Conductive Polymer Composites And Coated Metals As Alternative Bipolar Plate Materials For All-vanadium Redox-flow Batteries

Burak Caglar1*, Justin Richards2, Peter Fischer1, Jens Tuebke1

1Fraunhofer Institute for Chemical Technology (ICT) Applied Electrochemistry, Joseph-von-Fraunhofer str.7, 76327 Pfinztal, Germany

2Fraunhofer Institute for Chemical Technology (ICT) Applied Electrochemistry, Robert-Koch-Platz 8a, 38440 Wolfsburg, Germany

Adv. Mater. Lett., 2014, 5 (6), pp 299-308

DOI: 10.5185/amlett.2014.amwc.1023

Publication Date (Web): Mar 23, 2014

E-mail: burak.caglar@ict.fraunhofer.de

Abstract


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 and 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 µm Ti-DLC on 1.4301 which exhibits the highest hydrogen evolution overpotential of all investigated materials (710 mV µA/cm²). It also showed improved corrosion stability for anodic potentials.

Keywords

Vanadium redox flow battery, polymer composites, metallic bipolar plates, diamond like carbon coating, corrosion tests.

Upcoming Congress

Knowledge Experience at Sea TM