Facile synthesis of high-surface area mesoporous biochar for energy storage via in-situ template strategy Yuan Gao ⇑ , Yulin Zhang, Aimin Li, Lei Zhang Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education), School of Environmental Science and Technology, Dalian University of Technology, Linggong Road 2, Dalian 116024, China article info Article history: Received 19 March 2018 Received in revised form 5 July 2018 Accepted 24 July 2018 Available online 25 July 2018 Keywords: Crab shell In-situ template Carbon materials Mesoporous biochar Energy storage and conversion abstract A novel synthetic strategy was successfully developed to fabricate mesoporous biochar with high-surface area from crab shell as carbon precursor and its natural CaCO 3 as in-situ template. The influences of pyrolysis temperature on the pore structure were investigated via N 2 adsorption-desorption isotherms and scanning/transmission electron microscope. The as-prepared biochar at pyrolysis temperature of 900 °C possessed high surface area of 634 m 2 /g and large mesopore percentage of 70.80%. The maximum specific capacitance of biochar electrode reached 220 F/g. The excellent supercapacitor performance of this supercapacitor was strongly attributed to the thermal decomposition of CaCO 3 , producing high surface area and mesoporous structure for raw biochar. Ó 2018 Elsevier B.V. All rights reserved. 1. Introduction Currently, tremendous attentions have been devoted to explore low-cost, environmentally friendly, and high-efficient carbon- based electrode materials for supercapacitors, such as activated carbon, carbon nanotube, carbon nanofiber and graphene [1]. As a newly arisen carbon material, biochar has attracted emerging research attentions in the recent decade, which has only been applied in soil amendment, adsorbent and catalysts. Unfortunately, biochar suffers from relatively low surface area, limiting its appli- cation in storage high-quantity energy. Besides, the performance of carbon-based electrode is not only related to its surface area but also affected by its pore size distribution. Microporous biochar- based electrodes always suffer from the disadvantageous of poor diffusivity of electrolytes into the pores due to the space confine- ment, leading to an unsatisfactory capacitive performance. Thus, synthesis of high-surface area and mesoporous biochar is an effec- tive solution to address the above-mentioned issues. On the one hand, considerable efforts have been devoted to post-treat biochar via pyrolysis or activation to improve surface area [2,3]. On the other hand, hard and soft template strategies have been used as two common approaches for synthesizing mesopore-enriched carbon materials [4,5]. In hard template method, mesoporous silica monolith as a template is required to synthesize, then the removal of template after service has to use chemical etching with highly corrosive hydrofluoric acid. In soft template method, extra amphiphilic surfactants or block copolymers are served as additional template, while carcinogenic formaldehyde and phenol are inevitably used as precursors. Despite great efforts have been paid on these strategies, the processes are still somewhat fussy, time-consuming and costly. Herein, exploring an in-situ natural template from biomass waste would be more worthwhile. Niu et al. prepared porous carbons with high surface area using cattle bone as starting material and its own hydroxyapatite as natural defect mold [6]. The obtained carbon possessed high mesopore volume (1.829 cm 3 /g) and excellent capacity performance (1488 mA h/g). Inspired by their work, this study aimed at using crab shell to synthesize mesoporous biochar owing to its natural high ingredient, CaCO 3 . Many researchers have proved that CaCO 3 could be used as template to prepare hierarchical materials. For example, Gu et al. produced hierarchical porous carbon using micro-CaCO 3 as conformal template through chemical vapor deposition [7]. Yang et al. synthesized nitrogen-doped porous graphitic carbon by using melamine-formaldehyde resin as precursor and CaCO 3 as template [8]. Zhao et al. prepared hierarchical disordered meso- porous carbon with formaldehyde resin as precursor and CaCO 3 nanoparticle as template [9]. The shortcoming of additional CaCO 3 is that they cannot fully react with precursors. Thus, the role of CaCO 3 as template is not so strong as that of the natural ones in crab shell. https://doi.org/10.1016/j.matlet.2018.07.106 0167-577X/Ó 2018 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail address: gaoyuan1988@dlut.edu.cn (Y. Gao). Materials Letters 230 (2018) 183–186 Contents lists available at ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/mlblue