Nanostructured tin oxide layer as a porous template for the growth of manganese oxide nanobouquets and a conductive support network for supercapacitors

Abstract

As-prepared SnO2 layer with poor conductivity acted as a porous template for deposition of discrete γ-MnO2 with primary nanosheets and secondary nanobouquets along the pore channels inside the SnO2 barrier layer. The MnO2 tended to form aggregate nanosheets on the bare SSM (stainless steel mesh) substrate and CNT (carbon nanotube)-wrapped SSM without the SnO2 template. Porous SnO2 layer could prevent the nanosheets from aggregating effectively. After heat treatment, the SnO2 became electrically conductive and thus acted as a conductive and stable support for MnO2 nanobouquets. After the introduction of CNT layer between porous SnO2 layer and SSM substrate, the supporting CNT/SnO2 could provide large contact area, multiple pore channels, and conductive networks for transport of electrons and electrolyte ions. The tri-layered structure of CNT/SnO2/MnO2 realized larger capacitive current than bare, CNT-, and SnO2-supported MnO2 materials. The specific capacitance of CNT/SnO2/MnO2 could reach 427 F g−1 under a discharge current density of 1 A g−1, far greater than that of MnO2 (254 F g−1), CNT/MnO2 (325 F g−1), and SnO2/MnO2 (375 F g−1). An improved supercapacitive performance of the CNT/SnO2/MnO2 came from its lower internal resistance than the bare MnO2 electrode.