Contents lists available at ScienceDirect Journal of Energy Storage journal homepage: www.elsevier.com/locate/est Aerogel from fruit biowaste produces ultracapacitors with high energy density and stability Kenny Lee 1 , Luba Shabnam 1 , Shaikh Nayeem Faisal, Van Chinh Hoang, Vincent G. Gomes ⁎ School of Chemical & Biomolecular Engineering, The University of Sydney, NSW 2006, Australia ARTICLE INFO Keywords: Food waste Carbon aerogel Supercapacitors Nitrogen doping Specific capacitance Energy storage ABSTRACT Biomass waste from jackfruit and durian were used to produce carbon aerogel electrodes incorporating stable scaffolding of base material and natural nitrogen doping. Higher atomic doping of nitrogen in DCA (durian carbon aerogel) compared to JCA (jackfruit carbon aerogel) indicates preservation of nitrogen-containing functional groups during the synthesis. The specific surface area and proportion of mesopores is greater for DCA than for JCA samples. Electrochemical characterizations via cyclic voltammetry, galvanotactic charge discharge and electrochemical impedance spectroscopy show high specific capacitance for both DCA (591 F g -1 ) and JCA (292 F g -1 ) at 1 A g -1 current density with two-electrode configuration with excellent cycling stability and charge. 1. Introduction To meet the challenges of global warming and those of rapidly de- pleting fossil fuel, a global priority is to develop energy storage devices with high energy density [1,2]. The electrochemical supercapacitors (ECs), sometimes referred to as “electrical double layer capacitors” (EDLC) are recognized as ideal energy storage candidates for applica- tions ranging from portable medical and electronics devices to heavy hybrid and other transportation uses. Supercapacitors are promising for energy storage due to their superior cycling stability and excellent charge–discharge ability [3–6]. Electrochemical supercapacitors can store charge by accelerating redox reactions, which promote rapid en- ergy capture and delivery. However, the large-scale application of su- percapacitors is constrained by their low capacitance and stability [7]. To develop high-performance supercapacitors, carbon materials such as activated carbon (AC), carbon nanotubes (CNT) and graphene sheets have been used as electrodes due to their excellent thermal and chemical stability. Materials with a large proportion of mesopores with sizes between 2 and 50 μm, are favorable as they facilitate electrolyte diffusion in the electrode bulk while maximizing available surface area [8–10]. This approach has been successful in developing high surface area, aerogel-based electrodes which have higher capacitances (240 F g -1 ) than traditional carbon materials [11]. Another promising approach to enhance the capacitance of EDLC electrodes is to use materials that permit well-distributed pseudo- capacitance sites [12–14]. These sites are typically located along the electrode where the faradaic processes, such as electrochemical reac- tions or intercalation can generate current. Nitrogen doping is a process that induces pseudo-capacitance sites on carbon substrates to improve the capacitance of the material [15–25]. N-doped carbon aerogels with capacitance values of 467 F g -1 present nearly two orders of magnitude greater values than those for carbon aerogels without nitrogen doping [15]. Due to higher electronegativity of nitrogen compared to carbon, its introduction into carbon skeletons strengthens the positive charge density, which is conducive to enhanced electrical conductivity, surface wettability, surface polarity, as well as pseudo-capacitance. While focusing on increasing the capacitance of EDLC electrodes, emphasis has largely concentrated on reducing the cost of electrode production. One method to reduce carbon electrode cost is to utilize readily available organic wastes as precursors [16,26–29]. The struc- tural precision of natural biomass with their hierarchical pores, devel- oped over millions of years of biological evolution affords an out- standing resource as a template for the synthesis of carbon-based materials. Their integrated properties of high surface area, in-plane conductivity and interfacial active sites can facilitate electrochemical reactions, ionic diffusion and high charge carrier density. Thus, ex- ploration of natural biomass to utilize their structure through optimi- zation is a promising strategy to harness carbon materials for energy storage with high performance at low costs. Several methods for syn- thesizing carbon aerogel nanohybrids from organic biomass, such as https://doi.org/10.1016/j.est.2019.101152 Received 20 August 2019; Received in revised form 10 December 2019; Accepted 10 December 2019 ⁎ Corresponding author. 1 Had equal contributions in authorship. E-mail address: vincent.gomes@sydney.edu.au (V.G. Gomes). Journal of Energy Storage 27 (2020) 101152 2352-152X/ © 2019 Elsevier Ltd. All rights reserved. T