Sunday, 28 May 2017: 16:20
Grand Salon C - Section 15 (Hilton New Orleans Riverside)
Three dimensional (3-D) nanopores array has been widely regarded as the promising current collector for fabrication of pseudocapacitor electrodes, mainly due to its large surface area, efficient electron and ion transport, and strong structural stability. Typically, anodization of high purity aluminium (Al) is the facile method to achieve highly packed nanopores with straight channels, of which the structural parameters could be facilely tuned by anodization voltage and etching time. By deposition of conductive and active materials, each channel could serve as the unit cell to store the energy. Nevertheless, the drawbacks still exist in such structure from the following aspects: i) Each channel has the electronic connection only at the top of the nanopores, leading to long pathway for electron transport. ii) The ions diffusion pathway is cut off by the side walls of anodized aluminium oxide (AAO), resulting in the one dimensional diffusion way along the channel. iii) The volume/space occupied by AAO side walls has no contribution to the capacitance, resulting in the low efficient utilization of the nanostructure. To address above issues, we have engineered the 3-D interconnected nanopores array by anodization of unique Al alloy. In such an architecture, the side pores are uniformly distributed along the main channel of AAO, forming more porous and mechanically stable nanopores array. By controllable deposition of fluorine doped tin oxide (FTO) with the cost-effective method of ultrasonic spray pyrolysis, and electrochemical deposition of MnO2, the as-built pseudocapacitor electrode renders the highest areal capacitance of 322.6 mF cm-2 and volumetric capacitance of 80.65 F cm-3 at the discharging current density of 0.1 mA cm-2, and still maintains 236 mF cm-2 and 59 F cm-3 at the discharging current density of 1.5 mA cm-2. By contrast, the values for the pseudocapacitor electrode fabricated based on the traditional nanopores array current collector are 273.8 mF cm-2 and 68.45 F cm-3, respectively, and drastically degrade to 50 mF cm-2 and 12.5 F cm-3. The performance enhancement is much larger when the comparison falls on planar pseudocapacitor electrode. We ascribe the largely enhanced rate capability to two reasons: i) The interconnected nanopores structure offers more space, which benefits for loading of nanostructured MnO2. ii) The side pores allow ions to move freely into neighbouring channels, resulting in the faster ion diffusion. In this case, we regard such interconnected nanopores array as the superior current collector in pursuit of high performance pseudocapacitor electrode.
