Biomass Waste-Derived 3D Metal-Free Porous Carbon as a Bifunctional Electrocatalyst for Rechargeable Zinc–Air Batteries

The sluggish nature of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) coupled with the high cost of related noble-metal catalysts stimulate the research of active non-noble metal or metal-free oxygen catalysts. Though metal-free catalysts have been reported a lot, fewer catalysts show high activity toward ORR and OER, especially for biomass waste materials. This paper introduces a top–down strategy to fabricate a series of bifunctional metal-free catalysts derived from the plant residue. Among them, the catalyst BRCAC8502 shows an excellent electrocatalytic performance toward both ORR and OER (E1/2 = 0.85 V, Ei=10 = 1.68 V vs RHE). A zinc–air battery equipped by catalyst BRCAC8502 even displays a superior performance to that of Pt/C-RuO2. The excellent ORR and OER performances are mainly attributed to 3D hierarchical structures and rich active sites of the catalyst, including N functional groups, oxygen vacancies, and carbon defects. The strategy of preparing plant residues into the outstanding bifunctional catalyst demonstrated in this study may enlighten to the design of various other functional catalysts.