Large Pseudocapacitance in Quinone-Functionalized Zeolite-Templated Carbon

Abstract

Zeolite-templated carbon (ZTC), which can be obtained as a negative replica of a zeolite, consists of buckybowllike nanographenes assembled into a three-dimensional regular network. ZTC is characterized not only by this unique framework structure but also by a very large number of carbon edge sites. In this paper, we report that the edge sites of ZTC are easily functionalized by a large amount of quinone groups through electrochemical oxidation unlike general carbonaceous materials, and the quinone-functionalized ZTC shows a high electrochemical capacitance (ca. 300 500 F g ¹1 ) in an aqueous electrolyte solution (1 M H 2 SO 4 ) as a result of the large pseudocapacitance derived from a quinone/hydroquinone redox couple. Moreover, ZTC keeps its high capacitance even after thousands of charge discharge cycles.Fullerenes, 1 single-walled carbon nanotubes (SWCNTs), 2,3 and graphenes 4,5 are nanocarbon materials with 0D, 1D, and 2D topologies, respectively. Though fullerenes form poorly conductive van der Waals crystals, SWCNTs 6,7 and graphenes 811 are electrically conductive, and are promising as electrode materials for electrochemical capacitors. 12 Their building unit, a graphene sheet, has a large theoretical surface area (2630 m 2 g ¹1 ), and therefore potentially has a large capacitance. However, the actual BrunauerEmmettTeller (BET) surface areas of SWCNTs 13 and graphenes 8 are at most 1250 and 705 m 2 g ¹1 , respectively, because of the aggregation/stacking of the graphene sheets as a result of strong van der Waals interactions. To expose the entire surface, a graphene sheet has to be formed into a self-standing 3D network, like carbon schwarzite 14,15 or pillared graphene, 16 both of which are imaginary materials and have only been proposed theoretically. Thus far our group has demonstrated that it is possible to synthesize a graphene-based architecture with a 3D topology inside the confined-nanospace network of a zeolite crystal, as shown in Figures 1a1c. 1720The zeolite-templated carbon (ZTC) thus obtained consists of a buckybowl-like nanographene assembled into a 3D regular network (Figures 1c and 1d). Both sides of the buckybowllike unit are fully exposed, and, in addition, the narrow nanographene-based framework has a significant number of edge sites. 18 Consequently, ZTC has a very large geometric (theoretical) surface area of 3432 m 2 g ¹1 , and such a large surface area has indeed been observed experimentally.18 ZTC possesses unique spin/magnetic properties 21 and is predicted to have a unique band structure. 22 Moreover, it has a high hydrogen-storage capacity 23,24 and superior performance as an electrode for electrochemical capacitors.2527 Modifications of ZTC with electrochemically active species are expected to further enhance its performance. Graphene-based materials are generally modified by doping of graphene with other functional components such as metal nanoparticles, 2830 metal oxides/ hydroxides, 3134 and conductive polymers. 35 Another modification method is to functionalize graphenes...

Successful functionalization of superporous zeolite templated carbon using aminobenzene acids and electrochemical methods

“…The broad peak centered ca. 0.3 V mainly corresponds to the pseudocapacitive contribution of electroactive surface oxygen groups, which are known to be generated during the functionalization process in acid media when potentials higher than 0.8 V are used [5]. This is also observed in the experiment in the absence of ABA, where a broad redox process appears at about 0.30 to 0.40 V that is attributed to the formation of quinone groups over the ZTC surface.…”

“…1a). This fact has been already reported in the literature [5], [29] and is related to the oxidation of the ZTC, which is highly reactive because of a large number of edge sites [5], leading to a direct electro-oxidation mechanism upon positive polarization in acid media. The subsequent cycles show that the oxidation current decreases.…”

“…It is important to highlight here that quinone/carbonyl groups have been claimed to be electroactive specially in acid electrolyte [38], and are clearly observed in the case of ZTC [5], [29]. However, the pseudocapacitance contribution associated to redox reactions of quinonetype groups was similar for the ABA-modified samples (see Fig.…”

“…as a template by the method reported elsewhere [4], [5], [28] . 2 and 4-aminobenzoic acids (2-ABA and 4-ABA, respectively), sulfuric acid (1 M), perchloric acid (70%), and the potassium hydroxide were purchased from Wako Chemicals GmbH.…”

“…As an example, the introduction of surface oxygen groups through conventional chemical oxidation produces a strong damage of the 3D-dimensionally ordered structure [4]. It was found that the use of electrochemical techniques can control the process with high accuracy without high structural changes [4], [5]. This is because electrochemical techniques have several advantages compared to the conventional chemical routes: i) they are simple and can be immediately interrupted, providing a better control on the time of the treatment, ii) can be run at room temperature and atmospheric pressure, iii) can work with small amount of reagents and sample, iv) the reaction conditions are very reproducible and, v) they are processes with very high sensitivity and selectivity [6].…”