Pseudocapacitance of Bimetallic Solid-Solution MXene for Supercapacitors with Enhanced Electrochemical Energy Storage

MXenes, a family of 2D transition metal carbides, are considered promising high-rate pseudocapacitive materials because of their metallic-like conductivity and transition metal oxide-like surfaces. Currently, nearly 50 stoichiometric MXenes have been synthesized. However, only a few MXenes, such as Ti3C2, have shown stable pseudocapacitive charge storage so far. Further improving the inherent pseudocapacitance of MXenes without losing their cyclability remains a challenge. Herein, a mild method is reported to produce highly stable bimetallic solid-solution MXene Ti2VC2 using a solution of potassium fluoride and hydrochloric acid. The electrochemical properties of resulting multilayered clay-like and delaminated Ti2VC2 films are investigated, exceeding the performance of typical Ti3C2 in acidic electrolytes. These electrodes deliver up to 2000 F cm-3 and retain more than 90% of their initial capacitance after 20 000 cycles, surpassing most state-of-the-art supercapacitor materials known. The pseudocapacitive charge storage of Ti2VC2 is deeply investigated through in situ and ex situ experimental studies, confirmed the pseudocapacitive mechanism is a combination of hydrated H+ intercalation and surface redox. This work provides a practical route toward future rational design on the atomic scale for high-performance pseudocapacitive materials. A chemically stable bimetallic solid-solution MXene Ti2VC2 and its application as high capacitance and long lifetime proton pseudocapacitor electrodes are demonstrated. The hydrogel Ti2VC2 film show impressive volumetric capacitance (2670 F cm-3), surpassing the performance of most state-of-the-art supercapacitor materials. The pseudocapacitance mechanism combines with pseudo-intercalation and surface redox is revealed through in situ and ex situ experimental studies.image