Hybrid MXene Electrodes with Anomalous Electrochemical Response

MXenes are a family of two-dimensional (2D) transition metal carbonitrides, with a general structure of M<i>_n</i>₊₁X<i>_n</i>T<i>_x</i>, where M is the transition metal, X is carbon or nitrogen, and T represents the surface terminations (F, O, OH) and <i>n</i> = 1-4 indicates to the number of atomic layers in their structure. Since their discovery, MXenes have shown promising properties for electrochemical charge storage applications and various MXene compositions have been tested in different electrochemical systems, both in their multilayered and delaminated forms. However, usually these materials show capacitive-like response in aqueous electrolytes with the exception of protic electrolytes such as H₂SO₄ where redox peaks and a pseudocapacitive behavior is observed. Particularly, MXenes tested in aqueous neutral electrolytes exhibit quasi-rectangular cyclic voltammograms. In this presentation, we demonstrate that through changing MXenes’ electrode structure by hybridizing them with conducting large modifiers, these materials can show anomalous electrochemical response with distinct redox couples in neutral aqueous electrolytes. We primarily show this behavior on hybrid V₂CT_x electrodes, where the free-standing films exhibit a distinct cyclic voltammograms in various alkali cation containing electrolytes with broad cathodic and anodic peaks, unlike pristine V₂CT<i>_x</i> which has a capacitive response. The observed phenomena in hybrid structures indicates a different charge storage mechanism in these electrodes while maintaining the overall amount of the charge that can be stored. Our results open new avenues in understanding the charge storage mechanism in MXene electrodes which can be used to tailor the desired electrochemical response of these materials in different electrolyte systems.