Unveiling the dynamic capacitive storage mechanism of Co3O4 @NiCo2O4 hybrid nanoelectrodes for supercapacitor applications

We report a simple and cost-effective approach to the synthesis of hierarchical mesporous Co3O4@NiCo2O4 nanoforests on Ni foam for supercapacitor (SC) electrode applications by a coupled one-step solution and annealing process. The synthesized electrode exhibits capacitive activation during charge-discharge cycling (from 0.73 F/cm(2) of the pristine state to the peak value of 1.12 F/cm(2) after 2000 cycles with only 1.8% loss compared to the peak capacitance after another 2000 cycles). We attribute such dynamic capacitive activation to (1) enlarged electroactive surface area through the formation of Co3O4@NiCo2O4 core-shell structure and (2) enhanced electrical conductivity by forming oxygen vacancies and hydroxyl groups during charge-discharge cycling. Our findings provide a scientific explanation for the capacitive activation in cobalt oxide-binary nickel cobaltite compounds, and a new design guideline for the development of capacitive activation enabled, high performance transitional oxide electrodes. (C) 2014 Elsevier Ltd. All rights reserved.