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 (H 2 O 2 ) 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 H 2 O 2 generation. As the only superhydrophobic CL with initiating contact angles of 141.11°, PTFE 0.57 obtained the highest H 2 O 2 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 H 2 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 H 2 O 2 decomposition reaction was the major side reaction. Higher PTFE content increased the hydrophilicity of CL for excessive H + and insufficient O 2 diffusion, which induced H 2 O 2 decomposition into H 2 O. Simultaneously, the electroactive surface area of CLs decreased with higher PTFE content, from 0.0041 m 2 g –1 of PTFE 0.57 to 0.0019 m 2 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.