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.