Synthesis of coaxial carbon@NiMoO4 composite nanofibers for supercapacitor electrodes

Approaching high performance Ni(Co) molybdate electrode materials for flexible hybrid devices

Transition metal molybdates are widely used as electrode materials for supercapacitors due to their high theoretical specific capacitance and excellent electrochemical activity. It is an effective strategy to improve the electrochemical performance by reasonably designing electrode materials. Herein, we prepared several Ni_1-xCo_xMoO₄·nH₂O nanostructures through facile hydrothermal strategies. Benefiting from the synergistic effects between Ni and Co elements, the obtained electrode materials delivered a specific capacitance of 1390 F g⁻¹ at 1 A g⁻¹. The as-assembled device shows an energy density of 72.45 W h kg⁻¹ at a power density of 2688.8 W kg⁻¹. It also presents excellent cycling and mechanical stability after many times of charging and discharging processes and bending.

We prepare several Ni_1−xCo_xMoO₄·nH₂O nanostructures through facile hydrothermal strategies. The obtained electrode materials delivered a specific capacitance of 1390 F g⁻¹ at 1 A g⁻¹. The as-assembled device shows an energy density of 72.45 W h kg⁻¹ at a power density of 2688.8 W kg⁻¹.

Zn Metal Atom Doping on the Surface Plane of One-Dimesional NiMoO4 Nanorods with Improved Redox Chemistry

The effect of zinc (Zn) doping and defect formation on the surface of nickel molybdate (NiMoO₄) structures with varying Zn content has been studied to produce one-dimensional electrodes and catalysts for electrochemical energy storage and ethanol oxidation, respectively. Zn-doped nickel molybdate (Ni_1-xZn_xMoO₄, where x = 0.1, 0.2, 0.4, and 0.6) nanorods were synthesized by a simple wet chemical route. The optimal amount of Zn is found to be around 0.25 above which the NiMoO₄ becomes unstable, resulting in poor electrochemical activity. This result agrees with our density functional theory calculations in which the thermodynamic stability reveals that Ni_1-xZn_xMoO₄ crystallized in the β-NiMoO₄ phase and is found to be stable for x≤0.25. Analytical techniques show direct evidence of the presence of Zn in the NiMoO₄ nanorods, which subtly alter the electrocatalytic activity. Compared with pristine NiMoO₄, Zn-doped NiMoO₄ with the optimized Zn content was tested as an electrode for an asymmetric supercapacitor and demonstrated an enhanced specific capacitance of 122 F g^-1 with a high specific energy density of 43 W h kg^-1 at a high power density of 384 W kg^-1. Our calculations suggest that the good conductivity from Zn doping is attributed to the formation of excess oxygen vacancies and dopants play an important role in enhancing the charge transfer between the surface and OH^- ions from the electrolyte. We report electrochemical testing, material characterization, and computational insights and demonstrate that the appropriate amount of Zn in NiMoO₄ can improve the storage capacity (∼15%) due to oxygen vacancy interactions.

Design of NiO Flakes@CoMoO4 Nanosheets Core-Shell Architecture on Ni Foam for High-Performance Supercapacitors

As typical electrode materials for supercapacitors, low specific capacitance and insufficient cycling stability of transition metal oxides (TMOs) are still the problems that need to be solved. Design of core-shell structure is considered as an effective method for preparation of high-performance electrode materials. In this work, NiO flakes@CoMoO4 nanosheets/Ni foam (NiO flakes@CoMoO4 NSs/NF) core-shell architecture was constructed by a two-step hydrothermal method. Interestingly, the CoMoO4 NSs are vertically grown on the surface of NiO flakes, forming a two-dimensional (2D) branched core-shell structure. The porous core-shell architecture has relatively high surface area, effective ions channels, and abundant redox sites, resulting in excellent electrochemical performance. As a positive electrode for supercapacitors, NiO flakes@CoMoO4 NSs/NF core-shell architecture exhibits excellent capacitive performance in terms of high specific capacitance (1097 F/g at 1 A/g) and outstanding cycling stability (97.5% after 2000 circles). The assembled asymmetric supercapacitor (ASC) of NiO flakes@CoMoO4 NSs/NF//active carbon (AC)/NF possesses a maximum energy density of 25.8 Wh/kg at power density of 894.7 W/kg. The results demonstrate that NiO flakes@CoMoO4 NSs/NF electrode displays potential applications in supercapacitors and the design of 2D branched core-shell architecture paves an ideal way to obtain high-performance TMOs electrodes.