Role of functionalized carbon dots in tailoring anion exchange membranes for water electrolysis

Nanocomposite anion exchange membranes (AEMs) were developed by incorporating functionalized carbon dots (CDs) into a quaternary-ammonium-functionalized polysulfone (qPSU) matrix. Oxygen-functionalized (O-CDs), nitrogen-functionalized (N-CDs), and quaternary-ammonium-functionalized CDs (qCDs) were synthesized through a simple, low-cost hydrothermal route. The nature of CD functionalization strongly influenced membrane morphology, physicochemical properties, water dynamics, and ion transport. Among the investigated fillers, qCDs displayed the highest compatibility with the polymer matrix, ensuring uniform dispersion and leading to enhanced ion-exchange capacity, increased water uptake, improved water retention at elevated temperatures, and the highest ionic conductivity. When incorporated into a highly quaternized qPSU matrix (degree of quaternization, DQ ≈ 80%), the resulting nanocomposite membrane provided a high density of cationic sites and well-connected hydroxide-transport pathways. Under these conditions, the qPSU + qCDs membrane achieved, in AEM water electrolysis, a cell voltage of ∼1.75 V at 1.0 A cm −2 and 60 °C, delivering performance comparable to that of state-of-the-art AEMs.