Paper-Based Electrokinetic Power Generator

Wearable devices integrated with microprocessors and multifunctional sensors are gaining momentum in a variety of industries over the past decade. Such advancements significantly exceed the development pace of portable power sources. Most batteries, besides pausing serious sanitary and environmental concerns, are unfit for wearable devices, which require flexible, lightweight, reliable, and long-lasting systems with power densities of at least several tens W/kg. The autonomous scavenging of energy from the ambient environment offers a sustainable solution to power wearable sensors over long periods without the need to recharge. Nanogenerators (NG), such as triboelectric, piezoelectric, and thermoelectric generators, have been developed to harvest renewable energy from ambient sources that can be used to power portable electronics. Among them, moisture enabled generators or MEGs are a class of NG that generate electricity from moisture transport mechanisms, giving them a great advantage as water is inherently present in the air everywhere in the world. MEGs are typically made up of conductive materials that form an electric double layer when contacted by water. As water molecules move through a porous material, viscous shear forces create a charge gradient causing a potential difference and inducing current. Inspired by the Earth’s hydrological cycle, transpiration driven electrokinetic power generators (TEPGs) take advantage of transpiration forces using asymmetric wetting mechanisms to increase fluid transport without the need for flowing bodies of liquid water. The present research leverages the biodegrable nature, flexibility, and light weight of lignocellulosic paper and combines them with the excellent properties of carbon nanotubes to prepare electrically-conductive capillary pumps. This innovative papertronics is cost-effective, recyclable, and can be manufactured using easily scalable papermaking processes. As-produced TEPG materials were thoroughly characterized and achieved a sustained open circuit voltage and short circuit current of 225 mV and 7 μA, respectively, from the transport of a 10 µL aqueous aluminum sulfate solution. The power output was improved further by using an optimized active electrode design, yielding OCV and SCC values over 1 V and 3 mA, respectively. A single device exhibited an impressive maximum power density of 50 W/kg, which when connected in series and parallel, could supply power for some common electronic systems.