High-Density Phosphorus-Doping toward Metal-Free Carbon Sphere to Boost H2O2 Selective Electrosynthesis

Abstract

While heteroatom doping is competent to enhance 2e⁻-ORR activity of metal-free carbon catalysts, high-density phosphorus doping remains underexplored due to large atomic radius of P atom and oxidation tendency. Herein, we proposed an innovative strategy using low-cost ammonium polyphosphate and chitosan oligosaccharide as precursors. Phosphorus immobilization via sol-gel assembly followed by pyrolysis-induced carbon rearrangement enabled high-density -POx functionalization on high-curvature carbon spheres (P content >20 wt%), yielding NBC-xP catalysts (x=1-3, x represents the amount of APP added). NBC-2P exhibited the excellent electrocatalytic performance with 98.56% H2O2 selectivity at 0.4 V and the production rate of 2.43 mol g-1 h-1 in H-cell. Notably, the H2O2 production rate further increased to 14.32 mol g-1 h-1 in a gas diffusion electrode (GDE) flow cell. Density functional theory calculations verified that rational high-density -POx doping significantly reduced the H2O2 formation energy barrier, stabilizing 2e⁻-ORR pathway. This work elucidated the predominant role of high-density P-doping in modulating the electronic structure of active sites, which established a new paradigm for carbonaceous electrocatalyst design.