Hybrid Electrolyte Membranes Based on Sulfonated Poly (arylene ether sulfone ketone) Multiblock Copolymer for PEMFC Operating at Elevated Temperatue under Low Humidity

Abstract

Polymer electrolyte membrane fuel cells (PEMFCs) operated under low relative humidity (RH) have been received great attention due to simplifying thermal management and reducing the cost of the system. However, the state-of-the-art electrolyte membrane (Nafion), has several problems, such as high production cost, environmental incompatibility, and insufficient thermomechanical properties above 80 ^oC.^[1] To overcome these problems, aromatic hydrocarbon polymers are considered promising alternatives, such as sulfonated poly arylene ether sulfone ketone (SPESK) multiblock membranes have been reported.^[2]Nevertheless, SPESK membrane exhibits poor performance under low relative humidity (RH).

We have developed high proton conducting membranes based on modifying non-fluorinated aromatic ionomers using hygroscopic metal oxide and inorganic proton conductors. We have synthesized novel composite membrane using porous hygroscopic titanium dioxide nanotubes (TNTs) incorporated SPESK membrane. TNTs with average diameter of 90 nm were incorporated into SPESK solution so as to provide the proton migration pathway in SPESK membrane. Compared to pristine SPESK, SPESK-TNT delivered 2.4 times higher maximum power density at 80 ^oC under 30 % RH. The higher PEMFC performance under low RH was due to the hygroscopic property of TiO₂which can retain water and due to the tubular morphology which facilitates the proton transport channel through membrane.

We also fabricated inorganic proton cluster modified graphene oxide SPESK composite membrane. The deposition of phosphotungstic acid (PW) on the modified graphene oxide sheet with positively charged functional group was carried out through an electrostatic interaction between PW and the modified graphene sheets to make heterogeneous system. The modified graphene oxide (mGO) was synthesized through a simple condensation reaction. A mixture of mGO and PW aqueous dispersion was stirred to fabricate PW-mGO. The physico-chemical characterization of inorganic cluster and the modified graphene oxide was confirmed by UV-visible, IR and cyclic voltammetry studies and these results revealed that that an alteration of the electronic structure of deposited cluster as a result of strong hybridization between the graphene oxide and PW ^[3].These SPESK composite membranes exhibited much higher proton conductivity at relatively low humidity than the pristine SPESK, and the composite membrane showed higher maximum power density PEMFC operated under 18 % RH than that of pristine membrane. The synthesis of composite aromatic membranes, conductivity and fuel cell performance at elevated temperature under low relative humidity will be discussed in this presentation.

References

1.S. Bose, et al., Prog. Poly. Sci. 36 (2011) 813.

2.B. Bae, et al., Angew. Chem. Int. Ed. 49(2010) 317.

3.Y. Kim, and S. Shanmugam, ACS Appl. Mat. Int.,5  (2013) 12197.