NiMoO4 Electrode Research Articles

Effect of Transition Metal Cations on Stability Enhancement for Molybdate-Based Hybrid Supercapacitor.

The race for better electrochemical energy storage systems has prompted examination of the stability in the molybdate framework (MMoO4; M = Mn, Co, or Ni) based on a range of transition metal cations from both computational and experimental approaches. Molybdate materials synthesized with controlled nanoscale morphologies (such as nanorods, agglomerated nanostructures, and nanoneedles for Mn, Co, and Ni elements, respectively) have been used as a cathode in hybrid energy storage systems. The computational and experimental data confirms that the MnMoO4 crystallized in β-form with α-MnMoO4 type whereas Co and Ni cations crystallized in α-form with α-CoMoO4 type structure. Among the various transition metal cations studied, hybrid device comprising NiMoO4 vs activated carbon exhibited excellent electrochemical performance having the specific capacitance 82 F g-1 at a current density of 0.1 A g-1 but the cycling stability needed to be significantly improved. The specific capacitance of the NiMoO4 electrode material is shown to be directly related to the surface area of the electrode/electrolyte interface, but the CoMoO4 and MnMoO4 favored a bulk formation that could be suitable for structural stability. The useful insights from the electronic structure analysis and effective mass have been provided to demonstrate the role of cations in the molybdate structure and its influence in electrochemical energy storage. With improved cycling stability, NiMoO4 can be suitable for renewable energy storage. Overall, this study will enable the development of next generation molybdate materials with multiple cation substitution resulting in better cycling stability and higher specific capacitance.

In Situ Synthesis of Mesoporous NiMoO4 on Ball Milled Graphene for High Performance Supercapacitors

Hydrothermal method is used to in situ synthesize mesoporous graphene@NiMoO4 nanocomposites as supercapacitor electrodes. NiMoO4 nanorods are formed on fresh graphene surface, while scattered NiMoO4 nanoparticles are obtained on the surface of ball milled graphene. graphene@NiMoO4 nanocomposites electrodes exhibit a higher electrochemical performance compared with a pure NiMoO4 electrode, and the ball milled graphene@NiMoO4 electrodes have the maximum specific capacitance of 2100 F g−1 at 1 A g−1 discharge current and maintains at least 92% of its initial capacitance after 5000 operational cycles. Such an enhanced supercapacitive performance originates from the mesoporous structure, more electroactive sites, large specific surface area, high electrical conductivity and synergistic effect between NiMoO4 and the graphene.

Solubility-Dependent NiMoO4 Nanoarchitectures: Direct Correlation between Rationally Designed Structure and Electrochemical Pseudokinetics.

Tailoring the binary metal oxide along with developing new synthetic methods for controlling resultant nanostructures in a predictive way is an essential requirement for achieving the further improved electrochemical performance of pseudocapacitors. Here, through a rational design of the supersaturation-mediated driving force for hydrothermal nucleation and crystal growth, we successfully obtain one-dimensional (1-D) nickel molybdenum oxide (NiMoO4) nanostructures with controlled aspect ratios. The morphology of the 1-D NiMoO4 nanostructures can be tuned from a low to a high aspect ratio (over a range of diameter sizes from 80 to 800 nm). Such a controllable structure provides a platform for understanding the electrochemical relationships in terms of fast relaxation times and improved ion-diffusion coefficients. We show that the 1-D NiMoO4 electrode with a high aspect ratio (HAR) exhibits a much higher specific capacitance of 1335 F g-1 at a current density of 1 A g-1 compared to the other electrodes with a relatively low aspect ratio, which is due to the unique physical and chemical structure being suitable for electrochemical kinetics. We further demonstrate that an asymmetric supercapacitor consisting of the tailored HAR-NiMoO4 electrode can achieve an energy density of 40.7 Wh kg-1 and a power density of 16 kW kg-1.

2D high-ordered nanoporous NiMoO4 for high-performance supercapacitors

2D high-ordered nanocrystalline nanoporous NiMoO4 has been synthesized by nanocasting from mesoporous silica SBA-15. The structure has been characterized by means of low and wide-angle powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), BET, and BJH techniques, confirming formation of 2D high-ordered nanoporous structure of NiMoO4 with high specific surface area (174m2g−1), nanocrystalline walls (7–8nm) and uniform pore size distribution (5.4nm). The electrochemical properties of the nanoporous NiMoO4 have been evaluated as electrode material for supercapacitor in a three-electrode configuration in aqueous 3M KOH solution. The material exhibits superior electrochemical performance including high specific capacitance of 2351Fg−1 at 2Ag−1, excellent rate capability (1080Fg−1 at 80Ag−1), excellent cycling stability in 6000 continuous cycles at different current densities (only 9.3% loss after 3000 cycles at 5Ag−1), and high energy and power densities (117.5Whkg−1 in 0.6kWkg−1, and 54Whkg−1 in 24kWkg−1). The superior electrochemical performance of the 2D nanoporous NiMoO4 electrode has been attributed to its structural features, including 2D highly ordered nanoporous structure which facilitates mass transfer and electrolyte accessibility, high specific surface area which provides more active sites for the pseudocapacitive reactions, and nanosized walls which shorten diffusion paths. These results reveal that the nanoporous NiMoO4 is a promising candidate for high-performance supercapacitor electrode materials.