Carbon Nanofiber Gas-Diffusion Anodes Based on a Copolymer of Acrylonitrile with Methyl Acrylate for High-Temperature Polymer-Electrolyte Membrane Fuel Cell

Fuel cells on polybenzimidazole (PBI) membrane belong to high-temperature polymer-electrolyte membrane fuel cells (HT-PEMFC). When a polymer-electrolyte complex of PBI with o-phosphoric acid (PA) is applied as a proton-conducting membrane, the proton conductivity is provided without humidification above 120°C. Hydrogen-air HT-PEMFCs are able of operating effectively at 150–200°C, which allows application of technical hydrogen contaminated with CO as fuel. However, it should be noted that application of conventional “thin-film” Pt/C electrodes based on electrically conductive carbon black with Pt nanoparticles in aggressive PA environment results in electrochemical corrosion of carbon, which leads to the loss of Pt electrocatalyst particles and their aggregation (Ostwald ripening). Evidently, there is a need to replace the carbon black with more stable carbon nanostructured materials. It has been shown that self-supporting mats (essentially “felt”) based on carbon nanofibers (CNF) can be used as HT-PEMFC anodes. The CNF mats were obtained in three stages. At the first stage, the nanofiber precursor material was obtained by electrospinning of solution of a copolymer of acrylonitrile with methyl acrylate (with addition of ZrCl₄). Then, the mats were stabilized by thermal oxidation (350°C, air). Afterwards, the CNFs were kept in Zn(NO₃)₂ (porogen) solution and pyrolyzed (1000 \(^\circ \) C, vacuum). To improve the proton conductivity, N-phosphonoethylated cardo poly(benzimidazole) (PBI-PhT-P) was deposited on the CNF surface which leads to an improvement in the performance characteristics of HT-PEMFC. The obtained materials were examined by electron microscopy. Their specific surface area and specific volume were investigated by the N₂ and CO₂ adsorption methods (up to 597 m²/g and 0.170 cm³/g). After Pt deposition, the CNFs were successfully tested as anodes (up to 0.4 mA/cm² at 625 mV) in hydrogen-air HT-PEMFC.