With every moving day, the aspect that is going to be the most important for modern science and technology is the means to supply sufficient energy for all the scientific applications. As the resource of fossil fuel is draining out fast, an alternative is always required to satisfy the needs of the future world. Limited resources also force to innovate something that can utilise the resource more efficiently. This work is based on a simple synthesis route of biomass derived hard carbon and to exploring the possibility of using it as electrochemical supercapacitors. A cheap, eco-friendly and easily synthesized carbon material is utilized as electrode for electrochemical energy-storage. Four different hard carbons were synthesized from KOH activated banana stem (KHC), phosphoric acid treated banana stem derived carbons (PHC), corn-cob derived hard carbon (CHC) and potato starch derived hard carbons (SHC) and tested as supercapacitor electrodes. KOH-activated hard carbon has provided 479.23 F/g specific capacitance as calculated from its cycle voltammograms. A detailed analysis is done to correlate the results obtained with the material property. Overall, this work provides an in depth analysis of the science behind the components of an electrochemical energy-storage system as well as why the different characterization techniques are required to assess the quality and reliability of the material for electrochemical supercapacitor applications.

In this study, we adopted a simple method to synthesize a graphene-like-structured nanoporous carbon using a jute stick as a carbon precursor and studied the electrochemical properties for supercapacitors. The synthesized nanoporous carbon is composed of a graphene sheet-like network and amorphous carbon, and the ratio between these two components is tuned by the activation temperature. As the activation temperature is increased, the amorphous carbon is converted into a stable graphene-like network with a high specific surface area of 2396 m2/g, with a graphene sheet-like morphology and a highly ordered graphitic sp2 carbon. For supercapacitor application, the nanoporous carbon is studied in aqueous as well as organic electrolytes, and the material shows excellent electrochemical performance in both the cases. It exhibited a high specific capacitance of 282 F/g and shows excellent rate capability with almost 70% capacitance retention at high current rates. Furthermore, the assembled symmetric supercapacitor displays a remarkable energy density of 20.6 W h kg–1 at a high power density of 33 600 W kg–1, and the benchmark studies revealed that the nanoporous carbon developed in the present study is better than the commercially available supercapacitive carbon (YP-50 F). A cylindrical supercapacitor device of capacitance 20 F with 2.7 V was fabricated using the nanoporous carbon electrode and tested for running practical devices. The excellent electrochemical performance of the electrode material can be attributed to the high electrical conductivity of the ordered graphene network coupled with high specific surface area and optimum pore size distribution of nanoporous carbon. These results demonstrate a facile, low-cost, and eco-friendly design of materials for energy storage applications.

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Summary Graphitic porous carbon sheets (GPCS), which were synthesized at a low temperature of 900°C by KOH chemical activation technique, possess a specific surface area of 1246 m2 g‐1 with high pore volume. The size of the pores varied in micro‐mesopore regions and exhibited three‐dimensional sheet‐like morphology composed of multilayered graphene sheets with an inter planar distance of 0.360 nm. The GPCS material was tested as anode for Li‐ion battery (LIB) application in half cell mode (vs Li+/Li). The fabricated GPCS electrode shows excellent electrochemical properties in comparison with commercial graphite such as a high discharge specific capacity of 1022 mA h g‐1 after 10 cycles at 100 mA g‐1 and excellent specific capacity retention of 170 mA h g‐1 at a very high current rate of 8000 mA g‐1 and also retains a high capacity of 541 mA h g‐1 after 250 cycles at 500 mA g‐1, which suggests that GPCS material can be a promising electrode for LIB application. A brief comparison with commercial graphite and various carbonaceous materials from literature demonstrated that the GPCS electrode was potential material for high rate LIBs.

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Lithium-ion capacitors (LICs) with the capability of high energy and high power are considered to be attractive for advanced energy storage applications. However, the design and fabrication of suitable electrode materials with desirable properties by a facile approach using cost-effective precursors are still a great challenge. In this work, we have utilized petroleum coke, an unavoidable industrial waste with high carbon content, as a single carbon source to synthesize both a high surface area activated carbon cathode and a low surface area disordered carbon anode. A lithium-ion capacitor fabricated using all-petroleum coke-derived carbon materials exhibits a high energy density of 80 W h/kg and a high power density of 8.4 kW/kg as well as long life span (85% capacity retention after 10,000 charge–discharge cycles at 1 A/g). Systematic characterization analysis demonstrates that unique characteristics of carbon electrode materials including hierarchical pores, high surface area, and graphene-like structured activated carbon contribute synergistically to the outstanding performance of the petroleum coke-based LIC. More importantly, the facile approach adopted in the present study to synthesize both cathode and anode materials from a single source is an effective way for high value-added utilization of petroleum coke at the commercial level.