Facile polymer electrolyte membranes based on deep eutectic solvents and alginates for fuel cell applications

In this work, polymer electrolyte membranes were synthesized using deep eutectic solvents (DESs) and sodium alginate (SA). The prepared membranes were evaluated for their characteristics as polymer electrolyte membranes (PEM). Five biodegradable and non-toxic DESs were prepared and tailored in-house. Choline chloride was used as a hydrogen bond acceptor for DESs. Glycerol, urea, ethylene glycol, malonic acid, and fructose were employed as the hydrogen bond donors. The DESs prepared using chloride: glycerol, choline chloride: urea, choline chloride: ethylene glycol, choline chloride: malonic acid, and choline chloride: fructose samples were named as follows: DES-1, DES-2, DES-3, DES-4, and DES-5, respectively. Glycerol was also used to modify the DES-alginate films. All membranes showed enhanced proton conductivity in the range of 10 −4 to 10 −2 S/cm. It was also found that the SA/DES-5 membrane was originally mechanically inflexible; however, when glycerol was added to the SA/DES-5 membrane, it showed a positive effect on the membrane's flexibility and conductivity. • Deep eutectic solvents and sodium alginate-based membranes are reported. • Biodegradable and green deep eutectic solvents were tailored in-house with various hydrogen bond donors and acceptors. • The membranes demonstrated high proton conductivity in the range of 10 −4 to 10 −2 S/cm. • Glycerol was observed to have a positive effect on the membranes' mechanical properties.