Powering the Future with Natural Polymers

The development of sustainable and high-performance ionomer thin films is critical for advancing proton exchange membrane fuel cells (PEMFCs). In this work, we report on the design and characterization of ionomer thin films based on sulfonated polysulfone (SPSf) functionalized with lignosulfonates (LS) at varying LS-to-SPSf ratios (1:0.2, 1:0.6, and 1:1) and across multiple thickness regimes. Ionomer thin films serve a dual role in PEMFCs: as binders within the catalyst layer and as conduits for proton transport. While Nafion remains the benchmark ionomer due to its high proton conductivity, its environmental persistence and high cost—stemming from its perfluorinated structure—motivate the pursuit of greener alternatives. Hydrocarbon-based polymers such as polysulfone offer a promising low-cost and environmentally benign substitute; however, their performance as thin films is typically inferior to Nafion, especially in terms of ion transport properties. Here, we demonstrate that functionalizing SPSf with LS—a low-cost, naturally abundant byproduct of the pulp and paper industry—dramatically enhances the proton conductivity of the resulting ionomer thin films by three orders of magnitude, from 0.0203 mS/cm to 33.98 mS/cm, surpassing that of Nafion in the thin film regime. The synergy between SPSf and LS not only improves ionic transport but also introduces a sustainable pathway for next-generation ionomer design. This study highlights the potential of lignin-functionalized hydrocarbon ionomers as viable, high-performance alternatives to conventional fluorinated materials in PEMFC applications.