N-doped graphene integrated mixed phase Mo-NiCo2O4/CoMoO4 mariegold nanoflowers as positive electrode for high 2 V hybrid supercapacitors

Abstract

The quest for high-performance supercapacitor materials with extended potential windows and superior energy storage capabilities has driven the exploration of ternary transition metal oxide nanostructures. In this work, a novel mixed-phase Mo-NiCo₂O₄/CoMoO₄ composite anchored on nitrogen-doped graphene (NG) sheets was synthesized via a one-step hydrothermal approach. The NG sheets act as active substrates that not only facilitate the intimate growth of Mo, Ni and Co on nucleation sites but also influence the growth kinetics, leading to the formation of intricate marigold-like nanoflowers assembled from wavy lamellar nanosheets consisting of Mo-NiCo₂O₄/CoMoO₄. The unique heterojunctioned structures result in a mesoporous MoNiCoNG120 composite with high surface area and dense electroactive sites, achieving a remarkable specific capacitance of 280.40 Fg^-1 at 0.30 Ag^-1. To evaluate its device-level performance, symmetric (MoNiCoNG//MoNiCoNG) and asymmetric (MoNiCoNG//NG and MoNiCoNG//AC) supercapacitors were assembled. The MoNiCoNG//NG asymmetric device exhibited a high energy density of 51.28 Whkg⁻¹ and power density of 96.40 W kg⁻¹ at 0.08 A g⁻¹ retaining ∼80 % capacitance retention after 5000 charge-discharge cycles. The device successfully powered a 14-LED circuit for over 3 min using the cells assembled in series combination. These results highlight the potential of the MoNiCoNG composite as a next-generation electrode material for high-energy supercapacitors.