Eco-Friendly Synthesis and Mechanistic Exploration of Multifunctional Cu/Cr Self-Assemblies for Durable and...

Designing durable and high-performance proton exchange membranes (PEMs) remains a critical challenge for advancing polymer electrolyte membrane fuel cells (PEMFCs). In this study, we exploit the distinct coordination chemistries of Cu(II) and Cr(III) to construct multifunctional macromolecular self-assemblies of aspartic acid (L-AA) via a greener route, which were further incorporated (2 wt.%) into sulfonated poly(phenylene oxide) (SPPO) to yield composite membranes (SPCu and SPCr). The dual functionality of L-AA-Cr(III) (─COOH and ─NH₂ groups) enabled stronger H-bonding interactions with ─SO₃H groups, enhanced proton conduction, and water uptake compared to the L-AA-Cu(II) (─NH₂ only). Consequently, SPCr achieved a peak power density of 512.4 mW cm^-2 and a current density of 718.3 mA cm^-2 at 0.6 V, outperforming pristine SPPO by 88.1% and SPCu by 21%. Linear sweep voltammetry confirmed substantially lower H₂ crossover (0.96 mA cm^{- 2}), while accelerated degradation tests for 100 h at 80°C and 30% RH revealed only 19% OCV decay (1.7 mV h^-1) for SPCr. Post-ADT analysis further demonstrated 85.96% power retention for SPCr, establishing its superior long-term durability. These findings highlight the efficacy of multifunctional fillers in enhancing proton conduction, acid-base interactions, fuel cell performance, and long-term stability of PEMFC membranes.