Electrochemical behaviour of titanium/iridium(IV) oxide: Tantalum pentoxide and graphite for application in vanadium redox flow battery

• VRFB cell has been constructed and the electrochemical performances have been studied.
• V3+ to V4+ electron transfer state has been obtained.
• Dimensionally stable electro materials Ti/IrO2:Ta2O5 are prepared and studied.
• Energy density 33 Wh L−1 has been achieved for DSA electrodes.
• The columbic, voltage and energy efficiencies of Ti/IrO2:Ta2O5 have been estimated and compared with graphite electrode.

The present work describes the preparation and electrochemical characterisation of titanium/iridium(IV) oxide: tantalum pentoxide (Ti/IrO2:Ta2O5) electrodes for vanadium redox flow battery applications. The electrode surface morphology is examined by field-emission scanning electron microscopy, and their electrochemical behaviours are studied by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. A charge–discharge study has been performed at different current densities using vanadium sulphate as an electrolyte medium (1.7 M V3.5+ and 4 M H2SO4), and as-prepared Ti/IrO2:Ta2O5 and pristine graphite are used as the anode and cathode, respectively. To better understand the behaviour of the electrodes and for comparison, a vanadium redox flow battery is also constructed using graphite as the anode as well as the cathode, and its charge–discharge performance is examined. The electrochemical study revealed that the Ti/IrO2:Ta2O5 electrodes exhibit slightly higher catalytic activity and long-term stability than the graphite electrode in highly concentrated sulphuric acid medium. The Ti/IrO2:Ta2O5 electrodes also exhibit slightly higher energy density (33 Wh L−1) than the graphite electrode (31.5 Wh L−1). However, the energy efficiency of Ti/IrO2:Ta2O5 electrode at 40 mA cm−2 is 81%, which is lower than that of the graphite electrode (86% at 40 mA cm−2).

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