Review on Chitosan and Two-Dimensional MoS₂-Based Proton Exchange Membrane for Fuel Cell Application: Advances and Perspectives

Chitosan is a naturally occurring polysaccharide with abundant biomass resources that attracts interest due to its unique physicochemical properties. The importance of chitosan has risen recently (a) because it is a renewable and biodegradable material and (b) because it has the ability to form a membrane. Therefore, chitosan is highly preferable for green energy applications. This review describes the most recent advancements in chitosan chemistry, emphasizing elemental modifying reactions like sulfonation, phosphorylation, phthaloylation, and chemical cross-linking. However, the major issues of the chitosan (CS)-based polymer electrolyte membrane (PEM) are attaining high proton conductivity, leakage across fuel cells, and durability. To overcome the above-mentioned issues, chitosan and the emerging class of inorganic materials 2-D transition metal dichalcogenides especially MoS2 can be employed for proton-exchange membrane fuel cell applications. Surface functionalization of MoS2 can open new pathways for fabricating CS/MoS2 composite membranes. Current research also focuses on the following issues: (a) strategies for the development of PEM, (b) properties and structures of chitosan for fuel cell applications, and (c) chitosan utilization in different parts of the fuel cell. The present study also discusses progress and particular challenges that chitosan-based proton exchange membranes face. Moreover, strategies to control those issues and future aspects are discussed in detail.