Superior Activity of Carbon Felt Coated with PEDOT and Titanium Oxide Double Layers Towards V(II)/(VIII) Reaction in Redox Flow Batteries

Abstract

Energy consumption has become a great problem in the last few decades due to the dramatic increment in population and solo dependence on fossil fuels to fulfill energy requirements. The intense consumption of these limited non-renewable resources had harmful effects on humanity, making the adoption of renewable energy resources compulsory. High-efficiency storage systems are necessary for the integration of renewable energy sources into the electrical grid and for the provision of that energy when needed. For this application, all-vanadium redox flow batteries (VRFBs) hold great promise because of their high energy storage capacity, extended operational life, and long-life reusable solutions1. The enhancement of RFBs should be taken from many perspectives such as the enhancement of electrodes, membranes, or even the design of the cell. Enhancing the electrode performance is one of the important challenges that attracted the attention of researchers, with a variety of electrode modifications that have been studied such as using carbon, metals, and metal oxide materials2,3. Over a large number of metal oxides, TiO2 possesses interesting catalytic properties as it has been used in sensors, Li-ion batteries, and electrocatalysis, in addition to its ability to suppress the hydrogen evolution reaction (HER) which was a stumbling block for the negative side of VRFBs4.The goals of this work are to suppress the parasitic reaction of hydrogen evolution and improve the kinetics of the VRFBs' negative half-cell reaction (V(II)/V(III)). To achieve this goal, coating carbon felt (CF) with poly(3,4-ethylenedioxythiophene) (PEDOT) and Titanium Oxide double layers was proposed. The underlayer of PEDOT is expected to enhance the TiOx conductivity, and hence its electrocatalytic activity, but without enhancing the parasitic HER5. The PEDOT layer was formed using chronopotentiometric electropolymerization method, followed by the deposition of a TiOx layer using a solvothermal method. To understand the effect of the PEDOT and TiOx layers on the final electrode activity towards V(II)/V(III) redox reaction, several electrodes (CF\\PEDOT, CF\\G-PEDOT, CF\\TiOx CF\\PEDOT\\TiOx, and CF\\G-PEDOT\\TiOx) were fabricated. The physical and chemical properties of the synthesized electrodes were characterized using XRD, FESEM, EDX, UV-vis DRS, Raman spectroscopy, FTIR, contact angle measurements, and XPS. The performance of the fabricated electrodes towards V(II)/V(III) redox reaction was evaluated in 3-electrode and 2-electrode setups, using cyclic voltammetry, electrochemical impedance spectroscopy, and charging/discharging methods. The addition of an underlayer of PEDOT is found to generally enhance the TiO2 activity as a negative electrode in VRFB. References R. K. Sankaralingam, S. Seshadri, J. Sunarso, A. I. Bhatt, and A. Kapoor, J. Energy Storage, 41, 102857 (2021).Z. Huang, A. Mu, L. Wu, and H. Wang, J. Energy Storage, 45, 103526 (2022).Y. Lv et al., J. Mater. Sci. Technol., 75, 96–109 (2021).J. Vázquez-Galván et al., ChemSusChem, 10, 2089–2098 (2017).M. Heydari Gharahcheshmeh et al., Adv. Mater. Interfaces, 7, 2000855 (2020).