Interaction Mechanism and Pseudocapacitance of Polar and Non-Polar Polyfluorenes with 2D Titanium Carbide (MXene)

Two-dimensional (2D) materials have garnered tremendous interest due to their unprecedented physical and chemical properties. Recently, a large family of 2D metal carbides and nitrides (MXenes) have been discovered which exhibits metallic conductivity, hydrophilicity and several other attractive properties. MXenes have already shown a great promise in broad range of applications such as energy conversion and storage, water purification, catalysis, antibacterial agent, transparent conductive electrodes, electromagnetic shielding and others. One way to expand the MXenes applications is to tune their physical, chemical and electrochemical properties by mixing them with polymers to synthesize functional nanocomposites. Therefore, it is necessary to first understand the interaction mechanisms of polymers with 2D MXene layers. Here, we provide a mechanistic insight into interaction of ?-conjugated polymers with titanium carbide, Ti3C2Tx (MXene), using polyfluorene derivatives (PFD) having the same conjugated backbone but different lateral chain from apolar to polar. Three PFD having no polar, with polar nitrogen, and with charged nitrogen functionality were synthesized via the Suzuki polycondensation reaction. Detailed microscopic and spectroscopic results demonstrated that polar polymers with charged nitrogen ends tend to strongly interact with the Ti3C2Tx layers, causing an increase in interlayer spacing and large shifts in spectroscopic peaks. When optimized composites were tested as pseudocapacitive electrodes, improved capacitance values and excellent capacitance retention were observed. Our results provide a valuable insight into exploring new organic materials capable of intercalation between the layers of Ti3C2Tx, and other MXenes for energy storage applications and beyond.