Compromise mechanism of proton transfer in crown ether-based biomimetic proton exchange membranes: Insights from molecular dynamics simulations

Proton exchange membrane fuel cells (PEMFCs) have emerged as a key research area due to their ability to convert various gaseous energy sources (such as hydrogen and methanol) into electrical energy with high efficiency and zero pollution. The design of the proton exchange membrane (PEM), which is the site for proton transfer, is critical. To explore the influence of characteristic functional groups on proton transfer mechanism in biomimetic proton exchange membranes, the crown ether structure was introduced into polymer backbone chains to mimic biological ion channels. The motion behaviors of proton were qualitatively characterized through molecular dynamics simulation. It was found that protons are strongest complexed in the best matching 18CO6-PEM case based on the analysis of RDF, residence time, interaction energy, and number of hydrogen bonds. The characteristic groups of biological proton channels with smaller or larger pores can help protons detach from the complexation under the action of an electric field. The proton transfer in crown-ether biomimetic proton exchange membranes is not just a single mechanism, but a compromise between two mechanisms in parallel. This work provides a new perspective on designing proton conduction membranes by embedding large ring motifs with intrinsic cavities and the key parameters required for establishing the proton transfer model.