Key words: supercritical carbon dioxide, superhydrophobicity, thin films, hydrophobic polymer coatings, gas diffusion layers, fuel cell electrodes, hydrophobized carbon tissue
In this work a new method for uniform deposition of polymeric hydrophobic agent onto the surface of carbon tissue (a material for gas diffusion layers of fuel cells) from solutions in supercritical carbon dioxide (SC-СO2) is developed. The use of Teflon AF 2400 copolymer soluble in SC-СO2 is compared with a conventional method for hydrophobization of gas diffusion layer by deposition of Teflon 30N from aqueous suspension. Hydrophobic polymer compounds were deposited on rough surface of carbon tissue — a conducting material for gas diffusion layers with good mechanical and longevity characteristics — produced by Saati company. If the coating deposited from SC-СO2 is annealed at temperature exceeding the glass transition temperature for amorphous Teflon AF 2400 copolymer, a uniform thin fluoropolymer coating on carbon fibers is formed that imparts the most stable superhydrophobic properties to the surface of gas diffusion layer with minimal amounts of deposited agent. Moreover, the contact angles achieved in this work exceed those reported earlier in the literature for materials obtained using similar approaches. Prolonged exposure to water (1000 hours of direct exposure) or washing in the presence of detergent didn't induce any significant loss of the introduced superhydrophobic properties of the gas diffusion layer. Using the developed gas diffusion layer an electrode for phosphoric acid fuel cell was prepared. The achieved voltage-current characteristic of this cell indicates its satisfactory efficiency. The obtained results in general demonstrate good prospects of the developed approach in the production of gas diffusion layers for fuel cells.
doi:10.1134/S1990793111070049