Hierarchical nanochannels based on rod-coil block copolymer for ion transport and energy conversion

Abstract

Designable block copolymer (BCP) membranes are emerging for reverse electrodialysis to capture the salinity gradient energy between seawater and river water. However, present BCP based nanochannels are usually prepared from flexible blocks. Flexible blocks adopt random coil in phase-separated nanostructure that cage charge carriers, increasing the counterions transport resistance. To free the charge carriers, this work engineers a hierarchical ordered hybrid membrane composed of a rod-coil BCP containing positively charged ionic groups and a porous polymeric membrane with negatively charged groups. The rod-coil BCP can self-assembly into hierarchical ordered nanochannels. The rod block adopts rigid rod-like structure inside the channels which improves the orderliness of channels and effectively avoids embedding of ionic groups, dominating the ion transport. The porous polymeric membrane functioning as a supporting layer also participates in the ion transport. This hierarchical ordered device with asymmetric geometry and charge polarity achieves high performance in ion rectification and energy conversion. This strategy highlights the promise in BCP for salinity gradient energy conversion due to its designability and controllability.