Unique Nano-Architecture Electrodes for High-Performance Energy Storage

Abstract

Unique core/shell type nano-architecture electrodes based on of transition metal/transition metal oxides are designed and fabricated by the simple electrochemical and chemical routes. The high-performance pseudo-capacitors based on the metal core and NiO, Co3O4, MnO2, mixed transition metal oxides and surface modified transition metal oxides shell nano-heterostructures electrode is demonstrated. Various nano-architectures based on those provide enhanced effective surface area, better electronic charge transport and high specific capacitance. For example, a unique 1D Co-Ni/Co3O4-NiO core/shell type arrays of nano-heterostructures (NHs) are designed and fabricated by a facile electrochemical template assisted route, for the first time to the best of our knowledge. Co3O4-NiO shell layer is developed on the Co-Ni nanowires cores (Fig. 1). It is found that the nano-heterostructures electrode exhibits high specific capacitance of 2013 F g-1 at a current density of 2.5 A g-1. The electrode also shows high energy and power density (23 Wh kg-1 and 5.5 kW kg-1, at the high discharge current density of 20.8 A g-1). Along with these the NHs electrode also provides good capacitance retention and long cyclicality ideal for applications in pseudocapacitors devices. The remarkable electrochemical property of the NHs electrode as pseudocapacitor is demonstrated based on the effective nano-architectural design having large surface area of the 1D nano-heterostructures. Moreover, the 1D Co-Ni/Co3O4-NiO core/shell nano-heterostructures have two different highly redox active transition metal oxides at the surface, which take part in the Faradic reactions in this electrode. The thin (few nm) mixed-oxide layer also provides the short ion transport path, whereas the metal alloy core will act as the ‘highway’ for the fast electron conduction to the current collector. In another work novel 1D core/shell Ni/NiO nano-architecture electrode has been fabricated and employed as a pseudocapacitor, where significantly improved capacitive performance has been achieved through hydrogenation (Fig. 1). The specific capacitance of the asprepared 1D core/shell Ni/NiO nanoheterostructure (717 Fg−1 at a scan rate of 2 mVs−1) is nearly 1635 Fg−1 after the hydrogenation. The improved pseudocapacitive properties of hydrogenated Ni/NiO nano-heterostructures (NHs) are attributed to the incorporation of the hydroxyl groups on the NiO surface due to hydrogenation, where the metallic Ni NWs core of this unique 1D core/shell NH serves as the efficient channel for the fast electron conduction to the current collector. The H–Ni/NiO NHs exhibit good rate capability (retaining nearly 60% of their initial charge) and good long-term cycling stability with an excellent specific energy and power density of 49.35 W h kg−1 and 7.9 kW kg−1, respectively, at a current density of 15.1 Ag−1. However, the remarkable electrochemical property of the large surface area nano-heterostructures is demonstrated based on the novel nano-architectural design of the electrode with the coexistence of the highly redox active materials at the surface supported by highly conducting metal alloy channel/highway at the core for faster charge transport.