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NiMoO4 has attracted intensive attention as one of the promising ternary metal oxides because of its high specific capacitance and electrical conductivity compared to traditional transition-metal oxides. In this study, NiMoO4 nanorods uniformly decorated on graphene nanosheets (G-NiMoO4) are synthesized through a facile hydrothermal method. The prepared G-NiMoO4 composite exhibits a high specific capacitance of 714 C·g−1 at 1 A·g−1 and an excellent rate capability, with a retention ratio of 57.7% even at 100 A·g−1. An asymmetric supercapacitor (ASC) fabricated with the G-NiMoO4 composite as the positive electrode and Fe2O3 quantum dot-decorated graphene (G-Fe2O3-QDs) as the negative electrode delivers an ultrahigh energy density of 130 Wh·kg−1, which is comparable to those of previously reported aqueous NiMoO4-based ASCs. Even when the power density reaches 33.6 kW·kg−1, an energy density of 56 Wh·kg−1 can be maintained. The ASC device exhibits outstanding cycling stability, with a capacitance retention of 113% after 40,000 cycles. These results indicate that the G-NiMoO4 composite is a promising candidate for ASCs with ultrahigh energy density and excellent cycling stability. Moreover, the present work provides an exciting guideline for the future design of high-performance supercapacitors for industrial and consumer applications via the simultaneous use of various pseudocapacitive materials with suitable potential windows as the positive and negative electrodes. [ABSTRACT FROM AUTHOR]

Highlights: A freestanding MXene-derived defect-rich TiO2@reduced graphene oxides (M-TiO2@rGO) foam electrode was fabricated. M-TiO2@rGO presents fast Na+ storage kinetics due to capacitive contribution. M-TiO2@rGO foam electrode displays a capacity retention of 90.7% after 5000 cycles. Sodium ion batteries and capacitors have demonstrated their potential applications for next-generation low-cost energy storage devices. These devices's rate ability is determined by the fast sodium ion storage behavior in electrode materials. Herein, a defective TiO2@reduced graphene oxide (M-TiO2@rGO) self-supporting foam electrode is constructed via a facile MXene decomposition and graphene oxide self-assembling process. The employment of the MXene parent phase exhibits distinctive advantages, enabling defect engineering, nanoengineering, and fluorine-doped metal oxides. As a result, the M-TiO2@rGO electrode shows a pseudocapacitance-dominated hybrid sodium storage mechanism. The pseudocapacitance-dominated process leads to high capacity, remarkable rate ability, and superior cycling performance. Significantly, an M-TiO2@rGO//Na3V2(PO4)3 sodium full cell and an M-TiO2@rGO//HPAC sodium ion capacitor are fabricated to demonstrate the promising application of M-TiO2@rGO. The sodium ion battery presents a capacity of 177.1 mAh g−1 at 500 mA g−1 and capacity retention of 74% after 200 cycles. The sodium ion capacitor delivers a maximum energy density of 101.2 Wh kg−1 and a maximum power density of 10,103.7 W kg−1. At 1.0 A g−1, it displays an energy retention of 84.7% after 10,000 cycles. [ABSTRACT FROM AUTHOR]