Harvesting Energy From Water Flow Over Graphene

LETTER pubs.acs.org/NanoLett

Harvesting Energy from Water Flow over Graphene
Prashant Dhiman,†,|| Fazel Yavari,†,|| Xi Mi,‡ Hemtej Gullapalli,§ Yunfeng Shi,‡ Pulickel M. Ajayan,§ and NikhilKoratkar*,†,‡
†

Department of Mechanical, Aerospace, and Nuclear Engineering, ‡Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180, United States §Department of Mechanical and Materials Engineering, Rice University, Houston, Texas, United States
S b Supporting Information

ABSTRACT: Water flow over carbon nanotubes has been shown to generate aninduced voltage in the flow direction due to coupling of ions present in water with free charge carriers in the nanotubes. However, the induced voltages are typically of the order of a few millivolts,too small for significant power generation. Here we perform tests involving water flow with various molarities of hydrochloric acid (HCl) over few-layered graphene and report order of magnitude higherinduced voltages for graphene as compared to nanotubes. The power generated by the flow of ∼0.6 M HCl solution at ∼0.01 m/sec was measured to be ∼85 nW for a ∼30 Â 16 μm size graphene film, whichequates to a power per unit area of ∼175 W/m2. Molecular dynamics simulations indicate that the power generation is primarily caused by a net drift velocity of adsorbed ClÀ ions on the continuous graphenefilm surface. KEYWORDS: Graphene, energy harvesting, water flow, surface ion hopping ver the past decade a number of theoretical1À3 and experimental studies4À7 have demonstrated that flow of water or otherpolar liquids over one-dimensional structures such as carbon nanotubes generates a net potential difference and associated electric current in the nanotubes along the flow direction. A number ofmechanisms such as phonon drag (transfer of momentum from the flowing liquid to the acoustic phonons in the nanotube, which in turn drags free charge carriers in the nanotube),1 surface ion hopping,3...