Development of anion-exchange membranes (AEMs) with high ionic conductivity and sufficient chemical stability for the use in fuel cells is an outstanding scientific and technological challenge. A promising type of AEM materials are copolymers containing cationic cobaltocenium, mechanically stabilized by hydrophobic polyethylene backbone, which exhibit rapid hydroxide transport. Fundamental insight into the pathways of ion transport inside polyelectrolyte membranes will help the development of efficient AEMs. Generally, in an aqueous medium, the transport of hydroxyl ions proceeds through diffusion and through the Grotthuss mechanism. In this study, we analyze the OH- transport mechanism among the cobaltocenium groups with the aid of computer simulations: the cobaltocenium cations are placed between the graphene sheets which provide the hydrophobic environment and mimic nanoconfinement within the polymeric environment; a single OH- group per cation is included into the molecular model under different hydration levels. The molecular dynamics simulations of 400-500 atoms in a periodic cell are performed using the forces obtained from the density functional tight-binding approach capable of describing reactive processes. The dependence of the ion transport mechanism and conductivity, and of the diffusion coefficients on the parameters of the molecular model, will serve as input for the mean-field model describing the phase separation in AEM on the micrometer scale, leading to the formation of the ion-conductive channels. Ultimately, the promising modifications to the polymeric material, e.g. the optimum separation of the cations within the polymer, backbone, and side-chain modifications, suggested by theory and modeling will be used to guide the experimental design of AEMs.

Unraveling the mechanism of the hydroxide transport between the cobaltocenium groups in polyelectrolytes

ACS Spring Meeting 2021

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