Fast Hydroxide Conduction via Hydrogen-Bonding Network Confined in Benzimidazolium-Functionalized Covalent Organic Frameworks.

In both hydrophobic and hydrophilic nanochannels, confined water clusters spontaneously form dense internal hydrogen bond networks and hence exhibit fast mass-transfer kinetics. Covalent organic frameworks (COFs), a porous polymer, enables one-dimensional open channels to achieve ordered assembly guided by synthetic techniques and allows the accommodation of a large number of water molecules within the nanochannels. In the field of alkaline anion exchange membrane fuel cells, it has been a long-term pursuit of scientists to build abundant hydrogen bonds around hydrogen oxides (OH) to improve the conduction of OH by increasing the water content. Here, we designed and synthesized a OH conductor by assembling benzimidazolium into COFs, and a significantly high conductivity of 10 S cm was achieved at 353 K. Theoretical calculations showed that the water clusters confined in the pores of COFs and the regularly arranged hydroxides cooperatively formed a dense hydrogen bond network and OH conducted diffusive conduction through the Grotthuss hopping of protons in this hydrogen bond network.