Folie 1 -
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Modeling the Vanadium Oxygen Fuel Cell F.T. Wandschneider, M. Küttinger, P. Fischer, K. Pinkwart, J. Tübke, H. Nirschl
Transcript of Folie 1 -
Modeling the Vanadium Oxygen Fuel Cell
F.T. Wandschneider, M. Küttinger, P. Fischer, K. Pinkwart, J. Tübke, H. Nirschl
© Fraunhofer ICT – Slide 2
Contents
Redox Flow Batteries
Vanadium Redox Flow Battery
Vanadium Air Redox Flow Battery / Vanadium Oxygen Fuel Cell
Multiphysics Modeling and stationary simulation
Time-dependent simulation
Alterations to the stationary model
Performance degradation over time
Using a parametric study to emulate a time-dependent simulation
Result
Summary and outlook
© Fraunhofer ICT – Slide 3
Vanadium Redox Flow Battery
Figure by Jens Noack, Fraunhofer-ICT
© Fraunhofer ICT – Slide 4
Project work: Planned 2 MW / 20 MWh Redox Flow Battery at our Institute
Picture by Jens Noack, Fraunhofer-ICT
© Fraunhofer ICT – Slide 5
Vanadium Air Redox Flow Battery
Figure by Jens Noack, Fraunhofer-ICT
© Fraunhofer ICT – Slide 6
Vanadium Oxygen Fuel Cell
© Fraunhofer ICT – Slide 7
Multiphysics Modeling
Momentum
Liquid flow in vanadium half-cell and middle cell (porous media flow)
Gaseous flow in air half-cell
Mass and species
Diluted species in vanadium half-cell and middle cell
Concentrated species in air half-cell
Chemical reaction
„Bulk“ reaction within the porous electrode of the vanadium half-cell
Reaction at the membrane surface within the air half-cell
Electrochemistry
Local potentials depending on species concentration
Electric and ionic currents
© Fraunhofer ICT – Slide 8
Stationary Simulation (1)
Vanadium V2+
[mol/m³] Mass fraction
O2 [1] Solid electrodes
Porous electrode with liquid vanadium electrolyte
Membranes
Middle cell
Catalyst coating (separate domain)
Porous electrode with gaseous air (no reaction, only electric conduction)
Electric ground
Constant current
© Fraunhofer ICT – Slide 9
Stationary simulation (2)
0 10 20 30 40 50 60 70 800,5
0,6
0,7
0,8
0,9
1,0
1,1
1,2
1,3
term
ina
l vo
lta
ge
[V
]
current density [mA/cm²]
Experiment
Simulation
© Fraunhofer ICT – Slide 10
Time-dependent simulation Discharge cycle with a constant current density of 25 mA/cm²
0 5 10 15 20 25 30 350,0
0,2
0,4
0,6
0,8
1,0
term
inal voltage
[V
]
time [h]
Experiment
Simulation
© Fraunhofer ICT – Slide 11
Expanding the stationary model (1)
Additional Assumptions
No side reactions
No or negligible diffusion of vanadium ions
Applying FARADAY‘s law, the constant current leads to a constant change rate in the state-of-charge of the vanadium oxygen fuel cell the time variable can be replaced by a state-of-charge variable
The inlet concentrations of the species are either a function of the state-of-charge (vanadium electrolyte half-cell) or constant (air half-cell)
Taking all of this into consideration, the time-dependent simulation can be replaced by the stationary simulation with a state-of-charge parameter study
© Fraunhofer ICT – Slide 12
Performance degradation by flooding
Membrane Liquid film
Carbon coating
Platinum catalyst particles
Air
𝑂2 + 4 𝐻+ + 4 𝑒− 𝑃𝑡,𝑇𝑃𝐵
2 𝐻2𝑂
© Fraunhofer ICT – Slide 13
Expanding the stationary model (2)
𝑗𝑐𝑎𝑡ℎ = 𝑆𝑉 ψ 𝑗𝑐𝑎𝑡ℎ0
𝑐𝑠 𝑂2
𝑐𝑟𝑒𝑓 𝑂2 −𝑒𝑥𝑝 −
𝛼𝑐 𝕱
𝕽 𝑇 η𝑐
400 450 500 550 6000,0
0,2
0,4
0,6
0,8
1,0
Psi(t)
[1]
time [s]
ψ 𝑡 = 1
1 + 𝑐 𝑒𝑥𝑝 𝑘 𝑡 − 𝑡0
© Fraunhofer ICT – Slide 14
Resulting Simulation
0 5 10 15 20 25 30 350,0
0,2
0,4
0,6
0,8
1,0
te
rmin
al vo
lta
ge
[V
]
time [h]
Experiment
Sim. w/o logistic function
Sim. with logistic function
© Fraunhofer ICT – Slide 15
Summary and outlook
Vanadium Oxygen Fuel Cell as an interesting energy storage device
Our design can be modeled and simulated using COMSOL Multiphysics
Simulated data from stationary model shows very good agreement with experimental data
Time-dependent simulation does not consider degradation process
Altered stationary model can account for cathode degradation and reduce time-dependent simulation to a stationary parametric study of SOC, thus saving computing time
Model enhancement
Thermal effects
Membrane cross-over effects
© Fraunhofer ICT – Slide 16
Thank you for your attention!
The authors gratefully acknowledge the funding by the Department of Commerce
of the German Federal State of Baden-Württemberg
Dipl.-Ing. Frank Wandschneider Fraunhofer-Institute for Chemical Technology Department of Applied Electrochemistry Joseph-von-Fraunhofer-Strasse 7 D-76327 Pfinztal / Germany E-Mail: [email protected]
