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Nanosecond and microsecond-pulsed plasma-in-liquid treated copper oxide surfaces (2025 J. Phys. D: Appl. Phys. 58 305201)

Plasma in Liquids

Nanosecond and microsecond plasma-in liquid systems are explored to oxidize or regenerate a copper oxide surface in situ to serve as a catalyst for electrochemical CO2 conversion. The plasma excitation generates H2O2 in the liquid, which induces the dissolution of Cu into Cu(OH)2 and the recrystallization into Cu2O nanocubes at the interface. The plasma performance of the two excitation schemes is analyzed, showing that the H2O2 production of nanosecond plasma is more efficient than of microsecond plasmas. The nature of the Cu2O nanocubes is evaluated using electron microscopy and electrochemical characterization.

In-Liquid Plasma
FieldValue
Authors
P. Pottkämper
N. Unteregge
S. Weller
A. von Keudell
Release Date
2025-09-05
Identifier
38d88cf1-8355-4d37-972c-fee84c8ef29c
Permanent Identifier (URI)
https://rdpcidat.rub.de/node/1235
Is supplementing
J. Phys. D: Appl. Phys. 58 305201
Plasma Source Name
In-Liquid Plasma Cell
Plasma Source Application
Liquid Treatment
Surface Treatment
Plasma Source Specification
Pin-to-Pin
ns pulsed
us pulsed
high voltage
Plasma Source Properties
two different setups were used in this work: one in liquid system that can apply voltage pulses in the microsecond range an done in the nanosecond range. The reactor setup is the same in both cases: 25ml liquid volume, pin-to-pin electrodes made from 50 um tungsten wire, voltage between 16-24 kV, frequency between 1-100 Hz. The nanosecond pulse has a length of 12 ns with a rise time of 2-3 ns and the microsecond pulse has a length of 100 us and a rise time of 0.5 us.
Language
English (United Kingdom)
Plasma Source Procedure
Electrodes are prepared by inserting 50 um tungsten wire into stainless steel cannulas then the cannula is inserted into the electrode socket. Electrodes are replaced as needed. Next the reactor is filled with liquid (25ml volume). The liquids are stored at room temperature and therefore the measurements / liquid treatments are started at room temperature. After filling the reactor the top valve of the reactor is left open for pressure release. Then the Faraday cage is closed over plasma reactor to minimize the electrical noise. Then the power supply and function generator are swiched on and the desired frequency and voltage are set as needed. Lastly the plasma is switched on and operated for the desired time. After the plasma operation, the power supply is swiched off, the Faraday cage removed and the liquid drained from the reactor. When an electrolyte is used, the reactor is flushed with distilled water to remove residual electrolyte.
License
Creative Commons Attribution
Plasma Medium Name
distilled water
KOH solution
Plasma Medium Properties
two liquid mediums were used and compared: distilled water and a KOH electrolyte. The dist. water has a conductivity of 2 uS/cm, the electrolyte made of 0.05 mM KOH a conductivity of 6 uS/cm. The reactor can contain a volume of 25 ml of liquid and the reactor is filled completely for the experiment.
Plasma Medium Procedure
First the plasma cell is rinsed with dist. water before use. Then the desired liquid is inserted into the reactor. The distilled water is inserted into a wash bottle, which is then used to fill the chamber. The electrolyte is prepared in a concentrations of 0.05 mM and inserted via a single-use plastic pipette. The reactor os always filled from the top valve. The two bottom valves are kept closed and side valve is kept open to release the air in the reactor. After filling theside valve is also closed and the top valve is left open for pressure release.
Plasma Target Name
copper
Contact Name
Pottkaemper, Pia-Victoria
Plasma Target Properties
The samples consist of a layer of copper on a silicon oxide wafer. The copper samples are prepared in a HiPIMS coating process to the desired layer thickness 50 nm in this work. They are about 2 x 3 cm in size, however the size can vary by a few mm and does not need to be exact. The samples consist of copper and copper oxide since they oxidize in ambient air.
Plasma Target Procedure
The silicon oxide wafers are first cut to size and then inserted into the HiPIMS reactor, coated with the copper and then extracted. When the samples come into contact with ambint air, which is inevitable, an oxide layer forms. The samples therefore consist of copper and copper oxide. The copper samples are then treated with the plasma activated liquid. This is done by dropcasting liquid onto the copper. The reaction between the liquid and the samples takes place over multiple hours. Since the oxide crystals are sensitive the samples are carefully transport to the diagnostic setups.
Contact Email
pia-victoria.pottkaemper@ruhr-uni-bochum.de
Plasma Diagnostic Properties
The plasmas are investigated by voltage and current measurements. An Oscilloscope by Teledyne LeCroy GmbH model HD6104A is used for this. In case of the nanosecond plasma the voltage measurements are performed indirectly via Back Current Shunt built in the power cable. The voltage and current of the microsecond plasma were measured directly via probes. The Cyclic Voltammetry is perforemd on the copper samples using a Potentiostat by Biologic. The teflon cell is cleaned with ultrapure water and the sample is carefully installed to the bottom of the cell. Then the electrolyte is inseted into the cell (0.01 M KOH & 0.1 M K2SO4). A gas inlet is inserted into the liquid and the electrolyte is degased for 20 min with a low flow of argon. Then the gas inlet is removed and the electrodes are inserted into the cell. The sample is functioning as the driven electrode and a clamp is applied to it. During the electrochemical measurement an OCV, CV, EIS then OCV and CV measurement is performed in this order. After the measurement, the electrodes are extracted, the electrolyte is discarded and the cell is rinsed with ultrapure water. The SEM images were taken using an SEM by Jeol model JSM-7200F. The measurements performed at the Center for Interface-Dominated High Performance Materials (ZGH) at Ruhr-Univerity Bochum. The hydrogen peroxide concentrations on the liquid is measured by photometric spectroscopy using an essay kit by Merck model 118789 (Spectroquant). The assay is sensitive in the range of 0.015 to 6.00 mg/l H2O2. In this process, the PAL is diluted with distilled water in ratio 1/9 and then thoroughly mixed with the two phases of the assay anf then measured with the commercial photometer. The concentrations are calculated using a calibration curve determined from solutions with known H2O2 concentrations prepared by the same method. The conductivity and temperature of the liquids are measured by a thermocouple and conductivity meter by Greisinger model GLF100. The devide is rinsed with distilled water before use and then inseted into the liquid. It is then rinsed again.
Public Access Level
Public
Plasma Diagnostic Name
SEM
Cyclic Voltammetry
Funding Agency
German Science Foundation (DFG)
Project
SFB 1316
Subproject
B7

Data and Resources

Pia-Victoria Pottkämper