Molecular insights into enhanced water structuring and reduced water-hydronium preferential solvation in GO-Octadimethylsilane-Nafion composite membranes

Nafion membranes with Graphene oxide-Octadimethylsilane (GO-ODMS) fillers are designed in-silico using classical Molecular Dynamics simulations over fuel cell operating temperature forming composite NGOD-PEMs at hydrations of λ = 3, 6 and 9 at 298.15 K to 323.15 K. Molecular insights in hydrated NGOD-PEMs over the specified temperatures reveal contrasting changes in structural behaviour of water and water-hydronium preferential solvation, compare to pristine Nafion (PN) PEMs. GO-ODMS fillers increase repulsive interactions enhancing compactness of NGOD-PEMs by close sulphonate group (SO 3 − ) arrangements at all λ and temperatures, contrast to PN-PEMs. Hydrophobic ODMS induce water molecular ordering (WMO) within 10 Å from fillers due to varying hydrophobicity and hydrophobic attractions (HAs) with changing λ and temperature, showing WMO λ=3 > WMO λ=6 > WMO λ=9 for all temperatures. Observable WMO at λ = 3 and continuous to labile water channel formations at λ = 6 and 9, in NGOD-PEMs, are shown to depend on temperature, radius of gyration and molecular packing of ODMS at a given λ. Increase in hydrophobicity and HAs-induced WMO inside NGOD-PEMs, increases water overlapped concentrations (H 2 O overlap ) near -SO 3 − of NGOD-PEMs for all temperatures in contrary to that inside PN-PEMs, also resulting in H 2 O overlap,λ=9 > H 2 O overlap,λ=6 > H 2 O overlap,λ=3 . Higher H 2 O overlap near SO 3 − and water-hydronium rearrangements near GO-hydrophilic sites combinedly reduce preferential solvation parameters (f water,hyd|water ) in NGOD-PEMs than in PN-PEMs at λ = 6 and 9; whereas for λ = 3, f water,hyd|water for a given temperature varies marginally between NGOD-PEMs and PN-PEMs. Water-hydronium rearrangement near GO-hydrophilic sites along with enhance WMO near GO-ODMS and near closely arrange SO 3 − infer additional pathways for hydronium mobility through compact NGOD-PEMs with lower f water,hyd|water than in PN-PEMs.