Influence of the Polymer Precursor Structure on the Porosity of Carbon Nanofibers: Application as Electrode in High-Temperature Proton Exchange Membrane Fuel Cells

Polyacrylonitrile and polyheteroarylenes, such as polybenzimidazole (PBI) and a polymer of intrinsic microporosity (PIM-1), have been employed to prepare nanoporous electrospun carbon nanofiber (CNF)-based materials for high-temperature proton-exchange (or polymer-electrolyte) membrane (HT-PEM) fuel cells. The nanoporous CNF mats are obtained by Nanospider (needle-free) electrospinning method from polymer solution followed by pyrolysis at 1500 °C to form nanoporous electrospun polymer nanofiber self-supporting mats with micropores ( D < 2 nm) and mesopores ( D 2–50 nm). The nanoporous CNF samples are extensively characterized by N 2 and CO 2 adsorption applying the BET, BJH, Dubinin–Radushkevich (DR), NLDFT, and GCMC methods, CO 2 uptake, Raman spectroscopy, elemental analysis, electrical conductivity, electron microscopy, and XPS. The role of the polymer precursor on the obtained values of specific surface area (SSA) and volume for micro- and mesopores is presented and discussed. The PBI-based CNF material reaches a micropore SSA of 919 m 2 g –1 and CO 2 uptake of 4.0 mmol g –1 derived from CO 2 adsorption (273 K) data, and a micropore SSA of 873 m 2 g –1 according to the t -method derived from N 2 adsorption data. Close values confirm higher accessibility of micropores compared with the case of PIM-based CNF, where the micropore SSA values derived from CO 2 and N 2 adsorption data are different and indicate the partial inaccessibility of micropores for low-temperature nitrogen adsorption (77 K). Platinum-decorated CNF mats are successfully tested as electrodes for HT-PEM fuel cells, showing the feasibility of using the mats as cathodes; nevertheless, further optimization is required. For CNF anodes, the HT-PEM fuel cell performance reaches 0.69 V at 0.2 A cm –2 and 0.53 W cm –2 at 1.4 A cm –2 which permits the use of the Pt/CNF mats as anodes.