Review on Modification of Sulfonated Poly (-ether-ether-ketone) Membranes Used as Proton Exchange Membranes

Abstract

The proton exchange membrane fuel cell (PEMFC) is a type of modern power, but the traditional proton exchange membranes (PEM) of PEMFC are limited by high methanol permeability and water uptake. Poly-ether-ether-ketone (PEEK) is a widely used thermoplastic with good cost-effective property. Sulfonated poly (-ether-ether-ketone) (SPEEK) has high electric conductivity and low methanol permeability, as well as comprehensive property, which is expected to be used as PEMs. However, the proton exchange ability, methanol resistance, mechanical property and thermal stability of SPEEK are closely related to the degree of sulfonation (DS) of SPEEK membranes. Additionally, the proton conductivity, methanol permeability, and stability of SPEEK membranes applied in various conditions need to be further improved. In this paper, the research into modification of SPEEK membranes made by SPEEK and other polymers, inorganic materials are introduced. The properties and modification situation of the SPEEK and the composite membranes, as well as the advantages and disadvantages of membranes prepared by different materials are summarized. From the results we know that, the methanol permeability of SPEEK/PES-C membranes is within the order of magnitude, 10^-7cm²/s. The proton conductivity of the SPPESK/SPEEK blend membrane reaches 0.212 S cm^-1 at 80 °C. The cross-linked SPEEK membranes have raised thermal and dimensional stability. The non-solvent caused aggregation of the SPEEK ionomers. The proton conductivity of SPEEK/50%BMIMPF₆/4.6PA membrane maintains stable as 2.0 x 10^-2S cm^-1 after 600 h at 160 °C. Incorporation of aligned CNT into SPEEK increases the proton conductivity and reduces the methanol permeability of the composite membranes. The PANI improves the hydrothermal stability. More proton transfer sites lead to a more compact structure in the composite membranes. According to the results, the proton exchange capacity, water uptake, and conductivity of the SPEEK membranes are closely related to the structure, stability, mechanical and electrochemical property and methanol permeation of the PEMFC. The modification of SPEEK membranes will improve their applications in aviation, military and other industries. Some proposals for further research are put forward.

DOI: http://dx.doi.org/10.5755/j01.ms.21.4.9712