Abstract:  

This work reports the effects of activation temperatures on the porous development and electrochemical performance of activated carbons. Herein, activated carbons were prepared from the biowaste of mangosteen peel by using KOH activation at temperatures of 400, 600, and 800 °C. The results demonstrate that the specific surface area increases with increasing activation temperatures in which the well-developed porous structure after KOH activation at 800 ºC provides the highest specific surface area of 1039 m² g⁻¹. At 600 ºC, the activated carbon delivers the highest specific capacitance value of 182 F g⁻¹ at a current density of 0.5 A g⁻¹ in 3 M KOH aqueous electrolyte. This is correlated well with its high micropore fractions (99%). Moreover, it was found that the activation temperature changes the major contribution of oxygen-containing functional group on surface of activated carbon, which is beneficial for the enhancement of the specific capacitance value of activated carbon at the temperature of 600 °C. This work suggests that the activation temperature is a key to optimizing the electrochemical performance of activated carbons. Overall, our activated carbons can be considered as a strong candidate for use as electrode materials in supercapacitors.

Background Introduction:

In electrochemical capacitors (ECs) or supercapacitors (SCs), electrode materials play a crucial role in determining electrochemical performance. Among the electrode materials, carbons are widely used because of their high chemical stability and large specific surface area. Activated carbons (ACs) are carbonaceous materials with a well-developed porous structure and large surface area. A highly porous AC has been widely applied in several applications, especially in wastewater treatment and electrode materials in supercapacitors. In comparison with commercial carbon-based materials, AC derived from biomass is low-cost, environmentally friendly, and rich in surface functional groups. Therefore, numerous biomasses have been searched for use as raw materials or precursors in the preparation of activated carbon such as durian peel ,corn cob, and coconut shell.

In supercapacitors, the AC electrode stores the charge based on the accumulation of electrolyte ions onto the surface of a highly porous carbon, known as electric double layer capacitor (EDLC) . From this point of view, pores of carbon-based electrodes serve as channels for electrolyte ion transportation. Therefore, the specific surface area and porous structure are important keys to determine the electrochemical performance of carbon-based electrode materials . Generally, highly porous ACs are obtained by either physical or chemical activation. In comparison, a higher yield with well-developed porosities is obtained by chemical activation . In addition, the chemical activation uses lower temperatures of pyrolysis to obtain a higher specific surface area . Generally, the chemical activation involves the carbonization   of the raw materials by impregnation the materials with activating agents such as KOH, NaOH, ZnCl₂, H₃PO₄, etc., and subsequently heated at temperatures between 400 and 900 °C . Among the activating agents, KOH is widely used for the preparation of the extremely high specific surface area (>3000 m² g⁻¹) owing to its association with gasification reaction during the activation process. Mangosteen, known as a queen of fruit, is widely cultivated in Southeast Asia especially in Thailand, Indonesia, and Malaysia. The dark red shell of mangosteen composes about two-thirds of the whole fruit weight and is considered as agricultural waste . It has been reported that every 10 kg of mangosteen generated about 6 kg of mangosteen shells . Furthermore, the main components of mangosteen peel are lignin, cellulose, hemicellulose, and the minerals such as K, P, Mg, S, etc. which can be washed off. Along with high waste content, this makes mangosteen peel an ideal precursor to produce AC. Generally, the AC derived from mangosteen peel using chemical activation can be divided into one-step and two-step activation. The one-step activation involves the impregnation of mangosteen peel with the activating agents followed by activation/carbonization at temperatures above 500 °C. In two-step activation, the thermal conversion is firstly performed to convert the precursor to biochar at a temperature ≤500 °C and the obtained biochar is then impregnated with the activating agents of KOH . Finally, the AC derived from the biochar is obtained via the activation/carbonization at temperature ranging 700–900 °C. Compared with two-step activation, one-step activation provides a high specific surface area within a shorter preparation time . To the best of our knowledge, there are few reports on the study of KOH activation temperatures on electrochemical properties of activated carbon derived from biowaste of mangosteen peel .

In this work, we focus on the preparation, characterization, and electrochemical studies of AC derived from mangosteen peel by using a one-step KOH activation. Effects of the activation temperatures on the physical characteristics of AC were carried out by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and N₂ adsorption-desorption techniques in order to investigate the phase formation, morphology, and porosity properties of ACs, respectively. To evaluate the potential use of ACs as electrode materials in supercapacitors, the electrochemical performance of ACs was studied in 3M KOH aqueous electrolyte by using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) techniques.

Article Highlights:

• Highly porous activated carbons were successfully prepared from mangosteen peel waste by using KOH activation.
• Activated carbon with the specific surface area as high as 1039 m² g⁻¹ was produced at activation temperature of 800 ºC.
• The activated carbon electrode shows the highest specific capacitance value of 182 F g⁻¹ at 0.5 A g⁻¹ with the cycling stability higher than 90% after 1000 cycles.
• The enhancement of the capacitance value is responsible for the micropore fraction and the specific type of oxygen-containing functional group on surface of activated carbon.

Summary and Outlook:

This study highlights the use of mangosteen peel waste as a precursor for the preparation of a highly porous AC. The influence of activation temperatures on the development of porosities and electrochemical performance of activated carbons were investigated and compared. The results demonstrate that the porous development on surface of ACs depends strongly on activation temperatures. Higher activation temperature produces higher BET surface area and pore volume. At activation temperature of 800 °C, the specific surface area reaches up to 1039 m² g⁻¹. The electrochemical results show that the AC prepared at 600 ​°C delivers the maximum specific capacitance value of 182 F g⁻¹ ​at a current density of 0.5 A g⁻¹ in 3 M KOH aqueous electrolyte and maintains about 90% of its initial value after 1000 cycles. This is attributed to the fraction of micropore volume and the major contribution of the oxygen-containing functional group (O–C) on surface of activated carbon at lower current density. On the other hand, a large accessible surface area is responsible for a higher current density. Consequently, the activation temperature is considered as an important factor for achieving the excellent electrochemical performance. This is appropriate for use our AC as low-cost electrode materials in supercapacitors.

Article Details:

Mangosteen peel-derived activated carbon for supercapacitors

Jessada Khajonrit, Thongsuk Sichumsaeng, Ornuma Kalawa, Suphawi Chaisit, Atchara Chinnakorn, Narong Chanlek, and Santi Maensiri*

Article Link: https://doi.org/10.1016/j.pnsc.2022.09.004

A brief introduction of the author's group

Jessada Khajonrit graduated with a PhD in Applied Physics from the School of Physics, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima, Thailand, in 2016. He joined the Advanced Functional Materials (AMP) research group in 2012, focusing on nanomaterial technology, electrospinning, energy storage, supercapacitors, and material physics. Currently, he is a lecturer at Kalasin University, Thailand, in the Department of Science and Mathematics, Faculty of Science and Health Technology. His research aims to innovate and advance the field of energy storage and nanomaterials.

Thongsuk Sichumsaeng received her PhD in Physics from the School of Physics, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima, Thailand, in 2019. She joined the Advanced Functional Materials (AMP) research group in 2013, focusing on the synthesis and characterization of nanomaterials for energy storage applications. Currently, she is a public health technical officer in the Occupational and Environmental Diseases group at the Office of Disease Prevention and Control, Region 4 Saraburi, Saraburi, Thailand. Her research interests are the use of advanced techniques for characterization of the materials that related to occupational and environmental diseases.

Ornuma Kalawa graduated with a Ph.D. in Physics from the School of Physics, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima, Thailand, in 2020. From 2020 to 2022, she worked as a postdoctoral researcher in the Advanced Functional Materials (AMP) research group at the same university, specializing in nanomaterial technology, electrospinning, energy storage, supercapacitors, and material physics. Currently, she is a Public Health Technical Officer at the World Health Organization Collaborating Centre for Occupational Health (WHO CC - THA16), Division of Occupational and Environmental Diseases, Department of Disease Control, Ministry of Public Health, Thailand.

Suphawi Chaisit graduated with a Master's degree in Physics from the School of Physics, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima, Thailand, in 2018. She joined the Advanced Functional Materials (AMP) research group in 2016, focusing on nanomaterial technology, activated carbon, energy storage, and supercapacitors. Currently, she is a teacher at the Phetchaburi Rajabhat University Demonstration School, Phetchaburi. Her research aims to explore the field of activated carbon and supercapacitors.

Atchara Chinnakorn earned her PhD in Physics from the School of Physics, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima, Thailand, in 2024. Since 2017, she has been an integral member of the 3D Printing research group and has engaged in collaborative research with the Advanced Functional Materials (AMP) research group. Currently, she holds the position of research assistant at the National Metal and Materials Technology Center, one of Thailand's National Research Centers. Her research primarily focuses on the application and development of additive manufacturing technologies, commonly known as 3D printing, for a wide variety of materials, including nanofibers, hydrogels, polymers, composites, and metals.

Narong Chanlek received his Ph.D. degree in Physics from the University of Manchester, UK in 2012. He is currently a beamline scientist at the Synchrotron Light Research Institute, Thailand. His research interests include material characterizations, electron sources, X-ray techniques, and applications of synchrotron radiation.

Professor Santi Maensiri obtained his first degree in Physics at Khon Kaen University Thailand. He then received his M.Sc. (Ceramic Processing) from Leeds University, and D.Phil. (Materials Science) from the University of Oxford, UK. He has published more than 300 Scopus papers with citations over 11000 times and h-index of 56 in the areas related to applied physics, materials physics, materials science, and nanomaterials. He was appointed SUT’s Head of School of Physics, the Dean of Institute of Science, and later Vice Rector for Academic Affairs and Internationalization at Suranaree University of Technology (SUT), Thailand. He is currently the Dean of Institute of Science, the Director of Centre of Excellence in Advanced Functional Materials, and Director of NANOTEC-SUT Research Network on Nanotechnology for Nanomaterials and Advanced Characterizations. At the national level, he is presently serving as the President of the Materials Research Society of Thailand (MRS-Thailand, member of IUMRS). Professor Santi Maensiri is serving as the Editor-in-Chief of Science and Innovation of Advanced Materials (Materials Research Society of Thailand) and a member of the editorial boards for Materials Chemistry and Physics (Elsevier BV). For his research strength, he has received numerous awards, such as the National Research Award in Physical Science and Mathematics from The National Research Council of Thailand (NRCT) for two consecutive years (2012 and 2013), the 2013 TRF Senior Research Scholar from the Thailand Research Fund (TRF), and National Outstanding Researcher Award in Physical Science and Mathematics (Physics) also from NRCT, to name a few.