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

Transcription

1 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

2 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

3 Feedstock for composite based bipolar plates Graphite (conductive filler 1) Polymer (binding matrix) Carbon black (conductive filler 2) 3

4 Matrix selection for composite bipolar plates Thermosets (LT & HT) Cheap High thermal stability < 180 C Good chemical stability < 180 C Feasible for hotpressing LT Thermoplastics (PP) Very cheap Good chemical stability < 80 C Good thermal stability < 80 C Recycling possible Extrusion established Injection molding possible HT Thermoplastics (PPS) Excellent chemical stability > 180 C Excellent thermal stability > 180 C Recycling possible Extrusion established Injection molding possible Source: Epoxid: chemie.fu berlin.de, Phenolharz: kern.de, PPS,PP und Peek: Wikipedia

5 Filler selection for composite bipolar plates Source: ptonline.com Source: AMG Mining AG Source: celgard.com Source: adherent tech.com Source: tms.org Graphite (conductive filler) Polymer (binder) Binary compound Further conductive additives Multi component compound 5

6 Look inside the composites Graphite + polymer Graphite+ CB + polymer Graphite+ CB +CNT + polymer Graphite+ CNT + polymer Ggraphite+ CF + polymer 6

7 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

8 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

9 Why is compounding so ambitious bulk density disaster Relation between volume graphite to 80 wt%: 80 wt% kg/h 2660 l graphite in 15 l PPS (121 l graphite in 22 l PP)

10 Compounding successfully established

11 Further processing of these composites Thermosets Thermoplastics Established technology for LT and HT BPP Difficult with shapes and inlets Long production time Recycling not possible Limited opportunities for mass production Mass market entry barrier for PEM FC Established technology for LT BPP High accuracy and reproducibility Inlets and manifolds in one step Mass production technique Enables cheap and reproducible articles High initial investment for IM tool Limitations in size 11

12 Why is IM of these composites so ambitious? PP & PPS 5000 kn clamp force 350 MPa IM pressure > 80 wt% filling content very high viscosity very good thermal conductivity rapidly solidification 320 MPa with plastic with compound 0,2 sec Source: Jens Doerner, IPE Duisburg Challenging in processing but well established at ZBT since 2002 for low temperature bipolar plates based on PP 12

13 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

14 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

15 Finally it works very successful 15

16 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

17 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

18 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

19 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 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 kn clamp force 350 MPa IM pressure PE / PP 300 TECACOMP PPS HTE 19

20 Hot Compression Molding Compared To Injection Molding Hot Compression Molding Cycle time: Phenolic resin: +/ 3 min 5 min PPS Compound: +/ 10 min 20 min Injection Molding Cycle time: Standard process (thicker and smaller plates): +/ 10 seconds Variotherm process (bigger and/or thinner plates) +/ 2 min technology mass production cost savings 20

21 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: online.com/en/compounds/products/high content graphite compounds/ Processing: duisburg.de/en/portfolio/fuel cell components/injection moulded bpp/ 21