Development of biomass-based electrode materials for asymmetric supercapacitor applications

As the share of renewable energy resources in primary energy consumption increases, the need for different energy storage technologies is increasing day by day. Among these storage technologies, supercapacitors, in particular, provide significant advantages in various usage scenarios compared to fuel cells and batteries, due to their ultra-high power densities, fast charge-discharge rates, and very long cycle life. On the other hand, the energy densities of supercapacitors are still not at a sufficient level and this challenge limits the different applications of supercapacitors. For this purpose, scientists have carried out various research studies aiming to increase the energy density of supercapacitors in recent years. One of these studies is asymmetric supercapacitor applications. Contrary to Electrochemical double layer supercapacitors (EDLC) and pseudocapacitors, which reach their theoretical limits, asymmetric supercapacitors aim to expand the total working potential range of the supercapacitor by utilizing the different working potential ranges of two different electrodes and thus to increase the energy density. Within the scope of this thesis, asymmetric supercapacitors have been developed using activated carbons (AC) produced by chemical activation method from three different waste biomass are used as negative electrode material (anode) and synthesized metal oxide-conducting polymer nanocomposites (PANI-MnO2 and PPy-MnO2) as positive electrode material. Characterizations of activated carbons produced at different activation temperatures were conducted using elemental analysis, BET surface area and pore size distribution analysis, SEM, XPS, RAMAN and TGA analysis. The characterizations of the synthesized nanocomposites were performed using XRD, FTIR, CTEM and SEM analysis. The electrochemical performance of activated carbons and nanocomposites used as electrode materials was evaluated with CV, GCD and EIS methods in symmetric and asymmetric cell setups. The results showed that asymmetric supercapacitors, especially those prepared with PPy-MnO2 nanocomposite, can operate stably at 1.2 V and 1.5 V potential windows without compromising their specific capacitance values.