RESUMEN
Hybrid inorganic-organic Nafion membranes modified with metal oxides (typically TiO2, ZrO2, WO3) are a good alternative for fuel cell applications. However, one of their main limitations is associated with their relative low proton conductivity at temperatures above 80 °C. In this work, we overcome this issue using HfO2 as a filler. HfO2 was prepared by a sol-gel method, and it was compared with a recast Nafion membrane (named as recast). Deconvolved XPS spectra confirmed the presence of hafnia, while EDS analysis was used to determine its weight content resulting in a 1.88 wt%. FT-IR ATR experiments indicated that the HfO2 hybrid membrane possess a higher capability to retain water than the recast. Thus, the water uptake, swelling degree, conductivity tests and fuel cell evaluations were performed. The water uptake analysis revealed that the hybrid membrane presented a higher retention percentage at 100 °C (61%) than recast (29%). This improvement enabled a higher ionic conductivity at 80 °C and 100 °C. The hybrid membrane displayed a higher conductivity at 100 °C than the recast membrane (112 versus 82 mS cm-1), increasing the cell performance to 0.36 W cm-2; being this performance almost two-fold higher to that obtained for the recast membrane. In summary, herein we demonstrated that HfO2 can be considered as an excellent substitute to conventional fillers.
RESUMEN
The aim of this work is the evaluation of a Sulfonated Poly Ether-Ether Ketone (S-PEEK) polymer modified by the addition of pure Santa Barbara Amorphous-15 (SBA-15, mesoporous silica) and SBA-15 previously impregnated with phosphotungstic acid (PWA) fillers (PWA/SBA-15) in order to prepare composite membranes as an alternative to conventional Nafion® membranes. This component is intended to be used as an electrolyte in electrochemical energy systems such as hydrogen and methanol Proton Exchange Membrane Fuel Cell (PEMFC) and Electrochemical Hydrogen Pumping (EHP). The common requirements for all the applications are high proton conductivity, thermomechanical stability, and fuel and oxidant impermeability. The morphology of the composite membranes was investigated by Scanning Electron Microscopy- Energy Dispersive X-ray Spectroscopy (SEM-EDS) analysis. Water Uptake (Wup), Ion Exchange Capacity (IEC), proton conductivity, methanol permeability and other physicochemical properties were evaluated. In PEMFC tests, the S-PEEK membrane with a 10 wt.% SBA-15 loading showed the highest performance. For EHP, the inclusion of inorganic materials led to a back-diffusion, limiting the compression capacity. Concerning methanol permeability, the lowest methanol crossover corresponded to the composites containing 5 wt.% and 10 wt.% SBA-15.