Energy from the Nanofluidic Transport of Water through Nanochannels between Packed Silica Spheres

Abstract

Efficient harvesting of electrokinetic-streaming-potential requires a trade-off between high flow-rate and nanofluidic confinement. To attain the best out of these parameters, we have developed a periodic network of tetrahedral and octahedral voids interconnected through fine biconical nanofluidic channels by close-packing nearly monodisperse silica spheres of diameters 285, 620, 1000, 1750, and 2900 nm. The interstices of closepacked silica spheres (diameter 285 to 1750 nm) simultaneously exhibit surface-charge-governed ionic conductivity and fast flow of water. The power density harvested from streaming water was found to be increasing with increased diameter of the close-packed spheres up to 1750 nm (151 mWm −2 ), and to be decreasing with further rise in the sphere diameter. The power density was found to be dependent on the mass loading of the silica spheres, contact area of the electrodes, and pH of the streaming water. Pretreatment of the silica spheres with concentrated nitric acid further enhanced the efficiency of the energy harvesting through streaming potential. Harvesting of streaming potential from packed silica spheres was found to be a convenient way of obtaining energy from water flowing through the household water taps, as they can be connected in a series to add up energy generated in multiple devices.

Rational Design of MOF‐Based Hybrid Nanomaterials for Directly Harvesting Electric Energy from Water Evaporation

“…[ 6,14,17–20 ] It has been proposed that when water molecules are pressurized through narrow capillary channels formed by materials with charged surface, the counterions with the opposite charges within the electrical double layer (EDL) inside the capillary channels can collectively move along with the water molecules, leading to the generation of the electric potential and current. [ 18–20 ] Based on this mechanism, the material suitable for this novel energy‐harvesting process has two important characteristics. First, capillary channels can be formed by the material, and thus water molecules can move in the channels driven by the evaporation process.…”

Water‐Enabled Electricity Generation: A Perspective

“…Because carbon‐based materials have a high conversion efficiency, they account for the majority of the active materials used in water‐enabled electricity generation systems, with the focus being on graphene‐based materials, [ 15,22,24,36–39,44–46,48,55,66,68–81 ] CNPs and carbon nanofibers (CNFs), [ 13,14,16,25,53,64,67,82–91 ] polymers, [ 23,31,38,66,83,89,92–99 ] and biomaterials. [ 26,30,69,74,90,91,100–102 ] Solid oxide materials [ 10,12,13,19,20,54,64,103–106 ] are also favored as they are easily fabricated into an active layer and are stable even in harsh environments. Some other materials suitable for applications in WEEGs include Mg, [ 14,40 ] Si, [ 68,107 ] Ni‐Al, [ 65 ] Cu‐Zn [ 108 ] MoS 2 , [ 27 ] and glass fibers.…”

“…a) Distribution of materials used in applications. [ 10,12–16,19,20,22–27,30,31,33–40,44–48,53–55,64–80,82–108,117–123 ] b) Output voltage and power density for different materials. c) The output voltage and d) averaged voltage of single and integrated devices.…”

“…[ 114 ] While films consisting of TiO 2 nanostructures were the first metal oxide compositions developed for applications in WEEGs, [ 10 ] silica has also been used as an active material for harvesting energy. [ 54,105 ] An extensive‐network structure with many interconnected nanochannels is obtained with these materials. The surface of these nanochannels develops a negative surface charge when exposed to moisture.…”

“…[52] From the aspect of active materials, both the streaming current and the streaming potential can be optimized by tuning the zeta potential and the pressure difference applied along the channel. [53,54] The streaming current can also be enhanced with a larger contact area and smaller pore length. A high voltage output can be obtained with enhanced charge density, which lays the basics for performance optimization especially for water-droplet-based WEEGs.…”