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Conductive polymer composites and coated metals as alternative bipolar plate materials for all-vanadium redox-flow batteries

: Caglar, B.; Richards, J.; Fischer, P.; Tuebke, J.

Advanced materials letters 5 (2014), No.6, pp.299-308
ISSN: 0976-3961
ISSN: 0976-397X
Journal Article
Fraunhofer ICT ()

In this study polypropylene (PP) based conductive composites and metal doped diamond like carbon (DLC) coated metallic substrates are studied as alternative bipolar materials for all-vanadium redox flow battery (VRFB). Graphite and carbon nanotube (CNT) filled PP based bipolar plates were produced via twin-screw co-rotating extruder and injection molding. Addition of 3 wt. % CNTs into highly filled graphite-PP matrix increased in-plane and through-plane electrical conductivities from 10 S/cm to 50 S/cm and from 2 S/cm to 10 S/cm respectively. PP composites with 78 wt. % graphite and 2 wt. % CNT filling ratio showed flexural strength value of 48,01 MPa. Produced bipolar plates were examined with galvanostatic charge-discharge test in a single-cell VRFB. Energy efficiency of 85,43 % at 25 mA/cm2 and discharge power density of 78,48 mW/cm2 at 75 mA/cm2 were achieved and those values were found to be comparable with commercial bipolar plates. Titanium, vanadium, chromoium a nd tungsten doped diamond-like coating (DLC) films were coated on metallic substrates (e.g. stainless steel 1.4301 and titanium alloy 3.7165) by a physical vapor deposition. The metallic dopant is necessary to achieve high conductivities in the order of 100 S/cm. The values range from 0.5 to 35 S/cm for in-plane and from 10 to 110 S/cm for through-plane. The hydrogen evolution reaction (HER) and the anodic corrosions stability in 2 molar sulfuric acid constituted the main focus area for our investigations on metallic bipolar plates. An interesting material for coated metallic bipolar plate is the 10 m Ti-DLC on 1.4301 which exhibits the highest hydrogen evolution overpotential of all investigated materials (710 mV A/cm2). It also showed improved corrosion stability for anodic potentials.