Efficient ORR electrocatalytic activity of peanut shell-based graphitic carbon microstructures

Abstract

A hierarchical microporous graphitic carbon material intrinsically doped with sulfur and extrinsically doped with dual cobalt species [Co₃O₄ and Co(PO₃)₂, termed as CoOP] nanoparticles was prepared from a sustainable waste biomass, peanut shell, with CO₂ gas as the activating agent through a thermal-reduction method. The resulting CoOP@bio-C exhibits an overall superior ORR catalytic activity, stability and resistance to methanol crossover in alkaline media to commercial Pt/C, with onset and half-wave potentials of 0.91 and 0.81 V in 0.1 M KOH, a limiting current density of −5.7 mA cm⁻², and a small Tafel slope of 57 mV dec⁻¹, representing the best result among the biomass-based carbon electrocatalysts. In particular, comparative studies reveal the significant effect of the work function of corresponding catalytic materials on the ORR electrocatalysis. Dual-doped CoOP@bio-C with a work function of 5.42 eV, closer to that of Pt (5.65 eV), displays much better electrocatalytic activity than single-doped Co₃O₄@bio-C, single-doped Co(PO₃)₂@bio-C and bio-C-800 catalysts with work functions of 8.35, 6.61 and 5.02 eV, respectively, due to its good adsorption nature to O₂ and desorption nature to the reaction intermediates. The present result will be surely helpful for the design and synthesis of biomass resource-based ORR catalysts with great application potential.