Energy Conversion from Flowing Salinity Gradients over Nanoscale Metal Layers
Abstract
A recently discovered stable all-inorganic single-element nanostructure synthesized in a single step converts gravitational energy to electrical energy when solutions of alternating salinity gradients flow along its surface. This project attempts to carry out a mechanism-guided joint experimental and computational investigation into how this newly identified nanostructure operates, what its limits are, and how to overcome these limits. Current approaches for electric power generation from nanoscale conducting or semi-conducting layers in contact with moving aqueous droplets are promising as they show efficiencies of around 30%, yet they pose challenges regarding fabrication and scaling. Indeed, there has been no single-step synthesis approach for preparing energy transducers that is also feasible for covering large (m2) areas until now. Moreover, use of aqueous droplets pose performance limitations due to drop size (surface tension of water) and drop speed (terminal velocity on earth). The proposed concept differs in several crucial aspects from recent demonstrations of flow-induced power generation that are based on low-bandgap dielectric-semiconductor architectures. First, the starting materials, a suitable support and a standard-purity metal source (Fe, Al, Cr etc), are inexpensive, costing ~$1 to $2 g-1. Second, the metal nanofilm is formed on a given support in a single step using electron beam physical vapor deposition. Third, the amphoteric oxide nano-overlayer needed for establishing the EDL forms spontaneously and then self-terminates after ~3 to ~5 nm upon exposure to ambient air, depending on the thickness of the underlying metal nanofilm. Fourth, the high purity of the metal nanofilm prevents further growth of the oxide nano-overlayer, resulting in a stable structure. Fifth, the thickness of the metal film is comparable to the mean free path of the electrons in it, engendering hardness to it depending the metal used as well as a propensity for charge motion parallel to as opposed to away from the interface. Overcoming the challenges of fabrication (multi- to single-step synthesis) and scaling (cm2 to m2) opens opportunities for kinetic to electrical energy conversion in coastal areas, estuaries, near bodies of moving water, or energy recovery from large pumping stations near urban discharge facilities, desalination stations, or enhanced oil recovery operations. The proposed work also opens the possibility to run the device Ôin reverseÕ for silent propulsion or pumps without moving parts. There are two challenges: the first is to prepare and evaluate, at reasonable speed, a number of nanoarchitectures to pursue an exploratory investigation into the principles and limits of operation. The second is to pursue experiments aimed at elucidating the dynamics and the mechanism of operation so as to further extend the limits of operation and performance inside continuous liquid flow cells. There is currently no known approach to energy conversion using all-inorganic structures synthesized in a single step except for the one presented here. As such, the work is entirely novel and unique. The results presented herein have also been disclosed to the USPTO (Application #62732822, filed on 18 September 2018) while the electron-beam physical vapor deposition (PVD) methods for making high purity metal layers, including iron layers, are described in GeigerÕs U.S. patent number 9,738,966, which issued on 22 August 2017.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jun 10, 2019
- Source ID
- W911NF1910361
Entities
People
- Franz M Geiger
Organizations
- Army Contracting Command
- Defense Advanced Research Projects Agency
- Northwestern University