Elsevier

Ceramics International

Volume 45, Issue 4, March 2019, Pages 4208-4218
Ceramics International

Aloe peel-derived honeycomb-like bio-based carbon with controllable morphology and its superior electrochemical properties for new energy devices

https://doi.org/10.1016/j.ceramint.2018.11.091Get rights and content

Highlights

  • Honeycomb-like carbon (AP-HC) is prepared by modified hydrothermal method.

  • Controllable morphology transformation is realized in bio-based carbon.

  • A high specific surface area of 1286 m2 g−1 is obtained for AP-HC.

  • A PCE of 6.92% is achieved in DSSCs with biomass-derived carbon catalyst.

  • AP-HC demonstrates excellent electrochemical performances (264 F g−1) in SCs.

Abstract

In this study, aloe peel-derived honeycomb-like porous carbons (AP-HC) are controllably prepared by combining simple hydrothermal carbonization with chemical activation. A morphology transformation from the spherical structure (AP-SC) to the honeycomb-like structure (AP-HC) is achieved for biomass-derived carbon materials and is accompanied by an increase in the specific surface area from 13 to 1286 m2 g−1. The AP-HC as a counter electrode (CE) for dye-sensitized solar cells (DSSCs) exhibits remarkable catalytic activity for I3- ion reduction and a high power conversion efficiency (PCE) of 6.92% that matches the Pt-based DSSC's performance (7.19%). As a working electrode in supercapacitors (SCs), a high specific capacitance of 264 F g−1 at 0.5 A g−1 is achieved in a three-electrode system. Additionally, a high retention rate of ∼77.45% (ranging from 0.5 to 30.0 A g−1) and superior cycling performance (91% capacitance retention after 5000 cycles) are also demonstrated. This study provides an efficient strategy for fabricating morphology-controllable porous bio-based carbon with higher specific surface area (1286 m2 g−1) that exhibits significant potential for new energy devices.

Introduction

Global challenges based on limited natural resources and fossil energy reserves stimulated keen interest in the development of high-performance energy production and storage techniques. As new energy devices, dye-sensitized solar cells (DSSCs) and supercapacitors (SCs) attract significant attention owing to their low cost, simple fabrication, and environment friendliness [1], [2]. Thus, the development of high-performance and low-cost electrode materials is likely to satisfy the increasing demands for electrochemical energy devices. It is generally established that activated carbon (AC), carbon fiber, mesoporous carbon, carbon nanotube, carbon black, fullerene, graphene, etc., have been successfully used in DSSCs and SCs as electrode materials [1], [3], [4], [5], [6], [7], [8]. Specifically, biomass-derived ACs are attracting increasing attention considering of the availability of abundant raw materials and resource recycling utilizations [9], [10], [11], [12], [13].

Presently, various biomass resources or bio-wastes such as coffee waste [14], fallen leaves [15], mangosteen peel waste [16], human hair [17], willow catkin [18], cattle bones [19], potato waste residue [20], corn straw [21], indicalamus leaves [22], and rice straw [23] are employed to prepare bio-based carbon materials. These carbon materials, which have higher specific surface areas, exhibit potential for high-performance DSSC and SC applications. On the one hand, the higher specific surface area of the bio-based carbon provides more catalytic sites for I3- reduction, resulting in high power conversion efficiency (PCE) exceeding 7.0% in DSSCs [1], [2], [3]. On the other hand, it yields more active sites and channels for the migration and adsorption of electrolyte ions, resulting in a superior specific capacitance of 298 F g−1 at 0.5 A g−1, high energy density 109.9 W h kg−1 at 4.4 kW kg−1, and remarkable cycling stability (a capacitance retention of 96.4% after 5000 cycles) in SCs [18], [19]. Biomass waste manifest as precursors in the preparation of bio-carbons; therefore, biomass-derived carbon materials exhibit significant potential for application in SCs. However, to the authors’ knowledge, there is a paucity of studies on bio-based carbon materials as a counter electrode (CE) applied in DSSCs.

Typically, one-step pyrolysis carbonization, hydrothermal carbonization, and two-step chemical activation carbonization are used to prepared bio-based carbon materials. One-step carbonization produces carbon materials that exhibit low carbon yields, high decomposition rate, and heterogeneous pore size. In contrast, hydrothermal carbonization significantly increases the carbon yield, although extant studies indicate that the hydrochar typically exhibits a very low specific surface area of approximately 10 m2 g−1; this severely restricts the application of the as-synthesized carbon [24], [25], [26], [27]. Thus, chemical activation can be used to remedy the aforementioned deficiency. Activated products with high specific surface areas and multi-leveled pores are in demand for developing DSSCs and SCs; they provide more catalytic sites for I3- reduction and enhance migration and adsorption of ions. In this regard, combining hydrothermal carbonization and chemical activation is an effective strategy for preparing high-performance bio-based carbon materials with enhanced specific surface area. On the other hand, biomass-derived carbon prepared from various biomass resources as raw materials are reported, although only a few studies focused on controllable morphology. Therefore, the aim of the present study is to synthesize a highly potential bio-based carbon with controllable morphology and high specific surface area, via a highly efficient preparation process, and realize its application as an electrode material in DSSCs and SCs.

In this work, we report an aloe peel-derived 3D honeycomb-like porous carbon (AP-HC) fabricated via a straightforward method combining hydrothermal carbonization and chemical activation through KOH-activation. The as-prepared AP-HC exhibits a large specific surface area of 1286 m2 g−1; this results in superior properties of DSSCs and SCs. As a CE catalyst for I3- reduction in DSSCs, it achieves a PCE of 6.92%, which is close to that of Pt (7.19%). As a working electrode in SCs, the AP-HC exhibits a high specific capacitance of 264 F g−1 at 0.5 A g−1, with a remarkable capacitance retention of 77.45% at 30 A g−1. The enhanced performance of DSSCs and SCs with the bio-based carbon is attributed to the synergistic effects as a result of the high specific surface area and well-defined porosity of AP-HC.

Section snippets

Preparation of bio-based carbon materials

Controllable-morphology bio-based carbon materials were prepared via hydrothermal carbonization combining chemical activation. The preparation process of bio-based carbon materials is presented as a schematic illustration (Fig. 1a). Aloe peel (AP) was gathered from the Yangling region in Shaanxi, China. The collected AP was washed by using deionized (DI) water to remove impurities and then dried at 105 °C. The dried AP was further crushed into fine powder (average particle size = ~2 µm) by a

Morphological and structural characterizations

The XRD patterns of the as-synthesized AP-SC and AP-HC are shown in Fig. 2a. Two typical amorphous carbon materials were successfully prepared with two characteristic peaks at 2θ of 24.3° and 43.3°, corresponding to the (002) and (100) crystal planes, respectively, of typical graphitic structure. Additionally, it was evident that the pattern of the AP-HC revealed a relatively weaker intensity than that of the AP-SC, thereby indicating the presence of a lower graphitization degree and abundant

Conclusion

Using aloe peel waste as the raw materials, 3D honeycomb-like bio-based carbon was successfully prepared through a method combining hydrothermal carbonization and chemical activation. A morphology-controllable transformation from the spherical bio-carbon (AP-SC) to honeycomb-like porous bio-carbon (AP-HC) is achieved in the present study. The AP-HC exhibits a larger specific surface area of 1286 m2 g−1 and an optimal pore size distribution centered at 0.59 nm. The advantageous features afforded

Acknowledgments

Financial support from NSFC (51672208), National Science & Technology Pillar Program during the Twelfth Five-year Plan Period (2012BAD47B02), Sci-Tech R&D Program of Shaanxi Province (2010K01-120 and 2015JM5183), and Shaanxi Provincial Department of Education (2013JK0927) is greatly acknowledged. The project was partly sponsored by SRF for ROCS, SEM.

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