Organic-inorganic (polysiloxane) crosslinked sulphonated poly(ether ether ketone ketone) hybrid membranes for direct methanol fuel cells

A series of Ph-m-SPEEKK/polysiloxanes organic-inorganic hybrid proton exchange membranes (HMs) were prepared. The Ph-m-SPEEKK was synthesized from 2-phenylhydroquinone and 1,3-bis(4-fluorobenzoyl)benzene, and sulphonated in a controlled way until a 1.60 meq g(-1) ion exchange capacity was reached. The cross-linked polysiloxane phase (PSP) was prepared by the sol-gel route from PDMS as the linear fraction and phenyl-trimethoxysilane (PTMS) as crosslinker, the non-crosslinked PSP contained only PDMS. The crosslinked PSP was characterized by FTIR and solid state Si-29 NMR, which revealed that the PTMS is fully crosslinked in the PSP structure. SEM micrographs of the HMs showed no apparent macro phase separation of the organic-inorganic components. The macroscopic properties of the HMs investigated were water uptake, swelling, methanol permeability and proton conductivity. The methanol permeability of the crosslinked HMs decreased to a limiting value between 16.3 and 17.9 x 10(-7) cm(2) s(-1) at 60 degrees C. A continuous increase of the proton ion conductivity (64.1-90.0 mS cm(-1) at 80 degrees C and 95% RH) was achieved with the addition of increasing amounts of the crosslinked PSP content as compared with the non-crosslinked HM. The HM with a 20 wt% of PSP presented a proton conductivity of 90.0 mS cm(-1) and an activation energy for proton transport of 17.2 kJ mol(-1), both comparable to Nafion 117 and in a single DMFC test the electrode assembly fabricated with this HM reached a maximum power density of 38.0 and 30.5 mW cm(-2) for 2 and 5 M methanol concentrations, respectively, higher than Nafion 117 and the pristine Ph-m-SPEEKK membranes.

Automated summary

A series of organic-inorganic hybrid proton exchange membranes were prepared using Ph-m-SPEEKK/polysiloxanes. The crosslinked membranes showed decreased methanol permeability and increased proton conductivity compared to non-crosslinked membranes, with the addition of crosslinked polysiloxane phase. In a single DMFC test, the membrane with 20 wt% of PSP content achieved a higher power density compared to Nafion 117 and the pristine membranes.