In this work, NiCo 2 O 4 @NiCo 2 S 4 nanocomposite with a hierarchical structure is prepared by a multistep process. First, NiCo 2 O 4 nanowires array on Ni foam is prepared by a hydrothermal and a subsequent calcination process. Then, the NiCo 2 O 4 nanowires array is converted to NiCo 2 O 4 @NiCo 2 S 4 nanocomposite through a vapor-phase hydrothermal process. The NiCo 2 O 4 @NiCo 2 S 4 /Ni foam electrode exhibits a specific capacitance of 1872 F g –1 at 1 A g –1 , a capacitance retention of 70.5% at 10 A g –1 , and a retention ratio of 65% after 4000 charge–discharge cycles. The capacitance of NiCo 2 O 4 @NiCo 2 S 4 nanocomposite is much higher than that of the NiCo 2 O 4 nanowires array. The excellent electrochemical capacitive performances of the NiCo 2 O 4 @NiCo 2 S 4 nanocomposite can be attributed to the hierarchical nanostructure, which can provide large surface areas and short diffusion pathways for electrons and ions. By using the NiCo 2 O 4 @NiCo 2 S 4 /Ni foam as the positive electrode and activated carbon/Ni foam as the negative electrode, a hybrid supercapacitor device is fabricated. The device achieves an energy density of 35.6 W h kg –1 and a power density of 1.5 kW kg –1 at 2 A g –1 .

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Catalysts play an extraordinarily important role in accelerating the hydrogen sorption rates in metal-hydrogen systems. Herein, we report a surprisingly synergetic enhancement of metal-metal oxide cocatalyst on the hydrogen sorption properties of MgH: only 5 wt % doping of Ni into ultrafine TiO enables a significant increase in hydrogen desorption kinetics; it absorbs 4.50 wt % hydrogen even at a low temperature of 50 °C. The striking improvement is partially ascribed to the formation of a particular Ni@TiO core-shell structure, thereby forming versatile interfaces. This study provides insights into the way of designing high-efficiency catalysts in hydrogen storage and other energy-related fields.

For the first time, few-layer Ti3C2T x (FL-Ti3C2T x ) supporting highly dispersed nano-Ni particles with an interconnected and interlaced structure was elaborated through a self-assembly reduction process. FL-Ti3C2T x not only acts as a supporting material but also self-assembles with Ni2+ ions through the electrostatic interaction, assisting in the reduction of nano-Ni. After ball milling with MgH2, Ni30/FL-Ti3C2T x (few-layer Ti3C2T x supported 30 wt % nano-Ni via self-assembly reduction) shows superior catalytic activity for MgH2. For example, MgH2-5 wt % Ni30/FL-Ti3C2T x can release approximately 5.83 wt % hydrogen within 1800 s at 250 °C and absorb 5 wt % hydrogen within 1700 s at 100 °C. The combined effects of finely dispersed nano-Ni in situ-grown on FL-Ti3C2T x , large specific area of FL-Ti3C2T x , multiple-valence Ti (Ti4+, Ti3+, Ti2+, and Ti0) derived from FL-Ti3C2T x , and the electronic interaction between Ni and FL-Ti3C2T x can explain the superb hydrogen storage performance. Our results will attract more attention to the elaboration of the metal/FL-Ti3C2T x composite via self-assembly reduction and provide a guideline to design high-efficiency composite catalysts with MXene in hydrogen storage fields.

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