Modification of Carbon Electrodes with Mxene (Ti3C2Tx) for Vanadium Redox Flow Batteries

Abstract

MXenes, a group of two-dimensional materials, have gained considerable attention in the field of electrochemistry due to their outstanding electrical conductivity, high surface area, and hydrophilicity resulting from their rich surface chemistry. In this study, Ti3C2Tx MXene-coated carbon paper electrodes were prepared through drop-casting and tested for vanadium redox flow batteries (VRFBs). The resulting MXene-coated electrodes demonstrated a significant improvement in the electrochemical activity of the negative electrode of VRFBs (V(II)/V(III)) compared to heat-treated and untreated carbon paper.The electrochemical activity of the V(II)/V(III) reaction on MXene-coated electrodes was characterized using cyclic voltammetry and electrochemical impedance spectroscopy techniques. The cyclic voltammetry results indicated that the MXene-coated electrodes displayed a peak current ratio (ipa/ipc) closer to 1 than heat-treated and untreated carbon paper. Electrochemical impedance spectroscopy shows that ohmic and charge transfer resistance are significantly reduced, rivaling a heat-treated carbon paper electrode. VRFB tests were conducted using MXene-coated electrodes on the negative side at a current density of 130 mA/cm2. Carbon paper anodes with MXene loading of 0.1 mg/cm2 maintained voltage efficiency and coulombic efficiency above 70% and 95% for 50 cycles, respectively, which is comparable to that of heat-treated carbon paper, whereas using untreated carbon paper, the voltage efficiency dropped below 60%.Untreated carbon paper electrode has maximum discharge capacities of 77.4 mAh with a capacity loss of 36%. MXene-coated electrodes, on the other hand, showed impressive maximum discharge capacities of 178.8 mAh and a capacity loss of 19%.