Unexpected energy storage capability where water meets metal surfaces
Date:
January 19, 2022
Source:
Ruhr-University Bochum
Summary:
Researchers have used current and voltage measurements on individual
nanoparticles to determine that the capacitively stored charge at
platinum interfaces can be significantly higher than previously
assumed.
They attribute this to a special arrangement and bonding of water
molecules.
FULL STORY ========================================================================== Although interfaces between metals and water are the local areas where
crucial processes of energy technologies such as water splitting occur, comparably little is known about their structure and changes during such processes. For more than 100 years, the scientific description of such interfaces has been based on the model of the so-called electrochemical
double layer. It states that charge carriers in an aqueous solution are increasingly arranged in the boundary region to the metal, to compensate
for excess electrical charges on the metal side. In the process, the
opposing charges are separated by water molecules. Similar to a standard
plate capacitor, this nanoscopic charge separation in the interface
allows energy to be stored and released later.
Processes in which the molecular structure of the electrochemical
double layer changes are relevant to many green technologies, such as supercapacitors and fuel cells.
========================================================================== Thousands of times smaller than the diameter of a human hair
Nanoparticles, which are thousands of times smaller than the diameter
of a human hair, are investigated for such technical applications. Due
to their advantageous ratio of process-relevant surface area to
volume, they offer particularly good conditions for this. "In order
to track down the capacitance and the rearrangement processes in the electrochemical double layer on platinum and gold nanoparticles, it was
crucial to develop a method with which precise discharge currents can
be measured on individual nanoparticles in solution," reports Kristina Tschulik. Otherwise, it would not be possible to distinguish effects
related to the electrochemical double layer from effects caused by the interaction of neighbouring nanoparticles, since billions of them are
present on a conventional electrode.
The Iranian scientist Dr. Mahnaz Azimzadeh Sani, who was funded by
the German Academic Exchange Service (DAAD), used so-called colloidal nanoparticle dispersions. There, nanoparticles are separated from each
other and finely dispersed in aqueous solution, randomly striking a biased microelectrode every now and then. With the help of computer-aided
molecular dynamics simulations, on which researchers from the RUB
and the Universite' Paris-Saclay and Sorbonne Universite' in Paris
worked, it was possible to interpret similarities and differences in voltage-dependent measured capacitive currents of different types of nanoparticle dispersions. The measured unexpectedly high capacitances,
are attributed to the increased accumulate of dissolved ions in regions
between a compact water layer bound to platinum (and less trongl to gold)
and an adjacent water layer of a different arrangement. "Furthermore,
water molecules are detached from the metal surface when more negative
voltage is applied" explains Dr. Julia Linnemann, team leader at
Tschulik's chair. In the future, the RUB scientists want to find
out whether and why the double layer structure is different on large
electrodes consisting of many nanoparticles, in order to make the findings utilizable for commercial applications.
========================================================================== Story Source: Materials provided by Ruhr-University_Bochum. Original
written by Yvonne Kasper. Note: Content may be edited for style and
length.
========================================================================== Journal Reference:
1. Mahnaz Azimzadeh Sani, Nicholas G. Pavlopoulos, Simone Pezzotti,
Alessandra Serva, Paolo Cignoni, Julia Linnemann, Mathieu Salanne,
Marie‐Pierre Gaigeot, Kristina Tschulik. Unexpectedly
High Capacitance of the Metal Nanoparticle/Water Interface:
Molecular‐Level Insights into the Electrical Double Layer.
Angewandte Chemie International Edition, 2021; 61 (5) DOI: 10.1002/
anie.202112679 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/01/220119121400.htm
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