Theoretical Specific Capacity and Metal Ion Diffusion Pathway of NiMoO₄ Microspheres for Hybrid Supercapacitors

Transition metal molybdates are one of the most prominent materials for energy storage devices. The present investigation establishes a strong correlation between the structure and electrochemical performance of NiMoO₄ through Density Functional Theory (DFT). Initially, the NiMoO₄ microspheres are directly deposited on nickel foam using a hydrothermal method by tuning experimental parameters. When employed as electrode materials, the NiMoO₄ microspheres deliver a specific capacity of 168.9 mAh g^-1 at 1 A g^-1. In addition, the material retains 80% capacity over 7000 charge-discharge cycles with 98.3% coulombic efficiency, implying its excellent stability. DFT calculations are used to determine specific capacity and potassium ion diffusion for 5 layers of [110] planes of NiMoO₄. The potential energy landscape is created for [110] plane using the potassium atom minimum hopping algorithm and atomic simulation environment. The DFT results clearly align with the theoretical capacity of 203 mAh g^-1 close to the experimental results. A hybrid supercapacitor (HSC) is also developed with NiMoO₄//AC cell delivers a specific energy of 56.3 Wh kg^-1 at a specific power of 421 W kg^-1 with negligible capacity loss over 15 000 cycles. This investigation offers the development of battery-type electrodes for hybrid supercapacitors using the fundamental understanding of ion-diffusion in the materials' structure.