1
Modeling and Electrical Characterization of COCC/Ar Dielectric Barrier Discharges at Atmospheric Pressure Chenoui Mohamed*.
Tebani Hocine.
Benyoucef Djilali Laboratory of Electrical Engineering and Renewable Energy (LGEER).
Electrical Engineering Department.
Faculty of Technology.
Hassiba Benbouali University of Chlef.
Algeria.
E-mail : m.
chenoui@univ-chlef.
Abstract In this study, a one-dimensional fluid model is employed to analyze the electrical and physicochemical properties of dielectric barrier discharges (DBD.
in pure COCC and COCC/Ar mixtures at atmospheric pressure.
Validation against experimental data confirms the accuracy of the model, especially for discharge current characteristics, with a peak current of 2.
5 mA.
Time-resolved analysis revealed that CO and OCC represent the major species formed during COCC splitting, while O.
OCE, and minor carbon-based species appear at lower concentrations.
Charged species such as COCCA and COCEA were found to play a critical role in plasma kinetics, strongly correlating with current pulses during breakdown events.
Parametric studies highlighted the influence of argon fraction, frequency, voltage, and pressure on discharge Optimal CO production was obtained in COCC/Ar mixtures with 75Ae90% Ar, at intermediate frequencies 3 kHz, moderate pressures 760 Torr, and applied voltages up to 9 kV.
These findings provide valuable insights into plasma-assisted COCC conversion, emphasizing the importance of discharge conditions in enhancing efficiency and guiding the design of DBD reactors for sustainable carbon utilization.
Keywords:
Dielectric barrier discharge.
One-dimensional fluid model.
Discharge current CO2 conversion Introduction The significant rise in the concentration of carbon dioxide (COCC) in the atmosphere, driven primarily by fossil fuel combustion and industrial activity, is a primary cause of climate change and global warming .
Ae.
The mitigation of COCC emissions and its conversion into value-added products has, therefore, become a critical research Conventional thermochemical and catalytic approaches often require high temperatures, pressures, or costly materials, which limit their scalability and economic viability .
In this context, plasma-based technologies have emerged as attractive alternatives, offering the unique advantage of operating under mild conditions while efficiently producing reactive species that activate COCC molecules .
Ae Among plasma methods, dielectric barrier discharges (DBD.
have attracted particular attention due to their simple configuration, scalability to large surface areas, and ability to generate non-equilibrium plasmas at atmospheric pressure .
Ae In a DBD, the application of an alternating or pulsed high voltage across dielectric-covered electrodes produces numerous transient microdischarges.
These discharges accelerate electrons to energies sufficient to excite, ionize, and dissociate COCC molecules, driving both vibrational and electronic excitation pathways .
However, the efficiency of pure COCC splitting remains low because of its high vibrational energy thresholds and rapid deactivation through vibrationalAe translational (VAeT) relaxation processes .
To overcome these limitations, researchers have explored the addition of inert gases, particularly noble gases such as argon (A.
, into COCC discharges .
Ae.
admixture modifies the discharge dynamics by lowering the breakdown voltage, increasing plasma stability, and enhancing electron density through Penning ionization and energy-transfer collisions .
These effects broaden the electron energy distribution function (EEDF), increasing the probability of inelastic electronAe COCC collisions that lead to vibrational excitation and eventual dissociation .
conversion and energy efficiency under optimized conditions, although the precise mechanisms remain the subject of ongoing investigation .
Ae.
Experimental and modeling studies have demonstrated that Ar can improve COCC Recent numerical modeling efforts have provided valuable insights into the spatiotemporal evolution of species in DBD plasmas .
Ae.
Time-dependent one- dimensional .
D) fluid models, in particular, allow detailed tracking of electron density, ion kinetics, and neutral product formation under varying discharge These models complement experimental diagnostics by revealing microscopic discharge features that are otherwise difficult to capture, such as microdischarge lifetimes, electron heating mechanisms, and local field variations .
This study utilizes a time-resolved one-dimensional fluid approach model to examine the influence of argon addition on the plasma characteristics of carbon dioxide discharges at atmospheric pressure.
The model provides a systematic investigation of the temporal evolution of electron density, discharge current, and species concentrations in relation to temporal evolution and discharge spacing.
Special attention is given to the impact of Ar on CO production, as this represents the main target product of plasma-assisted COCC splitting.
The results are discussed in the context of existing experimental studies, providing deeper insight into how the operating parameters and gas composition can be tuned to improve efficiency.
Ultimately, the objective of this work is to advance the fundamental understanding of COCC plasma chemistry and to support the development of optimized plasma-based COCC conversion technologies.
Materials and Methods 1 Plasma Modeling Approach The geometry was developed using a one-dimensional approach following the framework described in Ref.
, as shown in Figure 1.
The applied one-dimensional representation is further illustrated .
2 Model Equations The dielectric barrier discharge model is governed by a set of coupled equations that describe the behavior of electrons, non-electron species, and the electrostatic field Electrons, ground state atoms, ions, and excited atoms are the particles that are considered in this simulation.
The numerical simulation is founded on a one- Boltzmann equation in combination with PoissonAos equation.
dimensional fluid model, constructed by solving the first two moments of the Figure 1.
Schematic of the DBD setup and One-dimensional geometry applied in the simulation.
The behavior of discharge plasma is determined by:
1 Electron transport equations A pair of driftAediffusion equations is solved to determine the electron density ne and mean electron energy nAu , assuming that convection effects from fluid motion are negligible e EcA[Oen A E Oe D Ecn ] = R Au EcA[Oen A E Oe D Ecn ] EAAN = R Au Au Au Au Where ( R )is the electron source and ( R )is the energy loss due to inelastic Au The electron diffusivity ( D ), energy mobility ( A ), and energy diffusivity Au ( D ) are computed from the electron mobility ( A ) using the following relations Au De = AeTe .
AAu = ( ) Ae .
DAu = AAu Te 2 Source coefficients The source coefficients are determined by the plasma chemistry using rate The electron source term ( R ) is determined by R = Eu x k N n AEAu Au i i n e i i =1 .
With ( AEAu ) indicates the energy loss from reaction .
The rate coefficients are evaluated from cross-section data available on the LXCAT database using the following integral expression.
k = A E0Cu AuA (Au ) f (Au )d Au cross section .
2 ) with A = mass ( K.
3 Electrostatic field With q represents the electron charge .
), and ( me ) corresponds to the electron Where ( f ) the electron energy distribution function (EEDF) and ( A ) collision OeEcAAu Au r Ecv = A .
A represents the charge density, which is the amount of electric charge per unit volume in a given space.
represent permittivity of free space and Au r permittivity of material dielectric E N .
A = q E Eu Z k nk Oe ne E E k =1 4 Non-electron species transport is the electric charge, q is the absolute value of electronic charge.
The evolution of the mass fraction ( ) for all non-electron species is obtained by solving the following equation.
k Ec E ( AA w ) Ec E j = R where w is the mass fraction for species k, j is the diffusive flux vector for species k, and R is the rate expression for species k.
5 Boundary conditions The electron flux to the electrodes and all reactor walls Oen.
ANe = Ve,th ne Oe Eu A p (AN p .
A p denotes the secondary electron emission coefficient, while n represents the unit normal vector to the wall.
The electron thermal velocity.
Ve,th , is expressed as:
Ve,th = .
6 Electric potential The driven electrode receives an electric potential .
V = V sin.
A .
K .
B e A .
7 Ion mobilities The standard formula for calculating ion mobility using polarizability is based on the Langevin polarization capture theory .
K = 13.
A CA
Where K ion mobility .
m2/V.
and polarizability of neutral gas .
reduced mass of the ion-neutral pair .
A A = 1 2
Amix A1 A2 A1 and A 2 represent the molar fractions of gases 1 and 2, while A1 and A2 denote their respective ion mobilities.
M ion C M neutral M ion M neutral 3 plasma chemistry The plasma chemistry implemented in the model comprising a detailed set of 108 reactions involving 19 species presented in Table 1 accounts for the key electronAe molecule, ionAemolecule, and neutralAeneutral processes governing COCC conversion in ionization, excitation, and dissociation of COCC and Ar are included presented in Table 2, as they provide the primary pathway for generating reactive species.
dielectric barrier discharges.
In particular, electron impact reactions such as Table 1.
Species in CO2/Ar model
Neutral
CO ,C2O
Negative ions CO2.
O2.
O3, eA.
OA.
O2A .
O3A
CO3A .
CO4A
Positive ions .
CO2 .
O .
Ar .
Ar2 Exited space O2 .
Ars Table 2.
Reactions explored in the model and their rate coefficients in .
for three-body and tow-body respectively.
CO2(X,v=1-.
refers to the first 16 vibrationally excited states of CO2.
Reaction Reaction rate References eA COCC Ie CO OA Cross section eA COCC IeeA COCC(X,v=1-.
Cross section
eA COCC Ie 2eA CO2A
Cross section
eA COCC Ie eA CO O
Cross section
eA CO Ie eA CO
Cross section
eA OCE Ie eA O3
Cross section
eA OCC Ie eA O2
Cross section
eA O Ie eA O
Cross section
eA Ar Ie Ar eA
Cross section
X10
eA Ar Ie Ars eA
Cross section
X11
eA Ar Ie ArA 2eA
Cross section
X12
eA Ars Ie ArA 2eA
Cross section
X13
eA Ars Ie Ar eA Cross section Elastic and ionization electron-impact reactions .
ElectronAeatom or molecule interactions eA Ar ArA Ie Ar Ar eA COCCA Ie CO O 0y10-11/(OoTeyT.
eA COCCA Ie C O2 94y10-13yTe-0.
eA OCC Ie 2eA O2 Ion-ion and ion-neutral reactions Ars Ar Ie Ar Ar Ars Ars Ie eA Ar Ar 625y10-16/OoTg .
2Ar Ar Ie Ar2 Ar Ar2 Ar Ie Ar 2Ar Ar CO2 Ie Ar CO2 Ar CO2 Ie CO O Ar 27y10-44/ (Tg/.
y exp(-170/ T.
O2A Ar Ie eA O2 Ar 7y10-16 Oo(Tg/.
y exp(-5590/ T.
O2A O2 Ie O O O2
O2A CO2 Ie CO O2 O
I10
OA CO Ie CO2 e
I11
OA O2 Ie O3 e
I12
OA O3Ie O2 O2 e
I13
OA CO2 CO2Ie CO3A CO2
I14
Ar COIe CO Ar
I15
Ar OIe O Ar
I16
Ar O2Ie O2 Ar
I17
Ar2 CO2Ie CO2 2Ar
I18
Ar2 COIe CO 2Ar
I19
Ar2 O2Ie O2 2Ar
I20
O2A O2 Ie O2 O2
I21
O2A O3Ie O2 O3A
I22
O CO2 Ie O2 CO
I23
O CO2Ie CO2 O
I24
CO2 OIe O CO2
I25
CO2 O2Ie O2 CO2
I26
O3A OIe O2 O2A
I27
O2 CO3AIe CO2 O2 O
I28
CO3A OIe CO2 O2A
I29
CO3A CO2 Ie CO2 CO2 O 5.
I30
CO4A OIe CO3A O2
I31
OA O2 IeO O O
I32
CO4A OIe CO2 O2 OA
CO4A CO2 Ie 2CO2 2O2
O2 CO4AIe CO2 O2 O2
I35
OA O3Ie O O3A
I36
O2A CO2 CO2Ie CO4A CO2
I37
O2A O CO2Ie O3 CO2
I38
OA O Ie O O
I39
O CO2Ie O2 CO
I40
O CO2Ie CO2 O
I50
CO4A O3Ie CO2 O3A O2
I34
I33
I51
O2A CO2 Ie O2 CO2 e 7y10-16 Oo(Tg/.
yexp(-5590/ T.
I52
CO4A OIe CO2 O3A
I53
O3A OIe O3 OA COCC COCC Ie CO O COCC 91y10-16 exp(-49430/T.
COCC OCC Ie CO O OCC 81y10-16 exp(-49000/T.
CO2 C Ie CO CO COCC O Ie CO OCC 8y10-17 exp(-26500/T.
CO O COCC Ie COCC CO2 4y10-46 exp(-1510/T.
CO O CO Ie COCC CO 2y10-46 exp(-1510/T.
CO O O2Ie COCC O2 2y10-46 exp(-1510/T.
CO OCC Ie COCC O 2y10-18 exp(-24000/T.
O O2 OCC Ie O3 O2
N10
O O2 CO2 Ie O3 CO2
N11
O O COCC Ie OCC CO2
N12
CO Ar Ie C O Ar 52y10-10(Tg/.
1exp(-129000/T.
N13 COCC Ar Ie CO O Ar 27y10-44(Tg/.
-1 exp(-170/T.
N14 O O Ar Ie O2 Ar 39y10-13exp.
00/T.
N15 O2 O Ar Ie O3 Ar 6y10-46(Tg/.
N16
O2 C2OIeCO2 CO
N17
O C Ar Ie CO Ar 14y10-41(Tg/.
08 exp(-2114/T.
N18
COCC CO Ie CO O CO 81y10-16 exp(-49000/T.
N19
O3 O Ie O2 O2
N20
CO OCE Ie COCC OCC
O OCE Ie OCC OCC
N22
CO2 C COIeC2O CO2
N23
O C2OIeCO CO
N21
Neutral-neutral reactions .
4 Plasma electrical properties Analysis of Dielectric Barrier Discharge Behavior in Pure COCC under Atmospheric Conditions was carried out using the same experimental configuration as .
, allowing comparison and validation of the present simulation model, examined a 1D geometry made up of two parallel plates and under a wide spectrum of discharge parameters and operating environments relevant to atmospheric pressure plasmas presented in Table 3.
Table 3.
Discharge parameters considered in this study Value Maximum applied voltage 6,8,9 (K.
Frequency Resistance Pressure 2,3,4 (KH.
E) 500,760,1000 (Tor.
Discharge gap 1 .
Preionization density Thickness of dielectric Electrode area 7 .
Molar mass CO2 ,Ar respectively 04401 , 0.
04 (Kg/mo.
Polarizability CO2 ,Ar respectively 91 ,1.
Gas temperature 300 (K) Relative permittivity of dielectric Gas mixture content CO2/Ar with Ar percentage 90 , 75 ,50 ,25 ,10 (%) Results and Discussion 106 .
The spatiotemporal characteristics of DBD in pure CO2 have been numerically The simulation is carried for atmospheric pressure, external voltage amplitude of 6 kV, frequency of 2 kHz and a gas temperature equal to 300 K.
Figure.
2 show the total current of the dielectric barrier discharge in pure carbon dioxide reveals a clear correlation between the applied voltage, gas voltage, and the discharge current.
As illustrated, the applied sinusoidal voltage drives the plasma dynamics, while the gas voltage shows a distinct phase shift due to the dielectric barrier effect, highlighting the capacitive nature of the discharge, the simulated current in the second AC cycle.
Breakdown occurs on the rising negative flank, with a sharp current pulse peaking at 0.
55 ms, the simulated peak current is 2.
5 mA and display good agreement with measured current.
Figure.
3 show Time evolution of the power density the maximum power deposition reaches approximately 4 W/cmA, after which it decreases rapidly to near zero before the next cycle begins.
This behavior is characteristic of capacitive .
on-therma.
, where energy is stored in the dielectric and suddenly released into the plasma during breakdown, the asymmetry in peak intensity with the first peak being slightly higher than subsequent ones-suggests stronger initial charging of the dielectric surface.
over time, surface charge accumulation modifies the local electric field, leading to slightly reduced subsequent breakdown intensity but maintaining Figure 2.
Evolution during a single cycle of the applied and gas voltages, along with the simulated and measured discharge currents in pure COCC DBD Figure 3.
Time evolution of the power density .
1 Temporal variation of plasma species densities To assess the effect of argon dilution on the discharge dynamics, a comparative analysis was carried out in .
% COCC 10% A.
gas mixture under identical operating conditions of pure COCC .
Figure.
4a presents the time-dependent behavior of neutrals species number densities in 100 period.
The results indicate rapid formation of CO and O2, which reach steady-state concentrations on the order of 1020 m-3, confirming their roles as primary products of COCCdissociation.
Atomic oxygen O and ozone O3 exhibit intermediate concentrations, with O3 showing a gradual increase and a transient fluctuation around 0.
03 s, likely due to recombination dynamics.
Trace species such as atomic carbon C and carbon suboxide cO remain at much lower levels Figure.
4b displays the transient evolution of selected charged species and current over one full AC cycle during COCC dielectric barrier discharge operation.
The Figure 4.
Time evolutions of the discharge species: .
neutral species.
,) COCC- derived negative ions, .
COCC-derived positive ions and .
Ar excited species and positive ions numerical analysis highlights that the densities of the negative ions COCEA and COCEA increase sharply during the discharge pulses, reaching peak values around 10 20 m-3.
Electron density follows a similar temporal profile, albeit at slightly lower magnitudes 1015 m-3, reflecting the influence of ionization and attachment processes during breakdown events.
The density of O2A remains relatively low and stable, suggesting limited contribution from oxygen-based negative ion chemistry under the considered conditions.
The current profile black curve, right axis exhibits two sharp peaks per cycle, corresponding to the breakdown phases during the positive and negative phases of the applied voltage cycle, consistent with typical DBD behavior.
The temporal correlation between the current peaks and the rise in charged species highlights the strong coupling between plasma kinetics and electrical response in the Figure.
4c depicts the densities of COCC derived positive ions.
CO2 is the most abundant ion peaking at 10ae1017 m-3, formed mainly by electron impact ionization and Penning reactions, followed by O2 1013 m-3 produced via dissociation and recombination pathways, whereas COA remains a minor species.
Figure.
4d shows the evolution of argon species a high density of Ars metastable 1015 m-3 forms rapidly at each ignition peak and decays slowly between discharges, playing a key role in sustaining the plasma through Penning ionization of COCC.
ArA ions are only transient and are immediately converted into Ar2A dimer ions, which become the predominant argon positive ion with densities reaching 1012 m-3.
2 Analysis of operating parameters A comprehensive parametric study was performed to analyze the impact of key operating conditions on the behavior of the dielectric barrier discharge in a COCC/Ar mixture at atmospheric pressure.
Operating conditions including applied voltage, excitation frequency, gas pressure, and gas composition were systematically varied in order to assess their impact on electrical characteristics and species densities.
1 Influence of Ar Dilution In this analysis, the operating conditions were fixed at 6 kV applied voltage, 2 kHz frequency, and 760 Torr pressure, while the argon concentration was systematically adjusted between 10% and 90%,the effect of argon admixture on COCC dielectric barrier significantly modifies the discharge behavior ,the current waveforms exhibit higher performance is shown in Figure.
Increasing the Ar fraction amplitudes in Ar rich mixtures, attributed to the lower ionization threshold of Ar and the efficient generation of electron avalanches, this is consistent with the strong increase in electron density as shown in Figure.
5b , which rises by nearly seven orders of magnitude when the Ar content increases from 10% to 90%.
The higher electron population promotes more efficient electron-impact dissociation of COCC, as confirmed by the CO density profiles.
Maximum CO concentrations are obtained in mixtures containing 75Ae90% Ar, where CO production reaches the order of 10ae10AA mAA as shown in Figure.
where the balance between electron impact excitation and vibrational energy transfer is optimized at higher Ar contents.
COCC depletion limits vibrational pathways, while higher COCC fractions increase collisional Figure 5.
Effect Ar Dilution on: .
Current waveform, .
Electron concentration, .
CO concentration.
2 Influence of frequency For this analysis, the applied voltage 6 kV.
Ar fraction 10%, and pressure 760 Torr were kept constant, while the frequency was varied from 2 to 4 kHz .
The effect of discharge frequency on the temporal evolution and spatial characteristics of the DBD plasma for COCC conversion is presented in Figure 6.
At the lower frequency of 2 kHz, the current waveform exhibits a smoother and less pronounced profile, with only moderate peak amplitudes, as shown in Figure 6a.
Correspondingly.
Figure 6b shows that the electron density remains relatively low, on the order of 10AAe10A mAA, and Figure 6c indicates that CO formation is limited under these conditions.
When the frequency is increased to 3 kHz, the discharge becomes significantly more energetic, displaying higher and sharper current peaks with increasing frequency, as illustrated in Figure 6a.
This enhancement is accompanied by a substantial rise in electron Figure 6.
Effect frequency on: .
Current waveform, .
Electron concentration, .
CO concentration.
up to 1012 m-3 near the cathode Figure.
This enhanced electron population promotes more effective COCC dissociation, leading to higher CO densities across the discharge gap as shown in Figure.
However, at higher frequency 4 kHz, although the current amplitude is further amplified with pronounced fluctuations, the electron density decreases compared to 3 kHz, indicating reduced discharge stability.
Consequently.
CO production is slightly more than at 3 kHz.
These results suggest that an intermediate frequency discharge intensity and stability, leading to the most efficient COCC conversion in the DBD reactor.
3 kHz provides the optimal balance between 3 Influence of applied voltage For this analysis, the frequency 2 kHz.
Ar fraction 10%, and pressure 760 Torr were kept constant, while the applied voltage was varied from 6 to 9 kV.
Figure.
the discharge current waveforms for applied voltages of 6, 8, and 9 kV.
The current exhibits the typical periodic behavior of filamentary DBDs, voltage enhances the discharge current amplitude, indicating stronger microdischarge activity with increasing voltage.
although a partial saturation is observed at the highest level .
kV) because the discharge begins to exhibit reduced stability beyond this threshold.
Figure.
shows a.
Higher applied voltages significantly enhance the electron density, increasing it by multiple orders of magnitude, which promotes more efficient COCC dissociation.
CO production increases significantly with voltage.
As shown in Figure.
ov Effect of applied voltage on: .
Current waveform, .
Electron concentration, .
CO concentration.
4 Influence of Gas Pressure For this study, the applied voltage 6 kV, frequency 2 kHz, and Ar fraction 10 % were maintained constant, and only the gas pressure was varied, ranging from 500 to 1000 Torr.
Figure .
8a illustrates at 500 Torr, the current pulses appear sharper, reflecting higher electron mobility and reduced collisional damping.
In contrast, at 1000 Torr, the waveforms broaden due to enhanced electron-neutral collisions, which slow down charge transport.
The 760 Torr case, corresponding to atmospheric pressure, lies in between these two regimes.
Figure 7.
The spatial distribution of electron density is shown in Figure.
At 500 Torr, the electron density reaches approximately 10-14 m-3 near the cathode and decays gradually across the 1 mm discharge gap.
Increasing the pressure to 760 Torr reduces the initial density to 10-13 m-3 , with a steeper decay profile.
At 1000 Torr, the electron ov Figure 8.
Effect of the gas pressure on: .
Current waveform, .
Electron concentration, .
CO concentration.
density falls to 10-11 m-3 , with a rapid decrease along the discharge length.
These results confirm the strong influence of collisional processes at higher pressures, which shorten the electron mean free path and suppress ionization rates.
The effect of pressure on CO production is presented in Figure.
For 500 Torr, the CO density increases steadily with the discharge gap, achieving values above 10 -17 m-3, indicating efficient COCC splitting under low-pressure conditions.
At atmospheric pressure 760 Torr.
CO formation remains significant but is reduced to 10 -16 at 1000 Torr, however.
CO densities decrease sharply to 10-14 m-3, confirming that high collisional quenching suppresses the generation of reactive species.
Conclusion This study investigated the electrical and physicochemical behavior of dielectric barrier discharges through simulation and comparison with experimental data.
The results confirmed that the model successfully reproduces key discharge behaviors, including the phase shift between applied and gas voltage, current peaks correlated with plasma breakdown, and the formation of major products such as CO and OCC.
Parametric analyses revealed that argon addition significantly enhances electron density and CO production, frequency strongly influences discharge stability with optimal conversion around 3 kHz, applied voltage increases dissociation efficiency up to a saturation point, where further voltage increase no longer improves COCC conversion due to energy losses in gas heating and recombination and higher pressures suppress COCC conversion due to collisional quenching.
Overall, the findings highlight the importance of optimizing operating parameters particularly Ar concentration, frequency, and applied voltage to achieve efficient COCC splitting in DBD reactors, offering valuable insights for the design of plasma-based COCC conversion systems.
in pure COCC and COCC/Ar mixtures at atmospheric pressure Acknowledgment This work was supported by the Laboratory of Electrical Engineering and Renewable Energy (LGEER).
Faculty of Technology.
Hassiba Benbouali University of Chlef.
CRedit Author Statement Author Investigation.
Software.
Data Curation.
Writing Original Draft Preparation.
Resources.
Benyoucef Djilali: Co-supervision.
Project Administration.
Writing Review and Editing.
Validation.
All authors have read and agreed to the published version of the manuscript.
Chenoui Mohamed:
Conceptualization.
Methodology.
Contributions:
Visualization.
Tebani Hocine: Supervision.
Writing Review and Editing.
Validation.
References