Performance enhancing stack geometry concepts

Performance enhancing stack geometry concepts Nicholas Gurieff 1,3, Chris Menictas 1,3, Victoria Timchenko 1,3, Maria Skyllas-Kazacos 2,3 and Jens Noack 3,4 1

School of Mechanical Engineering, UNSW Sydney, Australia 2

3

School of Chemical Engineering, UNSW Sydney, Australia

CENELEST, German-Australian Alliance for Electrochemical Technologies for Storage of Renewable Energy 4

Fraunhofer-Institute for Chemical Technology, Pfinztal, Germany

IFBF 2019, 8 - 11 July, Lyon, France

1 Š CENELEST

Research Problem - Voltage and Overpotential

• Overpotential increase and current limitations as reactants depleted during cycling • Mechanical design optimisation can address mass transfer limitations • Promise of improved power density and higher efficiency

2 © CENELEST

A. Tang, J. Bao, M. Skyllas-Kazacos, Studies on pressure losses and flow rate optimization in vanadium redox flow battery, J. Power Sources. 248 (2014) 154–162.

Modelling and Simulation

• Multi-physics simulation of electrochemistry and fluid dynamics with published parameters • Single cell geometries with flow-through porous felt electrodes • Vanadium electrolyte at 90% SOC charging at 160 mA cm-2 with 10 stoich flow rate

Figure – simulated flow cells with reactant concentrations

3 © CENELEST

Stack Geometry Concepts - Prior Work Trapezoidal and Radial Geometries

N. Gurieff, C.Y.Y. Cheung, V. Timchenko, C. Menictas, Performance enhancing stack geometry concepts for redox flow battery systems with flow through electrodes, J. Energy Storage. 22 (2019) 219–227.

4 © CENELEST

Wedge Shaped Cells MANIFOLD

OUTLET

POROUS ELECTRODE

ENDPLATE

MEMBRANE

INLET

N. Gurieff, V. Timchenko, C. Menictas, Variable Porous Electrode Compression for Redox Flow Battery Systems, Batteries. 4 (2018) 53.

5 © CENELEST

Simulation Results

0.7

50

0.6

40

0.5

30

0.4 0.3

20

0.2

10 0

0.1 Case 1

Case 2

Case 3

Minimum Limiting Current Density Differential Pressure 6 Š CENELEST

0.0

Pressure Drop (kPa)

Min. Limiting Current Density (mA cm-2)

Performance and Compression Variation

Laboratory Scale Prototype

• Computer aided design of adaptable cell for digital manufacuturing • Additively manufactured reducing cross-section flow frames • Ported endplates printed with corresponding wedges • CNC machined resin impregnated carbon plates • Laser cut gasket and reinforcing steel endplates Figure – rendering of test cell design 7 © CENELEST

Experimental Studies

• Assembled in two configurations – flat and reducing • 4.5 mm thick porous carbon felt pre-treated in air at 400°C • Proton exchange membrane pre-treated in H2O2 and H2SO4 • 100 mL of 2 M vanadium electrolyte with 3 M sulphate each side nitrogen purged and circulated with peristaltic pump Figure – assembled single cell 8 © CENELEST

Experimental Studies – Preliminary Testing

• 40 cycles per configuration • Single cycles at 20, 40, 60, 80 and 100 mA cm-2 • Repeated at higher flow rate • 10 cycles at 60, 80 and 120 mA cm-2

Figure – assembled single cell 9 © CENELEST

Experimental Studies – Preliminary Results

Average Energy Efficiency

Energy Efficiency (Improvement vs Baseline) 100% 80%

5%

5%

6%

60%

15% Flat Wedge

40% 20% 0%

20-100

60

80

Current Density (mA cm-2) 10 © CENELEST

120

Experimental Studies – Preliminary Results Charge-Discharge Cycling (V-t) at 120 mA cm-2 2.1 1.5 1.2 0.9 0.6 0.3

© CENELEST

0

1

2 3 Time (hours)

Wedge

1.8 Voltage (V)

Voltage (V)

1.8

11

2.1

Flat

4

1.5 1.2 0.9 0.6 0.3 5 0

1

2 3 Time (hours)

4

5

Experimental Studies – Contributing Factors

• Dry cell ohmic resistance testing • Lower contact resistance in baseline case expected due to non-linear relationship • Half cell pressure tests in parallel • Equal pressure drop in both cases consistent with simulation findings Figure – assembled single cell 12 © CENELEST

Concept Development

Figure – battery assembly with tanks 13 © CENELEST

Figure – stack assembly with wedge cells

Future Work – Alternative Geometries and Materials

Figures – printed radial flow frames with felt (left) and laser-cut gasket (right) 14 © CENELEST

Figure – cell with moulded conducting polymer plates and printed composite endplates

Performance enhancing stack geometry concepts Nicholas Gurieff CENELEST, German-Australian Alliance for Electrochemical Technologies for Storage of Renewable Energy, UNSW Sydney, Australia n.gurieff@unsw.edu.au Acknowledgements This research is supported by an Australian Government Research Training Program (RTP) Scholarship.

15 Š CENELEST

16 © CENELEST