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Published August 13, 2019 | Supplemental Material + Published
Journal Article Open

Energy Conversion via Metal Nanolayers


Current approaches for electric power generation from nanoscale conducting or semiconducting layers in contact with moving aqueous droplets are promising as they show efficiencies of around 30%, yet even the most successful ones pose challenges regarding fabrication and scaling. Here, we report stable, all-inorganic single-element structures synthesized in a single step that generate electrical current when alternating salinity gradients flow along its surface in a liquid flow cell. Nanolayers of iron, vanadium, or nickel, 10 to 30 nm thin, produce open-circuit potentials of several tens of millivolt and current densities of several microA cm^(−2) at aqueous flow velocities of just a few cm s^(−1). The principle of operation is strongly sensitive to charge-carrier motion in the thermal oxide nanooverlayer that forms spontaneously in air and then self-terminates. Indeed, experiments suggest a role for intraoxide electron transfer for Fe, V, and Ni nanolayers, as their thermal oxides contain several metal-oxidation states, whereas controls using Al or Cr nanolayers, which self-terminate with oxides that are redox inactive under the experimental conditions, exhibit dramatically diminished performance. The nanolayers are shown to generate electrical current in various modes of application with moving liquids, including sliding liquid droplets, salinity gradients in a flowing liquid, and in the oscillatory motion of a liquid without a salinity gradient.

Additional Information

© 2019 National Academy of Sciences. Published under the PNAS license. Edited by Catherine J. Murphy, University of Illinois at Urbana–Champaign, Urbana, IL, and approved July 2, 2019 (received for review April 16, 2019). M.D.B. gratefully acknowledges support from the PPG Fellowship Program at Northwestern University. This work was supported by the NSF under its Graduate Fellowship research program award to P.E.O. We also acknowledge support from Northwestern University's Presidential Fellowship program (P.E.O.), the Center for Water Research (E.J.L.), the Undergraduate Research program (C.E.W.), and the Dow Professorship program (F.M.G.). We are thankful to Dr. Wei Huang for the assistance with the first current measurements on the Agilent B1500A. F.M.G. gratefully acknowledges support from the NSF through Award CHE-1464916 and a Friedrich Wilhelm Bessel Prize from the Alexander von Humboldt Foundation. T.F.M. acknowledges support from the Office of Naval Research under Award N00014-10-1-0884. F.M.G. and T.F.M. acknowledge support from Defense Advanced Research Projects Agency through the Army Research Office Chemical Sciences Division under Award W911NF1910361. Author contributions: M.D.B., E.H.L., J.K., P.E.O., C.E.W., T.F.M., and F.M.G. designed research; M.D.B., E.H.L., J.K., P.E.O., C.E.W., T.F.M., and F.M.G. performed research; M.D.B., E.H.L., J.K., P.E.O., C.E.W., T.F.M., and F.M.G. contributed new reagents/analytic tools; M.D.B., E.H.L., J.K., P.E.O., C.E.W., T.F.M., and F.M.G. analyzed data; and T.F.M. and F.M.G. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission. This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1906601116/-/DCSupplemental.

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