One Porphyrin Per Chain Self-Assembled Helical Ion-Exchange Channels for Ultrahigh Osmotic Energy Conversion.

Ion-exchange membranes (IEMs) convert osmotic energy into electricity when embedded in a reverse electrodialysis cell. IEMs with both high permselectivity and ionic conductivity are highly needed to increase the energy conversion efficiency. The ionic conductivity can be improved by increasing the content of immobile charge carriers, but it is always accompanied by undesirable permselectivity decrease due to excess swelling. Until now, breaking the permselectivity-conductivity tradeoff still has remained a challenge. Here, we demonstrate a membrane with the least ion-exchange capacity (∼10 mequiv g), generating an ultrahigh power density of 19.3 W m at a 50-fold concentration ratio. The membrane is made of a porphyrin-core four-star block copolymer (-BCP), forming the high-density helical porphyrin channels (∼10 cm) under the synergistic effect of BCP self-assembly and porphyrin π-π stacking. The porphyrin channel shows high Cl selectivity and high conductivity, benefiting high-performance osmotic energy conversion. This economic and facile membrane design strategy provides a promising approach to developing a new generation of IEMs.