Atomic Zn Sites on N and S Codoped Biomass-Derived Graphene for a High-Efficiency Oxygen Reduction Reaction in both Acidic and Alkaline Electrolytes

Zn-N-C catalysts with nitrogen-coordinated atomic Zn in carbon are recently found to be an alternative to Pt catalysts for oxygen reduction reaction (ORR). Nevertheless, the activity of the so far reported atomic Zn catalysts is far from satisfactory with the origin of their ORR activity still remaining ambiguous. Herein, a catalyst with atomic Zn sites anchored on N and S codoped biomass-derived graphene (named A-Zng NSG) has been developed. The as-prepared A-Zn@NSG catalyst exhibits superior ORR performance with a half-wave potential of 0.805 V vs reversible hydrogen electrode (RHE) in 0.1 M HClO4 and 0.905 V vs RHE in 0.1 M KOH, surpassing all the reported Zn-N- C-based catalysts and comparable to the state-of-the-art nonprecious-metal-based ORR catalysts. Experimental results together with the computational results reveal the Zn-N-4 active site nature of the A-Zn@NSG catalyst for ORR More importantly, the surrounding S atoms of the Zn-N-4 active sites were found to be able to donate electrons to atomic Zn centers, which enhances the binding of adsorbed O species, promotes the cleavage of the O-O bond of the adsorbed OOH species, and in turn results in a heightened ORR activity of A-Zn@NSG. The present work reports the design and development of low-cost ORR catalysts for both basic studies and realistic use.