Abstract
Vanadium redox flow batteries currently have come closer to their suitability in the industrial as well as the private sector. However, they still suffer from high capital costs, mainly ruled by the conversion unit consisting of an assembly of sandwiched components, such as semipermeable membranes and carbon electrodes (MEA). The respective system power output scales with and determines the necessary geometric area of the MEA. By increasing the area specific power output of a MEA capital costs may be reduced. As electrodes commonly porous graphite felt (GF) electrodes are used which are made of a woven of carbon fibers. When pumping the (sulfuric acid) electrolyte through these graphite felts, the Vanadium (V) ions dissolved in the electrolyte can pass the carbon surface of the fibers where the anodic V2+/3+ and the cathodic V4+/5+ redox reactions take place, respectively. A big portion of the power losses result from the kinetic overpotentials that need to be applied on the porous carbon electrodes in order to drive the Vanadium reactions.(1) In recent years various modification methods of the carbon electrodes have been proposed.(2,3) Besides surface oxide groups there were a few attempts that involved nitrogen atoms which were supposed to offer a catalytic activity for the Vanadium reactions. This work aims to resolve the variable catalytic activity coming from distinctive nitride surface groups.(4,5) For this purpose, on glassy carbon there were synthesized artificial aromates containing a nitro group, which covalently bind to the carbon surface and provide an anchor site for the Vanadium redox reaction. The synthesis method is resulting in a narrow distribution of architecture of different surface nitrides. This allows for an exclusive examination of the catalysis of distinctive, specific nitrogen involving surface groups for the Vanadium reactions and shows pathways for advanced modification methods. Experimental results will comprise rotating disk electrode (RDE) measurements in an electrochemical half-cell. Moreover, x-ray photoemission spectroscopy results depict the surface coverage of the newly created adsorbants. In addition, the performance and changed efficiency of a single cell is presented, which is equipped with GF electrodes comprising the surface nitrides evaluated before. The project is financially supported by the Bavarian Ministry of Economics. (1) Parasuraman et al. Electrochimica Acta (2013) 101 27–40. (2) J.-Z. Chen et al. Journal of Power Sources (2015) 274 894–898. (3) K.J.Kim et al. Mat. Chem. And Phys. (2011) 131 547-553. (4) S. Wang et al. J. Phys. Chem. Lett. (2012) 3 2164−2167. (5) Y. Shao et al. Journal of Power Sources (2010) 195 4375–4379.
Published Version
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