Selenized Binary Transition Metals-Mxene Composite for the High-Performance Asymmetric Supercapacitors

The exploration of novel and efficient energy storage materials is crucial for the development of high-performance supercapacitors. Herein, we develop a new composite with multilayered MXene (Ti3C2Tx) nanoparticles and porous NiCo2Se4 nanosheets. The unique accordion-like nanostructure and strong interfacial interactions of MXene introduce the favorable nanocomposite with a larger surface area and reasonable cycling stability. The substitution of Se for the oxyhdryl in the Ni-Co based hydroxides modulates the orbital hybridization with the corresponding metallic cations, which effectively improves the electrochemical activity of Ni/Co and reduces the adsorption/desorption energy barrier of electrolyte ions. Based on the above considerations, we proposed a new Ni-Co TMSe and multilayer Ti3C2Tx MXene nanocomposite on NF (denoted as MXene-NiCo2Se4@NF) that could act as a binder-free electrode for SCs. In this regard, compared with the directly grown pure NiCo2Se4 electrode, the composite electrode exhibits a larger surface area, higher mass-loading, and lower internal resistance by the introduced MXene particles. The well-designed hierarchical structures make it possible for facilitated electrolyte diffusion, more active sites, fast electron transport, and improved nanostructure stability for a longer lifespan. Owing to such multifold attributes, the fabricated composite electrodes enable to attain a specific capacity of 786.25 C/g and 589.22 C/g at the current density at 1 A/g and 20 A/g with a good rate capability, respectively. The selenization improved the inherent conductivity of active materials and contributed to the lower deprotonation energy barrier, resulting in facile electron transfer in the Faradaic reaction process. Furthermore, the composite structure retained over 90% of capacity after 8000 cycles. The assembled asymmetrical device displays a high specific energy density of 64.36 Wh/kg, at a power density of 0.8kW/kg. These results suggest that the proposed composite structure can potentially be used as active material in various practical applications.