Rosette-like (Ni,Co)Se2@Nb2CTx MXene heterostructure with abundant Se vacancies for high-performance flexible supercapacitor electrodes

It is common knowledge that battery-type materials have ideal energy storage capacity due to the Faraday behavior that happens both on the outside and inside, but the slow reaction kinetics and limiting multiplicity performance are the key bottlenecks that limit their large-scale energy storage. Herein, a rosette-like V-(Ni,Co)Se2@Nb2CTx MXene (V-NCSN) with abundant Se vacancies heterostructure is prepared to study the Se vacancy enhancement mechanism in energy storage. Systematic characterization and DFT theoretical calculations illustrate that the special heterogeneous interface and vacancy structure can fundamentally modulate the electron structure of the host material, and rationalize the affinity relationship of OH– with the adsorption energy from −1.9 eV of NCSN to −2.4 eV of V-NCSN and enhance the kinetics of the V-NCSN electrode. The prepared V-NCSN-2 electrodes as cathode deliver incredible properties for large capacitance of 267.1 mAh/g (1922.7F g−1) at 2 A/g, outstanding long cycle durability and ultrahigh rate capacity with initial capacity vestigial of 74.6 % at 50 A/g. Furthermore, the V-NCSN-2//AC hybrid supercapacitor (HSC) is constructed with V-NCSN-2 electrode and activated carbon (AC) electrode, which depicts strengthened energy storage characteristic, in the light of the large reversible capacity of 57.0 mAh/g (110.8F g−1) at 2 A/g, outstanding energy density of 45.6 Wh kg−1 at 168.4 W kg−1, durable long cycle stability of 96.8 % undergoing 10,000 cycles. The construction of electrodes using two-dimensional MXene provides a competitive advantage for selenium-based cathode materials and a new strategy for the evolution of supercapacitors.