Structured-Gradient Hydrogel Moisture Electric Generator with Milliampere and Milliwatt Level Electrical Energy Output for Smart Agriculture

Moisture-electric generator (MEG) is attractive sustainable energy sources, but environmental fluctuations cause unstable output, and low power/short supply limit practical use. Here, we developed a MEG device based on an activated carbon structured-gradient hydrogel, which achieved milliampere and milliwatt level electrical energy output and continuous voltage output for over 1 month. Unlike conventional isotropic materials, this structure promotes the directional migration of water and ions, effectively accelerating charge accumulation and enabling continuous power generation. Concurrently, the synergistic effect between the humidity-induced hydrogel and the slow anodic corrosion of the aluminum electrode establishes an H⁺/Al³⁺ gradient diffusion, further improving the electrical output performance. A single MEG device (with an area of approximately 1 cm²) can stably output a voltage exceeding 1.6 V across a wide humidity range (20-80% RH) and a broad temperature spectrum (-40 to 60 °C), with continuous operation for over 740 h. Significantly, the single MEG achieves 22.1 mA/cm² current and 3.2 mW/cm² power density, both an order of magnitude higher than previous MEGs. Large-scale integration technology provides an effective pathway for amplifying the electrical output performance of MEG arrays, connecting 100 MEG units in parallel yields a continuous current of ∼45 mA, with a series configuration of 120 units providing ∼192 V. The MEG array can successfully power a 5 W black light bulb and a wireless sensing system directly, showing great potential application in smart agriculture. This work provides a idea for advancing the development of high-performance MEG devices and real applications.