Fabrication and electrochemical evaluation of micro-supercapacitors prepared by direct laser writing on free-standing graphite oxide paper Rajesh Kumar a, * , Ednan Joanni b , Raluca Savu c , Matheus S. Pereira d , Rajesh K. Singh e , Carlos J.L. Constantino d , Lauro T. Kubota f , Atsunori Matsuda a , Stanislav A. Moshkalev c, ** a Department of Electrical and Electronic Information Engineering, Toyohashi University of Technology,1-1 Hibarigaoka, Tempaku-cho, Toyohashi, Aichi, 441-8580, Japan b Centre for InformationTechnology Renato Archer (CTI), Campinas, 13069-901, Brazil c Centre for Semiconductor Components and Nanotechnology (CCS Nano), University of Campinas (UNICAMP), Campinas, 13083-870, Sao Paulo, Brazil d Faculty of Science and Technology, Department of Physics, S~ ao Paulo State University, Presidente Prudente, 19060-900, Sao Paulo, Brazil e School of Physical & Material Sciences, Central University of Himachal Pradesh (CUHP), Kangra, Dharamshala, HP,176215, India f Department of Analytical Chemistry, Institute of Chemistry, University of Campinas (UNICAMP), P.O. Box 6154, Campinas,13084-974, Sao Paulo, Brazil article info Article history: Received 16 October 2018 Received in revised form 3 May 2019 Accepted 4 May 2019 Available online 9 May 2019 Keywords: GO paper Pulsed laser Direct laser writing m-supercapacitors Areal capacitance Cycling stability abstract This article presents results of a pulsed UV laser method for the simultaneous reduction of graphite oxide (GO) and patterning of reduced graphene oxide (rGO). This direct laser writing method was applied to the fabrication of graphene-based, in-plane interdigitated micro-supercapacitors (m-SCs), prepared on free-standing GO paper (10 mm thick). The electrochemical performance of m-SCs was studied using two different electrolytes (KOH and NaCl). The results from cyclic voltammetry measurements exhibited typical electrical double layer behavior, with specific capacitances of 9.3 mF/cm 2 and 13.8 mF/cm 2 (at a scan rate of 10mV/s) for KOH and NaCl electrolytes, respectively. The m-SCs exhibited good performance, with retention of 95% of the original capacitance values after 3400 charge-discharge cycles. When compared to devices obtained by conventional lithographic techniques, the laser fabrication of planar m- SCs is faster, cost-effective and scalable. We believe this one-step and environmentally friendly laser- assisted method to be a good alternative for the fabrication of flexible energy storage devices. © 2019 Elsevier Ltd. All rights reserved. 1. Introduction Among the various alternative energy storage technologies, supercapacitors (SCs) are one of the most promising electro- chemical energy storing devices [1e 7]. Flexible SCs have lately attracted tremendous attention due to the many advantages such as their tailored size, light weight and high energy density capacity [8e10]. However, recent advances in SCs have led to the develop- ment of micro-SCs (m-SCs), further reducing the device volume and facilitating easy integration into micro devices [11]. Excellent flex- ibility, high rate capability, high power density, high energy density and long cycle life are potential advantages of m-SCs [12, 13]. Several techniques have been reported for fabrication/ patterning of m-SCs using processes like photolithography [14], hotwire chemical vapor deposition [15], pencil drawing [16], elec- trochemical deposition and post annealing [17], template plasma etching [18], layer-by-layer printing [19], electrophoretic deposi- tion [20], inkjet printing [21], screen printing [22], selective wetting-induced fabrication [23] and microfluidic etching [24]. Also, m-SCs have been designed on different substrates, using various electrode materials, such as conducting polymers [25], carbonaceous materials [26] and metal oxides [27]. However, these fabrication methods for m-SCs have several disadvantages that hinder their widespread adoption, since they require expensive raw materials or make use of toxic chemicals. The processing methods are also complex and time-consuming, raising the fabri- cation costs. In spite of the many alternatives already proposed for SC fabrication, there are still some challenges that must be over- come in order to achieve superior performance in all of the main characteristics. Laser based techniques rely on the optically induced local heating at the focusing area (laser spot), allowing the reduction of * Corresponding author. ** Corresponding author. E-mail addresses: rajeshbhu1@gmail.com, rajeshbhug@gmail.com (R. Kumar), stanisla@unicamp.br (S.A. Moshkalev). Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy https://doi.org/10.1016/j.energy.2019.05.032 0360-5442/© 2019 Elsevier Ltd. All rights reserved. Energy 179 (2019) 676e684