Ion engines in hydrogels boosting hydrovoltaic electricity generation

Hydrovoltaic electricity generators (HEGs), powered by ubiquitous water evaporation, are emerging due to their high spontaneity and continuity. However, the current performance of most HEGs is restricted to 50.00 μA cm−2, far from commercial applications. Herein, we propose an ion-engine HEG by establishing a concentration gradient of an ionisation group in hydrogels along the direction of ion migration. The distinctively designed ion gradient acts as an engine to accelerate ion migration by enhancing diffusion, hence increasing the generated current. Notably, the ion-engine HEG generates a record-breaking current density of 466.75 μA cm−2, 10 to 100 times higher than those of previously reported HEGs. The ion-engine HEG possesses the lowest internal resistance, which is the closest to that of commercial products. In addition, the high transparency, flexibility, and customisability of hydrogels offer HEGs a wide range of applications, such as night-time lighting, sweat monitoring, and powering small unmanned boats. These findings provide a fresh perspective on high-performance HEGs, which have great potential to serve energy technology and intelligent life.