A microreactor with superhydrophobic Pt–Al₂O₃ catalyst coating concerning oxidation of hydrogen off-gas from fuel cell

Highlights: • Pt–Al₂O₃ was modified to superhydrophobicity via grafting by FAS. • Hydrophobic modification greatly promoted catalytic activity and stability. • Catalytic activity heavily depended on hydrophobicity extent in humid condition. - Abstract: For polymer electrolyte fuel cells (PEFCs), Pt–Al₂O₃ catalyst coatings were developed to convert hydrogen off-gas of PEFCs to water. To ignite the hydrogen oxidation at room temperature with negligible induction period, the Pt–Al₂O₃ catalyst coatings on the walls were modified from hydrophilicity to superhydrophobicity via grafting by 1H,1H,2H,2H-perfluorooctyltriethoxysilane (FAS). The modified Pt–Al₂O₃ catalyst coatings were optimized in a channel plate reactor (CPR) that is similar to microchannel reactors in flow pattern, but is much simpler to be fabricated and can be used repeatedly. We showed that higher grafting density of FAS provided stronger repulsive force on produced water vapor (favorable effect) while more resistance for the reactants approaching to catalytic active sites (unfavorable effect). The suitable hydrophobic modification significantly promoted the catalytic activities and stabilities of the catalyst coatings under both humid and dry feed stream conditions. Under the humid feed stream condition, the most active catalyst coating of 5WM-Pt–Al₂O₃ showed the biggest contact angle of 150° and decreased the hydrogen concentration from 4 vol% to 632 ppm without a detectable induction period at 303 K. The microchannel reactor with superhydrophobic catalyst coatings showed great potential for conversion of hydrogen off-gas of PEFCs to water.