Superhydrophobic Air-Breathing Cathode for Efficient Hydrogen Peroxide Generation through Two-Electron Pathway Oxygen Reduction Reaction

Electrochemical catalysis of carbon-based material via two-electron pathway oxygen reduction reaction (ORR) offers great potential for in situ hydrogen peroxide (H₂O₂) production. In this work, we tuned catalyst mesostructure and hydrophilicity/hydrophobicity by adjusting polytetrafluoroethylene (PTFE) content in graphite/carbon black/PTFE hybrid catalyst layer (CL), aimed to improving the two-electron ORR activity for efficient H₂O₂ generation. As the only superhydrophobic CL with initiating contact angles of 141.11°, PTFE_0.57 obtained the highest H₂O₂ yield of 3005 ± 58 mg L^-1 h^-1 (at 25 mA cm^-2) and highest current efficiency (CE) of 84% (at 20 mA cm^-2). Rotating ring disk electrode (RRDE) results demonstrated that less PTFE content in CLs results in less electrons transferred and better selectivity toward two-electron ORR. Though the highest H₂ concentration (2 μmol L^-1 at 25 mA cm^-2) was monitored from PTFE_0.57 which contained the lowest PTFE, the CE decreased inversely with increasing content of PTFE, which proved that the H₂O₂ decomposition reaction was the major side reaction. Higher PTFE content increased the hydrophilicity of CL for excessive H⁺ and insufficient O₂ diffusion, which induced H₂O₂ decomposition into H₂O. Simultaneously, the electroactive surface area of CLs decreased with higher PTFE content, from 0.0041 m² g^-1 of PTFE_0.57 to 0.0019 m² g^-1 of PTFE_4.56. Besides, higher PTFE content in CL leads to the increase of total impedance (from 14.5 Ω of PTFE_0.57 to 18.3 Ω of PTFE_4.56), which further hinders the electron transfer and ORR activity.