An efficient and universally applicable oxygen activation strategy for carbon materials derived from various biomass: Enhancing the electrocatalytic performance for oxygen reduction reaction

Abstract

Biomass has been considered as the ideal precursor for the preparation of carbon-based material due to its advantages of abundant reserves and low price. However, the microstructure fine-tuning of the obtained carbon material remains challenging. In this study, an elaborate universal method was developed via oxygen activation, which can not only modify the surface composition but also can promote the formation of hierarchical structure. The wide applicability of this method has also been confirmed by various biomass precursors (corn stalks, cotton stalks, elephant grass and distiller's grains). Besides, the oxygen reduction reaction (ORR) catalytic performance of the fabricated catalysts was measured over a wide pH range, which was significantly improved in contrast to that of without activation, confirming the high efficiency of this method. During the pyrolysis process, the limited oxygen-etching will promote the formation of pore structure and local graphitization degree due to the reaction between oxygen and carbon, which will generate carbon dioxide and carbon monoxide and release heat energy, thus, the ORR performance will be enhanced. The onset potentials (E_onset) of oxygen activated C₅-CS, C₅-MG, C₅-EG and C₅-DG were increased by 0.25, 0.31, 0.26 and 0.37 V, and the diffusion-limiting current densities (j_l) were increased by 2.36, 1.40, 2.50 and 3.48 mA cm⁻², respectively, compared to those of the non-activated carbons under neutral conditions. This study provides a new strategy for the preparation of cost-effective ORR catalysts with wide applicability.