DUT-58 (Co) Derived Synthesis of Co Clusters as Efficient Oxygen Reduction Electrocatalyst for Zinc-Air Battery

To meet the requirement of fuel cells and metal-air batteries, non-noble metal catalysts have to be developed to replace precious platinum-based catalysts. Herein, Co nanoclusters (≈2 nm) are anchored on nitrogen-doped reduced graphene oxide (Co/N-r-GO) by using DUT-58 (Co) metal-organic framework and GO as precursors. Compared with single-atom catalysts usually with ultralow concentration (<0.5 wt%), Co nanoclusters are more beneficial to break the O-O bond to ensure four electronic way for oxygen reduction reaction (ORR), since they can provide more adsorption centers for reactants. Therefore, as expected, the sample with 6.67 wt% Co content (Co/N-r-GO-5%-850) exhibits better ORR activity with a higher half-wave potential of 0.831 V, a more positive onset potential of 0.921 V than Pt/C, and a comparable limiting current density in alkaline medium. The Co nanoclusters enhance the catalytic performance for ORR in three aspects: quantum size effects, metal-support interactions, and low-coordination environment of metal centers. Furthermore, the sample is assembled into a zinc-air battery as the outstanding durable ORR catalyst. It displays a higher specific capacity (795 mAh g^-1 at the current density 50 mA cm^-2) and power density (175 mW cm^-2) than Pt/C (731 mAh g^-1 and 164 mW cm^-2, respectively).