On the evolution of proton conductivity of Aquivion membranes loaded with CeO2 based nanofillers: Effect of temperature and relative humidity

Surface modified CeO2 nanoparticles were prepared by reacting nanometric CeO2 with a fluoroalkyl (C8F17-C2H4-PO(OH)2) or a fluorobenzyl phosphonic acid (C6F5-CH2-PO(OH)2). Both non-modified and fluorophosphonic acid modified CeO2 were used as fillers of composite Aquivion membranes, with loadings up to 5 wt%. Ex situ accelerated ageing using the Fenton reaction shows that non-modified CeO2 is a more efficient radical scavenger than the two fluorophosphonic acid modified fillers. Fluoride emission rate data for pristine Aquivion and for the composite membranes are consistent with the corresponding changes in the values of ion exchange capacity (IEC) and elastic modulus. The conductivity of membranes containing non-modified CeO2, measured as a function of relative humidity at 80 and 110 °C, decreases with increasing filler loading. For loadings > 2 wt%, an increase in temperature from 80 to 110 °C results in further conductivity drop and in the concomitant IEC decrease, due to partial filler solubilization, thus indicating that the composite membranes are unstable at temperature > 80 °C. However such conductivity drops are strongly reduced, especially at 80 °C, for composites with fluorophosphonic acid modified CeO2.