HIGHLY SULFONATED PEEK MEMBRANES WITH TUNED PHYSICOCHEMICAL PROPERTIES FOR PEM FUEL CELLS AND ELECTROCHEMICAL H2 PURIFICATION

The adverse impact caused by fossil fuel-based energy resources tends to shift the focus towards low-carbon-emitting hydrogen-based energy sources. Proton exchange membrane fuel cells (PEMs) are accepted worldwide as highly efficient next-generation energy devices. However, providing high-purity H2 is an important aspect regarding the efficiency of the fuel cells. Electrochemical H2 purification is attaining attention recently due to its high efficiency and duration. 1 Developing highly durable and efficient membranes is an essential part of the electrochemical systems. Sulfonated poly(ether ether ketone) (SPEEK) membranes are widely tested as a low-cost alternative for fluorinated membranes in PEMF-based electrochemical energy conversion systems. However, the duration and efficiency are some of the key challenges for the commercialization of the membrane compared to the conventional Nafion-based membranes. The efficiency of the SPEEK membranes is mainly dependent upon the percentage of introduction of sulfonic acid groups also. Herein, we have developed four SPEEK membranes based on an optimized sulfonation procedure on commercially available PEEK, and a sulfonation degree of 65% was selected for preparing the membranes. The mechanical and structural properties of the polymer membranes were tuned using different post-treatment procedures. Depending upon the type of heat treatment and the acid treatment procedures, the degree of crystallinity and physicochemical properties of the membranes varied, which are crucial for tuning the protonic conductivity and durability in PEMs and the H2 purification efficiency in the electrochemical conversion systems. The membrane obtained after postshowed a high conductivity of 0.18 S/cm at 60 °C that is comparable to the commercial Nafion membranes reported in the literature.