Carbon nanotube anodes decorated with Ag NWs/Ni(OH)2 NWs for efficient semitransparent flexible solid state supercapacitors

Abstract This work reports the electrochemical properties of flexible supercapacitors whose anodes were fabricated with carbon nanotubes (CNTs), silver nanowires (Ag NWs), and Nickel hydroxide nanowires (Ni(OH)2 NWs). The SEM analysis of the anodes demonstrated that the CNTs are oriented in a preferential direction, which favors the transport of charge carriers. Also, the Ag NWs, and Ni(OH)2 NWs have formed on the anodes a porous nanostructured network which look like a bird-nest, thus providing a high surface area for the charge storage. According to the optical transmittance spectra, the anodes made with the three components: CNTs, Ag NWs and Ni(OH)2 NWs presented an average transmittance of 46% in the visible region. The SC devices with anodes made with single CNT, CNT/Ag NWs, CNT/Ni(OH)2 NWs, and CNT/Ag NWs/Ni(OH)2 NWs were named CN, CN-Ag, CN-Ni, and CN-Ag/Ni, respectively. All these devices were semi-transparent and their cyclic voltammetry curves showed the presence of redox peaks, which suggest that these devices stored charge by redox reactions. In addition, the galvanostatic charge/discharge profiles of the SCs demonstrate that they can release energy for at least 10 h. The best SC device (CN-Ag/Ni) had a capacitance and energy density values of 88.6 F/g and 177.3 Wh/Kg, respectively. XPS, FTIR, and absorbance measurements were also carried out and confirmed the presence of oxygen vacancy defects, nickel hydroxides, silver oxides, and metallic silver in the anodes of the SCs. The presence of all these compounds was important because they acted as redox centers which all contribute simultaneously to the charge storage. Hence, the results presented here reveal that a flexible SC could be a feasible option as an energy source for portable devices.