Oxygen-Vacancy-Rich NiMnZn-Layered Double Hydroxide Nanosheets Married with Mo₂CT_x MXene for High-Efficiency All-Solid-State Hybrid Supercapacitors

Designing defect-rich multimetallic layered double hydroxide (LDH)-based nanohybrids and integrating them into particular device configuration are paramount to develop high-performance hybrid supercapacitors (HSCs) but remain a great challenge. Herein, oxygen-vacancy-rich NiMnZn-LDH/Mo2CTx 2D-on-2D nanohybrids are fabricated through electrostatic assembly of alkaline-etched NiMnZn-LDH (eLDH) nanosheets and exfoliated Mo2CTx MXene. The alkaline etching creates more oxygen vacancies and regulates the valence states of Ni/Mn active elements in eLDH. After “marrying” with the Mo2CTx MXene, the strong interplay of these two components will further modulate the surface electronic structure of eLDH, promote charge transport between interfaces, and increase the content of oxygen vacancies that can provide more accessible active sites for a Faradaic reaction. Thus, the obtained eLDH/Mo2CTx nanohybrids show a greatly enhanced specific capacity (1577 C g–1 at 2 A g–1) relative to pure eLDH, Mo2CTx, and initial NiMnZn-LDH. Also, the cycling stability of eLDH/Mo2CTx nanohybrids outperforms their monocomponent counterparts. Moreover, employing such 2D-on-2D nanohybrids as a positive electrode while pairing iron oxide (Fe2O3)/carbon nanotube nanohybrids as a negative electrode, three kinds of all-solid-state HSCs are further fabricated with the positive–negative-type, positive–negative–positive-type, and negative–positive–negative-type device geometries. Among them, the positive–negative–positive-type device exhibits an ultrahigh energy density (92.6 Wh kg–1 at 2695 W kg–1), superior to the positive–negative-type and negative–positive–negative-type devices and most of the other reported HSCs ones. This work may spur the development of defect-rich multimetallic LDH-based 2D nanohybrids and promote their applications in all-solid-state HSCs or other clean energy apparatuses.