Vol.:(0123456789) 1 3 Journal of Materials Science: Materials in Electronics https://doi.org/10.1007/s10854-020-03761-5 Hierarchical porous carbon derived from acai seed biowaste for supercapacitor electrode materials Luiz K. C. de Souza 1  · João Carlos Martins 1  · Diogo Padilha Oliveira 1  · Carlos Sergio Ferreira 1  · Alexandre A. S. Gonçalves 2  · Rayanne O. Araujo 1  · Jamal da Silva Chaar 1  · Maria J. F. Costa 3  · David V. Sampaio 4  · Raimundo R. Passos 1  · Leandro A. Pocrifka 1 Received: 19 March 2020 / Accepted: 7 June 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020 Abstract Creating energy storage devices from biomass waste has great scientifc and industrial signifcance by providing an eco- friendly and sustainable alternative to reuse biowaste. This study demonstrates the production of high-performance super- capacitor electrodes using acai seed as a precursor for creating carbon materials. Porous carbons were synthesized by carbonization and subsequent KOH activation to generate microporosity then mesoporosity upon further activation. The materials displayed large specifc surface areas and total pore volumes, with tunable pore structures depending on the degree of activation. The biomass-derived electrodes exhibited high specifc capacitances of 346 F g −1 at 1 mA cm −2 and good electrochemical stability in which 88% of the initial capacitance was retained after 5000 charges/discharges cycles at 7 mA cm −2 in 1 M KOH electrolyte. These results place these materials among the best biomass-derived supercapacitors reported thus far. This study provides a great alternative for the management of the large-scale biowaste, acai seed. 1 Introduction Population growth and economic development are among the main factors for the increasing energy demand needed to sustain society. Currently, energy demands are deplet- ing available resources such as fossil fuels, which are the primary energy source worldwide, leading to harmful con- sequences to the environment. Therefore, there is a need to discover new ways to reach society’s demand for energy. One of way is the development of advanced electrochemical energy storage devices, which, interestingly, can be created at low cost using biomass or biowaste to create carbon-based materials. This is technologically attractive to overcome the challenges faced by the energy and waste management sec- tors [1, 2]. Porous carbon materials such as microporous and mesoporous carbons, graphene and graphitic structures with heteroatoms, or a combination thereof, are widely used for energy storage devices such as supercapacitors [3–5]. This is because of the remarkable properties of carbon-based mate- rials such as high electrical conductivity, electrochemical stability, lightweight, tuned porosity, large surface area, and relatively low synthesis costs. These features make carbon materials suitable for several applications such as electric vehicles, medical devices, and renewable energy plants [6]. Much research has been done on the use of activated carbon for supercapacitor electrodes, including the use of biomass waste as synthesis precursors. For instance, activated carbons derived from the following biomasses have been reported: pistachio nutshells [7], corn straw [8], cotton [5], soymeal [9], orange peels [10], banana peels [11], sugarcane bagasse [12], sesame husks [13], and coconut shells [14]—all of which displayed excellent performance in electrochemical capacitors. However, the use of biowaste from the Amazon region to create carbon- based supercapacitor electrodes were not reported thus far; although there are promising raw materials in the Amazon with higher amounts of waste, the waste generated from * Luiz K. C. de Souza ls@ufam.edu.br 1 Department of Chemistry, Federal University of Amazonas, Manaus, AM, Brazil 2 Department of Chemistry and Biochemistry, Kent State University, Kent, OH, USA 3 Department of Materials Engineering, School of Engineering of Sao Carlos, University of Sao Paulo, Sao Carlos, SP, Brazil 4 Department of Physics, Federal University of Sao Carlos, Sao Carlos, SP, Brazil