Design and Development of a Vanadium Oxygen Fuel Cell

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.

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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.

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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

•

Almost double the VRB energy density

•

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

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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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