Subscriber access provided by NEW YORK UNIV
Article
The impact of nanosize on supercapacitance: Study of 1D nanorods and 2D thin-film of nickel oxide Ranjit A. Patil, Cheng-Ping Chang, Rupesh S. Devan, Yung Liou, and Yuan-Ron Ma ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 30 Mar 2016 Downloaded from http://pubs.acs.org on March 30, 2016
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 35
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Applied Materials & Interfaces
The impact of nanosize on supercapacitance: Study of 1D nanorods and 2D thin-films of nickel oxide Ranjit A. Patil,† Cheng-Ping Chang,† Rupesh S. Devan,† Yung Liou,‡ and Yuan-Ron Ma*,† †Department of Physics, National Dong Hwa University, Hualien 97401, Taiwan. ‡Institute of Physics, Academia Sinica, Taipei 11529, Taiwan.
ABSTRACT: We synthesized unique one-dimensional (1D) nanorods and two-dimensional (2D) thin-films of NiO on indium-tin-oxide thin films using hot-filament metal-oxide vapor deposition technique. The 1D nanorods have average width and length of ~100 nm and ~500 nm , and the densely-packed 2D thin-films have an average thickness of ~500 nm. The 1D nanorods perform as parallel units for charge storing. However, the 2D thin-films act as one single unit for charge storing. The 2D thin-films possess a high specific capacitance of ~746 F/g compared to 1D nanorods (~230 F/g) using galvanostatic charge-discharge measurements at a current density of 3 A/g. Since the 1D NiO nanorods provide plentiful surface areas than those of the 2D thinfilms, they are fully active at first few cycles. However the capacitance retention of the 1D nanorods decays faster than that of the 2D thin-films. Also, the 1D NiO nanorods suffer from instability due to the fast electrochemical dissolution and high nanocontact resistance. Electrochemical impedance spectroscopy verifies that, the low dimensionality of the 1D NiO nanorods induces the unavoidable effects that lead them to have poor supercapacitive
ACS Paragon Plus Environment
1
ACS Applied Materials & Interfaces
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 2 of 35
performances. On the other hand, the slow electrochemical dissolution and small contact resistance in the 2D NiO thin-films favour to achieve high specific capacitance and great stability.
KEYWORDS 1D nanorod, 2D thin-film, nickel oxide, pseudocapacitance, nanocontact resistance, electrochemical impedance.
INTRODUCTION Electrochemical supercapacitors have been expansively explored as alternative energy storage
devices due to the power and energy densities larger than those of batteries, fuels cells and conventional
electrochemical
capacitors
with
characteristic
energy
storing.1,2
Since
supercapacitors possess high energy and power densities, they can be used in hybrid vehicles, industrial equipment, and other renewable energy storage.3,4 Abundantly, available carbon materials have provided high specific capacitance in the electrochemical double layer (EDL) mechanism, because of the large surface areas with porous surfaces and interlaced networks. However, carbon materials have limitations in the energy and power density due to the high contact resistances among the interlaced networks.5 The contact resistance therefore develops a high internal series resistance, and become a forerunner in poor performance.6 Also, carbon materials result in major time-dependent changes that deteriorate the charge storing response.7 Alternatively, pseudocapacitive materials, such as metal oxides and conducting polymers, can provide much high specific capacitance. However, conducting polymers suffer instability and fading in supercapacitor performance because of swelling and shrinking during the reduction and
ACS Paragon Plus Environment
2
Page 3 of 35
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Applied Materials & Interfaces
oxidation process.8 There are some other factors in exchange of ions/electrons, such as desirable morphology, crystallinity, and barrier-free accessibility, for controlling performance of electrochemical supercapacitor. To understand notion of charge storage mechanism in pseudocapacitive materials, efforts should be taken to improve the surface area, reduce resistive elements, and as small as possible barrier for the exchange of ions to attain high specific energy and power density. Transition metal oxides possess high specific energy and power density with excellent capacitance retention. Among transitional metal oxides, ruthenium oxide and ruthenium hydroxide show excellent capacitor performance,9-11 but they cost very high and are insufficient in deposit. Some metal oxides, such as MnO2,12 NiO,13-17 MoO2,18 and V2O5.19, are abundant and low-cost materials with similar capacitive performance. Nickel oxide and nickel hydroxide attract special interest due to the high theoretical capacitances values of 2584 F/g and 2082 F/g, respectively,20 which is much higher than that of MnO2 (1380 F/g).21 Moreover, NiO nanostructures have received plenty of attention due to several unique properties, such as low field-emission turn-on field (7.4 V/µm) with large current density (~160 µA/cm2),22 p-type semiconductor,23 wide bandgap (~3.7 eV),24 high (low) transparency of the bleached (colored) state,24 fast coloration and bleaching times (
