A silver-nanoparticle-catalyzed graphite composite for electrochemical energy storage Xingliang He a , Dion Hubble b , Raul Calzada b , Aalap Ashtamkar a , Deepak Bhatia c , Sergio Cartagena a , Partha Mukherjee a , Hong Liang a, * a Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843-3123, USA b Department of Chemical Engineering, Texas A&M University, College Station, TX 77843-3122, USA c Department of Electrical Engineering, Texas A&M University, College Station, TX 77843-3122, USA highlights  A new composite containing silver nanoparticles and graphite is developed.  Ag NPs enhance the electrochemical performance for energy storage.  There was a six-fold improvement in specific capacitance.  Li þ enabled from double-layer to pseudocapacitive behavior. article info Article history: Received 13 October 2014 Received in revised form 11 November 2014 Accepted 12 November 2014 Available online 13 November 2014 Keywords: Graphite composite Silver nanoparticles Catalysis Pseudocapacitance Electron/charge transfer abstract A new composite containing silver nanoparticles and graphite is developed in order to improve elec- trochemical energy storage. The nanocomposite uses silver (Ag) nanoparticles as a catalyst to enhance the electrochemical performance. Results indicate that the graphite composite decorated with Ag shows up to a six-fold improvement in specific capacitance. Electron/charge transfer is enhanced through a shift from double-layer to pseudocapacitive behavior, mediated by Li þ intercalation. Decoration with Ag nanoparticles allows for improvements in electrochemical impedance response, ease of electronic/ionic charging, and overall energy storage capability. This research provides a promising alternative solution for the next generation of safe and cost-effective lithium-ion devices. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Electrochemical energy storage devices are in demand for portable electronics, smart grid, electric vehicles, and energy re- covery systems [1e8]. Lithium ion batteries (LIB) and super- capacitors (SC) are two typical mediums of storage. In device fabrication, significant efforts have been devoted to explore better candidate materials as anodes. Carbon-based materials [9,10], sili- con [11e 13], sulfur and sulfides [14e18], metal oxides [19,20], and metal carbides [21e23] are such representative materials. The performance in energy storage depends on the morphology and structure of the building blocks of these materials. In order to increase energy capacity, power density, and durability, nano- particles (NPs) [24e26], nanowires [27e29], nanotubes [30,31], hollow nanostructures [32], coreeshell nanostructures [33,34], and ordered mesoporous systems [35] have been utilized for active material. However, integration of the high energy capacity of a LIB with the high power density of a SC remains challenging in a single electrochemical energy storage device [36e39]. In principal, the electrochemical storage is based on the reactions of electrolyte- soluble charged species with the surface of the electrode. If such chemical reactions could be accelerated, a storage device should display an enhanced rate of electrochemical work. A suitable catalyst that is able to mediate the electrochemical reactions is needed to obtain the desirable large energy capacity and high po- wer density. To date, noble metal nanoparticles have been widely studied as efficient catalysts. Those metals include silver (Ag) [40], * Corresponding author. E-mail address: hliang@tamu.edu (H. Liang). Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour http://dx.doi.org/10.1016/j.jpowsour.2014.11.061 0378-7753/© 2014 Elsevier B.V. All rights reserved. Journal of Power Sources 275 (2015) 688e693