Elsevier

Energy

Volume 93, Part 2, 15 December 2015, Pages 1303-1307
Energy

3D (3-dimensional) porous silver nonwoven mats prepared with cellulosic templates and spray equipment for use as supercapacitor current collectors

https://doi.org/10.1016/j.energy.2015.10.013Get rights and content

Highlights

  • Porous Ag was fabricated with simple spray equipment and a cellulosic template.

  • We demonstrated the usefulness of the porous Ag as a current collector.

  • An electrode on the porous Ag had 1.24 times greater capacitance than that on a flat Ag plate.

Abstract

We developed a simple method for fabricating a 3D (3-dimensional) porous Ag nonwoven mat for use as the current collector in supercapacitors, and investigated the supercapacitive properties of this mat using cyclic voltammetry. The specific capacitance of an activated carbon electrode on the 3D porous Ag nonwoven mat was 1.24 times greater than that observed for an activated carbon electrode on a conventional 2D (2-dimensional) Ag plate. Additionally, the system with the 3D porous Ag nonwoven mat showed a lower charge transfer resistance of the AC (activated carbon) electrode. These findings demonstrate that the 3D porous Ag nonwoven mat is suitable for use as the current collector in supercapacitors.

Introduction

Supercapacitors are energy conversion devices with higher power densities than batteries and higher energy densities than common capacitors [1], [2]. On account of these properties, supercapacitors have attracted considerable attention due to their potential applications in diverse fields such as power electronics, military equipment, and hybrid electric vehicles [3], [4]. In addition, supercapacitors can play an important role in complementing the energy conversion functions of batteries and fuel cells by providing back-up power supplies to protect against power disruptions [5], [6].

Supercapacitors have four major components: current collectors, electrodes, electrolytes and separators [5]. Among these components, electrodes have been the most actively studied but relatively little attention has been given to current collectors [5], [7]. Typical current collectors are made from nickel (Ni), platinum (Pt), gold (Au), aluminum (Al), silver (Ag) or copper (Cu). Although Ag offers advantages such as high current-carrying capability (i.e., lowest resistivity at 1.63 × 10−8 Ωm) [8], [9] and good chemical and thermal stability [10], Ag current collectors have rarely been used in supercapacitors because of their price. However, an inexpensive and facile approach to using Ag is to employ it in the form of an Ag nanoparticle ink; such inks are chemically and thermal stable [10] and can be applied as metallic thin films using printing technology [11]. Previously, we demonstrated the usefulness of a solution processed Ag current collector in supercapacitors through a study of a 2D (2-dimensional) Ag plated polymer film as a current collector [11]. In the present study, we sought to enhance the efficiency of such solution processed Ag current collectors by fabricating a 3D (3-dimensional) porous Ag nonwoven mat current collector from a cellulosic template. This method was chosen in order to maximize the contact area between the electrode and electrolyte, such as in systems using Ni foam [12]. The 3D porous Ag nonwoven mat developed in the present work may also be useful in applications such as the cathodes of alkaline fuel cells owing to its good chemical and thermal stability [13], and could potentially be used in a variety of filtration applications where the antimicrobial and antibacterial properties of silver make silver membranes a very efficient filtration system [14].

Here we propose a simple method of making a 3D porous Ag nonwoven mat for use as a current collector in supercapacitors, and use cyclic voltammetry to investigate the supercapacitive properties of devices incorporating the proposed current collector. For comparison, we determined the electrochemical properties of a 2D Ag plated current collector under the same conditions. The 3D porous Ag nonwoven mat was fabricated using a cellulosic template with an Ag nanoparticle dispersed solution and simple spray equipment.

Section snippets

Experiment

We used a 3D porous Ag nonwoven mat and a 2D Ag plated stainless steel (i.e., SUS304) plate as the current collector. An Ag nanoparticle dispersed solution (Ag solution for use in screen printers, NPK Inc.) was coated onto a cellulosic template (clean wipe, Bemcot wipers, Asahi Kasei Fibers Corp.) and onto a SUS304 plate (Nilaco Corp., thickness = 20 μm) using simple spray equipment, which has conventional spray nozzle (IVEK Corp.) with a diameter of 250 μm. The spray nozzle was located about

Results and discussion

Thermal gravimetric analysis [16] (TGA, 10 °C/min under air, Perkin Elmer Inc.) of the cellulosic template and the Ag solution was conducted. As shown in Fig. 1, the cellulosic template showed marked weight loss at approximately 330 °C due to combustion of the cellulosic template, with 100% weight loss by approximately 540 °C. The Ag solution showed gradual weight loss up to 150 °C and then more rapid weight loss on further heating to 300 °C, with an overall weight loss of 16%. The initial

Conclusion

In this study, we demonstrated a simple method of making a 3D porous Ag nonwoven mat as the current collector for a supercapacitor. The 3D wire structure and the spaces between wires assist the movement of electrolyte ions from the electrolyte to the electrode surface during the charging and discharging of supercapacitors. Experiments comparing AC electrodes on a conventional current collector structure (i.e., a 2D structure) and on the 3D porous Ag nonwoven mat disclosed that the latter

Acknowledgments

This study was supported by the R&D program of the Korea Research Council for Industrial Science and Technology of Republic of Korea (Grant 2015K000217/ 10052802/ KM3710/ NK186C/ SC1050/ MO5970/ NM8270).

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