Elsevier

Current Applied Physics

Volume 12, Issue 1, January 2012, Pages 233-237
Current Applied Physics

Electrochemical properties of Mn-doped activated carbon aerogel as electrode material for supercapacitor

https://doi.org/10.1016/j.cap.2011.06.010Get rights and content

Abstract

Carbon aerogel (CA) was prepared by a sol-gel polymerization of resorcinol and formaldehyde, and it was activated with KOH to obtain activated carbon aerogel (ACA). Specific capacitance of carbon aerogel and activated carbon aerogel was measured by cyclic voltammetry and galvanostatic charge/discharge methods in 6 M KOH electrolyte. Activated carbon aerogel showed higher specific capacitance than carbon aerogel (136 F/g vs. 90 F/g). In order to combine excellent electrochemical performance of activated carbon aerogel with pseudocapacitive property of manganese oxide, 7 wt% manganese oxide was doped on activated carbon aerogel by an incipient wetness impregnation method. For comparison, 7 wt% manganese oxide was also doped on carbon aerogel by an incipient wetness impregnation method. It was revealed that 7 wt% Mn-doped activated carbon aerogel (Mn/ACA) showed higher specific capacitance than 7 wt% Mn-doped carbon aerogel (Mn/CA) (168 F/g vs. 98 F/g). The enhanced capacitance of 7 wt% Mn-doped activated carbon aerogel was attributed to the outstanding electric properties of activated carbon aerogel as well as the faradaic redox reactions of manganese oxide.

Highlights

► Carbon aerogel (CA) was prepared by resorcinol-formaldehyde method. ► Activated carbon aerogel (ACA) was prepared using KOH. ► ACA showed higher capacitance than CA. ► Mn/ACA showed higher capacitance than Mn/CA.

Introduction

Supercapacitors are commonly used for an electrochemical energy storage device, which is ideally suitable for rapid storage and release of energy. Specific storage energy of supercapacitors is much higher than that of conventional capacitors [1], [2], [3]. To develop supercapacitors with high performance, a large number of electrode materials have been employed [4], [5], [6], [7], [8], [9], [10], [11], [12]. Various carbonaceous materials, such as carbon nanotubes [3], [13], [14], activated carbons [15], templated carbons [16], [17], [18], [19], carbon aerogels [20], [21], [22], [23], [24 ], [25], and carbon xerogels [26], have been extensively investigated as electrodes for supercapacitor. In addition, transition metal oxide and conducting polymer have also been employed to enhance specific capacitance and power density of supercapacitors by taking advantage of pseudocapacitive behaviour [27], [28], [29], [30].

Carbon aerogel has a three-dimensional nano-network structure of primary carbon particles, providing versatile properties such as high surface area, outstanding electric conductivity, and high accessible area for electric double layer (EDL) [22], [23], [24 ], [31]. Conventional carbon materials, including carbon aerogels, have not only lower surface area for EDL than activated carbon but also limited power density and energy capacity. In order to overcome these problems, various modification methods of carbon materials have been suggested. Activation of carbon aerogel with KOH and CO2 increases surface area and pore volume of carbon aerogel due to the formation of micropores of carbon aerogel [32], [33]. It is known that these properties improve the performance of carbon aerogel as an electrochemical capacitor. As a result, composite materials for electrochemical capacitors have been developed, which are based on a combination of carbon materials and metal oxides [34], [35], [36], [37].

In this work, carbon aerogel was prepared by a sol-gel polymerization of resorcinol and formaldehyde in ambient conditions. In order to obtain activated carbon aerogel, KOH was used as an activation agent. To combine excellent electrochemical performance of activated carbon aerogel with pseudocapacitive property of manganese oxide, manganese oxide was doped on activated carbon aerogel by an incipient wetness impregnation. After impregnating manganese precursor on activated carbon aerogel, it was calcined at 250 °C for 5 h under air condition to obtain Mn-doped activated carbon aerogel. For comparison, Mn-doped carbon aerogel was also prepared. The prepared composites were fabricated as electrodes for supercapacitors and their electrochemical performance was examined.

Section snippets

Preparation of activated carbon aerogel electrode

Carbon aerogel was prepared by a sol-gel polymerization of resorcinol and formaldehyde according to the method in our previous work [38]. In order to obtain activated carbon aerogel, KOH was used as an activation agent. Preparation procedure for activated carbon aerogel is shown in Fig. 1. RF (resorcinol-formaldehyde) aerogel was carbonized at 500 °C under N2 stream. KOH was dissolved in DI water, and the carbonized carbon aerogel was added into the solution. After stirring the solution for

Physical properties of carbon aerogel (CA) and activated carbon aerogel (ACA)

Textural properties of carbon aerogel and activated carbon aerogel were examined by N2 adsorption-desorption isotherm measurements. Fig. 2 shows the N2 adsorption-desorption isotherms and pore size distributions of carbon aerogel and activated carbon aerogel. BET surface area and average pore diameter of carbon aerogel and activated carbon aerogel are listed in Table 1. Type IV isotherm with H2 type hysteresis loop was clearly observed in both carbon aerogel and activated carbon aerogel,

Conclusions

Carbon aerogel was activated using KOH as an activation agent. Activated carbon aerogel showed high BET surface area and exhibited outstanding electrochemical performance. In order to combine these properties of activated carbon aerogel with pseudocapacitive property of manganese oxide, manganese oxide was doped on activated carbon aerogel by an incipient wetness impregnation method. For comparison, manganese oxide was also doped on carbon aerogel. It was found that Mn-doped activated carbon

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