Surface nitrogen-modified 2D titanium carbide (MXene) with high energy density for aqueous supercapacitor applications

Abstract

Supercapacitors (SCs), environment-friendly high-power energy storage devices, have drawn great attention due to the increasing and urgent development of renewable energies. Ti₃C₂T_x (MXene), a 2D high conductivity material, has been shown to be a potential electrode material for SCs, because of its outstanding chemical and physical properties. However, the surface termination of –F and –OH could block the transport of electrolyte ions and thus decrease the energy storage performances. In this regard, nitrogen related functional groups have been introduced to modify the surface characteristics of Ti₃C₂T_x, in order to increase the electron conduction and energy storage capacity. Experimental results have shown that the presence of moieties such as –NH₂, Ti–O–N and O–Ti–N, could offer a synergistic effect on the electrochemical performance of SCs, which is mainly attributed to the intercalation-pseudocapacitance contribution according to the quantitative analysis. Furthermore, the role of O–Ti–N is more significant than that of Ti–O–N. Specifically, for the first time, we demonstrate that electrodes based on the N surface modified Ti₃C₂T_x film display largely enhanced electrochemical performances, with gravimetric capacitance of 415.0 F g⁻¹ at 2 mV s⁻¹, rate capacity of 75.9% at 200 mV s⁻¹ and cycling stability of above 90% retention after 18 000 cycles. In addition, symmetric SCs based on the N–Ti₃C₂T_x-300 film could deliver a maximum volumetric energy density of 21.0 W h L⁻¹ and an energy density of 10.2 W h L⁻¹, at a high power density of 18.3 kW L⁻¹.