ORIGINAL PAPER Electric double-layer capacitors with corn starch-based biopolymer electrolytes incorporating silica as filler K. H. Teoh & Chin-Shen Lim & Chiam-Wen Liew & S. Ramesh & S. Ramesh Received: 23 July 2014 /Revised: 8 November 2014 /Accepted: 19 December 2014 # Springer-Verlag Berlin Heidelberg 2015 Abstract Solid-state electric double-layer capacitors (EDLCs) based on corn starch biodegradable polymer electro- lytes are fabricated. Silica is added into the corn starch poly- mer electrolytes to improve the ionic conductivity and capac- itance of the EDLCs. The ionic conductivity as a function of temperature obeys the Arrhenius equation indicating ionic hopping mechanism in the polymer electrolytes. Linear sweep voltammetry shows that the prepared corn starch-based bio- polymer electrolyte is stable in the range from -2.5 to 2.5 V. Electrical capacitance performances of these capacitors are studied by cyclic voltammetry, galvanostatic charge–dis- charge, and AC impedance spectroscopy. The discharge char- acteristics have been found to be almost linear, which con- firms the capacitive behavior of the EDLC cell. The fabricated EDLC cells perform good cyclability up to 500 cycles with more than 90 % of coulombic efficiency. Keywords Polymers . Electrical properties . Transport properties Introduction Biodegradable materials have captured much interest in view of their applications in industrial and biomedical sectors [1, 2]. Employment of biodegradable polymers from renewable sources can reduce environmental problems and at the same time reduce the usage of synthetic polymers. The effort to promote green materials in polymer electrolytes has been widely supported by scientists worldwide. The car- bonaceous material from natural resources shows good potential to be used as electrode in EDLC application as reported by Arof and co-workers [3]. Li and co-workers reported that starch-derived activated carbon electrodes showed promising results for EDLCs [4]. According to Kumar and Brat, there is a trend towards the production of degradable polymers and the use of natural polymer blends in electrochemical devices [5]. Electric double-layer capacitors (EDLCs) are assembled in this present work because of their attractive properties. EDLCs have attracted numerous interests as alternative ener- gy storage systems compared with conventional capacitors and secondary batteries. EDLCs have been widely used be- cause of their advantages such as large capacitance, free of maintenance, toxic-free, higher specific power, and longer cy- cle life compared with batteries [6–8]. In addition, EDLCs have been widely used as memory back-up devices in many fields of electric equipment. EDLCs with liquid electrolyte have many disadvantages such as being leak-prone, self- discharging, corrosive, and bulky. Therefore, solid or gel poly- mer electrolytes have been attracting numerous attentions as they can overcome the leakage and safety issues [ 9]. Therefore, fabricating solid-state EDLC using solid polymer electrolytes is an alternative approach to improve the safety performance of EDLC. However, the ionic conductivity of polymer-salt based solid-state electrolytes is low and is not applicable in any electrochemical device. Therefore, there are several ways to enhance the ionic conductivity of polymer electrolytes such as mixed-salt system, addition of plasticizers and ionic liquids, doping of fillers, and polymer blending. The method of K. H. Teoh : C.<S. Lim : C.<W. Liew : S. Ramesh (*) Centre for Ionics University of Malaya, Department of Physics, Faculty of Science, University of Malaya, Lembah Pantai, 50603 Kuala Lumpur, Malaysia e-mail: rameshtsubra@gmail.com S. Ramesh Center for Advanced Manufacturing & Material Processing, Department of Mechanical Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia Ionics DOI 10.1007/s11581-014-1359-x