A new frontier towards the development of efficient SPEEK polymer membranes for PEM fuel cell applications: a review

Proton exchange membrane fuel cells (PEMFCs) have gained popularity over the last decade as a potential clean energy source for electric vehicles and portable electronic devices. Nafion is commonly used as a membrane material but suffers from high methanol crossover and cost. These drawbacks negatively influence the widespread commercial application of PEMFCs. Currently, the focus is on developing high-performance, low-cost PEMs to replace Nafion membranes. Sulfonated poly-ether-ketone-ether (SPEEK) has been identified as a promising alternative PEM in fuel cell applications due to its advantageous properties, such as low cost, mechanical and chemical stability, and ease of preparation and operation. The main purpose of this review is to demonstrate the benefits of SPEEK-based composite membranes over Nafion (R) by mixing the SPEEK material with fluorinated polymers, hydrocarbon polymers, carbon-based materials, metal oxide materials, etc. The ion-exchange capacity and proton conductivity of SPEEK polymers with different fillers are highlighted. SPEEK-based composite membranes are far more suitable for PEMFC and DMFC applications because SPEEK polymers are produced in an environmentally friendly manner. This critical review guides researchers in developing processes to maximise the properties of SPEEK-based membranes for fuel cell applications. SPEEK suffers from loss of conductivity at high temperatures and high methanol permeability. Modification of SPEEK using various materials will improve its properties.