Abstract
Three TiO2 deposition processes are used to coat the surface of Si nanowire array electrodes for electrochemical double layer capacitors in room temperature ionic liquid [Bmim][NTF2]. The fabrication processes are based on wet chemistry only and temperature treatments are kept below 450 °C. Successful TiO2 coatings are found to be those that are carried out at low pressure and with low TiO2 coverage to avoid nanowires breakage. The best TiO2 coated Si nanowire array electrode in [Bmim][NTF2] showed energy densities of 0.9 Wh·kg−1 and power densities of 2.2 kW·kg−1 with a nanowire length of ~10 µm.
Highlights
Current research on electrochemical double layer capacitors (EDLCs) is focussed on increasing the electrode’s effective surface area and chemical stability, with the aim to improve their storage capacity via increased energy and power densities and cycle life [1]
We present three different TiO2 coating processes applied to p-type metal-assisted electrochemical etching (MACE) fabricated Si nanowire arrays (NWAs) in the room temperature ionic liquids (RTILs) [Bmim][NTF2]
The cyclic voltammetry (CV) of the uncoated and TiCl4-treated Si NWA has current peaks. These are strongly correlated with the presence of NWs since no peaks are observed for bulk material in the same set-up and RTIL
Summary
Current research on electrochemical double layer capacitors (EDLCs) is focussed on increasing the electrode’s effective surface area and chemical stability, with the aim to improve their storage capacity via increased energy and power densities and cycle life [1]. Carbon-based materials with high porosities offer high chemical stability and large surface areas [2, 3, 4] Further improvement to their storage characteristics can be achieved by coating their surface with transition metal oxide nanoparticles such as RuO2, NiO, MnO2, V2O5, Co2O3, TiO2, SnO2, Fe2O3, and Fe3O4 [2, 3, 4, 5, 6, 7, 8, 9]. The use of the low temperature, wet chemical process together with TiO2 nanoparticles coatings which are low cost, environmentally friendly and available in abundance, makes the Si-based electrode a green energy candidate. The capacitance of the resulting electrodes is extracted using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronopotentiometry (CP)
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