High-density phosphorus-doping toward metal-free carbon spheres 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 the large atomic radius of P atom and oxidation tendency. Herein, we propose 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 –PO_x 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 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 a H-cell. Notably, the H₂O₂ production rate further increased to 14.32 mol g_cat⁻¹ h⁻¹ in a gas diffusion electrode (GDE) flow cell. Density functional theory calculations verified that rational high-density –PO_x doping significantly reduced the H₂O₂ formation energy barrier, stabilizing the 2e⁻-ORR pathway. This work revealed the synergistic role of APP-induced structural reconstruction and high-density –PO_x-mediated electronic modulation in optimizing metal-free carbon electrocatalysts for selective H₂O₂ electrosynthesis.