Annealing-induced heterogeneous crystallization of topologically confined SPEEK thin films

Abstract

Pt-supported SPEEK (sulfonated poly(ether ether ketone)) thin films, mimicking the ionomer-electrode interface in PEFCs, were synthesized with thicknesses from 12 to 105 nm. Thermal ellipsometry revealed a thickness-dependent decrease in Tg, with a 30 nm film showing surface crystallization preceding that at the buried interface, attributed to higher surface mobility. GIWAXS (grazing incidence wide angle X-ray scattering) confirmed this behavior, highlighting the interplay between surface mobility and interfacial interactions, which dominate below 30 nm, affecting proton conduction and emphasizing the role of MEA (membrane electrolyte assembly) hot-pressing in Nafion alternatives.