Processing Agricultural Cornstalks toward High-Efficient Stable Bifunctional ORR/OER Electrocatalysts

Bifunctional oxygen reduction/oxidation reaction (ORR/OER) electrocatalysts derived from biomass are one of the most valuable materials in terms of sustainability, ecological economy and industrial manufacturing, and are emerging as a desired alternative to the commercial Pt/C and IrO2 catalysts. This work demonstrates the processing of agricultural cornstalk waste of cornstalks into stable bifunctional ORR/OER catalysts with high-performance by a simple and cost-effective strategy. Rich hydrophilic active groups (e.g., hydroxyl groups) in the hierarchical porous structures of the native cornstalks enable the sufficient facile combination with transition metals (e.g., Co, Fe, Zn) and heteroatoms (e.g., B, N) from soluble Co(NO3)(2), ZnCl2, H3BO3, NH4Cl in a hydrothermal reaction. The pyrolytic evaporation of Zn2+ in a high-temperature carbonization process facilitates the generation of abundant micropores and mesopores to increase specific surface areas (941.44 m(2) g(-1)) and also hinders aggregation between neighboring transition metals. The synergistic effects of N, B, Fe and Co doping in hierarchical porous biochar-structures contributes to outstanding bifunctional ORR/OER activities and working stabilities, outperforming commercial Pt/C and IrO2 catalysts. Computational results further verify the valuable synergistic contributions based on density-functional theory (DFT). This approach opens up a new possibility for the fabrication of bifunctional biochar-based ORR/OER catalysts from artificial engineering and green processing for sustainable agricultural wastes.