Composite electrodes made with SiO2/BiOx/MoOx/graphene-SiC for efficient supercapacitors able to operate at high (60 °C)/low (-2 °C) temperatures

Flexible supercapacitors (SCs) were fabricated using graphene (GP) electrodes, which were coated with SiO 2 /BiO x /Graphene-SiC (BiO) or SiO 2 /BiO x /MoO x /Graphene-SiC (BiMo) nanostructured composites. The SCs made with configuration of BiO//BiO (BiO-SC) and BiMo//BiMo (BiMo-SC) had electrochemical parameters (capacitance, energy density) of (648.1 F/g, 90 Wh/kg) and (1045 F/g, 145.2 Wh/kg), respectively. The superior performance of BiMo-SC device was caused by the presence of multiple redox centers on their electrodes, such as Bi 3+ /Bi 0 and Mo 5+ /Mo 6+ /Mo 4+ as well as oxygen vacancies defects (which was confirmed by XPS and UV-Vis spectroscopies). Furthermore, the BiMo-SC device exhibited remarkable electrochemical stability, since it maintained 94% of initial capacitance after 1000 bending cycles. Additionally, the best BiMo-SC device was tested at 60 °C and at frozen state underwater (-2 o C) and obtained capacitances of 471.6 F/g and 477.9 F/g, respectively. Thus, the electrochemical performance of BiMo-SC device decreased by 50-54% when it is operating in harsh conditions (compared to the device tested at room temperature). Interestingly, the EIS analysis demonstrated that having BiMo (BiO x /MoO x mixture) in the SC electrode decreased the series resistance (Rs) and charge transfer (Rct) resistances by 11-30% (compared to the SC electrode containing only BiO), which promoted the facile charge storage/extraction. In general, this research demonstrated that BiMo composite is an effective material to keep the operation of devices in harsh conditions, which has been scarcely reported in literature. SCs able to operate in frozen state are relevant for providing energy to portable devices utilized outside in winter seasons.