ABSTRACT
We fabricate porous nanostructured 1µm thick ZnO-metal/metal oxide hybrid material thin films using a unique approach utilizing physical vapor deposition with postdeposition annealing. We study Pt, Pd, Ru, Ir and Sn as the metals and find they all form hybrid structures, however with differing physical and electrochemical properties. We investigate their applicability in microsupercapacitor electrodes in a LiCl aqueous electrolyte and find that the ZnO hybrid with Ir exhibits the highest capacitances. We follow with optimization and more detailed material studies of the ZnO-Ir hybrid showing that a significant amount of Ir is present in the material in the form of metallic Ir and indiffused Ir, while IrO2is also present in the nanoscale. We obtain electrodes with 5.25 mF · cm-2capacitance with 90% retention over 10 000 charge/discharge cycles in an aqueous LiCl electrolyte, which is better than the reported values for other Ir-based hybrids. Finally, we showed that the electrodes provide 2.64 mF · cm-2in a symmetric device with an operating voltage of 0.8 V. With this report, we discuss the influence of both Ir and IrO2on the capacitance, underlining the synergistic effect, and show them as promising inorganic matterials for integration with other supercapacitor electrodes.
ABSTRACT
The recent rapid development of transparent electronics, notably displays and control circuits, requires the development of highly transparent energy storage devices, such as supercapacitors. The devices reported to date utilize carbon-based electrodes for high performance, however at the cost of their low transparency around 50%, insufficient for real transparent devices. To overcome this obstacle, in this communication highly transparent supercapacitors were fabricated based on ZnO/MnO2 nanostructured electrodes. ZnO served as an intrinsically transparent skeleton for increasing the electrode surface, while MnO2 nanoparticles were applied for high capacitance. Two MnO2 synthesis routes were followed, based on the reaction of KMnO4 with Mn(Ac)2 and PAH, leading to the synthesis of ß-MnO2 with minority α-MnO2 nanoparticles and amorphous MnO2 with embedded ß-MnO2, respectively. The devices based on such electrodes showed high capacitances of 2.6 mF cm-2 and 1.6 mF cm-2, respectively, at a scan rate of 1 mV s-1 and capacitances of 104 µF cm-2 and 204 µF cm-2 at a very high rate of 1 V s-1, not studied for transparent supercapacitors previously. Additionally, the Mn(Ac)2 devices exhibited very high transparencies of 86% vs. air, far superior to other transparent energy storage devices reported with similar charge storage properties. This high device performance was achieved with a non-acidic LiCl gel electrolyte, reducing corrosion and handling risks associated with conventional highly concentrated acidic electrolytes, enabling applications in safe, wearable, transparent devices.
ABSTRACT
Catalyst-free growth of ZnO nanowires using reactive magnetron sputtering at room temperature is reported. We discuss the growth of the nanowires using reactive magnetron sputtering as a function of argon and oxygen flow values changing at a set ratio of 10:2. A transition from nanostructured Zn to nanowire ZnO growth is observed at 20 sccm Ar and 4 sccm O2. Densification and improved alignment of the nanowires is visible for increasing flow values up to 50 sccm Ar and 10 sccm O2. Nanowires exhibit stacking fault regions of zinc blende ZnO in wurtzite ZnO. The regions encompass the whole width of the nanowires and their quantum well behavior is manifested in the photoluminescence spectra. The nanowires were subsequently deposited on paper and PET substrates and electromechanical nanogenerators were fabricated. Manual pressing and depressing of the devices induced voltages of 50 µV and 2 µV for the devices on PET and paper substrates, respectively.
