Hydrogen evolution at the negative electrode vanadium

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Hydrogen evolution at the negative electrode vanadium ( hydrogen-evolution-at-negative-electrode-vanadium )

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Journal of Power Sources 248 (2014) 560e564 Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour Short communication Hydrogen evolution at the negative electrode of the all-vanadium redox flow batteries Che-Nan Sun a, *, Frank M. Delnick b, Loïc Baggetto a, Gabriel M. Veith a, Thomas A. Zawodzinski Jr.a,c,d,* a Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA b Power Sources Technology Group, Sandia National Laboratory, Albuquerque, NM 87185, USA c Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, TN 37996, USA d Department of Chemistry, King Abdulaziz University, Jeddah, Saudi Arabia highlights  The rate of hydrogen evolution in the all-vanadium redox flow battery (VRFB) is quantified.  The method for determining the electrochemical surface area of the VRFB electrode is proposed.  Higher surface area electrode leads to a higher hydrogen evolution rate. articleinfo abstract Article history: Received 23 August 2013 Received in revised form 27 September 2013 Accepted 29 September 2013 Available online 6 October 2013 Keywords: Hydrogen evolution Redox flow battery Side reaction Electrochemical surface area 1. Introduction There is increasing recognition of the need for large-scale en- ergy storage systems for effectively integrating intermittent and renewable energy sources to the modern electrical grid. [1,2] The redox flow battery (RFB), which provides a highly scalable method of energy storage, is one promising technology for this application and has therefore attracted a great deal of attention in recent years. [3e5] The all-vanadium redox flow battery (VRFB) [6e10] is a type of RFBs that employs four different oxidation states of vanadium ions, V2þ/V3þ and V4þ/V5þ in two reaction compartments which are separated by an ion-conducting membrane, to serve as the redox * Corresponding authors. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA E-mail addresses: sunc@ornl.gov, chenan.sun@gmail.com (C.-N. Sun), tzawodzi@ utk.edu (T.A. Zawodzinski). 0378-7753/$ e see front matter Published by Elsevier B.V. http://dx.doi.org/10.1016/j.jpowsour.2013.09.125 This work demonstrates a quantitative method to determine the hydrogen evolution rate occurring at the negative carbon electrode of the all vanadium redox flow battery (VRFB). Two carbon papers examined by buoyancy measurements yield distinct hydrogen formation rates (0.170 and 0.005 mmol min1 g1). The carbon papers have been characterized using electron microscopy, nitrogen gas adsorption, capacitance measurement by electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). We find that the specific electrochemical surface area (ECSA) of the carbon material has a strong influence on the hydrogen generation rate. This is discussed in light of the use of high surface area material to obtain high reaction rates in the VRFB. Published by Elsevier B.V. couples for the negative and the positive electrode reactions, respectively. Despite the apparent simplicity of the involved electrochemical reactions, optimizing the RFB is in reality very complex. Efforts have been made toward improving the VRFB performance by modifying electrodes, [11e15] membranes, [16e19] electrolytes, [7,20] and cell configuration. [13] However, self-discharge induced by vanadium ion crossover [21] and the tendency to develop asymmetrical valence of vanadium ion in positive and negative electrolytes due to side re- actions [22e24] are two important system challenges. Recently, va- nadium crossover through the membrane was effectively reduced by altering the polymer morphology [25] or employing anion exchange membranes. [19,26] However, the impact of the side reactions on VRFB operation still remains to be addressed. We recently demonstrated the possibility of integrating a reference electrode into the VRFB. [27,28] The presence of a refer- ence electrode enabled us to separate and individually study the electrochemical processes on the positive and negative electrodes.

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