Energy Conversion via Metal Nanolayers

TL;DR

This paper introduces stable, all-inorganic metal nanolayers that efficiently generate electricity from flowing liquids and salinity gradients, overcoming fabrication challenges of previous nanoscale power sources.

Contribution

It presents a novel single-step synthesis of metal nanolayers that produce electrical current through charge-carrier motion influenced by spontaneous oxide layers.

Findings

Nanolayers of Fe, V, Ni generate tens of mV and microA/cm^2.

Performance depends on intra-oxide electron transfer and oxidation states.

Effective in various liquid motion modes, including sliding droplets and salinity gradients.

Abstract

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 percent, 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. 10 nm to 30 nm thin nanolayers of iron, vanadium, or nickel produce several tens of mV and 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 nano-overlayer that forms spontaneously in air and then self terminates. Indeed, experiments suggest a role for intra-oxide 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.