Nitrogen and boron doped reduced graphene oxide as catalyst for oxygen reduction reaction in alkaline medium

This work presents a comprehensive investigation of graphene-based nanostructured materials with controlled heteroatom doping, synthesized through a top-down approach and evaluated as electrocatalysts for the oxygen reduction reaction (ORR). Graphene oxide was doped during its reduction process, to partially restore the graphene structure, with hydrazine and borane to obtain nitrogen, boron, and boron/nitrogen doped reduced graphene oxide (rGO-N, rGO-B, rGO-BN). All doped systems exhibited enhanced catalytic activity compared to their undoped counterparts. Mechanistic analysis revealed that rGO-B most effectively promoted the four-electron ORR pathway, limiting H2O2 formation. Voltammetric studies demonstrated remarkable catalytic performance for all materials, with overpotentials as low as -0.07 V vs SCE. Repeated voltammetric cycling under reductive or oxidative conditions induced “chemical annealing” effects, modulating ORR activity by altering the electrode surface. Scanning electrochemical microscopy (SECM) experiments focused on rGO-N provided insights into peroxide production and electron transfer kinetics, with reductive annealing doubling the heterogeneous rate constant. Overall, the study shows how the heteroatom doping, through hydrazine and diborane, and electrochemical annealing affect the ORR performance of this family of graphene-based electrocatalysts.