title: Harvesting energy from water flow over graphene?
abstract: It is reported excitingly in a previous letter (Nano Lett. 2011, 11, 3123) that a small piece of graphene sheet about 30 × 16 μm(2) immersed in flowing water with 0.6 M hydrochloric acid can produce voltage ~20 mV. Here we find that no measurable voltage can be induced by the flow over mono-, bi- and trilayered graphene samples of ~1 × 1.5 cm(2) in size in the same solution once the electrodes on graphene are isolated from interacting with the solution, mainly because the H(3)O(+) cations in the water adsorb onto graphene by strong covalent bonds as revealed by our first-principles calculations. When both the graphene and its metal electrodes are exposed to the solution as in the previous work, water flow over the graphene-electrode system can induce voltages from a few to over a hundred millivolts. In this situation, the graphene mainly behaves as a load connecting between the electrodes. Therefore, the harvested energy is not from the immersed carbon nanomaterials themselves in ionic water flow but dominated by the exposed electrodes.
authors.affiliation: State Key Laboratory of Mechanics and Control of Mechanical Structures, and Institute of Nanoscience, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Yin
authors.forename: Zhuhua
authors.initials: Z
authors.lastname: Zhang
authors.forename: Xuemei
authors.initials: X
authors.lastname: Li
authors.forename: Jianxin
authors.initials: J
authors.lastname: Zhou
authors.forename: Wanlin
authors.initials: W
authors.lastname: Guo
mesh_terms: D011211:Electric Power Supplies; D004574:Electromagnetic Fields; D004735:Energy Transfer; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006108:Graphite / Q000737:chemistry*; D008422:Materials Testing; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D012212:Rheology / Q000379:methods*; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D006108:Graphite