Design and Development of a Vanadium Oxygen Fuel Cell Chris Menictas1,2, Mandar Risbud1,2, Maria Skyllas-Kazacos1,2 and Jens Noack1,3 1CENELEST,
German-Australian Alliance for Electrochemical Technologies for Storage of Renewable Energy, UNSW Sydney, Australia 2UNSW
Sydney, Australia
3Fraunhofer
ICT, Germany
2018 MRS Fall Meeting, Boston, Massachusetts
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Introduction to CENELEST German-Australian Alliance for Electrochemical Technologies for Storage of Renewable Energy • Project to establish an international center (CENELEST) at UNSW Sydney. Co-operation to strengthen the partners‘s world-class expertise in redox flow batteries. • Develop other types of batteries and fuel cells. • Entire range of electrochemical energy storage system needs. • Utilising weather forecasting for renewable energy systems employing storage. • Expand global infrastructure access. • Central point of contact for industry and researchers.
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Vanadium Redox Flow Battery (VRB)
Conventional VRB System • Lare scale systems employ 1.6M – 1.8M vanadium ion concentration.
At Negative Electrode V II ⇌ V III + e
OCV Cell At Positive Electrode
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V V + e− ⇌ V(IV)
• Negative electrolyte, stable at higher temperatures.
• Positive electrolyte, thermal precipitation of V(V) can occur at higher temperatures. • Factors in MW/MWh range?
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Negative Tank Battery Stack Overall V II + V V ⇌ V III + V(IV)
Positive Tank
VRB 2 MW/20 MWh Demonstration System Fraunhofer ICT
Foto with courtesy of J. Schmalz GmbH & Co KG
Current project status: • 42 Stacks are have been connected in the first half module and brought into operation. The first testing cycles confirm data measured on individual stacks. • Approximately 360 tonnes of vanadium electrolyte has been filled in the tanks to date. 4
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VRB 2 MW/20 MWh Demonstration System Fraunhofer ICT
Electrolyte storage tanks on lower level below stacks. The first module has been operational since December 2017. 5
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Vanadium-oxygen hybrid fuel cell (VOFC) •
Membrane electrode assemblies (MEA) can be used to replace positive half-cell of VRB
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Almost double the VRB energy density
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Removal of the conventional positive half cell allows a possible increase in negative electrolyte energy density.
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Aim is a four fold increase in energy density.
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Suitable for electric vehicle applications – instant re-charge?
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VRB
Vanadium-oxygen hybrid fuel cell (VOFC) •
Membrane electrode assemblies (MEA) can be used to replace positive half-cell of VRB
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Almost double the VRB energy density
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Removal of the conventional positive half cell allows a possible increase in negative electrolyte energy density.
•
Aim is a four fold increase in energy density.
•
Suitable for electric vehicle applications – instant re-charge?
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VOFC
Vanadium-oxygen hybrid fuel cell (VOFC)
Controlled temperature up to 800C
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VOFC Focus Areas
Focus areas highlighted
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Prototype construction aspects
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Process for MEA production
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Catalysts for oxygen reduction
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Bench top trials
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Regeneration of electrolyte
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Increasing electrolyte energy density
Catalysts for oxygen reduction Process for producing MEA assemblies
Bench top trials
VOFC Project Increasing electrolyte energy density
Prototype construction
Modelling of flow cell
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UNSW Test Cells – Materials and Design – Prototype Construction
Designing and fabricating flow battery test cells using additive manufacturing. New sealing strategies
A UNSW Startup and CENELEST Partner 10
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UNSW Test Cells – Materials and Design – Prototype Construction
In-house manufacture and evaluation of system components Enables increased flexibility in cell design VOFC designed to operate at higher temperatures up to 800C
A UNSW Startup and CENELEST Partner 11
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Membrane Electrode Assemblies •
MEA fabrication
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Catalyst layer applied onto wetproofed carbon paper.
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Catalyst suspension applied via spray coating.
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Attached to pre-treated Nafion 115 via hot pressing
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Bonding conditions 1400C, 3kPa for 10 minutes
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Catalyst type loading varied
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MEA size 5cm x 5cm
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Membrane Electrode Assemblies
Membrane Electrode Assemblies Tested •
OCV voltage values obtained with platinum and non-noble metal catalysts.
Open circuit voltage comparison for different electrocatalysts used in Vanadium-oxygen fuel cell against VRB (50% SOC) 13
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Vanadium-oxygen hybrid fuel cell (VOFC)
1.10
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Discharge voltage curves obtained with commercial MEA assemblies.
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1.05 1.00 0.95
Electrolyte - 2M vanadium in 5M H2SO4
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Ambient Temperature 250C.
0.85 0.80
E/V
• Electrode Material - Toray carbon paper 120, heat treated at 4000C, 30 hours followed by MoO3 modification (≈ 4 mg ml-1). • Membrane – Pre-treated Nafion 115
0.90
0.75 0.70
2
10 mA/cm 2 15 mA/cm 2 20 mA/cm 2 25 mA/cm
0.65 0.60 0.55 0.50 0.45 0
200
400
600
800
Time/s
Performance of VOFC cell with commercial Pt/C electrodes at various current densities
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1000
Vanadium-oxygen hybrid fuel cell (VOFC) •
Effect of oxygen supply
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Standard 2M vanadium electrolyte
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Extended discharge
Effect of Oxygen supply on discharge voltage at 5mA/cm2 15
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Extended discharge at 800C at 50mA/cm2
Vanadium-oxygen hybrid fuel cell (VOFC) •
Effect of oxygen supply
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Standard 2M vanadium electrolyte
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Extended discharge
Extended discharge with regeneration 16
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Vandium Oxygen Fuel Cell + Electrolyser
Discharge (Pt, VOFC)
4V 2+ + O2 + 4H + ↔ 4V 3+ + 2H2 O Charge (Ir, Electrolyser) 17
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3.6M High Energy Density Vanadium Electrolyte
• Large scale commercial VRB systems typically utilise 1.6M vanadium concentration in their electrolytes.
2M Vanadium (II) Electrolyte
Dilute vanadium solutions V(V), V(IV), V(III) and V(II) 3.6M Vanadium (II) Electrolyte 18
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VOFC Employing 3.6M High Energy Density Electrolyte • Conventional VRB systems limited by thermal precipitation of V(V). • VOFC can operate at higher temperatures, only utilises negative vanadium electrolyte. • Stable operation achieved with 3.6M vanadium in the negative electrolyte
3.6M Vanadium solution on negative side and PtC (0.5 mg/cm2) on positive side with Nafion 115 membrane at 500C. 19
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VOFC Employing 3.6M High Energy Density Electrolyte
• Discharge curves obtained with increasing current density.
3.6M Vanadium solution on negative side and PtC (0.5 mg/cm2) on positive side with Nafion 115 membrane at 500C. 20
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VRB and VOFC Comparison
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Future Work
• Continue investigation on alternate catalysts for oxygen reduction.
• Testing of muti-cell VOFC stacks • Extended discharge with electrolyser • Negative electrolyte energy density increase
• VOFC system management and control
VOFC 3-cell stack 22
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Design and Development of a Vanadium Oxygen Fuel Cell Chris Menictas CENELEST, German-Australian Alliance for Electrochemical Technologies for Storage of Renewable Energy, UNSW Sydney, Australia c.menictas@unsw.edu.au Acknowledgement The VOFC project has been funded by the US Office of Naval Research
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