Modification of Nafion membrane with biofunctional SiO2 nanofiber for proton exchange membrane fuel cells

Proton currents are an integral part of the most important energy-converting structures in biology. We prepared a new type of bioinspired Nafion (Bio-Nafion) membrane composited of biofunctional SiO 2 (Bio-SiO 2 ) nanofiber and Nafion matrix . SiO 2 nanofibers were prepared by electrospinning silica sol prepared from tetraethyl orthosilicate . Meanwhile, Bio-SiO 2 nanofibers were synthesized by immobilizing amino acids (cysteine, serine , lysine, and glycine) on SiO 2 nanofibers, which acted as efficient proton-conducting pathways that involved numerous H + transport sites. In our study, the SiO 2 nanofibers biofunctionalized with cysteine were further oxidized, and the composite membranes were designated as Nafion-Cys, Nafion-Lys, Nafion-Ser, and Nafion-Gly, respectively. We then investigated the different polar groups ( SO 3 H, OH, and NH 2 ) of the amino acids that contributed to membrane properties of thermal stability, water uptake (WU), dimensional stability, proton conductivity , and methanol permeability . Nafion-Cys exhibited the highest proton conductivity of 0.2424 S/cm (80 °C). Nafion-Gly showed the lowest proton conductivity and WU because glycine contains the least number of hydrophilic groups among the amino acids. Overall, the introduction of Bio-SiO 2 nanofiber to composite membranes significantly improved proton conductivity, dimensional stability, and methanol permeability.