Spectroscopic, Microscopic and Electrochemical Characterization
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A Carbon-Free Ag-Co3O4 Composite as a Bifunctional Catalyst for Oxygen Reduction and Evolution: Spectroscopic, Microscopic and Electrochemical Characterization

机译：无碳Ag-CO3O4复合材料作为用于氧还原和进化的双官能催化剂：光谱，微观和电化学表征

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A key challenge for rechargeable metal-air batteries is the development of a cost-effective bifunctional catalyst for both oxygen evolution (OER) and reduction (ORR) reactions. Here, we took the advantages of high OER activity of Co3O4 spinel and high ORR activity of Ag to develop a carbon-free oxygen electrode, e.g., for Li-air batteries. The optimized Ag + Co3O4 catalyst was further characterized and exhibited a good bifunctional activity in alkaline media. From rotating ring-disk electrode results, the mixed Ag + Co3O4 catalyst revealed significantly lower (similar to 320 mV) overpotential for ORR than single Co3O4, and a slightly lower overpotential than pure Ag. A four-electron pathway was also elucidated. The OER activity of the mixed catalyst is 1.5-fold compared to pure Co3O4, although the Co3O4 loading is only 10%, suggesting a large synergistic effect. The potential difference between OER and ORR (i.e., the sum of the overpotentials at 1 mA cm(-2)) is ca.0.85 V, which is comparable to noble metal based catalysts. To better understand the origin of this synergism, an XPS analysis was performed, demonstrating that only after oxidation of the mixed catalyst, Co3O4 was reduced to Co(OH)(2) at potentials of the ORR, probably due to the presence of Ag+. This redox switching, which was not observed for pure Co3O4, is a probable explanation for the increased catalytic activity. The morphology and the electrochemically active surface area of Ag on the surface were examined by electron microscopy and lead-underpotential deposition, respectively. These results also show that when 88% of the Ag surface is blocked by Co3O4 particles, the residual 12% free Ag sites altogether have a higher activity for ORR than the (100%) pure Ag surface, i.e., the activity per Ag site is increased by more than a factor of 10. The combination of low cost and high performance endows this catalyst as a promising candidate for energy devices, and the present synergistic effect opens a new track for high activity.
机译：可充电金属电池的关键挑战是用于氧气进化（OER）和还原（ORR）反应的经济高效的双官能催化剂的开发。在这里，我们采用了Co3O4尖晶石的高oer活性和Ag的高Orr活性来开发无碳氧电极，例如Li-Air电池。优化的Ag + Co3O4催化剂进一步表征并在碱性培养基中表现出良好的双官能活性。通过旋转环盘电极结果，混合Ag + Co3O4催化剂显着降低（类似于320mV）的ORR的ORR，而不是单CO 3O4，并且比纯AG略低于过电位。还阐明了四种电子途径。与纯CO3O4相比，混合催化剂的oer活性为1.5倍，尽管CO3O4负载仅为10％，表明具有大的协同效应。 OER和ORR之间的电位差异（即，1 mA cm（-2）的过电量的总和是Ca.0.85 V，其与贵金属基催化剂相当。为了更好地理解这种协同作用的来源，进行XPS分析，证明仅在混合催化剂的氧化后，将CO 3 O 4还原成CO（OH）（2）在ORR的电位下，可能是由于Ag +的存在。该用于纯CO3O4未观察到的氧化还原切换是对增加的催化活性的可能解释。通过电子显微镜和铅外沉积检查表面上的形态和电化学活性表面积。这些结果还表明，当Co3O4颗粒的88％的Ag表面被Co3O4颗粒阻断时，残留的12％游离Ag位点总共具有比（100％）纯Ag表面的较高活性，即，每个AG位点的活性是增加了超过一个超过的10。低成本和高性能的组合赋予该催化剂作为能量装置的有希望的候选者，并且目前的协同效果为高活动开辟了新的轨道。

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