Structural and electronic engineering of biomass-derived carbon nanosheet composite for electrochemical oxygen reduction

Developing efficient, non-noble, and reliable electrocatalysts for the oxygen reduction reaction (ORR) to replace the precious metal Pt/C catalyst remains a colossal challenge. In this study, pomelo peel (PP) was used to obtain N/S, Ta-doped carbonaceous-based composite electrocatalystviaa two-step microwave-assisted pyrolysis method. We found that the chemical pretreatment was crucial to isolate cellulose fibers and obtain the nanosheet-structure precursors from irregularly structured biomass and to yield structural defects induced by N, S co-doping. The latter serves as an active site to anchor TaO_x, forming active ORR species. The obtained cell-PP-NS-700-Ta-900 composite exhibited most promising electrocatalytic activities (half-wave potential of 0.82 V (vs.RHE), a limiting current density of −5.24 mA cm⁻², and an electron transfer number of 3.87) in 0.1 M KOH solution, which are comparable to that of the benchmark Pt/C electrode, while the former presented better selectivity and short-term durability. The synergy of the formed multi-heterointerface/chemical phases of Ta-based compounds and high content of N-pyridinic, N-quaternary, and N-nitride (metal-N) nitrogen functionalities in carbon were experimentally revealed as the major feature contributing to the enhanced ORR activity. This work sheds light on a sustainable and effective strategy to design and synthesize cost-effective and high-performance carbon-based composite electrocatalysts from fruit waste biomass and unlocks the superb intrinsic catalytic activity of transition metal compounds.