Selective ion transport through three-dimensionally interconnected nanopores of quaternized block copolymer membranes for energy harvesting application.

A concentration gradient in an aqueous solution is a promising source of energy that can be converted into electrical energy by an ion-exchange polymer membrane. In concentration-gradient energy harvesters, ion transport through nanoporous channels is an emerging approach to enhance the energy conversion efficiency. Since massive but selective ion transport could be realized through nanochannels, the theoretical calculations predicted that nanoporous membranes can extract significantly larger energy than the conventional non-structured membranes. In this regard, scientists in the field have attempted to produce nanoporous membranes on a macroscopic scale based on 1D, 2D, and 3D materials. However, the fabrication of nanoporous membranes is often accompanied by technical difficulties, which entails high production cost, low throughput, and poor scalability. In this study, we took advantage of the self-segregating properties of block copolymers (BCPs) to address these issues. In particular, the non-solvent-induced phase separation method has been utilized to produce three-dimensionally interconnected nanopores within BCP membranes. In addition, the neutral BCP nanopores' surface was modified with positive charges to allow selective diffusion of anions in concentration-gradient cells. By mounting the porous BCP membranes between two aqueous solutions with different concentrations, we studied the BCP-membrane-mediated energy-harvesting performance.