Direct Experimental Quantification of Intrinsic Capacitive Properties of Monolayer Ti3C2T x MXene

Abstract Ti3C2Tx MXene is widely employed in energy storage because of its unique interfacial charge-storage properties. Understanding its intrinsic capacitive properties, especially the surface characteristics of a monolayer flake, is critical to optimizing device performance, but direct measurement at the monolayer level remains elusive. Here, we report, for the first time, direct experimental quantification of the intrinsic capacitance of monolayer Ti3C2Tx MXene by integrating optimized flake protection and parasitic-capacitance-shielding strategies. The quasi-static areal capacitance is 141 μF cm–2 in acidic electrolytes and 61–74 μF cm–2 in alkali-metal-ion electrolytes. Decoupling the pseudocapacitive and electric-double-layer contributions by resolving the concentration dependence reveals that pseudocapacitance accounts for ∼45% of the total in acidic electrolytes but <10% in alkali-metal-ion electrolytes. Temperature-dependent kinetics show that a lower proton-transfer activation energy facilitates the pseudocapacitive charge storage. This work quantifies how redox and double-layer mechanisms coexist on a monolayer Ti3C2Tx MXene surface and establishes a benchmark across the field.