Comparative environmental impact assessment of activated carbon electrodes for supercapacitors†

Activated carbon (AC) is considered as a potential material for electrodes in supercapacitors; however, its production process entails significant emissions to the environment. This study aims to assess the environmental impacts of manufacturing AC and electrodes for supercapacitors from waste materials, utilizing the life cycle assessment (LCA) principles. The process of producing AC involves raw material preparation, hydrothermal carbonization, and chemical activation processes, utilizing potassium hydroxide (KOH) as a chemical agent. The environmental impact of AC production and fabrication of AC electrodes was analyzed using the SimaPro software. A cradle-to-gate study was conducted to analyze the production of 1 kg of AC and one electrode from waste materials, including oil palm leaves, Sesbania, and filter cake, chosen based on the local availability in the study area. Life cycle data were compiled from the laboratory, ecoinvent database, and calculations based on the mass and energy balance. Using the ReCiPe midpoint (H) characterization method, potential environmental impacts were computed across eighteen categories. Sesbania AC exhibited the highest impact across fourteen out of eighteen categories for producing 1 kg of AC, with the largest impact observed in the marine ecotoxicity category due to the presence of KOH in the chemical activation process. For producing 1 farad (F) electrode, Sesbania showed the lowest environmental impact due to its high specific capacitance. Its environmental impacts of producing a 1 F electrode were unexpectedly lower than those of oil palm leaves because the predominant environmental impacts were from hydrothermal carbonization and pretreatment rather than KOH activation. Additionally, Sesbania exhibited significantly higher yields in hydrothermal carbonization, resulting in the use of relatively fewer materials and less energy, thereby leading to reduced impacts compared to other materials. The developed AC electrode showed excellent performance in several environmental impact categories, with AC production being the main contributor.