Anhydrous Phosphoric Acid Functionalized Sintered Mesoporous Silica Nanocomposite Proton Exchange Membranes for Fuel Cells

Abstract

A novel inorganic proton exchange membrane based on phosphoric acid (PA)-functionalized sintered mesoporous silica, PA-meso-silica, has been developed and investigated. After sintering at 650 °C, the meso-silica powder forms a dense membrane with a robust and ordered mesoporous structure, which is critical for retention of PA and water within the porous material. The PA-meso-silica membrane achieved a high proton conductivity of 5 × 10(-3) to 5 × 10(-2) S cm(-1) in a temperature range of 80-220 °C, which is between 1 and 2 orders of magnitudes higher than a typical membrane Nafion 117 or polybenzimidazole (PBI)/PA in the absence of external humidification. Furthermore, the PA-meso-silica membranes exhibited good chemical stability along with high performance at elevated temperatures, producing a peak power density of 632 mW cm(-2) using a H2 fuel at 190 °C in the absence of external humidification. The high membrane proton conductivity and excellent fuel cell performance demonstrate the utility of PA-meso-silica as a new class of inorganic proton exchange membranes for use in the high-temperature proton exchange membrane fuel cells (PEMFCs).

Toward Anhydrous Proton Conductivity Based on Imidazole Functionalized Mesoporous Silica/Nafion Composite Membranes

“…6(a), the recast Nafion shows a gradual decline in conductivity from 4.9 Â 10 À4 S cm À1 to 1.1 Â10 À5 S cm À1 at 130 C, while the composite exhibits a sustained increase in conductivity within the same temperature range. The poor performance shown by the pristine Nafion is intrinsic and consistent with the results in literature [32]. This can be attributed to the absence of humidification as an essential component to facilitate proton mobility through the Grothuss or vehicle mechanism.…”

Anhydrous proton exchange membranes comprising of chitosan and phosphorylated graphene oxide for elevated temperature fuel cells

“…For nanohybrid membranes, the incorporation of 2D conducting nanosheets can work as "bridges" to connect and shorten the distance for proton hopping. Therefore, CS/GO-X achieve higher and Nafion (0.06 mS cm -1 ), respectively [57]. PGO-filled membranes achieve enhanced anhydrous conductivities when compared with the CS control membrane, which are also comparable to those of Nafion and some other membranes in literatures [58,59].…”

Exceptional durability enhancement of PA/PBI based polymer electrolyte membrane fuel cells for high temperature operation at 200 °C

“…The peak intensity associated with P2O5 was obviously decreased, indicating the reduction in the formation of P2O5. Mesoporous silica maintains the mesoporous structure in the present of phosphoric acid because of its high thermal stability 43 . Phosphosilicate shows high proton conductivity and stability at medium temperature 44 , similar as the effect of Al2O3 45 and TiO2 46 in phosphoric acid based high temperature PEMs on the reduction of the acid loss and the cell resistance.…”

“…Phosphosilicate shows high proton conductivity and stability at medium temperature 44 , similar as the effect of Al2O3 45 and TiO2 46 in phosphoric acid based high temperature PEMs on the reduction of the acid loss and the cell resistance. Thus, the presence of mesoporous silica in the PA/PBI composite membranes could stabilize phosphoric acid in the form of phosphosilicate, significantly increasing the thermal stability and decreasing PA loss during the fuel cell operation at 200 o C. On the other hand, the facile and high proton diffusion ability of PWA confined in the mesopores of silica facilitates and maintains the high conductivity of the composite membranes, 43 despite the reduction of PA uptake ( Fig.2A). Proton conductivity can occur simultaneously through stabilized PA and PWA in the mesoporous silica, as shown schematically in Fig.4B.…”