Confined nanopores and hydrogen bonds of polyoxometalates for continuous electricity generation from fluctuating humidity

Abstract

Environmental humidity power generation technology is an important strategy to reduce the use of fossil fuels and solve the energy crisis. However, it remains a challenge to maintain a water adsorption gradient for the long-term output of continuous electrical energy when environmental humidity fluctuates. Herein, porous polyoxometalate (POM) nanomaterial [Cu^II(2,2′-bipy)(H₂O)₂Cl]_n[Cu^II-(2,2′-bipy)(H₂O)₂Al(OH)₆Mo₆O₁₈]_n (Cu-CuAlMo₆) was used to assemble thin-film devices, which achieved continuous power generation in fluctuating humidity. The device generated stable electrical output (0.203 V, 4 µA cm⁻², maximum power density of 0.06 µW cm⁻²) in 10% humidity, and maintained continuous electrical output (0.246 V, 14.5 µA cm⁻², maximum power density of 0.214 µW cm⁻²) in high humidity, even with condensed water for 8 days. A detectable electrical response was generated within 0.1 s under the humidity trigger and enabled real-time tracking of environmental and chemical information. First-principles calculations elucidated that hygroscopic sites constructed by the oxygen-containing groups and hydrogen bonds in the POM ensured efficient collection of humidity, and confined nanopores maintained the water adsorption gradient under high humidity. In addition, the unique charge transfer mechanism enabled the device to autonomously monitor environmental and chemical information in real-time. This work provides a reliable strategy for developing humidity power generation technology that continuously outputs in fluctuating environmental humidity, and is expected to form important components of multimodal real-time monitoring systems.