Nanoporous Hydrogels with Tunable Pore Size for Efficient Hydrovoltaic Electricity Generation

Abstract 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.