Generating electricity by moving a droplet of ionic liquid along graphene

Abstract

Since the early nineteenth century, it has been known that an electric potential can be generated by driving an ionic liquid through fine channels or holes under a pressure gradient. More recently, it has been reported that carbon nanotubes can generate a voltage when immersed in flowing liquids, but the exact origin of these observations is unclear, and generating electricity without a pressure gradient remains a challenge. Here, we show that a voltage of a few millivolts can be produced by moving a droplet of sea water or ionic solution over a strip of monolayer graphene under ambient conditions. Through experiments and density functional theory calculations, we find that a pseudocapacitor is formed at the droplet/graphene interface, which is driven forward by the moving droplet, charging and discharging at the front and rear of the droplet. This gives rise to an electric potential that is proportional to the velocity and number of droplets. The potential is also found to be dependent on the concentration and ionic species of the droplet, and decreases sharply with an increasing number of graphene layers. We illustrate the potential of this electrokinetic phenomenon by using it to create a handwriting sensor and an energy-harvesting device.

Friction of low-dimensional nanomaterial systems

“…This result was attributed to the absence of molecular reorientation on graphene with a chemically homogenous surface. Recently, Yin et al showed that the droplets of ionic liquid can easily slide on a graphene surface [86] and, in a much more interesting result, they found that the movement of the liquid−solid−gas three-phase boundary on a graphene surface can generate electricity [86,87]. All these results suggest that graphene is a promising material to construct efficient and intelligent channels for liquid flow.…”

Tuning dissociation using isoelectronically doped graphene and hexagonal boron nitride: Water and other small molecules

“…Properties of graphene and h-BN manifest themselves in various important applications such as desalination, 1 water purification, 2 energy storage, 3 energy generation, [4][5][6][7][8] and catalysis. [9][10][11] For example, sizeable voltages have been measured from forming water salinity gradients across graphene sheets and nanotubes, [4][5][6][7] and Siria et al demonstrated that water flowing osmotically through a BN nanotube produces remarkably large electric currents. 8 This was attributed to the possible dissociation and adsorption of water on the interior of the nanotube which influences the dynamics inside the nanotube.…”

Resistance switching of epitaxial VO2/Al2O3 heterostructure at room temperature induced by organic liquids

“…However, it is often difficult to achieve such high electric fields by conventional dielectric gates. 1,2 Recently, extra-high electric fields are achieved by approaches such as Schottky junctions, 3,4 polar adsorbates 5,6 or ionic liquids [7][8][9][10][11][12] as dielectric gates in field-effect transistor devices. 13,14 For example, Xu et al 15 studied the modulation of grain boundary barriers in ZnMgO/ZnO/sapphire heterostructure by DI water and they found that the electronic conduction property of ZnO layer far beneath the surface could be switched from Ohmic to Schottky junction.…”