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MnO 2 nanowires/graphite nanocomposites (MnO 2 -NW@Graphite) were successfully manufactured by an ultrafast, facile and cost-effective solid-state approach using microwave energy. Intensive research was conducted to investigate the effects of the material mass ratio, the microwave power and the microwave exposure time on the yield and morphology of the MnO 2 -NW@Graphite nanocomposites. The effect of the heating layer on the morphology was also studied. The morphology and structure of the nanocomposites were characterized using scanning electron microscope (SEM), X-ray power diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and thermal gravimetric analysis (TGA). In addition, the electrochemical performances of the MnO 2 -NW@graphite nanocomposites were evaluated in basic media using 1 M potassium hydroxide (KOH). The prepared nanocomposites exhibit a maximum specific capacity of 380.4 F/g at a current density of 1 A/g. The composites show high rate capabilities and good long-term stability with approximately 80% (303.57 F/g) retention of capacitance after 2000 cycles. With the low mass percentage (12.9%) of MnO 2 nanowires in MnO 2 -NW@Graphite, its outstanding electrochemical performance shows that it is a promising electrode material for supercapacitors. In addition, this microwave assisted approach towards the fabrication of MnO 2 nanowires is expected to achieve mass production for inexpensive energy materials. [ABSTRACT FROM AUTHOR]

A facile and energy efficient microwave synthesis of NiO/MnO 2 composite is presented in this study. The NiO nanoparticles (∼30 nm) and composite of NiO nanoparticles with nano-particle MnO 2 were grown on the surface of graphite. The morphologies and electrochemical performance of NiO@graphite and NiO/MnO 2 @graphite composite were tested and compared. The SEM results showed that addition of MnO 2 prevented the agglomeration of NiO nanoparticles. The electrochemical results of NiO/MnO 2 @graphite has demonstrated better performance than NiO@graphite, with higher specific capacitance of 102.78 mAh g −1 at 1 A g −1 and superior cycling stability with specific capacitance retention of 140% over more than 1500 cycles. The excellent electrochemical performance of NiO/MnO 2 @graphite makes it suitable for electrode material of supercapacitors. [ABSTRACT FROM AUTHOR]

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• Acid dopants have a great influence on the electrochemical performance of PANI film electrodes. • The dopants effect on morphology, doping level, redox sites accessibility, specific capacity and cycling stability of PANI electrodes were studied systematically. • PANI/HClO 4 has the best specific capacity performance with a maximum specific capacity of 1341 C g−1 at 5 mV s−1. • PANI/p-TSA exhibits the best cycling stability combined with an excellent specific capacity. • Flexible solid-state supercapacitor devices with excellent energy density and power density can be fabricated by using PANI/HClO 4 and PANI/p-TSA electrodes, respectively. Polyaniline (PANI), as one of the most promising electrode materials for flexible supercapacitors, faces the problems of limited capacitive behavior and poor cycling stability. Herein, we demonstrated that dopants have a great effect on the electrochemical performance of PANI. Selecting a suitable dopant can be used as an effective way for enhancing the electrochemical performance of PANI electrodes. All PANI electrodes were synthesized by electropolymerization method using hydrochloric acid (HCl), perchloric acid (HClO 4), sulfuric acid (H 2 SO 4), p-toluenesulfonic acid (p-TSA), phosphoric acid (H 3 PO 4) and phytic acid (PA) as dopants, respectively. The influence of dopants on morphology, doping level, redox sites accessibility and electrochemical performance of PANI electrodes were studied systematically. The results show that, PANI/HClO 4 has the best capacitive behavior with a maximum specific capacity of 1341 C g−1 at 5 mV s−1 along with a 57% capacity retention after 2000 cycles. Moreover, PANI/p-TSA shows the best cycling stability with 70% of capacity retention after 2000 cycles accompanied with a relatively high specific capacity (722 C g−1 at 5 mV s−1). Furthermore, PANI/HClO 4 and PANI/p-TSA were used as electrodes for the fabrication of flexible all-solid-state symmetric supercapacitors. Results indicate that PANI/HClO 4 device has higher energy density (12.57 Wh kg−1 at 283 W kg−1) than that of PANI/p-TSA (8.86 Wh kg−1 at 199 W kg−1). In contrast, PANI/p-TSA device with a capacity retention over 80% after 3000 cycles has better stability than PANI/HClO 4 device which maintains 73% capacity after 3000 cycles. This fundamental study provides a much easier route in achieving high performance flexible PANI-based electrodes and opens new opportunities for facilitating PANI-based electrodes as promising candidates for wearable electronics. [Display omitted] [ABSTRACT FROM AUTHOR]

The present study is aimed at providing a mechanistic insight into the influence of acid dopants on electrochemical performance of polypyrrole (PPy) film based flexible supercapacitor. PPy films were electrochemically deposited on carbon cloth using different kinds of acid dopants: hydrochloric acid (HCl), perchloric acid (HClO 4), sulfuric acid (H 2 SO 4), p-toluenesulfonic acid (p-TSA), phosphoric acid (H 3 PO 4) and phytic acid (PA). Results show that both the size and type of dopants have a great influence on the doping level, mass ratio of counterions, accessibility of redox sites and the electrochemical performance of the PPy film electrodes. Among the obtained electrodes, PPy/HCl exhibits the highest specific capacitance of 960 F g−1 at 5 mV s−1, yet with inferior cycling stability. Interestingly, PPy/p-TSA shows the best cycling stability with more than 75% of capacitance retention after 2000 cycles, also with a relatively high specific capacitance (572 F g−1 at 5 mV s−1). Moreover, the PPy/p-TSA is used to fabricate a flexible all-solid-state supercapacitor device which exhibits a maximum energy density of 6.2 Wh kg−1 and a power density of 2.64 KW kg−1, respectively. Intriguingly, the assembled PPy/p-TSA devices exhibit excellent cycling stability with 88% capacitance retention after 6000 cycles. This fundamental study provides new prospects for developing PPy-based electrode materials for future flexible and wearable supercapacitors. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Presents a letter to the editor related to neurologic complications of bariatric surgery.