Flexible Ti₃C₂T_x/PEDOT:PSS films with outstanding volumetric capacitance for asymmetric supercapacitors

MXenes are two-dimensional transition metal carbides/nitrides, and they have shown exciting application prospects for electrochemical energy storage in the future owing to their hydrophilicity, metallic conductivity and surface redox reactions, which are crucial for high-capacitance and high-rate electrode materials. However, the strong tendency of adjacent MXene flakes to aggregate or self-restack under the van der Waals force limits the electrochemical performance of MXene-based electrodes for practical applications. In this study, we developed a simple and effective method to prepare Ti₃C₂T_x/PEDOT:PSS hybrid films via filtering the Ti₃C₂T_x/Clevios PH1000 compound inks, followed by H₂SO₄ treatment. H₂SO₄ treatment could remove part of the insulating PSS from the Ti₃C₂T_x/PEDOT:PSS hybrid film, resulting in significant conductivity enhancement of the composite. Furthermore, the conductive PEDOT not only acted as a pillar between Ti₃C₂T_x sheets to expose more electroactive surfaces and reduce ion diffusion pathways but also played a role as a conductive bridge to form multidimensional electronic transport channels for accelerating the electrochemical reaction process. As a result, the as-prepared H₂SO₄-treated Ti₃C₂T_x/PEDOT:PSS (Ti₃C₂T_x/P-100-H) hybrid film exhibited 4.5-fold increase in the specific surface area and high volumetric capacitance of 1065 F cm^-3 at 2 mV s^-1 with superior rate performance in 1 M H₂SO₄ electrolyte. Especially, we assembled an asymmetric supercapacitor (ASC) with excellent flexibility based on a Ti₃C₂T_x/P-100-H hybrid negative electrode and rGO film positive electrode, which delivered high energy density of 23 mW h cm^-3 and high power density of 7659 mW cm^-3. Moreover, a simple luminous band was designed and powered by our two ASCs in series. The outstanding volumetric electrochemical performance and energy density of the ASC based on the flexible Ti₃C₂T_x/P-100-H hybrid film electrode demonstrated its promising potential as a strong power source for small portable and wearable electronic devices.