Oxygen-Vacancy-Rich NiMnZn-Layered Double Hydroxide Nanosheets Married with Mo₂CT_xMXene 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/Mo₂CT_x2D-on-2D nanohybrids are fabricated through electrostatic assembly of alkaline-etched NiMnZn-LDH (eLDH) nanosheets and exfoliated Mo₂CT_xMXene. The alkaline etching creates more oxygen vacancies and regulates the valence states of Ni/Mn active elements in eLDH. After "marrying" with the Mo₂CT_xMXene, 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/Mo₂CT_xnanohybrids show a greatly enhanced specific capacity (1577 C g^-1at 2 A g^-1) relative to pure eLDH, Mo₂CT_x, and initial NiMnZn-LDH. Also, the cycling stability of eLDH/Mo₂CT_xnanohybrids 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^-1at 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.