Development of novel catalysts coated non-fluorinated proton exchange membranes for water electrolysis

Hydrogen holds great potential as an energy carrier due to its high specific energy and environmen-tal benefits. However, its current production mainly relies on fossil fuel-based methods, such as methane steam reforming, which result in substantial pollution and greenhouse gas emissions. To tackle this challenge, there is an increasing shift towards sustainable conversion methods, such as water electrolysis, which can produce hydrogen using renewable energy sources. Among the various electrolysis methods, proton exchange membrane water electrolysis (PEMWE) is particularly nota-ble for its high current density, efficient electrocatalysts, low gas crossover rates, and its ability to function across a broad range of power inputs. Major progress has been made in PEM technology with the development of poly perfluorosulfonic acid (PFSA)-based membranes. These membranes offer high proton conductivity, exceptional chemical stability, and mechanical strength under vari-ous conditions, thanks to the strong C–F bonds in their molecular structure. However, PFSA mem-branes face several challenges, such as restricted operating temperatures due to their low glass tran-sition temperature, high production costs due to complex manufacturing processes, and environ-mental issues related to both production and degradation products, such as hydrogen fluoride (HF) and perfluoro compounds. To address these limitations, researchers have investigated alternative proton exchange membranes by modifying PFSA structures, integrating inorganic/organic composite materials, and developing sulfonated hydrocarbon-based polymers. Sulfonated hydrocarbon-based membranes show particu-lar promise due to their excellent thermal stability and mechanical strength, although their proton conductivity is still lower than that of PFSA-based membranes. Ongoing research seeks to improve these alternative membranes, aiming to strike a balance between performance, cost-efficiency, and environmental sustainability. In this PhD research, sulfonated poly(ether ether ketone) (SPEEK) was chosen as the matrix for a hydrocarbon-based membrane due to its superior thermo-mechanical and chemical stability, as well as its lower cost compared to the commercially available Nafion™ membrane. To enhance the per-formance of the fabricated SPEEK membrane, two approaches were undertaken. The first approach involved using carbon nanotubes (CNT) as nanofillers to improve mechanical property and chemi-cal stability of the prepared membranes. Plasma treatment was employed to modify the nanofillers. The modification of CNTs through oxygen treatment followed by MoS2 sputtering proved to be more effective than other methods, as the process was controllable, rapid, and posed minimal risk of introducing contaminants. After preparing the modified nanofillers, they were incorporated into the SPEEK matrix to fabricate hybrid membranes. The results of comprehensive characterization showed that the presence of these nanofillers positively impacted the performance of the mem-branes compared to the neat SPEEK membrane. The second approach focused on using a rein-forcement layer to improve the mechanical properties and enhance the durability of the fabricated membranes. To achieve this, polyether ether ketone (PEEK) mesh was selected as the reinforcement material for the SPEEK membranes. The PEEK mesh was modified using plasma treatment to en-hance its compatibility with the SPEEK membrane. Following this, several physico-chemical charac-terizations were performed to assess the performance of the reinforced membranes. The results demonstrated that these reinforced membranes exhibited higher mechanical strength and improved compatibility with the SPEEK membrane. In conclusion, plasma treatment offers a rapid and chemi-cal-free approach to modifying nanofillers and PEEK meshes, minimizing the risk of contamination during the process. Furthermore, these modifications lead to improved performance compared to their counterparts in the neat SPEEK membrane.