Effect of Surface Functional Groups on Polymer-Derived Activated Carbon in Aqueous Electrolyte for Supercapacitors
Authors: Kobayashi Shuto , Nishiyama Yuki , Tashima Daisuke 
Published: December 2024

Renewable energy sources such as solar power and wind power which do not require fossil fuels and utilize natural energy such as light energy and wind energy are rapidly expanding around the world, including within Japan. However, these power generation methods are easily affected by the weather and other external conditions, making it difficult to achieve a sufficient power supply when needed, and complicating the adjustment of the supply-demand balance of electricity [1].

In Japan, the existence of storage batteries that can store excess electricity and release it when needed is attracting attention as an alternative energy source. Electric double-layer capacitors, a type of storage battery, have been the primary focus of our attention. The material that most affects the performance of an electric double-layer capacitor is activated charcoal, which adsorbs ions from the electrolyte solution on its surface during charging and releases them during discharge [1][2].

In other words, the larger the specific surface area of activated carbon (m2/g) is, the more ions are adsorbed during charging, which theoretically increases the storage capacity, and research is being conducted daily on new methods to increase the surface area[3].

In this study, the activated carbon was provided by a company that manufactures activated carbon for other uses, and the objective was to improve performance by evaluating the activated carbon as a storage battery.

First, activated carbon, Ketjen black (conductive material), and PTFE (bonding material) were mixed at a ratio of 8:1:1 and pressed onto a nickel mesh using a heat press at a temperature of 130 °C and a pressure of 10 MPa to fabricate a circular electrode with a diameter of 1 cm.

The circular electrode was evaluated using a three-electrode method. The first is the capacity measurement of the storage battery F/g by cyclic voltammetry. The conditions were a voltage of -0.5 V to 0.5 V, sweep rate of 10 mV/s, number of cycles of 10, Pt as the counter electrode, Ag/AgCl as the reference electrode, and 0.5 mol/L of KOH as the electrolyte solution [4].

As another measurement method, the internal resistance (comprising solution resistance and charge transfer resistance) was measured using the electrochemical impedance method, under the same conditions as those employed for the cyclic voltammetry method [4].

As a result, it was confirmed that the attachment of basic functional groups to an activated carbon surface an improvement in performance in the activated carbon can be expected by increasing its capacity and decreasing its internal resistance. It has been confirmed that functional groups including basic functional groups exhibit unique properties, and the presence of the basic functional groups utilized in this study may be a factor in improving the hydrophilicity of the activated carbon and promoting the adsorption of ions [5].

Reference

[1] Lere Deguenon, Daniel Yamegueu, Sani Moussa kadri, Aboubakar Gomna, Overcoming the challenges of integrating variable renewable energy to the grid: A comprehensive review of electrochemical battery storage systems ,” Journal of Power Sources” ,PP1-2. (2022)

[2] Mustafa Ergin Sahin, Frede Blaabjerg, Ariya Sangwongwanich, A Comprehensive Review on Supercapacitor Applications and Developments ,” energies” , PP1-2. (2022)

[3] Surajudeen Sikiru, T.T. Dele-Afolabi, Mohammad Yeganeh Ghotbi, Zia Ur Rehman , Recent advancements in technology projection on electric double layer effect in battery recycling for energy storage , ” Journal of Power Sources”,PP.2(2024)

[4] Daisuke Tashima, Takuhiro Kashio, Takuya Eguchi, Seiji Kumagai, Toshiki Tsubota, John D.W. Madden, Recycling marine plastic waste to energy storage devices , Materials Letters: X ,PP.2-3(2023)

[5] Akihiko Yoshida, Ichiro Tanahashi, Atsushi Nishino, Effect of concentration of surface acidic functional groups on electric double-layer properties of activated carbon fibers,” Carbon”, (1990)

Figure 1