Transpiration Driven Electrokinetic Power Generator

Abstract

Transpiration is the process by which water is carried in plants from the roots to the leaves where evaporation takes place. Here, we report a transpiration driven electrokinetic power generator (TEPG) that exploits capillary flow of water in an asymmetrically wetted cotton fabric coated with carbon black. Accumulation of protons induced by the electrical double layer formed at the solid (carbon black)/liquid (water) interface gives rise to potential difference between the wet and dry sides. The conductive carbon black coating channels electrical current driven by the pseudostreaming mechanism. A TEPG of 90 mm × 30 mm × 0.12 mm yields a maximum voltage of 0.53 V, maximum current of 3.91 μA, and maximum energy density of 1.14 mWh cm–3, depending on the loading of the carbon black. Multiple TEPGs generate enough power to light up a light-emitting diode (20 mA × 2.2 V) or charge a 1 F supercapacitor.

Self-operating transpiration-driven electrokinetic power generator with an artificial hydrological cycle

“…S4, ESI †). 11 The fully wetted STEPG, however, interestingly generates V OC and I SC . The vertical setup limits the diffusion of calcium chloride to the positive (upper) electrode by gravity, so the solutions near the positive electrode and negative (lower) electrode have different CaCl 2 contents.…”

“…This result shows that the origins of the voltage and current generation are distinct for TEPGs. 11 With a high concentration of CaCl 2 , the wet region collects more water to facilitate capillary flow and generate a higher current based on pseudostreaming theory. In addition to the enhanced capillary flow, the internal resistance of the device also affects the I SC value, which will be discussed later along with Fig.…”

“…S5, S6 and Table S2, ESI †). 11 To verify the origin of the enhanced V OC with Ca 2+ ions, we calculated the surface charge density in the double layer caused by adsorption of water molecules and water molecules with Ca 2+ ions on oxygen-functionalized graphene by DFT calculation (details in the Experimental section). When oxygen-functionalized graphene is covered only by water, a double layer forms at the water/ graphene interface with a surface charge density of 0.0195 e Å À2 on the graphene layer ( Fig.…”

“…9,10 A transpiration-driven electrokinetic power generator (TEPG) is a good example of adopting the process of transpiration in plants to build a water-based energy harvester. 11 In nature, plants uptake essential nutrients through the transpiration process, which drives water from the roots and leaves (Fig. 1a).…”

“…1a). 11 At the interface between wet and dry carbon, the water content gradient drives continuous capillary flow of water from the wet to dry side. This capillary action on the conductive carbon surface induces a unique electrokinetic charge transfer through the carbon networks, called a pseudostreaming current (Fig.…”