PolyU Develops Efficient and Scalable Moisture-Electric Generators Made from Ionic Hydrogel

Finding simple and efficient green energy conversion technology is significant to achieve carbon neutrality and sustainable green energy development while satisfying the increased demand for electrical power. Moisture-electric generator (MEG), which is based on chemical energy from atmospheric moisture to generate electricity directly without causing pollutants and harmful gas emissions, is an emerging focus in the energy field. 

Practical Green Power Source
However, most MEGs suffer from intermittent electrical signals and low currents. In addition, the realisation of large-scale integration and practical applications is still a bottleneck in current research. Led by Prof Xiaoming Tao, Director of Research Institute for Intelligent Wearable Systems, a novel and efficient ionic hydrogel moisture-electric generator (IHMEG) is developed with versatile, flexible, lightweight and all-weather adaptable features. 

The IHMEG operates stably in a wide range of environmental conditions from 10% to 85% relative humidity (RH) and from -24 to 60 °C temperature. This provides a promising green power source in Hong Kong, where most of the RH fluctuates from 40% to 90% around the year.

Applicable Energy Source
Thanks to the synergistic effect of notable moisture-absorption capability and fast ion transport capability in the ionic hydrogel network, a single IHMEG unit of 0.25 cm2 can continuously generate direct-current electricity with a constant open-circuit voltage of ≈0.8 V for over 1000 hours, a high short-current density of 0.24 mA cm−2, and power density of up to 35 µW cm−2. 

Of great importance is that large-scale integration of IHMEG units can be readily accomplished to offer a device with a voltage up to 210 V, capable of directly driving numerous commercial electronics, including electronic calculators, energy watchbands, electronic ink screens and light-emitting-diode arrays. Also, the IHMEG power device is successfully employed to electroplate metal nickel (Ni) structures on the millimeter scale, which is a big advance and proves the practical application of scalable IHMEG with sufficient energy. 

Moreover, the application of IHMEGs as a direct-circuit (DC) power source can be easily designed and fabricated by connecting multiple IHMEG units in serial, parallel fashion or combinations according to operating requirements. With the progress in spontaneous energy generation from ubiquitous moisture, the IHMEG device shows great potential to develop versatile, efficient, scalable and green power sources for self-powered IoT and wearable electronics systems.

The research entitled “Ionic Hydrogel for Efficient and Scalable Moisture-Electric Generation” was published in Advanced Materials 2022, 34. The first author is a PhD graduate, Dr Su Yang.