posted on 2019-09-10, 12:35authored byQian Zhao, Jingkun An, Shu Wang, Yujie Qiao, Chengmei Liao, Cong Wang, Xin Wang, Nan Li
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°, PTFE0.57 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 PTFE0.57 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 PTFE0.57 to 0.0019 m2 g–1 of PTFE4.56. Besides, higher PTFE content in CL leads
to the increase of total impedance (from 14.5 Ω of PTFE0.57 to 18.3 Ω of PTFE4.56), which further
hinders the electron transfer and ORR activity.