Performance of catalyst coated sulfonated poly ether ether ketone membrane in PEM water electrolysis: effects of membrane modification by inclusion of MoS2-coated carbon nanotubes

Proton exchange membrane (PEM) water electrolysis is a promising technology for renewable hydrogen production, but substituting traditional perfluoro sulfonic acid membranes with fluorine-free membranes is needed to address the environmental concern about this component. This study presents a novel approach to enhancing the performance of fluorine-free sulfonated polyether ether ketone (SPEEK) membranes by incorporating functionalized nanofillers into the matrix of SPEEK membranes. Carbon nanotubes (CNT) are used as nanofillers and an innovative radio frequency (RF) sputtering plasma treatment technique is studied to modify CNTs, enabling efficient functionalization with oxygen (CNT-O) and molybdenum disulfide (CNT-O-MoS2) without chemical additives, which is different from what happens with conventional chemical treatments. The study shows that the integration of these modified nanofillers into the SPEEK matrix significantly improves mechanical strength, thermal stability, and proton conductivity, as required in PEM electrolysis cells. Among the tested nanofillers, CNT-O-MoS2 allows to enhance the oxidative stability of the fabricated membrane due to the sulfide groups and facilitates efficient ion transport through water channels, significantly improving the ionic conductivity of the prepared membrane. To evaluate electrochemical performance, catalyst-coated membranes (CCMs) were prepared using the decal method for both the fabricated membranes and Nafion 115. Notably, the SPEEK CNT-O-MoS2 membrane achieved a current density of 3 A cm−2 at 1.67 V, outperforming Nafion 115, which required 1.82 V for the same output. This research demonstrates the potential of hydrocarbon-based membranes as a viable, PFAS-free alternative for high-performance PEM water electrolysis applications.