1e:T567,Supercapacitors attract great interest because of the increasing and urgent demand for environment‐friendly high‐power energy sources. Ti 3 C 2 , a member of MXene family, is a promising electrode material for supercapacitors owing to its excellent chemical and physical properties. However, the highest gravimetric capacitance of the MXene‐based electrodes is still relatively low (245 F g −1 ) and the key challenge to improve this is to exploit more pseudocapacitance by increasing the active site concentration. Here, a method to significantly improve the gravimetric capacitance of Ti 3 C 2 T x MXenes by cation intercalation and surface modification is reported. After K + intercalation and terminal groups (OH − /F − ) removing , the intercalation pseudocapacitance is three times higher than the pristine MXene, and MXene sheets exhibit a significant enhancement (about 211% of the origin) in the gravimetric capacitance (517 F g −1 at a discharge rate of 1 A g −1 ). Moreover, the as‐prepared electrodes show above 99% retention over 10 000 cycles. This improved electrochemical performance is attributed to the large interlayer voids of Ti 3 C 2 and lowest terminated surface group concentration. This study demonstrates a new strategy applicable to other MXenes (Ti 2 CT x , Nb 2 CT x , etc.) in maximizing their potential applications in energy storage.1f:T4e5,Two-dimensional MXenes are promising for various energy-related applications such as energy storage devices and electrocatalysis of water-splitting. MXenes prepared from hydrofluoric (HF) acid etching have been widely reported. Nonetheless, the acute toxicity of HF acid impedes the large-scale fabrication of MXenes and their wide utilization in energy-related applications. It is thus greatly encouraging to explore a more innocuous protocol for MXenes synthesis. Thereby, a universal strategy based on thermal-assisted electrochemical etching route is developed to synthesize MXenes (e.g., Ti₂CT _x, Cr₂CT _x, and V₂CT _x). Furthermore, the cobalt ion doped MXenes show an exceptionally enhanced capability of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activity, demonstrating their multifunctionalities, which is comparable to the commercialized catalysts. Moreover, we successfully exploited our MXenes as cathodes for the novel aqueous rechargeable battery, with proficient retention and excellent electrical output performance. This work paves a nontoxic and HF-free route to prepare various MXenes and demonstrates practical applications of the materials.20:T423,Two-dimensional (2D) titanium carbide (Ti₃ C₂ ) is emerging as an important member of the MXene family. However, fluoride-based synthetic procedures remain an impediment to the practical applications of this promising class of materials. Here we demonstrate an efficient fluoride-free etching method based on the anodic corrosion of titanium aluminium carbide (Ti₃ AlC₂ ) in a binary aqueous electrolyte. The dissolution of aluminium followed by in situ intercalation of ammonium hydroxide results in the extraction of carbide flakes (Ti₃ C₂ T_x , T=O, OH) with sizes up to 18.6 μm and high yield (over 90 %) of mono- and bilayers. All-solid-state supercapacitor based on exfoliated sheets exhibits high areal and volumetric capacitances of 220 mF cm^-2 and 439 F cm^-3 , respectively, at a scan rate of 10 mV s^-1 , superior to those of LiF/HCl-etched MXenes. Our strategy paves a safe way to the scalable synthesis and application of MXene materials.

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