Atomic Co Clusters for Efficient Oxygen Reduction Reaction

Abstract: Environment-friendly energy storage and conversion technologies, such as metal–air batteries and fuel cells, are considered promising approaches to address growing environmental concerns. The oxygen reduction reaction (ORR) is the core of renewable energy conversion technology and plays an irreplaceable role in this fundamental issue. However, the complex multi-reaction process of the ORR presents a bottleneck that limits efforts to accelerate its kinetics. Traditionally, Pt and Pt-based catalysts are regarded as a good choice to improve the sluggish kinetics of the ORR. However, because Pt-based catalysts are expensive and have low durability, their use to resolve the energy crisis and current environmental challenges is impractical. Hence, exploring low-cost, highly active, and durable ORR catalysts as potential alternatives to commercial Pt/C is an urgent undertaking. Atomic cluster catalysts (ACCs) may be suitable alternatives to commercial Pt/C catalysts owing to their ultra-high atomic utilization efficiency, unique electronic structure, and stable nanostructures. However, despite the significant progress achieved in recent years, ACCs remain unusable for practical applications. In this study, a facile plasma bombing method combined with an acid washing strategy is proposed to fabricate an atomic Co cluster-decorated porous carbon supports catalyst (CoAC/NC) showing improved ORR performance. The typical atomic cluster features of the resultant CoAC/NC catalyst are confirmed using comprehensive characterization techniques. The CoAC/NC catalyst exhibits considerable ORR activity with a half-wave potential of as high as 0.887 V (versus a reversible hydrogen electrode (RHE)), which is much higher than that of a commercial Pt/C catalyst. More importantly, the CoAC/NC catalyst displays excellent battery performance when applied to a Zn-air battery, showing a peak power density of 181.5 mW∙cm−2 and long discharge ability (over 67 h at a discharge current density of 5 mA∙cm−2). The desirable ORR performance of the fabricated CoAC/NC catalyst could be mainly attributed to the high atom utilization efficiency and stable active sites endowed by the unique Co atomic clusters, as well as synergistic effects between the neighboring Co atoms of these clusters. Moreover, the high specific surface area and wide pore distribution of the catalyst offer abundant accessible active sites for the ORR. This work not only provides an outstanding alternative to commercial Pt catalysts for the ORR but also offers new insights into the rational design and practical application of ACCs.