Electrochemical properties of carbon from oil palm kernel shell for high performance supercapacitors Izan Izwan Misnon, Nurul Khairiyyah Mohd Zain, Radhiyah Abd Aziz, Baiju Vidyadharan, Rajan Jose * Nanostructured Renewable Energy Materials Laboratory, Faculty of Industrial Science &Technology, Universiti Malaysia Pahang, Kuantan, 26300 Pahang, Malaysia A R T I C L E I N F O Article history: Received 2 February 2015 Received in revised form 15 May 2015 Accepted 27 May 2015 Available online 30 May 2015 Keywords: amorphous materials supercapacitors pseudocapacitors energy storage A B S T R A C T Electrochemical properties of activated carbon (AC) derived from oil palm kernel shell (PKS) are evaluated and compared with other biomass derived AC for fabricating high performance electrochemical double layer capacitors (EDLC). Cleaned PKS are carbonized by pyrolysis and subsequently activated by physical and chemical methods. The chemically AC show a wider pore distribution (1.4–9.3 nm) whereas the physically activated one has uniform pores (1.5 nm). The electrochemical properties of the two types of AC are evaluated using cyclic voltammetry (CV), charge– discharge cycling (CDC) and electrochemical impedance spectroscopy (EIS) in three-electrode configuration. High specific capacitance (C S ) (210 F g 1 in 1 M KOH electrolyte at 0.5 A g 1 ) is obtained for chemically AC whereas the C S for the physically AC is 50% lower (123 F g 1 ). Galvanostatic CDC tests show that the electrodes maintained 95–97% of C S after 1000 cycles. The EIS revealed that the PKS AC has low series resistance (< 0.6 V) and relaxation time (0.69 s) which would therefore offers high power density in the EDLC devices. ã2015 Elsevier Ltd. All rights reserved. 1. Introduction Development of value-added commodities from waste bio- resources has two simultaneous impacts, viz. environmental remediation and wealth creation. Carbon, a functional material of high market value, is traditionally obtained from petroleum coke, pitch and coal; however, the non-renewability of these sources lead to search for alternatives such as biomass [1–3]. However, properties of carbon derived from biomass significantly vary; therefore, there is a dare need to optimize the source for a desired application. For electrochemical applications, a high specific surface area and pore volume would reduce the material need; and therefore, activated carbon (AC) with specific surface area as high as 2000 m 2 g 1 are routinely produced by chemical and physical methods [4,5]. The AC have attracted several industrial applications including electrodes for electrochemical double layer capacitor (EDLC) or also called supercapacitor, lithium ion batteries, hydrogen storage, catalyst host, adsorbents and healthcare [6–11]. For EDLC application, AC shows desirable performance in term of chemical stability, high electrical conductivity, and low cost. Although new generation allotropes of carbon such as carbon nanotubes and graphene offer higher electrical conductivity than the commercial AC, uniting their properties and mass production is a serious issue. The AC electrodes store electric charges via electrostatic charge accumu- lation at an electrode–electrolyte interface, which forms the basis of EDLC. Charging and discharging processes in the EDLC do not involve any chemical changes; therefore, these devices could be used for longer duration (10 4 – 10 6 cycles of charge–discharge) [12,13]. Currently, various AC from biomass precursors have been synthesized including utilization of coconut shell, wood, rice husk, walnut shell, banana peel, sugar cane bagasse, tea leaves and bamboo [9,10]. Chemical (ex: KOH, NaOH, ZnCl 2 ) and physical activation (ex: steam, CO 2 ) methods are routinely adopted for developing many biomass derived AC for EDLC application to enable specific capacitance (C S ) in the range 100–370 F g 1 in aqueous electrolytes [14–22]. Oil palm (Elaeis Guineensis), from whose fruits the palm oil is extracted, is fairly planted throughout the planet: a total of 15 million hectare of oil palm plantation is established, most of which is in the ASEAN region. The authors' country, Malaysia, alone offers 5 million hectare of oil palm plantation. Over 7.8 tons/hectare of processed fresh fruit bunches (FFB) are produced annually, 70% of which is removed as waste * Corresponding author. Tel.: +6095492451; fax.: +6095492766 E-mail address: rjose@ump.edu.my (R. Jose). http://dx.doi.org/10.1016/j.electacta.2015.05.163 0013-4686/ ã 2015 Elsevier Ltd. All rights reserved. Electrochimica Acta 174 (2015) 78–86 Contents lists available at ScienceDirect Electrochimica Acta journal homepa ge: www.elsev ier.com/locate/electacta