(Invited) Marine Plastic Waste-Based Supercapacitors for Saving Remote Island
Authors: Tashima Daisuke , Eguchi Takuya , Kumagai Seiji , Tsubota Toshiki , Madden John D. W. 
Published: December 2024

Marine plastic waste is a global environmental issue that needs urgent attention as it adversely affects the environment and living organisms, including human beings. More than 32–280 million metric tons of plastic are produced every year; however plastic production decreased in 2020 owing to a drop in demand caused by COVID-19[1-4]. Plastic production is expected to reach 53 million metric tons by 2030[5] and 155–265 million metric tons by 2060[3]. As the amount of plastic waste from sources other than packaging is decreasing, most of the waste is not treated as waste and is discharged into the ocean. Approximately 4.7–12.7 million metric tons of plastic waste is dumped into the sea annually[4,6], covering an area of 1.6 million km2[2]. About 150 million tons of plastic waste is reportedly present in the sea, which will likely remain in the sea until at least 2050. Properties of plastic further exacerbate this problem. Plastic shopping bags take more than a thousand years to completely decompose naturally, and plastics that have once entered the sea continue to harm the environment for an extremely long time[7]. Approximately 700 species, including endangered marine species, have been injured and killed[8]. Such deaths were attributed to glass and trees in the past; however, in recent years, 92% of these deaths have occurred owing to marine plastic waste/microplastic particles[8-10]. The effects of plastic waste and microplastic particles also affect coral reefs[11] and the Arctic[12]. This research will increase the applicability of activated carbon (AC) in marine plastic recycling. However, marine plastics are a mixture of various plastics, and it is difficult to recycle all of them from deposits, additives, and paints. Therefore, a recycling destination with high added value is required. In contrast, applications of AC have evolved from those in improving water quality to those in electrode materials, and especially as a storage battery. Its application prospects differ from other storage batteries in terms of charge and discharge characteristics; therefore, it is regarded as a power storage device whose demand will continue to rise in the future. Moreover, impurities in the electrode materials of ordinary secondary batteries can have a large adverse effect on battery capacity, internal resistance, and cycle life. Supercapacitors with carbon electrodes can be charged and discharged even if some impurities are present. Therefore, this study presented the production of AC as one of the treatment methods for marine plastic waste and evaluated the performance of AC and its performance as a supercapacitor electrode. The aim of this study was to develop methods to manage marine plastic waste (Fig.1(A)) through the production of activated carbon (AC). The specific surface area, micropore volume, and mesopore volume of marine plastic AC prepared under arbitrary temperature and activator weight ratio were measured (Fig1(B),(C)), and the specific capacitance and supercapacitor electrode performance were evaluated. At an activation temperature of 800 °C and a weight ratio of 1:7 between the raw material and 8 M KOH solution, a specific capacitance of 201 F/g and a high surface area of 2389 m2/g were obtained. Accordingly, marine plastic waste-based AC can be used as the electrode material in supercapacitors.

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Figure 1