Enhancing the Capacitive Performance of Carbonized Wood by

Subscriber access provided by Kaohsiung Medical University

Energy, Environmental, and Catalysis Applications

Enhancing the Capacitive Performance of Carbonized Wood by Growing FeOOH Nanosheets and PEDOT Coating Fuen Xin, Yufeng Jia, Jie Sun, Liqin Dang, Zong-Huai Liu, and Zhibin Lei ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b11069 • Publication Date (Web): 04 Sep 2018 Downloaded from http://pubs.acs.org on September 6, 2018

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 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 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.

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 36 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

Enhancing the Capacitive Performance of Carbonized Wood by Growing FeOOH Nanosheets and PEDOT Coating Fuen Xin, Yufeng Jia, Jie Sun, Liqin Dang, Zonghuai Liu, Zhibin Lei*

Key Laboratory of Applied Surface and Colloid Chemistry, MOE, Shaanxi Engineering Lab for Advanced Energy Technology, Shaanxi Key Laboratory for Advanced Energy Devices, School of Materials Science and Engineering, Shaanxi Normal University, 620 West Chang’an Street, Xi'an, Shaanxi, 710119, China, Fax: 86-29-81530702; Tel: 86-29-81530810; Email: [email protected]

*Corresponding Author: Prof. Zhibin Lei, School of Materials Science and Engineering, Shaanxi Normal University, 199 South Chang’an Road, Xi'an, Shaanxi, 710062, China. Email: [email protected]; Tel: 86-29-81530810; Fax: 86-29-81530702

ORCID Zhibin Lei: 0000-0002-6537-9889

1 / 36

ACS Paragon Plus Environment

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

Abstract Carbonized wood (CW) achieved by pyrolysis of various nature woods have received ever-increasing attentions in energy storage and conversion. However, their charge storage capacity are rather low due to their intrinsic ion adsorption mechanism. This work reports the enhanced capacitive performance of CW by growing electroactive FeOOH nanosheets and coating conductive poly(3,4-ethylenedioxythiophene) (PEDOT) network. Those vertically grown FeOOH nanosheets on both the external surface and inside the channel of CW offer more opened active sites for Faradaic reactions, while the porous and conductive PEDOT network significantly boosts the electrode conductivity, facilitates the ion transport and protects the FeOOH sheets from destruction during cycling. Accordingly, the CW-FeOOH-PEDOT ternary electrodes exhibits 4.3 times higher volumetric capacitance than the CW electrode and remains 90% capacitance upon increasing the current density from 10 to 50 mA cm−2. Remarkable, the electrode maintains 103% of its capacitance even after 10000 cycles of galvanostatic charge-discharge at 200 mA cm−2. Besides these unique electrochemical behaviors, the CW-FeOOH-PEDOT also preserves the good mechanical strength of the pristine CW electrode. This property allows easy processing of CW-based electrodes into robust energy storage device towards practical applications.

Keywords: carbonized wood, FeOOH nanosheets, PEDOT conductive network, composite electrode, enhanced performance, supercapacitor.

2 / 36


Page 2 of 36

Page 3 of 36 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


1. INTRODUCTION Batteries and supercapacitor represent two important electrochemical energy storage devices that have shown extensive applications in various portable electronic devices, uninterrupted power supply and hybrid electronic vehicles.1-3 In particular, supercapacitors have received tremendous attentions due to their fast charge-discharge rate, high power density, and extremely stable cycling life.4-6 The energy stored in a supercapacitor depends on the electrodes utilized. With the high conductivity, good electrochemical stability, and controllable porosity, various carbon materials have been widely investigated as supercapacitor electrodes.7-10 However, the carbon-based supercapacitors store less energy due to their intrinsic ion adsorption mechanism. In contrast, much higher energy density can be delivered in pseudocapacitors as they rely on fast and reversible redox reactions to store energy. However, performances of metal oxides electrodes are severely hindered by their poor electrode conductivity and limited cycling stability. Activated carbons (ACs) derived from chemical activation of various biomasses have gained tremendous attentions in energy storage and conversion in view of their low production costs, tunable specific surface area and exceptional cycling stability.11-14 However, the key problem of current ACs electrodes lies in their dominated tortuous micropores, which elongate the ion diffusion pathway and increase electron transfer resistance especially for thicker electrodes. It is known that the structure of the ACs largely depends on the texture of the starting biomass.12-13, 15 Among

various

biomasses,

natural

wood-based

materials

have

received

ever-increasing attentions with respect to their easy processing, biodegradable nature and inherent architecture composed of aligned microscaled channels which are used for water and nutrition ingredient delivery.16-20 Pyrolysis of the nature wood usually 3 / 36



yields the carbonized wood (CW) which can well inherit the structure of starting natural wood. The unique anisotropic feature endows CW with extensive applications in electrochemical energy storage and conversion,21-26 water treatment27 and catalysis reactor for steam reforming reaction.28 As compared with conventional activated carbons dominated by tortuous micropores, the aligned microchannels in CW help to significantly promote ion transport along the tree growth direction.21 However, pure CW electrode still delivers a low volumetric capacitance due to its empty space formed by those abundant microchannels. To address this problem, the usual method is to activate CW with CO2 or KOH. While this treatment creating more tortuous micropores on the CW for efficient charge storage, the mechanical strength of CW is dramatically decreased. Another effective way is to introduce pseudocapacitive components inside the channels. For example, needle-like MnO2 nanosheets have been incorporated into the CW interior to achieve an areal capacitance up to 4155 mF cm−2, while exhibiting good rate performance and satisfying cycle life.21 In contrast to the MnO2-based positive electrode, iron oxides represent one of important family of negative electrodes for asymmetric supercapacitor because of their large theoretical capacity, abundant resource, and more negative operating potential in alkaline electrolyte.29-35 However, iron oxides electrodes suffer from rather low electrical conductivity (for example, ~10−14 S cm−1 for Fe2O3),36 and limited electrochemical stability. To resolve these problems, various nanostructured iron oxides have been integrated with conductive substrates to gain an enhanced performance.30,

37-38

However, even with conductive polymers or carbon layer

coating,39-42 the cycling stabilities of these iron oxide-based electrodes are still unable to meet the requirement of practical applications. Poly(3,4-ethylenedioxythiophene) 4 / 36


Page 4 of 36

Page 5 of 36 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


(PEDOT), as one of attractive polymers, has shown great potential in energy fields because of its ultrahigh conductivity (4380 S cm−1) and good electrochemical stability.43-47 Inspired by these characters, this work reports the enhanced capacitive performance of CW by growing pseudocapacitive FeOOH nanosheets and PEDOT coating (Scheme 1). The electroactive FeOOH grown on both the external surface and inside the CW channels offer sufficient electroactive sites for reversible faradaic redox reactions, while the conductive PEDOT network covering on the CW-FeOOH surface serves as an interconnected electron-highway that not only significantly improve the electrode conductivity, but also effectively protect the FeOOH nanosheets from structural destruction and possible detachment during cycling process. As a result, the CW-FeOOH-PEDOT ternary electrode exhibits a significantly enhanced volumetric capacitance of 126 F cm−3, while preserving 91% of its initial capacitance upon increasing the current density from 10 to 50 mA cm−2. Moreover, the CW-FeOOH-PEDOT electrode retains 103% of its capacitance after 10000 cycles of continuous charge-discharge at 200 mA cm−2. These performances are far superior to the pristine CW electrode. 2. EXPERIMENTAL SECTION 2.1 Electrode Preparation The CW was obtained by pyrolyzing the commercial available basswood at 800−1000 °C in flowing Ar. Specifically, the bulky basswood was cut into small pieces with typical geometric size of 10 mm × 10 mm × 1.0 mm. Pyrolysis of the basswood pieces at different temperature for 90 min yields the black product with a bulky density varying from 0.4 to 0.45 g cm−3. For better deposition of pseudocapacitive FeOOH, the pristine CW was immersed into a mixed solution containing 6 wt% HNO3 and 18 5 / 36



wt% H2SO4, followed by refluxing at 100 °C for 5 h. Such acid treatment endow CW with more hydrophilic nature, as confirmed by the improved surface wettability test as shown in Figure S1. Electrochemical deposition of FeOOH on CW was performed by a galvanostatic technique in a conventional three-electrode cell with CW (geometric size of 8 mm × 8 mm × 0.8 mm) as the working electrode, Pt foil as counter and Ag/AgCl as reference electrode. The electrolyte solution is composed of 0.1 M Na2SO4, 0.2 M CH3COONa and 0.1 M Fe(NH4)2(SO4)2·6H2O. Electrodeposition of FeOOH was conducted at constant current density of 0.125 mA cm–2, and its mass loading on CW was determined using a microbalance.33 By tuning the deposition time from 2 to 10 h, mass loading of electroactive FeOOH can be facilely controlled in the range of 30−89 mg cm−3. The obtained electrodes were denoted as CF-FeOOH-xh, where x is the deposition time of FeOOH in hours. Polymerization of EDOT on CW or CW-FeOOH was carried out by a constant potential of 1.0 V (vs Ag/AgCl) in 60 mL aqueous solution consisting of 0.05 M EDOT, 0.07 M sodium dodecylsulphate and 0.1 M LiClO4. After electrochemical polymerization for 10, 30 and 50 min, the final products were rinsed with copious water and dried at room temperature. 2.2 Characterization Methods The microstructures of the products were observed by field-emission scanning electron microscopy (FESEM) on SU8020 and field-emission transmission electron microscope (FETEM, Tecnai G2 F20 S) with an acceleration voltage of 200 kV. N2 adsorption/desorption was analyzed on ASAP 2460 at −196 °C. Specific surface area was calculated using the Brunauer–Emmett–Teller (BET) equation. Raman spectra were collected on a Renishaw in Via Raman microscope with an excitation wavelength of 532 nm. The phase structure of samples was analyzed on a DX-2700 6 / 36


Page 6 of 36

Page 7 of 36 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


X-ray diffractometer with Cu Kα radiation of wavelength (λ = 0.154 nm). X-ray photoelectron spectroscopy (XPS) spectra were collected on an AXIS ULTRA spectrometer (Kratos Analytical) using a monochromatized Al Ka X-ray source (1486.71 eV). The Fourier-transform infrared spectroscopy (FT-IR) were collected on a Bruker Nicolet Is10 spectrometer. The surface wettability was evaluated on the Dataphysics OCA 20 contact angel system by dropping 2.0 µL water on the sample surface. The conductivity of samples was obtained by recording the I-V curves at applied voltage in the range of 0−10 mV,48 followed by converting the measured resistance into corresponding conductivity using the equation: κ = l/(R × A),49 where A is the geometric area contacting the platinum foils, R is the resistance (ohm) and l is the height of the electrode. Prior to the measurement, CW, CW-FeOOH or the CW-FeOOH-PEDOT electrodes with nearly the same geometric size was fixed between two platinum foils to keep a good electrical contact.48 Stress-strain property of samples was obtained on a Song dun LDW-5 Universal Testing Machine with a program-controlled computer. 2.3 Electrochemical Measurements Performances of the CW-based electrode were evaluated in a three-electrode system with a Pt foil as the counter, Ag/AgCl electrode as reference electrodes and 2.0 M KOH as aqueous electrolyte. The working electrode was prepared by directly attaching the bulky CW-based electrodes between two pieces of nickel foam. The electrochemical measurements were carried out by cyclic voltammetry (CV), galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS) on a Gamry Reference 3000 electrochemical workstation. The gravimetric and volumetric capacitance of the electrodes were calculated from the discharge curves according to the following equations:48, 50 Cv = I × ∆t/ (∆V × V) and Cg = I × ∆t/ (∆V × 7 / 36



Page 8 of 36

m), where I is the discharge current (A), ∆t is the discharge time (s), ∆V is the voltage change (V), V and m are the geometric volume (cm−3) and the mass (g) of the whole CW-based electrodes, respectively. The EIS measurements were performed in the frequency range of 0.01 Hz to 100 KHz by applying an ac voltage of 5 mV. 3. RESULTS AND DISCUSSION Figure S2 shows SEM images of the CW products derived from nature basswood. Despite different carbonization temperatures, all the CW can well inherit the structure of starting wood. They exhibits highly porous structure with macropore sizes varying from 2 µm to tens of micrometers that are separated by carbon wall with 2 µm in thickness. For the growth of FeOOH, CW electrode pyrolyzed at 900 °C was applied as the substrate, which has a specific surface area of 235 m2 g−1. Electrodeposition of FeOOH was performed by typical galvanostatic technique and its mass loading were controlled by changing the deposition time from 2 to 10 h. We firstly characterize the structure of FeOOH by XRD and XPS. Figure 1a shows the XRD patterns of CW-FeOOH with deposition time of 4 h. In addition to the peak at 2θ = 25.4° that is attributed to the carbonaceous materials,51 four weak XRD peaks occurring at 2θ = 21.3°, 33.2°, 36.6° and 53.2° can be well indexed to (110), (130), (111) and (221) planes of FeOOH (JCPDS 29-0713), respectively, suggesting the effective deposition of low crystalline FeOOH on the CW. The survey XPS spectrum of CW-FeOOH-4h presents only Fe, O and C elements without other impurities (Figure 1b). XPS spectrum of Fe 2p (Figure 1c) includes two mains peaks at 711.3 (Fe 2p3/2) and 725.4 eV (Fe 2p1/2), accompanied by two shake-up satellite peaks at 719.5 and 733.9 eV, showing valence state of Fe3+ in the CW-FeOOH.34,

52

In the deconvoluted O 1s

spectrum (Figure 1d), the lower binding energy at 530.1 eV is due to the Fe-O-Fe 8 / 36


Page 9 of 36 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


bond, while the strong peaks at 531.7 eV and the weak peak at 533.6 eV correlate with Fe-O-H bond and adsorbed water in FeOOH,53 respectively. These results coincide with previous results and suggest the successful growth of FeOOH on the CW substrate. The morphology and microstructure of FeOOH on the surface of CW was examined by SEM and TEM. Figure 2a-e displays the top-view SEM images of CW-FeOOH prepared with various deposition time. As the deposition time varies from 2 to 10 h, the FeOOH on CW surface continuously remains the unique sheet-like morphology except slight increase in sheet thickness and lateral size (Figure 2a1-e1). This structure evolution gives rise to gradual increase of FeOOH volumetric mass loading from 30 to 89 mg cm−3 and areal mass loading from 2.8 to 8.3 mg cm−2 (Figure S3). Elemental mapping in Figure 2f presents uniform distribution of C, Fe and O elements, implying that the hydrophilic surface induced by acid treatment greatly favors the uniform nucleation of FeOOH nanosheets.33 TEM images of CW-FeOOH-4h in Figure 2g reveals that the FeOOH varies from 10 to 20 nm in thickness. These FeOOH nanosheets not only reduce ion transport length but also provide abundant active sites for redox reactions. Shown in Figure 2h is the high-resolution TEM image of FeOOH, in which a clear lattice spacing distance of 0.27 nm can be indexed to the (130) plane of FeOOH (JCPDS 29-0713). Uniform growth of FeOOH nanosheets is not only on the external surface of CW, but also in the interior of CW substrate. Figure 3a shows the cross-sectional SEM images of CW-FeOOH-4h. Evidently, no distinct sheets aggregation is observed, revealing the effectiveness of the constant current technique in controlling the uniform growth of FeOOH nanosheets. The magnified SEM images in Figure 3b and 3c present unique hierarchical structure, where FeOOH nanosheets with average lateral 9 / 36



Page 10 of 36

size of ~400 nm are vertically and densely grown on the channel surface. It is noted that sheet-like structure helps to maximize the utilization of

FeOOH for faradaic

reaction, while a large number of spaces formed between these FeOOH nanosheets dramatically enhances the ion penetration rate. Figure 3d-f show the SEM images of CW-FeOOH-4h after electrochemical polymerization of PEDOT for 10 min. Clearly, those vertically grown FeOOH nanosheets can not be observed. Instead, a porous network made up of interconnected nanofibers with typical diameter of 10−20 nm is clearly seen (Figure 3f), demonstrating the uniform coating of PEDOT on the outer surface of CW-FeOOH electrode. It is note that porous and conductive PEDOT network can dramatically promotes both ion and electron transport. The corresponding elemental mapping shown in Figure 3g gives a low-density of C, moderate-density of Fe, O and a high-density of S signals. Difference in element density can be interpreted by the gradient variation of element composition in the ternary electrode, with PEDOT layer on the upper surface and CW substrate at the most underlying layer. Formation of PEDOT network on the CW-FeOOH surface is also evidenced by Raman spectrum and FT-IR spectroscopy. As shown in Figure 4a, besides D band (1347 cm−1) and G band (1589 cm−1) assigned to the CW, an intensive peak at 1429 cm−1 is observed. This peak is ascribed to the stretching vibration of thiophene rings.44 The peak at 990 cm−1 is due to the C−C anti-symmetric stretching mode,54 and peaks at 697 and 856 cm−1 are related to the symmetric and asymmetric C-S-C deformation of PEDOT, respectively.55 The band at 439 and 572 cm−1 are caused by SO2 bending and oxy-ethylene ring deformation, respectively.56 In the FTIR Spectra (Figure S4), the bands of 1488 cm‒1 is assigned to the C=C stretching vibrations of polythiophene, and the bands at 1177 and 1137 cm‒1 correspond to the C−O−C bond in ethylenedioxy 10 / 36


Page 11 of 36 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


group.57 The 927 and 845 cm−1 are related to the C-S-C bond of thiophene ring.58 Figure 4b shows the S 2p and Fe 2p XPS spectrum of CW-FeOOH-PEDOT. Two distinct peaks at 163.9 and 164.8 eV correspond to the S 2p3/2 and S 2p1/2 of S atoms in PEDOT chains, respectively. The additional weak and broad peak appearing at 168.2 eV is assigned to the sulfon groups, suggesting existence of partially oxidized S.55, 59 In the Fe 2p XPS spectrum, the nearly same peaks position as compared with that of the CW-FeOOH (Figure 1c) means that the oxidation state of Fe3+ remains unchanged even after PEDOT coating. Figure 4c compares the conductivity of three samples. As expected, growth of nonconducting FeOOH nanosheets on the CW decreases the conductivity of CW from 23.8 to 8.4 S m−1. Whereas, coating PEDOT layers on the CW-FeOOH-4h electrode significantly improves its conductivity to 34.8 S m−1. This conductivity enhancement would facilitate rapid electron transfer during reversible Faradaic redox reactions. Figure 4d presents the strain-stress curves of the CW-based electrode. Evidently, growing FeOOH nanosheets on CW and the subsequent PEDOT coating have not markedly lower the mechanical strength of the composite electrode. This property enables easy processing of the CW-based electrodes into practical energy storage devices. The electrocapacitive performances of CW-FeOOH electrode with different deposition time were evaluated in 2.0 M aqueous KOH electrolyte. As shown in Figure S5, all the CW-FeOOH-xh electrodes displays nearly rectangular CV curves, suggesting Faradaic redox reaction proceeds as:32 FeOOH + H2O + e− → Fe(OH)2 + OH− Fe(OH)2 + OH− → FeOOH + H2O + e− Figure 5a presents the charge-discharge profile of the CW-FeOOH-xh electrodes tested at a current density of 10 mA cm−2. As compared with pristine CW electrode, 11 / 36



growing FeOOH nanosheets dramatically increases the discharge time, suggesting the enhanced charge storage capacity arising from the significant contribution of FeOOH nanosheets. Moreover, the symmetric charge and discharge curves reveals the highly reversible redox reactions between CW-FeOOH and electrolyte. Figure 5b compares the specific volumetric capacitance of CW-FeOOH electrodes at 10 mA cm−2. The maximal volumetric capacitance of 110 F cm−3 is achieved at mass loading of 50 mg cm−3, and then it declines to 69 F cm−3 at a higher mass loading of 89 mg cm−3. By assuming that the volumetric capacitance of CW-FeOOH is contributed form FeOOH nanosheets and the CW substrate, gravimetric capacitance of FeOOH can be calculated which are included in Figure 5b. Clearly, the FeOOH reaches a maximal specific capacitance of 1167 F g−1 at electrodeposition time of 4 h (50 mg cm−3) and then decreases to 496 F g−1 at longer deposition time of 10 h (89 mg cm−3). This observation means that thicker FeOOH nanosheets with larger lateral size at higher mass loading results in a longer ion diffusion length and a lower electrode utilization efficiency. Taking the theoretical capacity of FeOOH (2606 F g−1)60 into consideration, the capacitance of 1167 F g−1 indicates that about 45 wt% FeOOH nanosheets are involved in the faradaic reactions and contributes to the pseudocapacitance. Accordingly, the specific capacitance of FeOOH achieved at deposition time of 4 h is much higher than previous iron-based electrode,29-30 including FeOOH nanoparticles on carbon fiber cloth (1066 F g−1),32 F-doped FeOOH nanorods on carbon cloth (1094 F g−1),52 FeOOH quantum on graphene (365 F g−1),61 Fe2O3 fibers on active carbon fibers (988 F g−1)34 and Fe2O3 nanoneedles on ultrafine Ni nanotube (418.7 F g−1).62 Shown in Figure 5c is the cycling stability of CW-FeOOH-4h electrode at a constant current density of 200 mA cm−2. While it exhibiting nearly 100% Coulombic efficiency, only 85% capacitance is retained after 5000 cycles. The capacitance decay 12 / 36


Page 12 of 36

Page 13 of 36 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


is likely caused by the increased solution resistance (1.28 vs 2.49 ohm) and larger charge transfer resistance (0.65 vs 0.97 ohm) as indicated by the Nyquist plots in Figure 5c. Ccapacitive performance of CW-FeOOH is further enhanced by coating the conducting

PEDOT

network.

CV

curves

of

CW,

CW-FeOOH-4h

and

CW-FeOOH-PEDOT electrodes at scan rate of 10 mV s−1 are compared in Figure 6a. Clearly, the much higher current response of CW-FeOOH-PEDOT electrode indicates a vital role of conducting PEDOT in boosting the electrode charge storage capacity. A control experiment by growing PEDOT on CW for 10 min reveals that contribution of PEDOT to the specific capacitance is limited despite a slightly improved rate capability (Figure S6). Figure 6b plots the charge discharge profiles of the three electrodes at 10 mA cm−2. Consistent with the CV results, the discharge time of CW gradually increases with FeOOH growth and PEDOT coating, confirming the enhanced charge storage capacity. In addition, coating porous PEDOT network on CW-FeOOH dramatically reduces the electrode internal resistance. This is evident by comparing the voltage drop at the initial of discharge curve (IR drop), which are 47, 39 and 16 mV for CW, CW-FeOOH-4h and CW-FeOOH-PEDOT electrode, respectively. The galvanostatic charge-discharge curves of CW-FeOOH-PEDOT electrode are shown in Figure 6c, in which the symmetric charge and discharge profiles at the given current density clearly reveal the excellent reversibility of the electrochemical reaction between the electrodes and electrolyte. Moreover, even at high current density of 50 mA cm−2, the IR drop of CW-FeOOH-PEDOT electrode is only 75 mV, indicating high-rate performance arising from porous and conducting PEDOT coating. The significantly reduced IR drop means a fast ion and electron kinetics, and 13 / 36



enables the CW-FeOOH-PEDOT electrode to exhibit high-rate performace. Figure 6d presents the variation of volumetric capacitance with the current density. Specific capacitance at 10 mA cm−2 are calculated to be 29, 110 and 126 F cm−3 for CW, CW-FeOOH and CW-FeOOH-PEDOT electrode, respectively. They retain 61%, 81% and 91% of their corresponding capacitances even at high current density of 50 mA cm−2. To elucidate the superior rate performance of CW-FeOOH-PEDOT electrode, we conducted its EIS and compared its Nyquist plots with those of CW and CW-FeOOH-4h electrode (Figure 6e), with the equivalent circuit used for fitting being also included. The initial points intersecting the real axis at ultra-high frequency represent the solution resistance (Rs).48 It remains comparable for three electrodes because all of them operate in the same electrolyte with the similar interfacial contact resistance (inset in Figure 6e). The semicircle at high frequency is referred to the charge transfer resistance (Rct), which indicates the electron transport behavior, and thus strongly depending on the electrode conductivity (Figure 4c). Besides reducing the Rct, porous PEDOT network also promotes ion access to the electroactive FeOOH.63 This is evident by comparing the Warburg resistance (W0), which decreases from 0.7 Ohm for CW-FeOOH-4h to 0.24 ohm after PEDOT coating for 10 min (inset in Figure 6e). Alternatively, contribution of porous PEDOT network to the enhanced electrode performance was also investigated by extending the PEDOT polymerization time. As shown from the SEM images in Figure S7 and S8, deposition of PEDOT with longer polymerization time yields a dense PEDOT layer composed of aggregated particles. The disappearance of porous PEDOT network implies an increased ion penetration resistance, and thus a poor rate capability as confirmed by the change of W0 from 0.24 to 0.96 ohm and the capacitance retention decreased from 91% to 86% upon increasing the PEDOT deposition time from 10 to 50 min (Figure S9). 14 / 36


Page 14 of 36

Page 15 of 36 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 addition to promoting the ion and electron kinetics, porous PEDOT wrapping also enhances the cycling stability. Figure 6f presents the cycling stability of the CW-FeOOH-PEDOT electrode at 200 mA cm−2. The gradually increased capacitance at initial 2000 cycles is probably due to the progressive penetration of electrolyte ions into the interior of electrode. However, in the subsequent 8000 cycles, the electrode retains 103% of its initial capacitance, which is much superior to 85% of CW-FeOOH electrode (Figure 5c). Moreover, performance of CE-FeOOH-PEDOT is also better than most of the reported ternary electrode, including Zn-MnO2-PEDOT,63 PAA@MnO2/PPy electrodes64 and other polymer-coated electrodes in term of the cyclability and rate performance (Table S1). This comparison implies that the PEDOT network could serve as an effective protective layer to restrict the electroactive FeOOH nanosheets from destruction or degradation during cycling. The almost identical CV curves tested at different cycling stages also support this conclusion (inset in Figure 6f). In order to examine the structure change of the CW-FeOOH-PEDOT, SEM characterization was performed. As displayed in Figure S10, the electrode still preserves its initial structure without obvious morphology change except the occurrence of some white aggregates, presumably due to the unwashed KOH electrolyte. In addition, the 100% Coulombic efficiency during the whole 10000 cycles reveals the excellent reversibility of the CW-FeOOH-PEDOT electrode, which is unusual for polymer-based electrodes. 4. CONCLUSIONS We have demonstrated that growth of the electroactive FeOOH nanosheets and subsequent PEDOT coating can substantially improve the performance of CW electrode. Those vertically grown FeOOH nanosheets significantly reduces the ion diffusion length and simultaneously provides abundant active site for efficient 15 / 36



electrochemical reactions. Whereas, porous and conductive PEDOT coating not only improve the electron and ion kinetic, but also protects those electroactive FeOOH nanosheets from destruction during cycling. Accordingly, the ternary electrode delivers 4.3 times higher volumetric capacitance, extremely high rate capability and outstanding cycling performance. Besides, the good mechanical strength of CW-FeOOH-PEDOT electrode offer a platform for easy processing of the CW-based electrodes into various robust energy storage devices towards practical applications. ACKNOWLEDGEMENTS This work was supported by the National Natural Science Foundation of China (Nos. 51772181) and 111 project (B14041).

The Supporting Information is available free of charge on the ACS Publication website at DOI: 10.1021/XXXXX Contact angle test of CW before and after acid treatment, top-view and cross-sectional SEM images of CW prepared at different temperatures, volumetric and areal mass loading of FeOOH at different electrodeposition time, FT-IR spectrum of CW-FeOOH-PEDOT, CV profiles of CW-FeOOH-xh electrodes at 10 mV s−1, rate performance of CW-PEDOT, top-view, cross-sectional SEM images, Nyquist plots and rate performance of CW-FeOOH-PEDOT with PEDOT deposition time of 10, 30 and 50 min, SEM images of CW-FeOOH-PEDOT after 10000 cycling, and performance comparison of CW-FeOOH-PEDOT with other ternary electrode in literatures.

16 / 36


Page 16 of 36

Page 17 of 36 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


REFERENCES 1.

Simon, P.; Gogotsi, Y., Materials for Electrochemical Capacitors. Nat. Mater. 2008, 7, 845-854.

2. Liu, J.; Chen, M.; Zhang, L.; Jiang, J.; Yan, J.; Huang, Y.; Lin, J.; Fan, H. J.; Shen, Z. X., A Flexible Alkaline Rechargeable Ni/Fe Battery Based on Graphene Foam/Carbon Nanotubes Hybrid Film. Nano Lett 2014, 14, 7180-7. 3.

Guan, C.; Sumboja, A.; Wu, H.; Ren, W.; Liu, X.; Zhang, H.; Liu, Z.; Cheng, C.; Pennycook, S. J.; Wang, J., Hollow Co3O4 Nanosphere Embedded in Carbon Arrays for Stable and Flexible Solid-State Zinc–Air Batteries. Adv. Mater. 2017, 29, 1704117.

4.

Zhang, L. L.; Zhao, X. S., Carbon-Based Materials as Supercapacitor Electrodes. Chem. Soc. Rev. 2009, 38, 2520-2531.

5.

Lei, Z.; Zhang, J.; Zhang, L. L.; Kumar, N. A.; Zhao, X. S., Functionalization of Chemically Derived Graphene for Improving Its Electrocapacitive Energy Storage Properties. Energy Environ. Sci. 2016, 9, 1891-1930.

6.

Guan, C.; Liu, X.; Ren, W.; Li, X.; Cheng, C.; Wang, J., Rational Design of Metal-Organic Framework Derived Hollow NiCo2O4 Arrays for Flexible Supercapacitor and Electrocatalysis. Adv. Energy Mater. 2017, 7, 1602391.

7.

Wang, H.; Yu, S.; Xu, B., Hierarchical Porous Carbon Materials Prepared Using Nano-ZnO as a Template and Activation Agent for Ultrahigh Power Supercapacitors. Chem. Commun. 2016, 52, 11512-11515.

8.

Lin, X.-X.; Tan, B.; Peng, L.; Wu, Z.-F.; Xie, Z.-L., Ionothermal Synthesis of Microporous and Mesoporous Carbon Aerogels from Fructose as Electrode Materials for Supercapacitors. J. Mater. Chem. A 2016, 4, 4497-4505.

9.

Sun, X.; Cheng, P.; Wang, H.; Xu, H.; Dang, L.; Liu, Z.; Lei, Z., Activation of 17 / 36



Graphene Aerogel with Phosphoric Acid for Enhanced Electrocapacitive Performance. Carbon 2015, 92, 1-10. 10. Wang, H.; Zhi, L.; Liu, K.; Dang, L.; Liu, Z.; Lei, Z.; Yu, C.; Qiu, J., Thin-Sheet Carbon Nanomesh with an Excellent Electrocapacitive Performance. Adv. Funct. Mater. 2015, 25, 5420-5427. 11. Liu, Y.; Huang, B.; Lin, X.; Xie, Z., Biomass-Derived Hierarchical Porous Carbons: Boosting the Energy Density of Supercapacitors via an Ionothermal Approach. J. Mater. Chem. A 2017, 5, 13009-13018. 12. Cheng, P.; Gao, S.; Zang, P.; Yang, X.; Bai, Y.; Xu, H.; Liu, Z.; Lei, Z., Hierarchically Porous Carbon by Activation of Shiitake Mushroom for Capacitive Energy Storage. Carbon 2015, 93, 315-324. 13. Cheng, P.; Li, T.; Yu, H.; Zhi, L.; Liu, Z.; Lei, Z., Biomass-Derived Carbon Fiber Aerogel as a Binder-Free Electrode for High-Rate Supercapacitors. J. Phys. Chem. C 2016, 120, 2079-2086. 14. Huang, B.; Liu, Y.; Xie, Z., Biomass Derived 2D Carbons via a Hydrothermal Carbonization Method as Efficient Bifunctional ORR/HER Electrocatalysts. J. Mater. Chem. A 2017, 5, 23481-23488. 15. Wang, J.; Nie, P.; Ding, B.; Dong, S.; Hao, X.; Dou, H.; Zhang, X., Biomass Derived Carbon for Energy Storage Devices. J. Mater. Chem. A 2017, 5, 2411-2428. 16. Jiang, F.; Li, T.; Li, Y.; Zhang, Y.; Gong, A.; Dai, J.; Hitz, E.; Luo, W.; Hu, L., Wood-Based Nanotechnologies toward Sustainability. Adv. Mater. 2018, 30, 1703453. 17. Song, J.; Chen, C.; Zhu, S.; Zhu, M.; Dai, J.; Ray, U.; Li, Y.; Kuang, Y.; Li, Y.; Quispe, N.; Yao, Y.; Gong, A.; Leiste, U. H.; Bruck, H. A.; Zhu, J. Y.; Vellore, A.; 18 / 36


Page 18 of 36

Page 19 of 36 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


Li, H.; Minus, M. L.; Jia, Z.; Martini, A.; Li, T.; Hu, L., Processing Bulk Natural Wood into a High-Performance Structural Material. Nature 2018, 554, 224-228. 18. Song, J.; Chen, C.; Wang, C.; Kuang, Y.; Li, Y.; Jiang, F.; Li, Y.; Hitz, E.; Zhang, Y.; Liu, B., Superflexible Wood. ACS Appl. Mater. Interfaces 2017, 9, 23520-23527. 19. Zhu, M.; Li, T.; Davis, C. S.; Yao, Y.; Dai, J.; Wang, Y.; AlQatari, F.; Gilman, J. W.; Hu, L., Transparent and Haze Wood Composites for Highly Efficient Broadband Light Management in Solar Cells. Nano Energy 2016, 26, 332-339. 20. Zhu, M.; Li, Y.; Chen, G.; Jiang, F.; Yang, Z.; Luo, X.; Wang, Y.; Lacey, S. D.; Dai, J.; Wang, C., Tree‐Inspired Design for High‐Efficiency Water Extraction. Adv. Mater. 2017, 29, 1704107. 21. Chen, C.; Zhang, Y.; Li, Y.; Dai, J.; Song, J.; Yao, Y.; Gong, Y.; Kierzewski, I.; Xie, J.; Hu, L., All-Wood, Low Tortuosity, Aqueous, Biodegradable Supercapacitors with Ultra-High Capacitance. Energy Environ. Sci. 2017, 10, 538-545. 22. Luo, C.; Zhu, H.; Luo, W.; Shen, F.; Fan, X.; Dai, J.; Liang, Y.; Wang, C.; Hu, L., Atomic-Layer-Deposition Functionalized Carbonized Mesoporous Wood Fiber for High Sulfur Loading Lithium Sulfur Batteries. ACS Appl. Mater. Interfaces 2017, 9, 14801-14807. 23. Li, Y.; Fu, K. K.; Chen, C.; Luo, W.; Gao, T.; Xu, S.; Dai, J.; Pastel, G.; Wang, Y.; Liu, B., Enabling High-Areal-Capacity Lithium–Sulfur Batteries: Designing Anisotropic and Low-Tortuosity Porous Architectures. ACS Nano 2017, 11, 4801-4807. 24. Chen, C.; Zhang, Y.; Li, Y.; Kuang, Y.; Song, J.; Luo, W.; Wang, Y.; Yao, Y.; Pastel, G.; Xie, J., Highly Conductive, Lightweight, Low‐Tortuosity Carbon 19 / 36



Frameworks as Ultrathick 3D Current Collectors. Adv. Energy Mater. 2017, 7, 1700595. 25. Zhu, H.; Luo, W.; Ciesielski, P. N.; Fang, Z.; Zhu, J.; Henriksson, G.; Himmel, M. E.; Hu, L., Wood-Derived Materials for Green Electronics, Biological Devices, and Energy Applications. Chem. Rev. 2016, 116, 9305-9374. 26. Zhu, H.; Shen, F.; Luo, W.; Zhu, S.; Zhao, M.; Natarajan, B.; Dai, J.; Zhou, L.; Ji, X.; Yassar, R. S., Low Temperature Carbonization of Cellulose Nanocrystals for High Performance Carbon Anode of Sodium-Ion Batteries. Nano Energy 2017, 33, 37-44. 27. Chen, F.; Gong, A. S.; Zhu, M.; Chen, G.; Lacey, S. D.; Jiang, F.; Li, Y.; Wang, Y.; Dai, J.; Yao, Y., Mesoporous, Three-Dimensional Wood Membrane Decorated with Nanoparticles for Highly Efficient Water Treatment. ACS Nano 2017, 11, 4275-4282. 28. Wang, Y.; Sun, G.; Dai, J.; Chen, G.; Morgenstern, J.; Wang, Y.; Kang, S.; Zhu, M.; Das, S.; Cui, L., A High‐Performance, Low‐Tortuosity Wood‐Carbon Monolith Reactor. Adv. Mater. 2017, 29, 1604257. 29. Nithya, V. D.; Arul, N. S., Review on α-Fe2O3 Based Negative Electrode for High Performance Supercapacitors. J. Power Sources 2016, 327, 297-318. 30. Zeng, Y.; Yu, M.; Meng, Y.; Fang, P.; Lu, X.; Tong, Y., Iron-Based Supercapacitor Electrodes: Advances and Challenges. Adv. Energy Mater. 2016, 6, 1601053. 31. Guan, C.; Zhao, W.; Hu, Y.; Ke, Q.; Li, X.; Zhang, H.; Wang, J., High-Performance Flexible Solid-State Ni/Fe Battery Consisting of Metal Oxides Coated Carbon Cloth/Carbon Nanofiber Electrodes. Adv. Energy Mater. 2016, 6, 1601034. 32. Owusu, K. A.; Qu, L.; Li, J.; Wang, Z.; Zhao, K.; Yang, C.; Hercule, K. M.; Lin, 20 / 36


Page 20 of 36

Page 21 of 36 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


C.; Shi, C.; Wei, Q.; Zhou, L.; Mai, L., Low-Crystalline Iron Oxide Hydroxide Nanoparticle Anode for High-Performance Supercapacitors. Nat. Commun. 2017, 8, 14264. 33. Li, T.; Yu, H.; Zhi, L.; Zhang, W.; Dang, L.; Liu, Z.; Lei, Z., Facile Electrochemical Fabrication of Porous Fe2O3 Nanosheets for Flexible Asymmetric Supercapacitors. J. Phys. Chem. C 2017, 121, 18982-18991. 34. Li, T.; Zhang, W.; Zhi, L.; Yu, H.; Dang, L.; Shi, F.; Xu, H.; Hu, F.; Liu, Z.; Lei, Z.; Qiu, J., High-Energy Asymmetric Electrochemical Capacitors Based on Oxides Functionalized Hollow Carbon Fibers Electrodes. Nano Energy 2016, 30, 9-17. 35. Guan, C.; Chao, D.; Wang, Y.; Wang, J.; Liu, J., Confined Fe2O3 Nanoparticles on Graphite Foam as High-Rate and Stable Lithium-Ion Battery Anode. Particle & Particle Systems Characterization 2016, 33, 487-492. 36. Lu, X.; Zeng, Y.; Yu, M.; Zhai, T.; Liang, C.; Xie, S.; Balogun, M. S.; Tong, Y., Oxygen-Deficient Hematite Nanorods as High-Performance and Novel Negative Electrodes for Flexible Asymmetric Supercapacitors. Adv. Mater. 2014, 26, 3148-3155. 37. Zhai, T.; Sun, S.; Liu, X.; Liang, C.; Wang, G.; Xia, H., Achieving Insertion-Like Capacity at Ultrahigh Rate via Tunable Surface Pseudocapacitance. Adv. Mater. 2018, 30, 1706640. 38. Guan, C.; Liu, J. L.; Wang, Y. D.; Mao, L.; Fan, Z. X.; Shen, Z. X.; Zhang, H.; Wang, J., Iron Oxide-Decorated Carbon for Supercapacitor Anodes with Ultrahigh Energy Density and Outstanding Cycling Stability. ACS Nano 2015, 9, 5198-5207. 39. Wang, L.; Yang, H.; Liu, X.; Zeng, R.; Li, M.; Huang, Y.; Hu, X., Constructing 21 / 36



Page 22 of 36

Hierarchical Tectorum-like α-Fe2O3/PPy Nanoarrays on Carbon Cloth for Solid-State Asymmetric Supercapacitors. Angew. Chem. Int. Ed. 2017, 56, 1105-1110. 40. Tang, P.-Y.; Han, L.-J.; Genç, A.; He, Y.-M.; Zhang, X.; Zhang, L.; Galán-Mascarós, J. R.; Morante, J. R.; Arbiol, J., Synergistic Effects in 3D Honeycomb-Like

Hematite

Nanoflakes/Branched

Polypyrrole

Nanoleaves

Heterostructures as High-Performance Negative Electrodes for Asymmetric Supercapacitors. Nano Energy 2016, 22, 189-201. 41. Lu, X.-F.; Chen, X.-Y.; Zhou, W.; Tong, Y.-X.; Li, G.-R., α-Fe2O3@PANI Core–Shell Nanowire Arrays as Negative Electrodes for Asymmetric Supercapacitors. ACS Appl. Mater. Interfaces 2015, 7, 14843-14850. 42. Zhang, Z.; Wang, H.; Zhang, Y.; Mu, X.; Huang, B.; Du, J.; Zhou, J.; Pan, X.; Xie, E., Carbon Nanotube/Hematite Core/Shell Nanowires on Carbon Cloth for Supercapacitor Anode with Ultrahigh Specific Capacitance and Superb Cycling Stability. Chem. Eng. J. 2017, 325, 221-228. 43. Nara, K.; Seyoung, K.; Ho, L. S.; Hoon, L. B.; Ho, K. Y.; Yong‐Ryun, J.; Bong‐Joong, K.; Kwanghee, L., Highly Conductive PEDOT:PSS Nanofibrils Induced by Solution‐Processed Crystallization. Adv. Mater. 2014, 26, 2268-2272. 44. Yao, B.; Wang, H.; Zhou, Q.; Wu, M.; Zhang, M.; Li, C.; Shi, G., Ultrahigh-Conductivity Polymer Hydrogels with Arbitrary Structures. Adv. Mater. 2017, 29, 1700974. 45. Zhang, M.; Yu, X. W.; Ma, H. Y.; Du, W. C.; Qu, L. T.; Li, C.; Shi, G. Q., Robust Graphene Composite Films for Multifunctional Electrochemical Capacitors with an Ultrawide Range of Areal Mass Loading toward High-Rate Frequency Response and Ultrahigh Specific Capacitance. Energy Environ. Sci. 2018, 11, 22 / 36


Page 23 of 36 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


559-565. 46. He, X.; Yang, W.; Mao, X.; Xu, L.; Zhou, Y.; Chen, Y.; Zhao, Y.; Yang, Y.; Xu, J., All-Solid State Symmetric Supercapacitors Based on Compressible and Flexible Free-Standing 3D Carbon Nanotubes (CNTs)/Poly(3,4-ethylenedioxythiophene) (PEDOT) Sponge Electrodes. J. Power Sources 2018, 376, 138-146. 47. Qin, L.; Tao, Q.; El Ghazaly, A.; Fernandez-Rodriguez, J.; Persson, P. O. A.; Rosen, J.; Zhang, F., High-Performance Ultrathin Flexible Solid-State Supercapacitors Based on Solution Processable Mo1.33C MXene and PEDOT:PSS. Adv. Funct. Mater. 2018, 28, 1703808. 48. Liang, X.; Nie, K. W.; Ding, X.; Dang, L. Q.; Sun, J.; Shi, F.; Xu, H.; Jiang, R. B.; He, X. X.; Liu, Z. H.; Lei, Z. B., Highly Compressible Carbon Sponge Supercapacitor Electrode with Enhanced Performance by Growing Nickel-Cobalt Sulfide Nanosheets. ACS Appl. Mater. Interfaces 2018, 10, 10087-10095. 49. Lee, J.-S.; Kim, S.-I.; Yoon, J.-C.; Jang, J.-H., Chemical Vapor Deposition of Mesoporous Graphene Nanoballs for Supercapacitor. ACS Nano 2013, 7, 6047-6055. 50. Zhi, L.; Zhang, W.; Dang, L.; Sun, J.; Shi, F.; Xu, H.; Liu, Z.; Lei, Z., Holey Nickel-Cobalt Layered Double Hydroxide Thin Sheets with Ultrahigh Areal Capacitance. J. Power Sources 2018, 387, 108-116. 51. Huang, B.; Peng, L.; Yang, F.; Liu, Y.; Xie, Z., Improving ORR Activity of Carbon Nanotubes by Hydrothermal Carbon Deposition Method. J. Energy Chem. 2017, 26, 712-718. 52. Chen, L.-F.; Yu, Z.-Y.; Wang, J.-J.; Li, Q.-X.; Tan, Z.-Q.; Zhu, Y.-W.; Yu, S.-H., Metal-Like Fluorine-Doped β-FeOOH Nanorods Grown on Carbon Cloth for Scalable High-Performance Supercapacitors. Nano Energy 2015, 11, 119-128. 23 / 36



Page 24 of 36

53. Chen, J.; Xu, J.; Zhou, S.; Zhao, N.; Wong, C.-P., Amorphous Nanostructured FeOOH and Co–Ni Double Hydroxides for High-Performance Aqueous Asymmetric Supercapacitors. Nano Energy 2016, 21, 145-153. 54. Zeng, Y.; Han, Y.; Zhao, Y.; Zeng, Y.; Yu, M.; Liu, Y.; Tang, H.; Tong, Y.; Lu, X., Advanced Ti-Doped Fe2O3@PEDOT Core/Shell Anode for High-Energy Asymmetric Supercapacitors. Adv. Energy Mater. 2015, 5, 1402176. 55. Anothumakkool, B.; Soni, R.; Bhange, S. N.; Kurungot, S., Novel Scalable Synthesis of Highly Conducting and Robust PEDOT Paper for a High Performance Flexible Solid Supercapacitor. Energy Environ. Sci. 2015, 8, 1339-1347. 56. Kurra,

N.;

Hota,

M.

K.;

Alshareef,

H.

N.,

Conducting

Polymer

Micro-Supercapacitors for Flexible Energy Storage and AC Line-Filtering. Nano Energy 2015, 13, 500-508. 57. Wang, S.; Sun, C.; Guan, S.; Li, W.; Xu, J.; Ge, D.; Zhuang, M.; Liu, T.; Ma, X., Chitosan/Gelatin

Porous

Scaffolds

Assembled

with

Conductive

Poly(3,4-ethylenedioxythiophene) Nanoparticles for Neural Tissue Engineering. J. Mater. Chem. B 2017, 5, 4774-4788. 58. Wang, M.; Kovacik, P.; Gleason, K. K., Chemical Vapor Deposition of Thin, Conductive, and Fouling-Resistant Polymeric Films. Langmuir 2017, 33, 10623-10631. 59. Mitraka, E.; Jafari, M. J.; Vagin, M.; Liu, X.; Fahlman, M.; Ederth, T.; Berggren, M.; Jonsson, M.; Crispin, X., Oxygen-Induced Doping on Reduced PEDOT. J. Mater. Chem. A 2017, 5, 4404-4412. 60. Chen, X.; Chen, K.; Wang, H.; Xue, D., Composition Design Upon Iron Element Toward Supercapacitor Electrode Materials. Mater. Focus 2015, 4, 78-80. 24 / 36


Page 25 of 36 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


61. Jiaqi, L.; Mingbo, Z.; Xiaoqin, S.; Haibo, Z.; Hui, X., Amorphous FeOOH Quantum Dots Assembled Mesoporous Film Anchored on Graphene Nanosheets with Superior Electrochemical Performance for Supercapacitors. Adv. Funct. Mater. 2016, 26, 919-930. 62. Li, Y.; Xu, J.; Feng, T.; Yao, Q.; Xie, J.; Xia, H., Fe2O3 Nanoneedles on Ultrafine Nickel Nanotube Arrays as Efficient Anode for High-Performance Asymmetric Supercapacitors. Adv. Funct. Mater. 2017, 27, 1606728. 63. Zeng, Y.; Zhang, X.; Meng, Y.; Yu, M.; Yi, J.; Wu, Y.; Lu, X.; Tong, Y., Achieving Ultrahigh Energy Density and Long Durability in a Flexible Rechargeable Quasi-Solid-State Zn-MnO2 Battery. Adv. Mater. 2017, 29, 1700274. 64. Lu, X.; Shen, C.; Zhang, Z.; Barrios, E.; Zhai, L., Core–Shell Composite Fibers for High-Performance Flexible Supercapacitor Electrodes. ACS Appl. Mater. Interfaces 2018, 10, 4041-4049.

25 / 36



Caption for Figures Scheme 1. Schematic showing the preparation procedure and the structure of CW-FeOOH-PEDOT ternary electrode.

Figure 1. (a) XRD patterns of CW, CW-FeOOH-4h and CW-FeOOH-PEDOT electrodes. (b) Survey XPS spectrum, (c) Fe 2p and (d) O 1s XPS spectrum of the CW-FeOOH-4h electrode.

Figure 2. Top-view SEM images of CW-FeOOH-xh electrode with x = 2 (a, a1), 4 (b, b1), 6 (c, c1), 8 (d, d1) and 10 (e, e1). (f) SEM images and corresponding elemental mapping of CW-FeOOH-4h. (g) TEM and (h) HRTEM images of FeOOH nanosheets of CW-FeOOH-4h electrode.

Figure 3. Cross-sectional SEM images of CW-FeOOH-4h (a-c) and CW-FeOOH-PEDOT electrode (d-f) with PEDOT polymerization time of 10 min. (g) SEM images and corresponding elemental mapping of CW-FeOOH-PEDOT.

Figure 4. (a) Raman spectrum, (b) S 2p, Fe 2p XPS spectra of CW-FeOOH-PEDOT electrode. (c) Conductivity and (d) stress-strain curves of CW, CW-FeOOH-4h and CW-FeOOH-PEDOT electrodes.

Figure 5. (a) Galvanostatic charge-discharge curves of CW-FeOOH-xh with different electrodeposition time of FeOOH. (b) Variation of volumetric capacitance CW-FeOOH-xh, mass loading, and calculated gravimetric capacitance of FeOOH with the deposition time of FeOOH nanosheets. (c) Cycling stability and Coulombic efficiency of CW-FeOOH-4h electrode at 200 mA cm−2 for 5000 cycles. The inset giving the Nyquist plots before and after cycling.

Figure 6. Comparison of electrochemical performance of CW, CW-FeOOH-4h and CW-FeOOH-PEDOT electrodes in 2.0 M KOH aqueous electrolyte. (a) CV at 10 mV s−1 and (b) galvanostatic charge-discharge profiles at current density of 10 mA cm−2. (c) Galvanostatic charge-discharge curves of the CW-FeOOH-PEDOT electrode at various current densities. (d) Rate performance, (e) Nyquist plots, equivalent circuit used for fitting and the derived parameters Rs, Rct, W0. (f) Cycling stability and Coulombic efficiency of CW-FeOOH-PEDOT electrode at 200 mA cm−2 for 10000

26 / 36


Page 26 of 36

Page 27 of 36 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


cycles, with inset showing the CV curves at 10 mV s−1 recorded at different cycling stage

27 / 36



Scheme 1. Schematic showing the preparation procedure and the structure of CW-FeOOH-PEDOT ternary electrode.

28 / 36


Page 28 of 36

Page 29 of 36

C 1s

(221)

(130)

(111)

(b)

(110)

(a)

O 1s

Intensity(a.u.)

Intensity (a.u.)

CW−FeOOH−PEDOT

CW−FeOOH-4h

Fe 2p

CW

JCPDS: 29-0713

10

20

30

40

50

60

70

900

80

800

700

2 Theta (degree)

(c)

(d)

Intensity (a.u.)

725.4 eV Fe 2p1/2 733.9 eV 719.5 eV

740

735

730

725

720

600

500

400

300

200

Binding energy (eV)

711.3 eV Fe 2p3/2

Fe 2p

Intensity (a.u.)

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


715

710

705

Fe-O-H 531.7 eV

O 1s

533.6 eV H-O-H

538

536

Fe-O-Fe 530.1 eV

534

532

530

528

526

Binding energy (eV)

Binding Energy (eV)

Figure 1. (a) XRD patterns of CW, CW-FeOOH-4h and CW-FeOOH-PEDOT electrodes. (b) Survey XPS spectrum, (c) Fe 2p and (d) O 1s XPS spectrum of the CW-FeOOH-4h electrode.

29 / 36



Figure 2. Top-view SEM images of CW-FeOOH-xh electrode with x = 2 (a, a1), 4 (b, b1), 6 (c, c1), 8 (d, d1) and 10 (e, e1). (f) SEM images and corresponding elemental mapping of CW-FeOOH-4h. (g) TEM and (h) HRTEM images of FeOOH nanosheets of CW-FeOOH-4h electrode.

30 / 36


Page 30 of 36

Page 31 of 36 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. Cross-sectional SEM images of CW-FeOOH-4h (a-c) and CW-FeOOH-PEDOT electrode (d-f) with PEDOT polymerization time of 10 min. (g) SEM images and corresponding elemental mapping of CW-FeOOH-PEDOT.

31 / 36



(a)

1347

(b)

1589

S 2p

Intensity (a.u.)

Intensity(a.u.)

439 990

572

174 Fe 2p

171

200

(c)

400

600

168

730

725

720

715

710

705

(d)2.0

40

CW CW−FeOOH-4h CW−FeOOH−PEDOT

1.5

30 Stress (MPa)

23.8 20

1.0

0.5

8.4

10

719.4 eV

Binding Energy(eV)

34.8

-1

735

Raman shift (cm-1)

162 Fe 2p3/2 711.3 eV

725.4 eV

740

1200 1400 1600 1800 2000

165

Fe 2p1/2

856

800 1000

163.9 eV

164.8 eV

732.5 eV 697

S 2p3/2

S 2p1/2 S 2p 168.2 eV

1429

Conductivity (S m )

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 32 of 36

0.0

0 CW

CW −FeOOH-4h CW −FeOOH-PEDOT

0

1

2

3 4 Strain (%)

5

6

7

8

Figure 4. (a) Raman spectrum, (b) S 2p, Fe 2p XPS spectra of CW-FeOOH-PEDOT electrode. (c) Conductivity and (d) stress-strain curves of CW, CW-FeOOH-4h and CW-FeOOH-PEDOT electrodes.

32 / 36


-0.6 -0.8 -1.0

120

1200

Mass contens of FeOOH (mg cm ) -1

Calculated specific capacitance of FeOOH (F g )

100

900

80 600

60 40

300

20

200

400

600

800

Time (s)

1000

1200

0

2 4 6 8 10 Deposition time of FeOOH nanosheets (h)

-1

0

0

(c)100 80

4

1st cycle 5000th cycle

100%

100

85%

80

3

60 40

60

2

40 1 Rct

Rs

20

20

0 0

1

2

3

4

5

Coulombic efficiency (%)

-3 -3

Potential (V vs Ag/AgCl)

-0.4

-3

Volumetric capacitance of CW-FeOOH (F cm ) -3

Intensity (mg cm or F cm )

CW-FeOOH-2h CW-FeOOH-4h CW-FeOOH-6h CW-FeOOH-8h CW-FeOOH-10h CW

-0.2

-Z'' (ohm)

(b) 140

(a)

Specific capacitance of FeOOH (F g )

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


Capacitence retention (%)

Page 33 of 36

Z' (ohm)

0

0 0

1000

2000

3000

4000

5000

Cycle number

Figure 5. (a) Galvanostatic charge-discharge curves of CW-FeOOH-xh with different electrodeposition time of FeOOH. (b) Variation of volumetric capacitance CW-FeOOH-xh, mass loading, and calculated gravimetric capacitance of FeOOH with the deposition time of FeOOH nanosheets. (c) Cycling stability and Coulombic efficiency of CW-FeOOH-4h electrode at 200 mA cm−2 for 5000 cycles. The inset giving the Nyquist plots before and after cycling.

33 / 36



(b) CW-FeOOH-4h

50 CW

0 -50 -100

16 mV

39 mV

47 mV

CW−FeOOH CW−FeOOH−PEDOT

-0.4

-2

10 mA cm

-0.6 -0.8 -1.0

-150 -0.8 -0.6 -0.4 Potential (V vs.Ag/AgCl)

(d) 150

400

800 1200 Time (s)

1600

2000

12

CW

10

CW −FeOOH CW −FeOOH−PEDOT

-Z'' (ohm)

CW CW-FeOOH-4h CW-FeOOH-PEDOT

10

8 6 4

Electrodes CW

1.30

0.41

0.46

2

CW-FeOOH-4h

1.26

1.12

0.70

Rs (ohm) Rct (ohm) W0 (ohm)

CW-FeOOH-PEDOT

1.26

0.36

0.24

10

20

30

40 -2

Current density (mA cm )

50

0

2

4

6

8

1000

1500

2000

100%

100 80 60 40

10

12

Z' (ohm)

14

80

100 50

60 −1

10 mV s

0

40

-50 1st cycle 5000th cycle 10000th cycle

-100

20 -150 -1.2

0

100

103%

150

0

0

0

500

Time (s)

-3

61%

20

0

(f)

81%

90

-0.8

(e) 14 91%

120

-0.6

-1.0 0

-0.2

-0.4

Capacitence retention (%)

-1.0

−2

10 mA cm −2 20 mA cm −2 30 mA cm −2 40 mA cm −2 50 mA cm

2000

-1.0

-0.8 -0.6 -0.4 Potential (V vs.Ag/AgCl)

4000

6000

20

-0.2

8000

Coulombic efficiency (%)

-2


100

(c) -0.2

CW

-0.2

-2

CW-FeOOH-PEDOT


-1

10 mV s


150


(a)

Volumetric capacitance (F cm )

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

Page 34 of 36

0 10000

Cycle number

Figure 6. Comparison of electrochemical performance of CW, CW-FeOOH-4h and CW-FeOOH-PEDOT electrodes in 2.0 M KOH aqueous electrolyte. (a) CV at 10 mV s−1 and (b) galvanostatic charge-discharge profiles at current density of 10 mA cm−2. (c) Galvanostatic charge-discharge curves of the CW-FeOOH-PEDOT electrode at various current densities. (d) Rate performance, (e) Nyquist plots, equivalent

34 / 36


Page 35 of 36 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


circuit used for fitting and the derived parameters Rs, Rct, W0. (f) Cycling stability and Coulombic efficiency of CW-FeOOH-PEDOT electrode at 200 mA cm−2 for 10000 cycles, with inset showing the CV curves at 10 mV s−1 recorded at different cycling stages.

35 / 36



TOC graphic

36 / 36


Page 36 of 36

Enhancing the Capacitive Performance of Carbonized Wood by

Recommend Documents