Benchmarking a fuel cell stack compression process Mussawar Ahmad, WMG Academic Supervisors Prof Robert Harrison, Automation Systems Group, Warwick University Dr James Meredith, Sheffield University Industrial Supervisors Dr Axel Bindel, HSSMI Dr Ben Todd, Managing Director, Horizon Fuel Cells UK IREC 2015

 Background  Compression  Importance  Literature values  Spring equivalent model  Horizon fuel cell compression system performance  Conclusion  Proposed further work Overview

 Supporting Horizon Fuel Cell UK with fuel cell manufacturing  Developing assembly methods and processes  Three critical assembly processes identified  Alignment  Sealing  Compression Background

Repeating cell

a) b) c) MEA

Assembly process criticalities The fuel cell assembly Venn…

1. Magnitude  GDL - Mass transport vs. ohmic losses  Sealing  Mechanical stresses 2. Homogeneity  Hotspots Cell Voltage (V) Cell Current (A) Excessive and insufficient compression Ohmic losses Mass transport losses Activation losses Importance of compression

Trendline – coefficient of determination – 0.92 Useful tool to help fuel cell researchers identify a ballpark figures for GDL compression Porosity and PTFE loading also do need to be considered Literature Comp. Ratios

Spring equivalent model Gaskets sit parallel to GDL Effect gaskets have on GDL compression can be estimated Identify force required to reach compression ratio F t = total force A GDL = SA GDL E GDL = YM GDL A g = SA gasket E g = YM Gasket CR = GDL compression ratio a = ratio of gasket thickness over GDL thickness BUT, some fuel cells use incompressible gaskets…

 Horizon Fuel Cells UK designed a fuel cell compression system  Compression characteristics are tested  Typical methodologies for compression characteristic assessment:  FE Modelling  Piezoresistive arrays  Pressure sensitive films Fuel Cell Compression System

Methodology Cut compression film to size Place a film between each cell in 4 cell stack Apply compressive force Wait 1 minute to settle Reapply force Wait 1 minute to settle Remove films Scan films Use MATLAB code to assess compression Repeat at a range of compressive forces MATLAB code converts grayscale scan of film to contour plot 3 colour contour to make data easier to visualise Local averaging carried out so non-useful data is lost

Results and Discussion 10MPa20MPa 30MPa Non-uniform compression CoV through z-axis does not exceed 10% Good symmetry through y-axis Non-symmetry through x-axis Could be due to: Compression system calibration Component manufacturing tolerances Stack/cell assembly tolerances

Conclusion Optimal fuel cell compression is important Potential for cheap and easy maximisation of fuel cell performance Increase stack life BUT Compression methods need to be optimised Assembly processes need more rigour Methodology for fuel cell researchers: 1.Estimate optimal CR based on literature values 2.Use spring equivalent model to estimate required force 3.Use compression system to apply force

Fuel cell variants? Further Work Fuel Cell Assembly Criticalities Sealing? What are the requirements of a fuel cell assembly production line? Compression characterisation Alignment? These are intrinsically linked to assembly quality EquipmentTesting Supply chain

Further Work This has been examined first to better understand the dependencies

Questions Mussawar Ahmad, WMG Academic Supervisors Prof Robert Harrison, Automation Systems Group, Warwick University Dr James Meredith, Sheffield University Industrial Supervisors Dr Axel Bindel, HSSMI Dr Ben Todd, Managing Director, Horizon Fuel Cells UK Acknowledgements

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