Ce–Mn bimetallic oxide-doped SPEEK/SPPO blend composite membranes to induce high oxidative tolerance and proton conductivity for hydrogen fuel cells

Abstract

Utilizing the potential of transition metals to quench free radicals in hydrogen fuel cells, we prepared cerium–manganese-based bimetallic oxide (CeMnO_x) nanostructures by alkali-aided deposition precipitation to harness as fillers in hydrocarbon-based polymer electrolyte membranes (PEMs). To improve the stability of the PEMs, a blend of sulfonated poly ether ether ketone (SPEEK) and sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO) with different weight ratios was employed as a membrane backbone. The interfacial adhesion and coupling configuration of three-dimensional CeMnO_x with sulfonic moieties of blend polyelectrolytes enhances the bound water content in the PEMs. It also constructs an extensive hydrogen bonding network with proton transport channels, uplifting the proton conductivity (K^m) by promoting vehicular and Grotthuss-type transport. Reversible redox cycling of Ce³⁺–Ce⁴⁺ and Mn²⁺–Mn³⁺ endorses the quenching of harsh radicals and augments the oxidative stability of the membranes. Composite PEMs exhibit only 4–9% mass loss and 2–5% K^m loss after exposure to Fenton's solution. SSM-73 membrane showed a peak power density of 431.2 mW cm⁻² with a maximum current density of 1272.6 mA cm⁻² at 75 °C in 100% RH and showed a high OCV retention of 88% over 50 h. The fuel cell performance of SSM-73 was 50% higher than that of its corresponding blend membrane, i.e., SS-73, which showed a peak power density of 287 mW cm⁻² and a maximum current density of 872.3 mA cm⁻².