Mesoporous NiCo2O4 nanoneedles@MnO2 nanoparticles grown on nickel foam for electrode used in high-performance supercapacitors

Mesoporous NiCo2O4@MnO2 nanoneedle arrays as electrode materials for supercapacitor grown on a conductive nickel foam were prepared by a facile hydrothermal route. The interconnected mesoporous structure of the NiCo2O4 nanoneedle arrays provides a large specific surface area for charge storage. The electrochemically active MnO2 nanoparticles covered on the surface of NiCo2O4 nanoneedle result in a favorable synergistic storage effect because of charge redistribution at the NiCo2O4 vertical bar MnO2 interface, which reduces the interfacial polarization and facilitates ion diffusion. The initial specific capacitance of NiCo2O4@MnO2 (S2) is 1001 F g(-1) at current density of 15 A g(-1). The capacity retention of S2 is about 87.4% after 4000 cycles, and the specific capacitance of S2 electrode only decreases from 1001 F g(-1) to 736 F g(-1) even after 10,000 cycles. The first-principles calculations show that a chemical bonding between the NiCo2O4 and MnO2 is not only helpful for stabilizing the composites but also leads to a charge redistribution at the interface, which may lead to a smaller interfacial polarization and thus beneficial for the interfacial capacity. The excellent electrochemical performance of NiCo2O4@MnO2 composites (S2) can be ascribed to the high surface area, unique architecture, MnO2 nanoparticle modification, reduced charge transfer resistance and stable interface between NiCo2O4 and MnO2. The simple material synthesis and architectural design strategy provides new insights in opportunities to exhibit promising potential for practical application in energy storage. (C) 2018 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.