The development of smart negative electrode materials with high capacitance for the uses in supercapacitors remains challenging. Although several types of electrode materials with high capacitance in energy storage have been reported, carbon-based materials are the most reliable electrodes due to their high conductivity, high power density, and excellent stability. The most common complaint about general carbon materials is that these electrode materials can hardly ever be used as free-standing electrodes. Free-standing carbon-based electrodes are in high demand and are a passionate topic of energy storage research. Electrospun nanofibers are a potential candidate to fill this gap. However, the as-spun carbon nanofibers (ECNFs) have low capacitance and low energy density on their own. To overcome the limitations of pure CNFs, increasing surface area, heteroatom doping and metal doping have been chosen. In this review, we introduce the negative electrode materials that have been developed so far. Moreover, this review focuses on the advances of electrospun nanofiber-based negative electrode materials and their limitations. We put forth a future perspective on how these limitations can be overcome to meet the demands of next-generation smart devices.

In situ corrosion inhibition in acid cleaning processes by using green inhibitors is at the forefront of corrosion chemistry. Plant extracts, especially alkaloids, are known to be good corrosion inhibitors against mild steel corrosion. In this research, alkaloids extracted from Acacia catechu have been used as green corrosion inhibitors for mild steel corrosion in a 1 M H₂SO₄ solution. Qualitative chemical tests and FTIR measurements have been performed to confirm the alkaloids in the extract. The inhibition efficiency of the extract has been studied by using weight-loss and potentiodynamic polarization methods. A weight-loss measurement has been adopted for the study of inhibitor’s concentration effect, with a variation employed to measure the inhibition efficiency for time and temperature. The weight-loss measurement revealed a maximum efficiency of 93.96% after 3 h at 28 °C for a 1000 ppm alkaloid solution. The 1000 ppm inhibitor is effective up to a temperature of 48 °C, with 84.39% efficiency. The electrochemical measurement results revealed that the alkaloids act as a mixed type of inhibitor. Inhibition efficiencies of 98.91% and 98.54% in the 1000 ppm inhibitor concentration solution for the as-immersed and immersed conditions, respectively, have been achieved. The adsorption isotherm has indicated the physical adsorption of alkaloids. Further, the spontaneous and endothermic adsorption processes have been indicated by the thermodynamic parameters. The results show that alkaloids extracted from the bark of Acacia catechu can be a promising green inhibitors for mild steel corrosion.

The residual ions of the acid cleaning processes induce the further corrosion of the metals, and this could be minimized using green inhibitors. Alkaloids extracted from plant parts could be cost effective and efficient inhibitors. In this work, alkaloids from Solanum xanthocarpum stem were successfully extracted, and they were characterized by qualitative chemical tests and spectroscopic measurements. As-extracted alkaloids were employed as green corrosion inhibitors for mild steel. The effectiveness of the inhibitor was determined by the weight loss and electrochemical measurement methods. From the weight loss measurement, the maximum inhibition efficiency of 93.14% was achieved. The temperature effect study revealed that the inhibitor can work up to a temperature of 58 °C. This could be one of the highest working temperatures among the reported green inhibitors. The electrochemical measurement reveals that the alkaloids could inhibit effectively up to 98.14% of the corrosion and serve as a mixed-type green inhibitor. A study on the kinetic parameters reflects that the inhibitor forms a potential barrier for the protection of a mild steel surface against corrosion. The values obtained from the thermodynamic parameters study reflect that the process is a spontaneous endothermic process. Based on the findings, it is revealed that the alkaloids extracted from S. xanthocarpum can serve as an excellent, eco-friendly and a promising green inhibitor against mild steel corrosion.