Influence of KOH/Coke Mass Ratio on Properties of Activated Carbons Made by Microwave-Assisted Activation for Electric Double-Layer Capacitors

Abstract

Activated carbons (ACs) are obtained by microwave-assisted activation of petroleum coke with KOH as an activation agent and used as electrode materials for electric double-layer capacitors. The pore structure and functional groups of ACs are characterized by Fourier transform infrared spectroscopy and the nitrogen adsorption technique. The results show that both the specific surface area (S BET) and the total pore volume (V t) of ACs go through a maximum as the KOH/coke mass ratio increases. At 5:1 of the KOH/coke mass ratio, S BET of AC (denoted as AC5/1) made by microwave-assisted activation is 2312 m2 g−1, with V t of 1.13 m3 g−1, while S BET of AC made by conventional activation is only 532 m2 g−1, with V t being at 0.24 m3 g−1. The microwave-assisted KOH activation process is capable of creating and enlarging micropores of petroleum coke by increasing the KOH/coke ratio from 3:1 to 5:1. Nevertheless, some micropores are destroyed when the KOH/coke ratio is 6:1. The specific capacitance of AC5/1 electrode remains at 246.0 F g−1 even after 1000 charge−discharge cycles. For the capacitor made of AC5/1 or AC3/1 heated at 1073 K, the energy retention ratio after 1000 cycles is 75.1 or 79.6%.

High-performance super capacitors based on activated anthracite with controlled porosity

“…Carbon materials have been crucial for various fields of electrical energy storages such as capacitors, super capacitors, and secondary batteries with various electrodes [3][4][5][6][7][8][9][10][11].…”

“…However, the majority of the activated carbons obtained from biomass precursors have low bulk densities and physically weak structures, which are not appropriate for specific harsh purposes for example huge number of charge/discharge cyclic activities in EDLC and secondary battery electrodes [3]. Therefore, new carbon materials such as carbon nanotubes and graphene-based carbons have been synthesized as effective materials for these purposes [1][2][5][6][7][8][9][10][11]. Some recent super capacitors were made of a set of asymmetric electrodes.…”

“…On the other hand, it has been known that coal-based activated carbons have relatively good stability for EDLC applications [5][6][8][9]. Anthracite with high carbon M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 4 content has been used in synthesizing activated carbons [12][13].…”

A facile and green preparation of durian shell-derived carbon electrodes for electrochemical double-layer capacitors

“…Numerous studies have been conducted to explore the electrochemical performance of activated carbon-based electrodes for EDLCs [10][11][12][13][14][15]. It has been reported that the capacitance of electrode critically depends on the pore structure and surface chemistry of activated carbon [16][17][18][19][20][21]. To improve its electrochemical performance, activated carbons must be modified with proper activation methods.…”

“…To improve its electrochemical performance, activated carbons must be modified with proper activation methods. The most extensively used methods is through one-step or two-step chemical and/or physical (thermal) activations using various modifiers such as ZnCl 2 , H 3 PO 4 , KOH, K 2 CO 3 , CO 2 , or steam [15,18,19,22,23]. However, such conventional processes are energy-intensive in conjunction with high temperature carbonization process (mostly conducted at above 700 1C) and often cause environmental issues due to the generation of wastewater containing toxic chemicals.…”