Nanoporous Hydrogels with Tunable Pore Size for Efficient Hydrovoltaic Electricity Generation.

Hydrovoltaic electricity generators represent an emerging technology for converting low-grade water-based energy into electricity, and hydrogels are favored for their water absorption and ion-responsive properties. However, the controllable fabrication and precise micromorphological characterization of nanoporous hydrogels remain challenging, hindering the understanding of ion transport within confined water channels. In this work, a nanoporous hydrogel with tunable pore sizes is presented, developed through a multiple hydrogen-bonding crosslinking strategy using γ-polyglutamic acid and hydroxylated carbon nanotubes. The pore size can be systematically tuned from 78 to 161 nm, and cryo-electron microscopy confirms the presence of hydrated nanochannels. The results highlight the critical role of streaming potential in electricity generation, with the device achieving a threefold increase in voltage by reducing the pore size. The optimized device delivers an open-circuit voltage of 1.05 V and a short-circuit current of 100 µA with a 0.1 m NaCl droplet. Moreover,a practical application is demonstrated through a sweat-monitoring patch that visually responds to ion concentration changes. This work advances the design of high-efficiency hydrovoltaic systems by establishing a clear link between tunable nanoscale architecture and device performance, paving the way for scalable energy harvesting and sensing technologies.