The effect of zinc (Zn) doping and defect formation on the surface of nickel molybdate (NiMoO 4 ) 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-x Zn x MoO 4 , 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 NiMoO 4 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-x Zn x MoO 4 crystallized in the β-NiMoO 4 phase and is found to be stable for x≤0.25. Analytical techniques show direct evidence of the presence of Zn in the NiMoO 4 nanorods, which subtly alter the electrocatalytic activity. Compared with pristine NiMoO 4 , Zn-doped NiMoO 4 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 NiMoO 4 can improve the storage capacity (∼15%) due to oxygen vacancy interactions.

The ability to tune the interfacial region in core–shell nanocomposites with a surface reconstruction as a source for surface energy (de)­stabilization is presented. We consider Zn-doped nickel molybdate (NiMoO4) (ZNM) as a core crystal structure and AWO4 (A = Co or Mg) as a shell surface. Based on the density-functional theory method, the interfacial models of Zn-doped NiMoO4@AWO4 (ZNM@AW) core@shell structures are simulated and revealed to undergo surface reconstruction on the (−110) and (−202) surfaces of the AW shells, where the surface degradation of ZNM@MW(−110) is observed. The theoretical simulation is validated against the electrochemical performance of supercapacitor studies. To verify, we synthesize the hierarchical ZNM@AW core@shell semiconductor structured nanocomposites grown on a nickel foam conductive substrate using a facile and green two-step hydrothermal method. The morphology and chemical and electrochemical properties of the hierarchically structured nanocomposites are characterized in detail. The performance of the core@shell is significantly affected by the chosen intrinsic properties of metal oxides and exhibited high performance compared to a single-component system in supercapacitors. The proposed asymmetric device, Zn-doped NiMoO4@CoWO4 (ZNM@CW)||activated carbon, exhibits a superior pseudo-capacitance, delivering a high areal capacitance of 0.892 F cm–2 at a current density of 2 mA cm–2 and an excellent cycling stability of 96% retention of its initial capacitance after 1000 charge–discharge cycles. These fundamental theoretical and experimental insights with the extent of the surface reconstruction sufficiently explain the storage properties of the studied materials.

Nickel-based bimetallic oxides (BMOs) have shown significant potential in battery-type electrodes for pseudo-capacitors given their ability to facilitate redox reactions. In this work, two bimetallic oxides, NiMoO4 and NiWO4, were synthesized using a wet chemical route. The structure and electrochemical properties of the pseudo-capacitor cathode materials were characterized. NiMoO4 showed superior charge storage performance in comparison to NiWO4, exhibiting a discharge capacitance of 124 and 77 F.g−1, respectively. NiMoO4, moreover, demonstrates better capacity retention after 1000 cycles with 87.14% compared to 82.22% for NiWO4. The lower electrochemical performance of the latter was identified to result from the redox behavior during cycling. NiWO4 reacts in the alkaline solution and forms a passivation layer composed of WO3 on the electrode, while in contrast, the redox behavior of NiMoO4 is fully reversible.

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The electronic properties and stability of gadolinium-doped bismuth molybdate composites are critical characteristics that determine the efficiency of storing energy reversibly as a propitious electrode for energy storage applications. Gd-doped Bi2MoO6 is presented, which is based on the orthorhombic phase host Bi2MoO6 lattice, where variable amounts of Gd dopant are substituted in the Bi site, resulting in significantly improved energy storage performance. The doping effects with the aim of better understanding the electronic structure of Gd-doped Bi2MoO6 and fine-tuning the properties of energetically favorable material that possesses the most stable crystal structure are reported. The measured X-ray photoelectron spectra of Gd (4d) confirm the presence of the Gd­(III) state. The enhanced stability of Gd0.05 Bi 1.95MoO6 has been attributed to the ability to distribute electron density evenly. In a three-electrode configuration, using aqueous NaOH electrolyte, the Gd0.05Bi 1.95MoO6 electrode demonstrated a high specific areal capacitance of 2.15 F cm–2 (the equivalent of 191.5 mAh g–1). The results reported herein are important as they provide an insight into the factors influencing highly energetic and fast reactive species in the Gd­(III) composites, which could be a potential anode material for energy storage applications. The optimized anode material is coupled with Ni–Co–Cu ternary oxide cathode and evaluated as a device. The asymmetric supercapattery showed 153 mAh g–1 at a current density of 4 mA cm–2 with an excellent retention of 89% after 1000 long cycles.