Marine biomass (MB) offers an environmentally friendly and readily available carbon source from the ocean. However, the high concentration of alkali and alkaline earth metals (AAEMs) in MB typically reduces the carbon yield and inhibits micropore formation during heat treatment due to catalytic gasification. In this study, we successfully synthesized activated carbon (AC) with a high specific surface area (> 1,500 m2/ g) and significant mesopore content (60%, mean pore size: 3.4 nm) from MB by employing preheating, controlled acid purification, and CO₂ activation. The formation of mesopores in the MB-derived AC was driven by catalytic gasification induced by intrinsic and residual AAEMs during preheating and physical activation processes. We evaluated the potential of the MB-derived AC as an electrode material for electric doublelayer capacitors (EDLCs). The material demonstrated high specific capacitance values of 25.9 F/g and 29.4 F/g at 2.7 V and 3.3 V, respectively, during charge–discharge cycles. These high capacitance values at elevated voltages were attributed to the increased number of solvated ions (e.g., 1.93 mmol/g at 3.3 V) present in the mesopores. Fluorine-19 nuclear magnetic resonance (19F solid-state NMR) analysis revealed a substantial increase in solvated ion concentration within the mesopores of the MB-derived AC electrode at 3.3 V, demonstrating enhanced ion mobility and diffusion. These findings highlight the potential of MB-derived AC as a promising electrode material for high-voltage energy storage applications.

Marine biomass-derived activated carbon as an electrode material for electric double-layer capacitors
    Abstract
        Graphical abstract
    1 Introduction
    2 Experimental
        2.1 Preparation of activated carbons
        2.2 Characterizations
        2.3 Preparation of EDLCs
        2.4 Electrochemical characterizations
        2.5 19F NMR spectroscopy
    3 Results and discussion
    4 Conclusion
    Acknowledgements 
    References

• Jueun Choi(Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6‑1 Kasuga‑koen, Kasuga, Fukuoka 816‑8580, Japan)
• Koji Nakabayashi(Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6‑1 Kasuga‑koen, Kasuga, Fukuoka 816‑8580, Japan, Institute for Materials Chemistry and Engineering, Kyushu University, 6‑1 Kasuga‑koen, Kasuga, Fukuoka 816‑8580, Japan)
• Jin Miyawaki(Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6‑1 Kasuga‑koen, Kasuga, Fukuoka 816‑8580, Japan, Institute for Materials Chemistry and Engineering, Kyushu University, 6‑1 Kasuga‑koen, Kasuga, Fukuoka 816‑8580, Japan)
• Seong‑Ho Yoon(Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6‑1 Kasuga‑koen, Kasuga, Fukuoka 816‑8580, Japan, Institute for Materials Chemistry and Engineering, Kyushu University, 6‑1 Kasuga‑koen, Kasuga, Fukuoka 816‑8580, Japan)
• Keiko Ideta(Institute for Materials Chemistry and Engineering, Kyushu University, 6‑1 Kasuga‑koen, Kasuga, Fukuoka 816‑8580, Japan)
• Hyeonseok Yi(Institute for Materials Chemistry and Engineering, Kyushu University, 6‑1 Kasuga‑koen, Kasuga, Fukuoka 816‑8580, Japan)
• Toru Kato(Environment and Process Research Department, The Japan Research and Development Center for Metals, 1‑5‑11 Nishishinbashi, Minato‑ku, Tokyo 105‑0003, Japan)
• Koji Saito(Nippon Steel Technology Co., Ltd., 1‑6‑1 Otemachi, Chiyoda‑ku, Tokyo 100‑0004, Japan)
• Hiroko Watanabe(Nippon Steel Technology Co., Ltd., 1‑6‑1 Otemachi, Chiyoda‑ku, Tokyo 100‑0004, Japan)
• Yoong Ahm Kim(Department of Polymer Engineering, Graduate School and School of Polymer Science and Engineering, Chonnam National University, 77 Yongbong‑ro, Buk‑gu, Gwangju 61186, Republic of Korea) Corresponding author