Proton-conducting materials are a key component of proton exchange membrane fuel cells (PEMFCs) and the advantage of clear structural information in crystal materials offers a pathway for the investigation of the proton-conducting mechanism and pathway. In this work, a new Cd2+ coordination polymer material (compound 1) with the formula {[Cd3(bipy)3(H2O)4][Fe(CN)6]2·2H2O·2(bipy)}n was successfully synthesized by a solution diffusion method and its proton conduction ability was further determined. Crystal structure analysis confirms the coordination of [Fe(CN)6]3–, 4,4′-bipyridine, and H2O molecules to Cd2+ in the three dimensional structure of compound 1. Also, we confirmed that compound 1 of 500–800nm particle size could be synthesized on a large scale by a facile stirring method. Proton-conductivity analyses revealed that compound 1 shows a water-mediated proton conduction behaviour because the conductivity increased apparently with the increase of relative humidity. Further investigation shows that the highest proton-conductivity of 8.36×10−4 S cm−1 was observed at 60°C and 95% relative humidity, and the mechanism analysis suggests a Vehicle mechanism exists in the proton conduction process of compound 1.

Herein, nonequilibrium molecular dynamics simulations are conducted to study the hydraulic permeation and vehicle transport of protons in proton exchange membranes (PEMs) with different structures. The results indicate that water molecules and hydronium ions are transported in porous PEMs in the form of clusters. Water molecules are more concentrated in the bulk areas of pores, whereas hydronium ions had a high‐density profile near the pore surface areas since sulfonate ions of the side chain exhibit a stronger adsorption effect on hydronium ions. Due to the confined pore size, the slip flow of water molecules and hydronium ions occurs near the pore surfaces and it becomes more significant as side chain separation or pore size increases. As pore size decreases, the reduction of movement region and the deep attractive potential near the pore wall lower the specific enthalpy due to enhanced molecule‐wall collisions. In addition, the transport diffusivity coefficients of positively charged hydronium ions are smaller than that of water molecules due to the stronger Coulomb interactions and hydrogen bonding with negatively charged side chains. Transport diffusivity coefficients of water molecules and hydronium ions increase as pore size and side chain separation increase.