Contents lists available at ScienceDirect Energy Storage Materials journal homepage: www.elsevier.com/locate/ensm An integrated electrochemical device based on earth-abundant metals for both energy storage and conversion Yasin Shabangoli a , Mohammad S. Rahmanifar b , Maher F. El-Kady c,d , Abolhassan Noori a , Mir F. Mousavi a,c, ⁎ , Richard B. Kaner c,e,⁎⁎ a Department of Chemistry, Tarbiat Modares University, Tehran 14115-175, Iran b Faculty of Basic Sciences, Shahed University, Tehran 18151-159, Iran c Department of Chemistry and Biochemistry, University of California, Los Angeles (UCLA), Los Angeles, CA 90095, USA d Department of Chemistry, Faculty of Science, Cairo University, Giza 12613, Egypt e Department of Materials Science & Engineering, UCLA, Los Angeles, CA 90095, USA ARTICLE INFO Keywords: Layered double hydroxide (LDH) Supercapacitor Water splitting Integrated electrochemical device Morphology-tunable nanostructure ABSTRACT With rising energy consumption in the world and the negative environmental and human health impacts of fossil fuels, the demand for renewable energy sources is increasing. The energy generated by renewable energy sources can be stored either in a chemical (water splitting) or an electrochemical (battery or supercapacitor) form, that are two distinct processes. Here, we introduce an integrated solar-powered system for both electrochemical energy storage and water electrolysis. A nickel-cobalt-iron layered double hydroxide (Ni-Co-Fe LDH) was successfully synthesized on nickel foam as a substrate using a fast, one-step electrodeposition approach. The Ni-Co-Fe LDH exhibited excellent electrochemical properties both as an active electrode material in supercapacitors, and as a catalyst in the oxygen evolution reaction (OER). When employed as the positive electrode in a supercapacitor, along with activated carbon as the negative electrode in an asymmetric configuration, the ultrathin and porous Ni-Co-Fe LDH nanoplatelets delivered an ultrahigh specific energy of 57.5 W h kg -1 with an outstanding specific power of 37.9 kW kg -1 and an excellent cycle life. As an OER electrocatalyst, Ni-Co-Fe LDH exhibited superior electrocatalytic performances with a very low overpotential of 0.207 V versus a reference hydrogen electrode (RHE) at 10.0 mA cm -2 , and a small Tafel slope of 31 mV dec -1 . The superior energy storage and catalytic OER properties of the Ni-Co-Fe LDH nanoplatelet array can be attributed to both the synergistic effects among the metal species and the unique mesoporous structure of the LDH that provides facilitated charge/ion diffusion pathways and more available active sites. 1. Introduction Exploring the possibility of renewable and green energy technolo- gies to replace fossil fuels is among the most significant challenges for a sustainable future. The sun and wind are among the most important and readily exploitable sources of renewable energy available today. However, the sun does not shine all the time, even during the day, and the wind does not blow on demand. Thus, the intermittent nature of these renewable energy sources necessitates development of appro- priate energy conversion and storage technologies. Electrochemical methods including, water splitting, solar energy conversion, super- capacitors, batteries and fuel cells, are promising routes to mitigate the world energy crisis [1–5]. Nature has often been a great source of inspiration to solve scientific and technological problems. For example, plants represent a hierarchical multifunctional design with an intriguing ability to harvest, store and manipulate energy with limited types of required input sources, i.e. the sun, water, and carbon dioxide. Inspired by nature, recent work on integrating energy harvesting, storage, and conversion into a single device has attracted a great deal of attention [6–8]. To achieve this, attempts have been made to realize smart multifunctional energy storage and conversion materials. Such materi- als integrate properties of, for example, a water splitting catalyst with energy storage activity and/or photoresponsivity [9,10]. By adopting this strategy, the dream is to achieve a sustainable way of living utilizing solar-driven vehicles, mobile devices, water purification systems and healthcare services. Among various power sources, supercapacitors have drawn great http://dx.doi.org/10.1016/j.ensm.2017.09.010 Received 29 July 2017; Received in revised form 6 September 2017; Accepted 20 September 2017 ⁎ Corresponding author at: Department of Chemistry and Biochemistry, University of California, Los Angeles (UCLA), Los Angeles, CA 90095, USA. ⁎⁎ Corresponding author at: Department of Materials Science & Engineering, UCLA, Los Angeles, CA 90095, USA. E-mail addresses: mousavim@modares.ac.ir (M.F. Mousavi), kaner@chem.ucla.edu (R.B. Kaner). Energy Storage Materials xxx (xxxx) xxx–xxx 2405-8297/ © 2017 Published by Elsevier B.V. Please cite this article as: Shabangoli, Y., Energy Storage Materials (2017), http://dx.doi.org/10.1016/j.ensm.2017.09.010