Molecular insights into thermal conductivity alteration of graphene oxide-Nafion nanocomposite membranes

Effective thermal management in Proton Exchange Membrane Fuel Cells (PEMFCs) is essential for improving durability, performance, and water balance. This study investigates molecular mechanisms governing thermal conductivity (TC) enhancement in graphene oxide (GO) reinforced Nafion membranes under hydration levels ranging from λ = 3–15 and GO loadings of 0.8 wt% and 1.6 wt%. Molecular dynamics simulations predict up to a 12% increase in TC at intermediate-to-high hydrations ( λ =6–15), mainly due to strengthened hydrogen-bond networks and percolated water clusters. Cluster analysis indicates a transition from fragmented to percolated water domains above λ > 6, forming continuous heat pathways. This is supported by the pair interactions, revealing that GO’s hydroxyl groups anchor hydrogen bonds, enhancing local water structuring and connectivity. Negligible changes in water and hydronium mobility with the presence of GO emphasize that thermal enhancement arises mainly from phonon-mediated transport in such systems. However, at very high hydration ( λ =15) and low GO content, water-mediated heat transfer dominates, yielding a TC comparable to that of pristine Nafion. Also, the vibrational density of states (VDOS) results imply improved phonon coherence that weakens at λ = 15 with low GO. Additionally, the probability density function (PDF) results at λ = 15 demonstrate the formation of denser water shells with parallel orientations around GO, which weakens its contribution to heat transfer. Thus, GO plays a dual role in optimizing Nafion’s thermal behavior, which depends on the hydration level. The improved properties of the GO-reinforced membrane can benefit the electrochemical reaction rates in PEMFCs by reducing the temperature gradient across the membrane-catalyst interface.