Challenges in processing and marketing high temperature compounds for bipolar plates – opportunities in applying it

Dipl.‐Chem. Thorsten Derieth, ZBT GmbH Mag. (FH) Hans‐Peter Koch, Ensinger GmbH Bipolar plate ‐concepts for PEM‐FCs

Metal plates Compound plates

DANA

Source: Gräbener Maschinetechnik GmbH Source: Wilhelm Eisenhuth GmbH

Difference in volume & weight

Influences in HT‐PEM‐FC • T > 160°C • Phosphoric acid media • Electrochemical potential • Mechanical stress

2 Feedstock for composite based bipolar plates

Polymer (binding matrix) Carbon black Graphite (conductive filler 2) (conductive filler 1)

3 Matrix selection for composite bipolar plates

Thermosets (LT & HT) LT‐Thermoplastics (PP) HT‐Thermoplastics (PPS)

Cheap Very cheap Excellent chemical stability > 180°C High thermal stability < 180°C Good chemical stability < 80°C Excellent thermal stability > 180°C Good chemical stability < 180°C Good thermal stability < 80°C Recycling possible Feasible for hotpressing Recycling possible Extrusion established Extrusion established Injection molding possible Injection molding possible

Source: Epoxid: chemie.fu‐berlin.de, Phenolharz: kern.de, PPS,PP und Peek: Wikipedia Filler selection for composite bipolar plates

Source: ptonline.com

Source: adherent‐tech.com Source: AMG Mining AG Source: celgard.com

Source: tms.org

Further Multi Graphite Polymer Binary conductive component (conductive filler) (binder) compound additives compound

5 Look inside the composites

Graphite + polymer Graphite+ CB + polymer

Graphite+ CB +CNT + polymer

Graphite+ CNT + polymer Ggraphite+ CF + polymer

6 Why is compounding so ambitious – weight to volume ratio

96 vol% processing not possible

62 vol% functionality for bipolar plates

33 vol% no functionality for magnetism Why is compounding so ambitious – weight to volume ratio

71 vol% process ability nearly not possibly in PPS > 74  close packing of spheres

62 vol% process ability in PP is possibly Why is compounding so ambitious –bulk density disaster

Relation between volume graphite to polymer @ 80 wt%: 177:1 @ 80 wt% & @100 kg/h  2660 l graphite in 15 l PPS (121 l graphite in 22 l PP) Compounding successfully established Further processing of these composites

Thermosets Thermoplastics

Established technology for LT‐ and HT‐BPP Established technology for LT‐BPP Difficult with shapes and inlets High accuracy and reproducibility Long production time Inlets and manifolds in one step Recycling not possible Mass production technique Limited opportunities for mass production Enables cheap and reproducible articles Mass market entry barrier for PEM‐FC High initial investment for IM‐tool Limitations in size

11 Why is IM of these composites so ambitious? PP & PPS

5000 kN clamp force > 80 wt% filling content  very high viscosity 350 MPa IM‐ pressure very good thermal conductivity  rapidly solidification

320 MPa

with plastic

0,2 sec with compound

Source: Jens Doerner , IPE Duisburg

Challenging in processing but well established at ZBT since 2002 for low temperature bipolar plates based on PP

12 Why is IM of these composites so ambitious ? PP vs. PPS

Difference between processing temperature and solidification temperature as indicator for a good process ability

Processing temp. Solidification temp.

Source: reproduced from Hiekisch, Fa. Ticona PPS meets all the other requirements for use in HT‐PEM‐FC

13 Opportunities to realize HT bipolar plates via IM

Instead of one cavity tool with many redirections a two cavity tool with center gate  equal flow lines

First testing series have been produced successful – meanwhile a standard process at ZBT

14 Finally it works very successful

15 Plastic‐Material‐Concepts For HT‐PEMs

Phenolic resin

+ already in use for HT PEMFC experience with this material and therefore confidence + well suited for the hot compression molding process well trusted procedure to produce smaller amounts of plates ‐ unsuitable for injection molding material not recyclable, time consuming and costly procedure, ‐ long‐term impairment caused by phosphoric acid (> 180 °C) poor performance and failures in the long run at temperatures > 180 °C

16 Plastic‐Material‐Concepts For HT‐PEMs

Polyphenylenesulfide (PPS)

+ material is hot compression moldable bridge technology for PPS plates, only low investment required ‐ longer cycle time at compression molding no cost saving opportunity, but the possibility to gain experience ‐ not yet in use commercially customers are evaluating PPS, first feedback is very positive, invest in tooling + very positive feedback as to resistivity against H3PO4 better performance, long term stability + processable by means of injection molding or extrusion shorter cycle time, larger and thinner plates by means of variotherm tooling , recyclable + operating temperatures up to 200 °C leads to higher performance of the fuel cell

17 Status In Marketing Of Highly Filled PPS Compounds

TECACOMP HTE‐Compounds in the market  Tests with PPS based compounds have been carried out or are carried out currently from most of the important bipolar plate producers in Europe, US and Japan  Due to the advantages (compared with phenolic resins) offered by the PPS compounds, customers indicate interest after having done first trials with this material  Different fuel cell concepts ‐ asking for different bipolar‐plate‐materials ‐ are on the market currently and it is not certain which will be the most preferred one.  That leads to a lower willingness to invest in more suitable technology The hot compression technology  Hot compression molding of PPS based compounds is state of the art. It is basically easy to switch from phenolic resin to the thermoplastic compound with the same machinery.  Hot compression molding of PPS compounds provide the chance to gain first experience with this material but without the need to invest in expensive machinery  Due to longer cycle times of PPS during the hot compression molding process (compared with phenolic resins) this technology is not suitable to bring down the costs of bipolar plates made of PPS compounds.

18 Status In Marketing Of Highly Filled PPS Compounds

The injection molding process  To extract the advantages of this material in terms of cost saving, means to have to switch to the injection molding technology  To invest in variotherm technology (to obtain larger and thinner plates) will pay off at something like 100.000 pieces a year  To process the highly filled TECACOMP HTE‐Compounds means to work at the borderline in respect of temperature control and the injection pressure. Due to this fact one need to have a strong injection molding machine.

5000 kN clamp force PE / PP 350 MPa IM‐ pressure

300

TECACOMP PPS HTE

19 Hot Compression Molding Compared To Injection Molding

Hot Compression Molding Injection Molding Cycle time: Cycle time: Phenolic resin: +/‐3 min – 5 min Standard process (thicker and smaller plates): PPS Compound: +/‐ 10 min – 20 min +/‐ 10 seconds Variotherm process (bigger and/or thinner plates) +/‐ 2 min

technology

mass production

cost savings

20 Status In Marketing Of Highly Filled PPS Compounds

 Eisenhuth GmbH in Osterode will soon start a program to produce injection molded bipolar plates. It is very likely that their efforts are successful as ZBT in Duisburg already managed to produce such a product by means of injection molding.  Ensinger Compounds . has PPS compounds available that fits to the hot‐compression‐technology to get started and to gain experience . has got injection moldable PPS compounds for serial production . Produces different grades of PP compounds for the use in LT PEM fuel cells, redox flow batteries and alkaline electrolyses

. For more information: Compounds: www.ensinger‐online.com/en/compounds/products/high‐content‐graphite‐compounds/ Processing: www.zbt‐duisburg.de/en/portfolio/fuel‐cell‐components/injection‐moulded‐bpp/

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