Osmotic energy-based systems for self-powered sensing

Converting osmotic energy into electric energy through ion transport process has various advantages, including no CO2 emissions and minimal daily variability. Thus, it can be a promising strategy to build self-powered sensors. Specifically, there are mainly two approaches to construct osmotic energy-based self-powered sensors. One is harvesting osmotic energy as power supplies for existing sensors. The other is directly establishing active self-powered sensors. Both of the two approaches have developed rapidly in recent years. In this review, recent publications about osmotic energy conversion systems for self-powered sensors are presented. Firstly, the related history and mechanism are systematically summarized. Then, the recent progress of relevant power supplies and active sensors in recent 8 years are successively introduced. Considering nanopore/nanochannel-based selective membrane as one of the key units of ion transport-based energy conversion systems, the introduction is made around different kinds of selective membranes, including symmetric membranes with single-channel/pore, porous structures built by plenty of nanochannels/nanopores, and Janus membranes with asymmetric pore structures. Finally, future challenges of osmotic energy conversion systems for self-powered sensors are listed and analyzed. We believe this review could provide valuable guidance for relevant researchers to promote osmotic energy conversion technology and self-powered sensors to a broader range of applications.