A Critical Review of the Advancement Approach and Strategy in SPEEK-Based Polymer Electrolyte Membrane for Hydrogen Fuel Cell Application

Due to rising energy demand and global warming, the world is shifting from nonrenewable energy to renewable sources, such as fuel cells (FCs), due to their high energy conversion efficiency and environmental friendliness. A proton exchange membrane fuel cell (PEMFC) is an environmentally friendly and efficient FC. It converts the chemical energy stored in hydrogen fuel into electrical energy. A polymer electrolyte membrane (PEM) is a core element of the membrane electrode assembly (MEA). It transfers a proton from the anode to cathode, restricts electron flow across the membrane surface, and prevents reactant mixing. Sulfonated poly­(ether ether ketone) (SPEEK)-based membranes are effective PEMs as compared to commonly used Nafion membranes due to their excellent chemical, thermal, and mechanical stability as well as cost-effectiveness. However, it suffers from poor proton conductivity. Normally, the proton conductivity of SPEEK can be improved by enhancing the degree of sulfonation (DS) and temperature and reducing the relative humidity (RH). However, the high DS of SPEEK and temperature with low RH tend to reduce the mechanical strength of PEM, which consequently sacrifices the membrane’s lifetime. Therefore, the design of efficient SPEEK PEMs requires further modifications to improve the proton conductivity and strength, which can simultaneously enhance single-cell performance and durability. Therefore, this article reviews the advancements and various strategies to achieve high-performance and long-lived SPEEK-based PEMs. First, the tuning of SPEEK was performed by varying the DS of SPEEK. Second, the progress of modifying SPEEK with inorganic nano additives and metal–organic frameworks (MOFs) was also discussed comprehensively. The review also summarizes the influence of electrically and magnetically aligned nanoparticles on FC performance and membrane durability. Thus, the present review paper can be used as a reference for controlling different parameters to develop both efficient and durable SPEEK-based PEMs that can potentially compete with Nafion-based membranes for FC applications.