Quasi-parallel arrays with a 2D-on-2D structure for electrochemical supercapacitors

Abstract

Construction of two-dimensional nanostructured arrays is important to improve the specific capacitance and rate performance of supercapacitors. In this work, we demonstrate a novel type of pseudocapacitive NiMn oxide@MnO₂ quasi-parallel array assembled via 2D-on-2D structures. The quasi-parallel arrays markedly reduce the “dead area” caused by the bending stack of traditional 2D assembled structures, which obviously increases the number of active sites of the MnO₂ electrode. The small aspect ratio of the quasi-parallel arrays ensures mechanical adhesion and electrical connection between the active material and the current collector. Therefore, the NiMn oxide@MnO₂ arrays exhibit outstanding pseudocapacitive performance, including high specific capacitance (801 F g⁻¹ at 1 A g⁻¹, capacity: 151.3 mAh g⁻¹), long-term cycling stability, and outstanding rate capability (79% capacitance retention rate at 40 A g⁻¹). The constructed asymmetric supercapacitor based on a NiMn oxide@MnO₂ cathode and an activated graphene anode exhibits extraordinary cyclic stability (96% capacitance retention after 10 000 cycles). This new type of quasi-parallel array could become a versatile electrode platform, which would open up a wide range of applications in supercapacitors, batteries and electrocatalysis.