Hydrophilicity/porous structure-tuned, SiO2/polyetherimide-coated polyimide nonwoven porous substrates for reinforced composite proton exchange membranes

Polyimide nonwoven fabric-reinforced, flexible phosphosilicate glass composite membranes for high-temperature/low-humidity proton exchange membrane fuel cells

“…Meanwhile, it is known that proton conductivity of a reinforced composite membrane is strongly dependent on a porous structure of a reinforcing substrate (in other words, interconnectivity and amount of impregnated proton-conducting electrolytes) because the reinforcing porous substrate is inert to proton transport. [18][19][20] The morphological results shown in Fig. 2 demonstrate that the highly developed porous structure (average porosity $ 77%) of the PI nonwoven substrate exerts a positive influence on the formation of three-dimensionally interconnected phosphosilicate glass networks in the PI-GC membrane.…”

“…The change in the area (DA) of the samples was estimated using the equation DA (%) ¼ [(A wet À A dry )/A dry ]  100. [18][19][20] The inplane proton conductivities of the PI-GC membrane and SPAES membrane were evaluated with an impedance analyzer (VSP classic, Bio-Logic) using a four probe method over a frequency range of 1  10 À1 to 2  10 5 Hz, [18][19][20][21][22][23] wherein the sample dimension is 3 cm  1 cm (width  length). Prior to measuring proton conductivity, the PI-GC membrane and SPAES membrane were pre-equilibrated in a temperature/humidity control chamber (SH-241, ESPEC) under a given condition of temperature and RH.…”

“…The state of water in the membranes was examined by a thermogravimetric analyzer (TGA, SDT Q600, TA Instruments). 15,18,19 The TGA experiment was performed in a temperature range from room temperature (via isothermal heating at 100 C for 40 min to ensure the evaporation of physically adsorbed water) to 400 C at a heating rate of 10 C min À1 under a nitrogen atmosphere. Prior to the TGA measurement, the membranes were placed in an oven at 30 C/95% RH for 4 h, and then preequilibrated at 30 C/50% RH for 2 h. The fraction of physically adsorbed water was quantified by measuring the weight loss below 100 C. The amount of chemically adsorbed water was obtained by subtracting the physically adsorbed water content from the total water content.…”

“…This is similar to the morphology of conventional electrospun polymeric nonwovens. [18][19][20] A salient feature of the PI-GC membrane, as compared to the bulk phosphosilicate glass, is the presence of the PI reinforcing framework. Fig.…”

“…In the present study, as a new strategy to resolve these stringent limitations of typical silicate glass electrolytes, we develop polyimide (PI) nonwoven fabric-reinforced phosphosilicate glass composite membranes (hereinafter, referred to as ''PI-GC membranes''). Here, the PI nonwoven fabric, which is manufactured herein by an electrospinning process, [18][19][20] is employed as a mechanical reinforcing framework endowing the PI-GC membrane with mechanical flexibility and toughness. The phosphosilicate glass, which will act as a three-dimensionally interconnected proton-conducting matrix in the PI-GC membrane, is fabricated directly inside the PI nonwoven framework via in situ sol-gel synthesis of GPTMS/H 3 PO 4 followed by hydrothermal treatment.…”