Electrochemical Behavior of Vanadium Carbide in Neutral Aqueous Electrolytes

The V_2C compound, belonging to the group of two-dimensional transition metal carbonitrides, or MXenes, has demonstrated a promising electrochemical performance in capacitor applications in acidic electrolytes; however, there is evidence to suggest that V_2C is unstable in an acidic environment. On the other hand, the performance of V_2C in neutral aqueous electrolytes is still moderate, and has not yet been systematically studied. The charge storage mechanism in a V_2C electrode, employed in neutral aqueous electrolytes, is investigated via cyclic voltammetry testing and in situ x-ray diffraction (XRD). Good specific capacitances are achieved, specifically 208 F/g in 0.5 M Li_2SO_4, 225 F/g in 1 M MgSO_4, 120 F/g in 1M Na_2SO_4, and 104 F/g in 0.5 M K_2SO_4. Using in situ XRD, we observe that, during the charge and discharge process, the c-lattice parameter shrinks or expands by up to 0.25 Å in MgSO_4, and 0.29 Å in Li_2SO_4 which demonstrates the intercalation/de-intercalation of cations into the d-V_2C layer.