Suppressing the Coffee-Ring Effect in Semitransparent MnO2 Film for

Subscriber access provided by UNIV OF CALIFORNIA SAN DIEGO LIBRARIES

Article

Suppressing the Coffee-ring Effect in Semi-transparent MnO2 Film for High-performance Solar-powered Energy Storage Window Huanyu Jin, Jiansheng Qian, Limin Zhou, Jikang Yuan, Haitao Huang, Yu Wang, Wing Man Tang, and Helen Lai Wa Chan ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b00402 • Publication Date (Web): 08 Mar 2016 Downloaded from http://pubs.acs.org on March 13, 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 28

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

Suppressing the Coffee-ring Effect in Semi-transparent MnO2 Film for High-performance Solar-powered Energy Storage Window

Huanyu Jin†, Jiasheng Qian†, Limin Zhou‡, Jikang Yuan†, Haitao Huang†, Yu Wang†, Wing Man Tang†* and Helen Lai Wa Chan† Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Hong Kong ‡ Department of Mechanical Engineering, The Hong Kong Polytechnic University, Hung Hom, Hong Kong †

*Corresponding Author E-mail: [email protected]

Keywords: coffee-ring effect, semi-transparent, MnO2 film, flexible, energy storage

ACS Paragon Plus Environment


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

ABSTRACT We introduce a simple and effective method to deposit a highly uniform and semitransparent MnO2 film without coffee-ring effect (CRE) by adding ethanol into MnO2 ink for transparent capacitive energy storage devices. By carefully controlling the amount of ethanol added in the MnO2 droplet, we could significantly reduce the CRE and thus improving the film uniformity. The electrochemical properties of supercapacitor (SC) devices using semitransparent MnO2 film electrodes with or without CRE were measured and compared. The SC device without CRE shows a superior capacitance, high rate capability and lower contact resistance. The CRE-free device could achieve a considerable volumetric capacitance of 112.2 F cm-3, resulting in a high volumetric energy density and power density of 10 mWh cm-3 and 8.6 W cm-3, respectively. For practical consideration, both flexible SC and large-area rigid SC devices were fabricated to demonstrate their potential for flexible transparent electronic application and capacitive energy-storage window application. Moreover, a solar-powered energy storage window which consists of a commercial solar cell and our studied semitransparent MnO2-film-based SCs was assembled. These SCs could be charged by the solar cell and light up a light emitting diode (LED), demonstrating their potential for self-powered systems and energy-efficient buildings.


Page 2 of 28

Page 3 of 28

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


INTRODUCTION Over the last decade, printing technologies have been extensively investigated for realizing lowcost and large-area electronic devices via the development of printable materials and relatively convenient solution processes.1-4 A lot of printed electronic devices including thin-film transistors, light-emitting diodes, photo-detectors and solar cells have been fabricated.5-10 Such a huge sensor network requires a compatible energy storage system.11 Fully printable energy storage devices have great potential for the realization of self-powered printed electronic systems, leading to the rapid development of printed batteries and supercapacitors (SCs).12-14 As a highefficient energy storage device with features such as high power density, ultra-long cycle life and fast charge and discharge rate, a supercapacitor plays an essential role in the next generation printed electronics.15-26 Good transparency is also very important for the future generation of energy storage devices and systems as many transparent electronic devices, displays and smart windows require a transparent power source to operate.27-30 To date, many transparent SCs have been developed.3135

However, most of them are suffering from several limitations: (i) They usually require

relatively complicated fabrication processes. For example, a transfer process is needed to produce a transparent supercapacitor based on mono-layer graphene.34,35 Active materials have to be deposited on transparent electrodes through electrochemical deposition method.33 These processes will not only lead to a relatively high-cost production, but also limit their scalability to large-area manufacturing; (ii) Most transparent SCs are based on carbon materials such as carbon nanotube or graphene, which limit their capacitance, resulting in low energy density.31,34-35 Using printing methods with pseudocapacitive inks for producing supercapacitors could overcome these limitations. However, with capillary flow during the ink droplet evaporation, a ring-like



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

pattern so-called coffee-ring effect (CRE) is observed when the drop dries on a solid surface,36-42 leading to a non-uniform deposition of ink materials. Hence, for the realization of high resolution and uniformly printed transparent film for high performance SCs, we should not only choose appropriate inks with pseudocapacitive properties but also find effective ways to suppress the CRE which may lead to a non-uniform deposition.36-42 In this study, an aqueous MnO2 ink was chosen as a printable active material. MnO2 is a low-cost pseudocapacitive material with a high theoretical specific capacitance of 1370 F g-1 and a potential candidate for capacitive energy storage application.19 Herein, we introduce a simple and effective method to deposit a highly uniform and semitransparent MnO2 film without CRE by adding ethanol into MnO2 ink for transparent capacitive energy storage devices. By carefully controlling the amount of ethanol added in the MnO2 droplet, we could significantly reduce the coffee-ring effect and thus improving the film uniformity. The electrochemical properties of SC devices using semi-transparent MnO2 film electrodes with or without CRE were measured and compared. The SC device without CRE shows a superior capacitance, high rate capability and lower contact resistance. What’s more, this device could achieve a considerable volumetric capacitance of 112.2 F cm-3, resulting in a high volumetric energy density and power density of 10 mWh cm-3 and 8.6 W cm-3, respectively. For practical consideration, both flexible SC and large-area rigid SC devices were fabricated to demonstrate their potential for flexible transparent electronic application and capacitive energystorage window application. Moreover, a solar-powered energy-storage window which consists of a commercial solar cell and our studied semi-transparent MnO2-film-based SCs was assembled. These SCs could be charged by the solar cell and light up a light emitting diode (LED), demonstrating their potential for self-powered systems and energy-efficient buildings.28


Page 4 of 28

Page 5 of 28

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


EXPERIMENTAL SECTION Synthesis of MnO2 ink. All chemicals were analytical grade and were used directly without further purification. MnO2 ink was synthesized through a template reduction method which was reported previously.43 In short, we first prepared carbon particles by microwave hydrothermal treatment.44 The diameter of the carbon particles is ~ 200 nm. 10 mg as-prepared carbon particles was dissolved into 160 mL deionized water and sonicated for 5 minutes using ultrasonic cleaning machine to form carbon particles suspension. Then 5 mL 0.1 M KMnO4 solution was added into the carbon particles suspension under continuous stirring and maintained at room temperature for 48 h. When the reaction was completed, the solution was filtered using filter paper to remove the excess reactants. The pH value of the solution was then tuned to neutral by dialysis. The concentration of the MnO2 ink is about 0.5 mg mL-1. Fabrication of electrode based on CRE-free semi-transparent MnO2 film (CFTMF). Certain volume of MnO2 ink was first dropped on FTO or flexible ITO substrate. By adding an appropriate amount of ethanol into the ink droplet (MnO2 ink:ethanol = 20:1), a highly uniform CFTMF could be successfully deposited on the substrate after solvent evaporation. Assembly of the semi-transparent SC devices. The LiCl/polyvinyl alcohol (PVA) gel was chosen as electrolyte for the SC devices. Firstly, the LiCl/PVA gel was prepared by mixing 12.5 g of LiCl, 6 g of PVA into 60 mL of deionized water and the mixture was heated to 85 °C under stirring until the solution became clear. Two pieces of MnO2-coated FTO or ITO substrate were immersed into LiCl/PVA gel and then sandwiched with a thin film of ethyl cellulose as a transparent separator. The assembled devices were heated at 45 °C for 12 h to remove excess water in the electrolyte and the solid-state symmetric semi-transparent SCs were prepared.



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

Material characterization and electrochemical measurement. The morphology of the samples was characterized by field-emission scanning electron microscopy (JEOL JSM-633F) and optical microscope (Olympus BX51). The analysis of the sample surface properties was conducted using X-ray photoelectron spectroscopy (XPS, PHI 5600). Transmittance of the MnO2 film and SC devices was measured by a UV-visible absorption spectrometer (Shimadzu Scientific Instruments, UV2550). The surface wettability of the MnO2 film was measured by an imaging system (Rame-hart, inc. USA). The cyclic voltammetry (CV), cycle life and galvanostatic charge/discharge (GCD) measurements were investigated by CHI 600B electrochemical workstation. Calculation methods. Volume of the semi-transparent MnO2 film in the SC device was calculated according to the following equation: v=A×2T where A is the area of MnO2 film and T is the MnO2 film thickness in a single electrode. Volumetric capacitance of the SC device can be calculated from CV curves based on following equation: Cv=A/(2svU) where A is the area of the CV curve, s is the scan rate, U is the potential window, and v is the volume of the semi-transparent MnO2 film in the SC device. Volumetric capacitance of the SC device could also be calculated from GCD curves using the following equation: Cv=(I∆t)/(v∆U) where I is the discharge current, ∆t is the discharge time, ∆U is the operating window after IR drop and v is the volume of the semi-transparent MnO2 film in the SC device.


Page 6 of 28

Page 7 of 28

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


Areal capacitance of the SC device is calculated from CV curves based on the following equation: Ca=A/(2asU) where A is the area of the CV curve, s is the scan rate, U is the potential window and a is the area of the semi-transparent MnO2 film. Areal capacitance of the SC device could also be calculated from GCD curves by the following equation: Ca=(I∆t)/(a∆U) where I is the discharge current, ∆t is the discharge time, ∆U is the operating window after IR drop and a is the area of the semi-transparent MnO2 film. Specific capacitance of the semi-transparent MnO2 film could be calculated based on the following equation: Cs=A/(2msU) where A is the area of the CV curve, s is the scan rate, U is the potential window, and m is the mass of the semi-transparent MnO2 film in the SC device. Volumetric energy density and power density of the SC devices could be calculated by the following equations: Ev=0.5CU2/ v Pv=Ev/t where C is the capacitance of the SC devices, U is the operating window, t is the discharge time and v is the volume of the semi-transparent MnO2 film in the SC device. Gravimetric energy density and power density of the SC device could be calculated from GCD curves based on the following equations:



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

Eg=0.5CU2/m Pg=Eg/t where C is the capacitance of the SC devices, U is the operating window, m is the total mass of the active materials in the device and t is the discharge time.

RESULTS AND DISCUSSION The MnO2 ink used in this study was synthesized at room temperature via an environmentally benign method which was reported previously.43 Figure 1a (Top view) shows the digital images of the evaporation process of MnO2 droplets with (right) or without (left) the addition of ethanol. According to the images, after 15 minutes, particles are accumulated along the edge of the droplet without adding ethanol, forming a coffee-ring. However, no coffee-ring effect is observed for the droplet with ethanol addition. When evaporation is completed, the droplet with ethanol inclusion forms a uniform film without CRE. Experimental result shows that the amount of ethanol added into the MnO2 droplet can greatly influence the quality of the deposited MnO2 film (Figure S1). A deficient supply of ethanol could not reduce the CRE, whereas an excess amount of ethanol will result in sediment. Hence, the ethanol content in the MnO2 ink has to be optimized. As shown in Figure S1, the optimum ethanol to MnO2 ink ratio to suppress the CRE is 1 to 20. According to the previous report, the MnO2 flake was negatively charged.43 The MnO2 ink used in this study is a colloidal suspension as the Tyndall light scattering is clearly seen (Figure S2).45 Different water-to-ethanol ratio will influence the solution polarity in the colloidal suspension which can greatly affect the particle aggregation.46 It is believed that adding an appropriate amount of ethanol in MnO2 ink droplet could tailor the viscosity and surface tension of the ink as supported by the contact angle images of MnO2 ink droplets shown


Page 8 of 28

Page 9 of 28

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


in Figure 1a (side view), as well as the stability of colloidal solution, which may make the MnO2 flakes trapped at the droplet/air interface, leading to a uniform deposition (Figure S3).42,46-48 Figure 1b shows the digital image of a patterned MnO2 film with a mass loading of 0.05 mg cm-2 with ethanol addition deposited by the above drop-drying method on a fluorine doped tin oxide (FTO) coated glass. The film is semi-transparent, uniform and could be printed in different sizes and patterns. Another notable feature of the film is the strong adhesion with the FTO glass (Figure S4). During a mechanical test, no damage or crack is observed on the MnO2-coated FTO glass when a Kapton tape is removed from its surface, indicating good mechanical property of the film. The scanning electron microscopy (SEM) image of a dried MnO2 droplet with an addition of ethanol is shown in Figure 1c. According to the SEM image, the deposited MnO2 film is uniform with a porous structure, which is good for electrolyte transport.21 By contrasting the SEM image of MnO2 film without ethanol addition (Figure S5), no obvious difference is observed, indicating that adding ethanol into MnO2 ink would not affect the morphology of the finally dried film but just suppressing the CRE. Figure 1d is the cross-sectional SEM image of the sample in Figure 1b. This image reveals a uniform MnO2 film with a thickness of about 300 nm. Increasing the mass loading of MnO2 can increase the film thickness (Figure S6). For a SC electrode, electrolyte permeation and transportation which is related to the hydrophilicity of the active materials is the key issue affecting the electrode performance.19 As shown in Figure 1e and Figure S5(b), the contact angle of the semi-transparent MnO2 film with a loading mass of 0.05 mg cm-2 with and without ethanol addition is 18° and 19.5o respectively, which indicates their good surface wettability. The good hydrophilicity of the films is attributed to the porous structure which is good for aqueous liquid permeation.21,49



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 10 of 28

To further investigate the properties of the deposited CRE-free MnO2 film including surface roughness, transmittance and the oxidation state of manganese, we performed the atomic force microscopy (AFM), UV-visible spectra and X-ray photoelectron spectra (XPS) measurements. The root mean square roughness of the film measured by AFM was 13.6 nm, demonstrating its relatively good smoothness (Figure 2a). The mean diameter of the MnO2 flake is about 64 nm. As the transmittance of the film is thickness dependent, we prepared four samples with the mass loading of 0.1 mg cm-2, 0.05 mg cm-2, 0.025 mg cm-2 and 0.0125 mg cm-2. The UV-visible spectra (Figure 2b) show that all the MnO2 films prepared in this study have good transparency in the visible range from 400 nm to 800 nm. The absorption between 400 nm and 550 nm is commonly observed in MnO2 films.50,51 According to the XPS result shown in Figure S7, there were four elements (Mn, C, K and O) presented on the film. The C signal was attributed to carbon particles (raw materials for synthesizing the MnO2 ink). K signal was due to residual KMnO4. To evaluate the manganese oxidation state, high resolution Mn and O peaks were carefully analyzed. As shown in Figure 2c, the Mn 2p core level spectrum has two distinct peaks at binding energies of 642.4 eV (Mn 2p3/2) and 654.2 eV (Mn 2p1/2), corresponding to Mn-O bonding in the MnO2 film.52-53 From the O 1s spectrum, the peak area of Mn–O–Mn bond at 530.2 eV, Mn–OH bond at 531.9 eV, and H–O–H bond at 532.9 eV normalized to that of Mn-OMn bond is analyzed to be 1, 0.09 and 0.001, respectively (Figure 2d).54 The mean manganese oxidation state (Ox state) can be calculated using the following equation:54 Ox state = [4(SMn−O−Mn − SMn−OH) + 3SMn−OH] / SMn−O−Mn

(1)

where S stands for the normalized peak area of different components of the O 1s spectra. Ox state was calculated to be about 3.9, indicating Mn4+ ions were dominated in the film.


Page 11 of 28

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


To evaluate the electrochemical performance of CRE-free semi-transparent MnO2 film (CFTMF), typical symmetric SC devices using CFTMF on FTO (FTO@CFTMF) electrodes were fabricated. Figure 3a shows the schematic diagram of the fabrication process for the CFTMF-based SC device. Firstly, uniform CFTMF was deposited on FTO glass by the above drop-drying method. After packaging two electrodes using polymer gel electrolyte and a transparent ethyl cellulose separator, a semi-transparent solid-state SC device was successfully fabricated. A series of SC device based on FTO@CFTMF electrodes with a mass loading of 0.1 mg cm-2, 0.05 mg cm-2, 0.025 mg cm-2 and 0.0125 mg cm-2 were prepared to optimize the capacitance. The cyclic voltammetry (CV) measurements were conducted to evaluate the areal capacitance, volumetric capacitance and specific capacitance of the FTO@CFTMF based symmetric device (Figure S8). The volume of the devices was calculated based on the dimension of the CFTMF. As shown in Figure S8d, at a scan rate of 200 mV s-1, the SC device with MnO2 mass loading of 0.05 mg cm-2 reveals the highest areal capacitance. This optimum device was then undergone further investigation. Figure 3b shows the optical microscope images of the MnO2 films (in micro-size) with and without CRE. It demonstrates that adding ethanol into MnO2 ink during solvent evaporation is a promising method to suppress the coffee-ring effect for high resolution micro-printing technology.48,55 To investigate how the CRE in MnO2 film affects the electrochemical performance of SCs, a symmetric SC with semi-transparent MnO2 film with CRE (CTMF) on FTO (denoted as FTO@CTMF) electrodes was also fabricated for comparison. A series of measurements were taken including CV, galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). The CV curves of SC without CRE in the voltage range from 0 to 0.8 V reveal a near rectangular shape under the scan rate from 10 to 200



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 12 of 28

mV s-1, suggesting good capacitive behavior, and fast charge/discharge characteristic (Figure 3c). For the SC with CRE, the CV curves deviate from the near rectangular shape especially at high scan rate (Figure 3d), indicating a quick reduction of energy storage capacity. The Nyquist plot of the SC devices with or without CRE measured in the frequency range from 10 mHz to 10 MHz is shown in Figure 3e. The diameter of the semicircle in the high-frequency range of the impedance spectra for the SC device without CRE is smaller than that of its counterpart with CRE, indicating that the CRE-free SC device has smaller charge transfer resistance (Rct). The equivalent series resistance (ESR) values for the SC device with and without CRE which can be deduced from the first x-intercept of the Nyquist plot are 120 and 90 ohm respectively. By suppressing the CRE, MnO2 flake could be deposited uniformly which will lead to a smaller Rct and ESR. Figure 3f describes the internal resistance (IR) drop of the devices with or without CRE at various current densities. It is clearly seen that the SC without CRE has smaller IR drop than the SC with CRE at the current density from 0.05 mA cm-2 to 1 mA cm-2, showing the conductivity was significantly improved after suppressing the CRE. Generally, MnO2 has poor conductivity and the thickness of MnO2 film can greatly influence the performance of MnO2based supercapacitor. The CRE causes too many active materials deposited on the droplet edge, thus affecting the charge transfer. The GCD curves collected at the current density of 0.1 mA cm-2 is shown in Figure S9, which clearly reveals CRE-free SC has lower IR drop and longer discharge time. According to Figure 3g, the volumetric capacitance of SC with and without CRE at a scan rate of 10 mV s-1 is 109.8 F cm-3 and 106.1 F cm-3 respectively. When the scan rate is increased to 200 mV s-1, the SC without CRE still has a volumetric capacitance of 85.5 F cm-3 (77.9 % of the initial capacitance), while the retention of SC with CRE under the same condition is only 45.6 %. The enhanced rate capability should be mainly attributed to the good uniformity


Page 13 of 28

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


of the CRE-free semi-transparent MnO2 film which could create well-balanced electron pathway for the charge transfer through the whole electrode, resulting in a faster electronic response. All these results reveal that the CRE has negative effects on the electron transport, internal resistance and rate capability and thus should be eliminated. Volumetric energy density and power density are two key parameters for next-generation energy storage devices.20-26 Calculating from the GCD curves of SC devices without CRE (Figure S10a), the as-prepared device could achieve a considerable volumetric capacitance up to 112 F cm-3 at the current density of 0.1 mA cm-2 (Figure S10b), resulting in a maximum energy density and power density of 10 mWh cm-3 and 8.6 W cm-3 respectively (Figure S11). Table S1 compares the performance of the studied CFTMF-based SC device with other transparent SCs reported in the literature. As compared with previous results, the proposed CFTMF-based SC exhibits high specific capacitance, energy density and power density, suggesting that the SC in this study has promising applications for energy storage. For application consideration, a CFTMF-based SC on flexible transparent indium tin oxide coated polyethylene terephthalate (ITO/PET) substrates was also fabricated. Figure 4a shows the digital image of CFTMF on flexible ITO/PET substrate under mechanically bent condition. This image indicates that the CFTMF has good flexibility and thus could be used as an active material for flexible transparent SCs. According to Figure 4b, the CV curves under flat and bent conditions are almost the same and reveal a near rectangular shape, indicating the excellent capacitive behavior and flexibility of the semi-transparent solid-state SCs. Based on Figure 4c, after 100 cycles GCD test at a current density of 0.5 mA cm-2 under bent condition, no significant capacitance drop of the SC was observed, indicating its excellent mechanical stability for flexible energy storage systems. For comparison, we also tested the cycling stability of the



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 14 of 28

FTO@CFTMF based SC at a scan rate of 100 mV s-1 for 10 000 cycles. As shown in Figure 4d, the device remained 95.12 % of the initial capacitance after 10 000 cycles. This indicates that the device has good cyclic stability and is suitable for the long-term charging and discharging application. The excellent performance of the device could be attributed to the following reasons: (1) the novel deposition method obviously suppresses the CRE, leading to a uniform film deposition; (2) the CFTMF is highly porous and hydrophilic, enabling effective electrolyte transport and active-site accessibility; (3) CFTMF has strong adhesion with the substrate, thus significantly reducing the contact resistance between active material and current collector, enabling a high-rate capability and long-term stability; (4) CFTMF has good flexibility, endowing its potential for flexible energy storage devices. As mentioned earlier, energy efficient buildings are important in our future life.28 Many types of smart window electrodes have been developed for energy harvesting or storage.27-30 One of the most promising smart windows is integrating solar cells into energy storage devices to construct self-powered windows for next generation buildings. By virtue of good transparency, high energy density, fast charge and discharge rate and ultra-long cycle life, a CFTMF-based SC is a potential candidate as the energy storage part for a self-powered window. We successfully fabricated a self-powered window by combining CFTMF-based SCs on FTO glass with a commercial solar cell, demonstrating the great potential of CFTMF-based SCs for the selfpowered buildings. Since the operating voltage of the studied single SC is 0.8 V which could not meet the requirement for practical applications, four SC devices are connected in series to produce 3.2 V.

Figure 5a shows the schematic diagram of 4 CFTMF-based SC devices

connected in series. A FTO glass (15 cm×15 cm) was etched into four areas by zinc powder with a loading mass of 10 mg cm-2 and 2 M hydrochloric acid. Each area has a dimension of 15 cm×3


Page 15 of 28

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


cm with a gap of 1 cm between them. Then the MnO2 film was deposited on each area by the above drop and dry method. After assembling two pieces of as-prepared FTO glass with a transparent ethyl cellulose separator and LiCl/PVA gel in the middle, the energy storage window based on four SC devices was fabricated. The transmittance of the SC device is shown in Figure S12. The device could achieve a transparency of 50 % at the wavelength of 700 nm. Figure 5b is the digital image of the as-assembled solar-powered window by combining the SC devices with a commercial solar cell. Inset of Figure 5b is the equivalent circuit diagram. The SCs in the solarpowered window could be successfully charged to ~ 3 V under sunlight within 35 s (Figure 5c). The inset shows the charged SC devices could light up a light emitting diode.

4. Conclusions In summary, we successfully realized a uniformly deposited semi-transparent MnO2 film by suppressing the CRE via the addition of ethanol into MnO2 ink. The uniform coating technique could be applied to both macro and micro film deposition. This CFTMF film could be used as electrode materials for flexible and transparent SCs. The as-prepared device could achieve a high volumetric capacitance of 112 F cm-3, resulting in a maximum energy density and power density of 10 mWh cm-3 and 8.6 W cm-3, respectively. What’s more, a successful demonstration of solarpowered window reveals the great potential of CFTMF based SCs for self-powered buildings.

Acknowledgements H. Jin and J. Qian contributed equally to this work. We thank Peihua Yang and Prof. Wenjie Mai from Jinan University, Xu Xiao and Prof. Jun Zhou from Huazhong University of Science and Technology and Dr. Bolei Chen for helpful discussions and suggestions.



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 16 of 28

References (1) Kim, Y. H.; Heo, J S, Kim, T. H.; Park, S.; Yoon, M. H.; Kim, J.; Oh, M. S.; Yi, G. R.; Noh, Y. Y. and Park, S. K. Flexible Metal-Oxide Devices Made by Room-Temperature Photochemical Activation of Sol-Gel Films. Nature 2012, 489, 128-132. (2) Nau, S.; Wolf, C.; Sax, S. and List-Kratochvil, E. J. Organic Non‐Volatile Resistive Photo‐Switches for Flexible Image Detector Arrays Adv. Mater. 2015, 27, 1048-1052. (3) Minemawari, H.; Yamada, T.; Matsui, H.; Tsutsumi, J. Y.; Haas, S.; Chiba, R.; Kumai, R. and Hasegawa, T. Inkjet Printing of Single-Crystal Films Nature 2011, 475, 364-3677. (4) Cao, Q.; Kim, H. S.; Pimparkar, N.; Kulkarni, J. P.; Wang, C.; Shim, M.; Roy, K.; Alam, M. A. and Rogers, J. A. Medium-Scale Carbon Nanotube Thin-Film Integrated Circuits on Flexible Plastic Substrate Nature 2008, 454, 495-500. (5) Yan, H.; Chen, Z.; Zheng, Y.; Newman, C.; Quinn, J. R.; Dötz, F.; Kastler, M. and Facchetti, A. A High-Mobility Electron-Transporting Polymer for Printed Transistor Nature 2008, 457, 679-686. (6) Kim, S. H.; Hong, K.; Xie, W.; Lee, K. H.; Zhang, S.; Lodge, T. P. and Frisbie, C. D. Electrolyte-Gated Transistors for Organic and Printed Electronics Adv. Mater. 2013, 25, 18221846. (7) Lewis, J. A. and Ahn, B. Y. Device Fabrication: Three-Dimensional Printed Electronics Nature 2015, 518, 42-43. (8) Liu, Z.; Parvez, K.; Li, R.; Dong, R.; Feng, X. and Müllen, K. S. Transparent Conductive Electrodes from Graphene/PEDOT:PSS Hybrid Inks for Ultrathin Organic Photodetectors Adv. Mater. 2015, 27, 669-675. (9) Stüwe, D.; Mager, D.; Biro, D. and Korvink, J. G. Inkjet Technology for Crystalline Silicon


Page 17 of 28

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


Photovoltaics Adv. Mater. 2015, 27, 599-626. (10) Mei, A.; Li, X.; Liu, L.; Ku, Z.; Liu, T.; Rong, Y.; Xu, M.; Hu, M.; Chen, J.; Yang, Y.; Grätzel, M, and Han, H. A Hole-Conductor-Free, Fully Printable Mesoscopic Perovskite Solar Cell with High Stability Science 2014, 345, 295-298. (11) Qin, Y.; Wang, X. and Wang, Z. L. Microfibre-Nanowire Hybride Structure for Energy Scavenging Nature 2008, 451, 809-813. (12) Hu, L.; Choi, J. W.; Yang, Y.; Jeong, S.; Mantia, F. L.; Cui, L. F. and Cui, Y. Highly Conductive Paper for Energy-Storage Devices Proc. Natl. Acad. Sci. USA 2009, 106, 2149021494. (13) Kaempgen, M.; Chan, C. K.; Ma, J.; Cui, Y. and Gruner, G. Printable Thin Film Supercapacitors using Single-Walled Carbon Nanotubes Nano Lett. 2009, 9, 1872-1876. (14) Xu, Y.; Schwab, M. G.; Strudwick, A. J.; Hennig, I.; Feng, X.; Wu, Z. and Müllen, K. Screen‐Printable Thin Film Supercapacitor Device Utilizing Graphene/Polyaniline Inks Adv. Energy Mater. 2013, 3, 1035-1040. (15) Simon, P. and Gogotsi, Y. Materials for Electrochemical Capacitors Nat. Mater. 2008, 7, 845-854. (16) El-Kady, M. F.; Strong, V.; Dubin, S. and Kaner, R. B. Laser Scribing of High-Performance and Flexible Graphene-Based Electrochemical Capacitors Science 2012, 335, 1326-1330. (17) Lee, J. A.; Shin, M. K.; Kim, S. H.; Cho, H. U.; Spinks, G. M.; Wallace, G. G.; Lima, M. D.; Lepró, X.; Kozlov, M. E.; Baughman, R. H. and Kim, S. J. Ultrafast Charge and Discharge Hiscrolled Yarn Supercapacitors for Textiles and Microdevices Nat. Commun. 2013, 4, 1970-1-8. (18) Bae, J.; Song, M. K.; Park, Y. J.; Kim, J. M.; Liu, M. and Wang, Z. L. Fiber Supercapacitors Made of Nanowire-Fiber Hybrid Structure for Wearable/Stretchable Energy Storage Angew.



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 18 of 28

Chem. Int. Ed. 2011, 50, 1683-1687. (19) Xiao, X.; Li, T.; Yang, P.; Gao, Y.; Jin, H.; Ni W.; Zhan, W.; Zhang, X.; Cao, Y.; Zhong, J.; Gong, L.; Yen, W. C.; Mai, W.; Chen, J.; Huo, K.; Chueh, Y. L.; Wang, Z. L. and Zhou, J. FiberBased All-Solid-State Flexible Supercapacitors for Self-Powered Systems ACS Nano 2012, 6, 9200-9206. (20) Jin, H.; Peng, Z.; Tang, W. M. and Chan, H. L. W. Controllable Functionalized Carbon Fabric for High-Performance All-Carbon-Based Supercapacitors RSC Adv. 2014, 4, 3302233028. (21) Xiao, X.; Peng, X.; Jin, H.; Li, T.; Zhang, C.; Gao, B.; Hu, B.; Huo, K. and Zhou, J. Freestanding

Mesoporous

VN/CNT

Hybrid

Electrodes

for

Flexible

All‐Solid‐State

Supercapacitors Adv. Mater. 2013, 25, 5091-5097. (22) Yu, D.; Goh, K.; Wang, H.; Wei, L.; Jiang, W.; Zhang, Q.; Dai, L. and Chen, Y. Scalable Synthesis of Hierarchically Structured Carbon Nanotube-Graphene Fibres for Capacitive Energy Storage Nat. Nanotechnol. 2014, 9, 555-562. (23) Lu, X.; Yu, M.; Wang, G.; Zhai, T.; Xie, S.; Ling, Y.; Tong, Y. and Li, Y. H‐TiO2@ MnO2//H‐TiO2@C Core–Shell Nanowires for High Performance and Flexible Asymmetric Supercapacitors Adv. Mater. 2013, 25, 267-272. (24) Lu, X.; Yu, M.; Zhai, T.; Wang, G.; Xie, S.; Liu, T.; Liang, C. and Li, Y. High Energy Density Asymmetric Quasi-Solid-State Supercapacitor Based on Porous Vanadium Nitride Nanowire Anode Nano Lett. 2013, 13, 2628-2633. (25) Xiao, X.; Ding, T.; Yuan, L.; Shen, Y.; Zhong, Q.; Zhang, X.; Cao, Y.; Hu, B.; Zhai, T.; Gong, L.; Chen, J.; Tong, Y.; Zhou, J. and Wang, Z. L. WO3-x/MoO3-x Core/Shell Nanowires on Carbon Fabric as an Anode for All-Solid-State Asymmetric Supercapacitors Adv. Energy Mater.


Page 19 of 28

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


2012, 2, 1328-1332. (26) Jin, H.; Zhou, L.; Mak, C L.; Huang, H.; Tang, W. M. and Chan, H. L. W. High-Performance Fiber-Shaped

Supercapacitors

using Carbon

Fiber

Thread

(CFT)@

Polyanilne and

Functionalized CFT Electrodes for Wearable/Stretchable Electronics Nano Energy 2015, 11, 662-670. (27) Yang, P.; Sun, P.; Chai, Z.; Huang, L.; Cai, X.; Tan, S.; Song, J. and Mai, W. Large-scale Fabrication of Pseudocapacitive Glass Windows that Combine Electrochromism and Energy Storage Angew. Chem. Int. Ed. 2014, 53, 11935-11939. (28) Dyer, A. L.; Bulloch, R. H.; Zhou, Y.; Kippelen, B.; Reynolds, J. R. and Zhang, F. A Vertically Integrated Solar-Powered Electrochromic Window for Energy Efficient Buildings Adv. Mater. 2014, 26, 4895-4900. (29) Kwon, H. K.; Lee, K. T.; Hur, K.; Moon, S. H.; Quasim, M. M.; Wilkinson, T. D.; Han, J. Y.; Ko, H.; Han, I. K.; Park, B.; Min, B. K.; Ju, B. K.; Morris, S. M.; Friend, R. H. and Ko, D. H. Optically Switchable Smart Windows with Integrated Photovoltaic Devices Adv. Energy Mater. 2015, 5, 1401347-1-6. (30) Ge, D.; Lee, E.; Yang, Y.; Cho, Y.; Li, M.; Gianola, D. S. and Yang, S. A Robust Smart Window: Reversibly Switching from High Transparency to Angle‐Independent Structural Color Display Adv. Mater. 2015, 27, 2489-2495. (31) Chen, T.; Peng, H.; Durstock, M. and Dai, L. High-performance Transparent and Stretchable All-Solid Supercapacitors Based on Highly Aligned Carbon Nanotube Sheets Sci. Rep. 2014, 4, 3612-1-7. (32) Lin, H.; Li, L.; Ren, J.; Cai, Z.; Qiu, L.; Yang, Z. and Peng, H. Conducting Polymer Composite Film Incorporated with Aligned Carbon Nanotubes for Transparent, Flexible and



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 20 of 28

Efficient Supercapacitor Sci. Rep. 2013, 3, 1353-1-6. (33) Qiu, T.; Luo, B.; Giersig, M.; Akinoglu, E. M.; Hao, L.; Wang, X.; Shi, L.; Jin, M. and Zhi, L. Au@MnO2 Core–Shell Nanomesh Electrodes for Transparent Flexible Supercapacitors Small 2014, 10, 4136-4141. (34) Xu, P.; Kang, J.; Choi, J. B.; Suhr, J.; Yu, J.; Li, F.; Byun, J. H.; Kim, B. S. and Chou, T. W. Laminated Ultrathin Chemical Vapor Deposition Graphene Films Based Stretchable and Transparent High-Rate Supercapacitor ACS Nano 2014, 8, 9437-9445. (35) Chen, T.; Xue, Y.; Roy, A. K. and Dai, L. Transparent and Stretchable High-Performance Supercapacitors Based on Wrinkled Graphene Electrodes ACS Nano 2014, 8, 1039-1046. (36) Yunker, P. J.; Still, T.; Lohr, M. A. and Yodh, A. G. Suppression of the Coffee-Ring Effect by Shape-Dependent Capillary Interactions Nature 2011, 476, 308-311. (37) Harris, D. J.; Hu, H.; Conrad, J. C. and Lewis, J. A. Patterning Colloidal Films via Evaporative Lithography Phys. Rev. Lett. 2007, 98, 148301-4. (38) Kim, D.; Jeong, S.; Park, B. K. and Moon, J. Direct Writing of Silver Conductive Patterns: Improvement of Film Morphology and Conductance by Controlling Solvent Compositions Appl. Phys. Lett. 2006, 89, 264101-3. (39) Sempels, W.; Dier, R. D.; Mizuno, H.; Hofkens, J. and Vermant, J. Auto-Production of Biosurfactants Reverses the Coffee Ring Effect in a Bacterial System Nat. Commun. 2013, 4, 1757-1-8. (40) Deegan, R. D.; Bakajin, O.; Dupont, T. F.; Huber, G.; Nagel, S. R. and Witten, T. A. Capillary Flow as the Cause of Ring Stains From Dried Liquid Drops Nature 1997, 389, 827-829. (41) Hu, H. and Larson, R. G. Marangoni Effect Reverses Coffee-Ring Deposition J. Phys. Chem. B 2006, 110, 7090-7094.


Page 21 of 28

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


(42) Majumder, M.; Rendall, C. S.; Eukel, J. A.; Wang, J. Y. L.; Behabtu, N.; Pint, C. L.; Liu T. Y.; Orbaek, A. W.; Mirri, F.; Nam, J.; Barron, A. R.; Hauge, R. H.; Schmidt, H. K. and Pasquali, M. Overcoming the “Coffee-Stain” Effect by Compositional Marangoni-Flow-Assisted DropDrying J. Phys. Chem. B 2012, 116, 6536-6542. (43) Qian, J.; Jin, H.; Chen, B.; Lin, M.; Lu, W.; Tang, W. M.; Xiong, W.; Chan H. L. W.; Lau, S. P. and Yuan J. Aqueous Manganese Dioxide Ink for Paper-Based Capacitive Energy Storage Devices Angew. Chem. Int. Ed. 2015, 54, 6800-6803. (44) Tang, T.; Ji, R.; Cao, X.; Lin, J.; Jiang, H.; Li, X.; Teng, K. S.; Luk, C. M.; Zeng, S.; Hao, J. and Lau, S. P. Deep Ultraviolet Photoluminescence of Water-Soluble Self-Passivated Graphene Quantum Dots ACS Nano 2012, 6, 5102-5110. (45) Omomo, Y.; Sasaki, T.; Wang, L. and Watanabe, M. Redoxable Nanosheet Crystallites of MnO2 Derived via Delamination of a Layered Manganese Oxide J. Am. Chem. Soc. 2003, 125, 3568-3575. (46) Gacem, N. and Diao, P. Effect of Solvent Polarity on the Assembly Behavior of PVP Coated Rhodium Nanoparticles Colloids Surf. A 2013, 417, 32-38. (47) Anyfantakis, M. and Baigl, D. Dynamic Photocontrol of the Coffee-Ring Effect with Optically Tunable Particle Stickiness Angew. Chem. Int. Ed. 2014, 53, 14077-14081. (48) Li, J.; Ye, F.; Vaziri, S.; Muhammed, M.; Lemme, M. C. and Östling, M. Efficient Inkjet Printing of Graphene Adv. Mater. 2013, 25, 3985-3992. (49) Kim, S. K.; Koo, H. J.; Lee, A. and Braun, P. V. Selective Wetting‐Induced Micro‐Electrode Patterning for Flexible Micro‐Supercapacitors Adv. Mater. 2014, 26, 5108-5112. (50) Hu, Y.; Zhu, H.; Wang, J. and Chen, Z. Synthesis of Layered Birnessite-Type Manganese Oxide Thin Films on Plastic Substrates by Chemical Bath Deposition for Flexible Transparent



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 22 of 28

Supercapacitors J. Alloys Compd. 2011, 509, 10234-10240. (51) Huang, Q.; Chen, B.; He, R.; He, Z.; Cai, B.; Xu, J.; Qian, W.; Chan, H. L.; Liu, W.; Guo, S.; Zhao, X. Z. and Yuan, J. Capture and Release of Cancer Cells Based on Sacrificeable Transparent MnO2 Nanospheres Thin Film Adv. Healthcare Mater. 2014, 3, 1420-1425. (52) Si, W.; Yan, C.; Chen, Y.; Oswald, S.; Han, L. and Schmidt, O. G. On chip, All Solid-State and Flexible Micro-Supercapacitors with High Performance Based on MnOx/Au Multilayers Energy Environ. Sci. 2013, 6, 3218-3223. (53) Choi, C.; Lee, J. A.; Choi, A. Y.; Kim, Y. T.; Lepró, X.; Lima, M. D.; Baughman, R. H. and Kim, S. J. Flexible Supercapacitor Made of Carbon Nanotube Yarn with Internal Pores Adv. Mater. 2014, 26, 2059-2065. (54) Toupin, M.; Brousse, T. and Belanger, D. Charge Storage Mechanism of MnO2 Electrode Used in Aqueous Electrochemical Capacitor Chem. Mater. 2004, 16, 3184-3190. (55) Torrisi, F.; Hasan, T.; Wu, W.; Sun, Z.; Lombardo, A.; Kulmala, T S.; Hsieh, G W.; Jung, S.; Bonaccorso, F.; Paul, P J.; Chu, D. and Ferrari, A. C. Inkjet-Printed Graphene Electronics ACS Nano 2012, 6, 2992-3006.


Page 23 of 28

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


Figure 1. (a) (Top view) Evaporation process of a MnO2 ink droplet with or without ethanol addition. (Side view) Contact angle of a MnO2 ink droplet with or without ethanol addition on glass substrate during the drying process. Scale bar is 0.5 cm (top view) and 1 mm (side view). (b) CRE-free semi-transparent MnO2 film with mass loading of 0.05 mg cm-2 and square pattern



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 24 of 28

(1.5 cm×1.5 cm) deposited on a FTO glass (15 cm×15 cm). (c) and (d) SEM images of the front and cross-section of the sample in (b). Scale bar is 500 nm. (e) Contact angle of a water droplet on CRE-free semi-transparent MnO2 film. Scale bar is 1 mm.

Figure 2. (a) AFM image of the deposited CRE-free MnO2 film with mass loading of 0.05 mg cm-2. Scale bar is 500 nm. (b) UV-visible spectra of CRE-free semi-transparent MnO2 film with mass loading of 0.1 mg cm-2, 0.05 mg cm-2, 0.025 mg cm-2 and 0.0125 mg cm-2. (c) Highresolution XPS spectra of Mn 2p from the CRE-free MnO2 film with mass loading of 0.05 mg cm-2. (d) High resolution scan of O 1s. The spectrum can be decomposed into three components: Mn–O–Mn (red line), Mn–OH (blue line), and H–O–H (green line).


Page 25 of 28

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


Figure 3. (a) Schematic diagram showing the fabrication process of the CFTMF-based SC device. (b) Optical microscope images of the films with and without CRE. Scan bar: 200 µm. CV curves of SC (c) without and (d) with CRE at scan rates from 10 mV s-1 to 200 mV s-1. (e) EIS spectrum of SC with and without CRE. Inset is the high resolution spectrum. (f) IR drop of SC with and without CRE as a function of current density from 0.05 mA cm-2 to 1 mA cm-2. (g) Volumetric capacitance of SC with and without CRE with scan rate varied from 10 mV s-1 to 200 mV s-1.



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

Figure 4. (a) Digital image of CFTMF on a flexible ITO/PET substrate. (b) CV curves of ITO/PET@CFTMF based SC under flat and bent condition. (c) Cycle performance of the ITO/PET@CFTMF based SC device under bent condition at a current density of 0.5 mA cm-2 for 100 cycles. The inset is the GCD curve of last five cycles. (d) Cycle performance of the FTO@CFTMF based SC device at a scan rate of 100 mV s-1 for 10k cycles. The inset is the CV curves of the 1st and 10 000th cycle.


Page 26 of 28

Page 27 of 28

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


Figure 5. (a) Schematic diagram of the fabrication process for 4 CFTMF SC devices connected in series on a 15 cm×15 cm FTO glass substrate. (b) Digital image of a solar powered window which consists of a commercial solar cell and the as-prepared 4 CFTMF SC devices connected in series. (c) The charge and discharge curve of the solar-powered CFTMF-based SC devices. The inset shows a LED powered by the charged SC devices.



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

Table of Contents Graphic


Page 28 of 28

Suppressing the Coffee-Ring Effect in Semitransparent MnO2 Film for

Recommend Documents