A double-gradient structured hydrogel for an efficient moisture-electric generator

Moisture-electric generators (MEGs), which convert moisture potential into electrical energy, provide a promising alternative for energy generation due to the widespread and abundant distribution of air humidity in the surrounding environment. However, the low and intermittent electric output of MEGs presents challenges for their direct use in practical applications. In this study, an efficient hydrogel-based MEG integrated with hydrophilicity and ion concentration gradients based on a rational combination of polyvinyl alcohol, cellulose nanofibers, phytic acid, lithium bromide, and multi-walled carbon nanotubes was developed for the first time. The assembled MEG demonstrates outstanding power generation performance, with a single unit providing an output voltage of 1.0 V and a power density of 26.5 μW cm −2 (53.0 μW cm −3 ), enabled by the synergistic effect of its double-gradient structure. Notably, an increased current (4.0 mA) and voltage (45.3 V) were achieved using parallel and series integration of MEG banks, respectively. Scalable MEGs can directly power commercial electronic devices without the need for rectifiers or capacitors. This study provides new insights into MEGs design, contributing to the future development of sustainable power sources.