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Dual hydrophobic grafted chains facilitating quaternary ammonium aggregations of hydroxide conducting polymers: a theoretical and experimental investigation

Ran, Jin, Fu, Cenfeng, Ding, Liang, Cao, Pengrui, Xu, Tongwen
Journal of materials chemistry 2018 v.6 no.14 pp. 5714-5723
ammonium, anion-exchange membranes, fuel cells, hydrophobicity, polymers, quaternary ammonium compounds, simulation models, thermodynamics, water uptake
Establishment of connective hydroxide conducting channels is highly desired for alkaline anion exchange membranes (AAEMs). Herein, we offer a feasible strategy of grafting long alkyl chains onto both the quaternary ammonium cation (QA) center and backbone to achieve the formation of well-developed pathways for OH⁻ transport. Theoretical simulations reveal that QA groups are prone to aggregation driven by the thermodynamic incompatibility between the backbone and grafted chains. With increasing length of alkyl chains, micro-phase separation is facilitated. Experimentally, the C16C6-X40Y10 AAEM having the largest population of the longest alkyl chains in this work gives rise to the highest hydroxide conductivity of 61 mS cm⁻¹ at 30 °C, although its water uptake is only 15.8%. The alkaline anion exchange membrane fuel cell with the incorporation of C16C6-X40Y10 yields a maximum power density of 322 mW cm⁻² at 60 °C. These results represent the advancements of this dual grafted structure in improving hydroxide conductivities, and this configuration can act as a general platform for developing promising AAEMs in the future.