Hydrophobization of Carbon-Supported Catalysts with 2,3,4,5,6-Pentafluorophenyl Moieties for Fuel Cells

Surface Characteristics of Microporous and Mesoporous Carbons Functionalized with Pentafluorophenyl Groups

“…The in situ diazonium reduction reaction is a relatively common method for the surface functionalization of carbon materials. 14,15 In this reaction, the diazonium salt is reduced, and then the aryl groups are grafted onto the carbon surface. The reduction process can be driven by electrochemical methods or by thermal decomposition.…”

“…Therefore, the in situ diazonium reduction reaction has been used to surface-functionalize microporous carbon blacks, carbon nanotubes, and mesoporous carbons with various aryl moieties such as the nitrophenyl and alkylphenyl groups. 14 As a subset of high surface area carbon materials, mesoporous carbon powders are of interest primarily as their pores (2−50 nm in diameter) are more accessible to both solution and gas phase species than in microporous carbons. Among them, colloid-imprinted carbons (CICs), with their fully tunable and monodisperse pore sizes, have been shown to be promising when used as catalyst supports in PEMFCs, as the stationary phase in chromatography, and in other applications.…”

“…In the present work, we demonstrate that it is possible to increase the hydrophobicity of the CICs by attaching pentafluorophenyl (−PhF 5 ) groups to the internal pore surfaces through the in situ diazonium reduction reaction (Scheme 1) without significantly affecting the pore size. 14,15 This type of surface modification may also increase the resistance of the carbons to electrochemical corrosion when used as the cathode support in PEMFCs or as electrode materials in RFBs, work that is currently underway in our group. 33 This is because of the enhanced surface hydrophobicity 8 caused by both the high electronegativity and low polarizability of the fluorine atoms.…”

Layer-by-Layer Polydimethylsiloxane Modification Using a Two-Nozzle Spray Process for High Durability of the Cathode Catalyst in Proton-Exchange Membrane Fuel Cells

“…These effects significantly limit the performance and long-term operation of PEMFCs. 8,9 Various strategies have been reported in the literature to mitigate carbon corrosion, 10 including (I) improving carbon oxidation resistance by synthesizing highly crystalline carbon materials, surface modification, and hightemperature heat treatment, 11−13 and (II) carbon support replacement with other materials, such as metal oxides. 14−16 Among these methods, the surface modification of carbon materials with hydrophobic functional groups or hydrophobic chemicals has been reported to improve carbon corrosion resistance successfully.…”

“…The carbon corrosion phenomenon can cause local flooding of the cathode catalyst layer due to the increased hydrophilicity of the modified surface with oxygen groups, as well as loss of the electrochemical active Pt surface area for oxygen reduction reaction (ORR) by accelerating the agglomeration and detachment of the Pt nanoparticles on the carbon support. These effects significantly limit the performance and long-term operation of PEMFCs. , Various strategies have been reported in the literature to mitigate carbon corrosion, including (I) improving carbon oxidation resistance by synthesizing highly crystalline carbon materials, surface modification, and high-temperature heat treatment, − and (II) carbon support replacement with other materials, such as metal oxides. − Among these methods, the surface modification of carbon materials with hydrophobic functional groups or hydrophobic chemicals has been reported to improve carbon corrosion resistance successfully. ,, However, these methods comprised complicated processes and required difficult post-treatments to be compatible with the continuous membrane electrode assembly (MEA) fabrication process.…”