Harvesting green energy from ubiquitous moisture is attracting growing interest in directly powering wearables and portable electronics. However, it is still challenging to fabricate high-performing moisture-electric generators (MEG) with high and stable output.
An Australian company, Strategic Element, has collaborated with the University of New South Wales and CSIRO to develop a flexible, self-charging battery technology that harvests electricity from humidity in the air or skin surface to self-charge itself within a minute. These batteries can directly be used to power electronics and Internet of Things (IoT) devices.
This technology has the potential to enable batteries to self-charge from the moisture in the air, potentially removing the need for manual charging or wired power. The expected outcomes of the project are new electronic materials for a wide range of uses in flexible electronics and significant advances in energy-efficient data storage devices.
Currently, most high-performing MEGs are fabricated with carbon-based materials, which are environment-friendly and abundant on earth, including carbon nanotubes, carbon nanoparticles, and graphene oxide. Among them, graphene oxide exhibits the most promising potential in achieving high electric generation because of its high specific surface area, good mechanical properties, and excellent moisture absorption.
Benefitting from exceptional physicochemical properties, graphene-based materials are able to harvest energy from external factors such as moisture and heat. Graphene oxide is formed by the oxidation of graphite which is cheap and readily available.
For their study, researchers used porous graphene oxide treated with hydrochloric acid for fabricating MEGs, which exhibited great moisture absorption ability. The resulting MEG enables a stable voltage of 0.85 V and a current of 9.28 μA (92.8 μA per square centimeter), which is “amongst the highest values reported so far.” More interestingly, the electric output gets further improved by simply assembling four MEG units in series or parallel.
To test its flexibility, the team fabricated a battery on a piece of carbon cloth, then bent it from 0° to 120° over one second period. The flexible MEG remained 93% of the maximum voltage it started out with after 2000 times bending, which shows great potential in flexible and wearable applications.
Further development challenges include battery cell size whilst increasing current output at lower humidity levels and demonstrator device development.