High-Temperature All Solid-State Microsupercapacitors based on SiC

Nov 16, 2015 - ... at the operation temperature of 450 °C and a scan rate of 200 mV s–1. ... Amit Sanger , Ashwani Kumar , Arvind Kumar , Pawan Kum...
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High-Temperature All Solid-State Microsupercapacitors based on SiC Nanowire Electrode and YSZ Electrolyte Chun-Hui Chang,†,‡ Ben Hsia,† John P. Alper,† Shuang Wang,†,§ Lunet E. Luna,† Carlo Carraro,† Shih-Yuan Lu,*,‡ and Roya Maboudian*,† †

Department of Chemical and Biomolecular Engineering, University of California, Berkeley, California 94720, United States Department of Chemical Engineering, National Tsing-Hua University, Hsinchu 30013, Taiwan § Advanced Institute of Materials Science, Changchun University of Technology, Changchun 130012, China ‡

S Supporting Information *

ABSTRACT: We demonstrate a symmetric supercapacitor by using yttria-stabilized zirconia (YSZ) as the electrolyte and silicon carbide nanowires (SiC NWs) as the electrode. The stacked symmetric SiC NWs/YSZ/SiC NWs supercapacitors exhibit excellent thermal stability and high areal capacitance at temperatures above 300 °C. The supercapacitor functions well at a record high temperature of 450 °C, yielding an areal capacitance of 92 μF cm−2 at a voltage scan rate of 100 mV s−1. At this temperature, it is also capable of withstanding current densities up to 50 μA cm−2, yielding a maximum areal power density of 100 μW cm−2. Good cycling stability is demonstrated with a capacitance retention of over 60% after 10 000 cycles at the operation temperature of 450 °C and a scan rate of 200 mV s−1. KEYWORDS: supercapacitors, solid-state, high temperature, SiC, YSZ

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INTRODUCTION Supercapacitors have attracted much attention as promising energy storage devices due to their high power densities, long cycle life, and fast charge/discharge capability.1 Recently, supercapacitors that can withstand harsh environments such as high temperature (in particular, >300 °C) have received interest due to their relevance for space, military, and electric vehicle applications.2 This motivation has sparked the search for suitable active materials and electrolytes that can work stably and reliably at high temperatures.2−4 Much recent work on supercapacitor electrode materials has focused on high surface area carbon-based nanomaterials such as carbon nanotubes,2,5,6 porous carbon,7−9 and graphene,10,11 in order to achieve high specific capacitance and, hence, energy density. These carbonaceous nanomaterials, however, oxidize at high temperatures in the presence of oxygen.7−9 On the other hand, silicon carbide is known to be stable in many harsh physicochemical environments, including high temperature oxidizing environment.12,13 Silicon carbide (SiC) has already been demonstrated as a feasible supercapacitor electrode material. Sawtooth-like SiC nanostructures with incorporated Ni particles have been shown to provide a specific capacitance of 1780 F g−1.14 For microsupercapacitor electrodes, a SiC passivation layer was shown to mitigate oxidative corrosion of silicon nanowire based electrodes.15 By utilizing high surface area silicon carbide nanowires (SiC NWs), supercapacitor electrodes have been fabricated, yielding areal capacitance of around 240 μF cm−2 in aqueous electrolyte.16 SiC nanowires © XXXX American Chemical Society

thus are a promising candidate as an electrode material for high-temperature solid-state supercapacitors. On the other hand, electrolytes for high-temperature supercapacitor applications must meet the requirements of good thermal stability and high ionic conductivity at high temperatures.3,4 Most modern commercial supercapacitors utilize aqueous or organic liquid based electrolytes. Aqueous electrolytes,17−19 despite functioning well at room temperature, cannot sustain their performances at high temperatures. Organic electrolytes,20−22 dissolved in volatile organic solvents such as acetonitrile, are also limited to moderate operating temperatures. Ionic liquids,3,23−25 ionogels,5,26 polymer composites,27−29 perovskites,30,31 and ceramic electrolytes32−34 have been the subject of recent investigations for electrolytes with increased thermal stability. Nevertheless, it has been found that many room temperature ionic liquids degrade at temperatures above 250 °C.35 On the other hand, yttria-stabilized zirconia (YSZ), a common electrolyte for solid oxide fuel cells,36 is stable at temperatures up to 1200 °C and requires temperatures higher than 300 °C to exhibit reasonable ionic conductivity. Thus, YSZ is a promising solid-state electrolyte candidate with both high ionic conductivity and thermal stability. Solid electrolytes may also minimize some of the problems associated with liquid electrolytes such as electrolyte leakage, corrosion, selfReceived: September 8, 2015 Accepted: November 16, 2015

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DOI: 10.1021/acsami.5b08423 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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Figure 1. Schematics for fabrication of a stacked SiCNWs/YSZ/SiCNWs device. of about 50 °C min−1 to 1000 °C and held there for 1 h to obtain the SiC NWs/YSZ composite. To obtain thicker and more continuous YSZ layers, we repeat the above procedures three more times to acquire the final 4-layer-YSZ/SiC NWs composite. Fabrication of Sandwiched Supercapacitor Structure. A symmetric capacitor is fabricated in a stacked configuration with two SiC NWs electrodes and a YSZ layer in-between as the electrolyte (Figure 1). A YSZ paste is prepared by mixing 0.1 g of YSZ powder with about 0.12 g of a high-temperature Ni-based conductive adhesive paste (Durabond 952). The symmetric capacitor is assembled by coating a thin layer of the YSZ paste onto one of the YSZ-deposited SiC NWs electrode and stacking the other YSZ/SiC NWs electrode on top of it face down. Characterization. The morphologies of the SiC NWs and YSZ coated SiC NWs electrodes are characterized by scanning electron microscopy using a Zesis Gemini Ultra-55 analytical SEM. The YSZ thin film is characterized with Raman spectroscopy and X-ray diffraction (Siemens D5000). The electrochemical performances of the supercapacitor are evaluated using an electrochemical workstation (CH Instruments, 660 D Model) in a two-probe measurement. Alumel wires (Omega #SPAL-010) are contacted with both sides of the fabricated device (Figure 1) using the Durabond adhesive. After 24 h of room temperature curing, the assembled device is introduced into the center of an open-to-air furnace for high-temperature testing under ambient condition. In this work, cyclic voltammetry (CV) is used to determine the areal capacitance at different temperatures within a potential window of −1 to +1 V and a scan rate of 0.1 V s−1. Galvanostatic charging/discharging tests are also conducted from −1 to +1 V and used to compute the energy density (Wh cm−2) and power density (W cm−2) of the supercapacitors at various temperatures. The device stability is evaluated by conducting cyclic voltammetry with a constant scan rate of 0.2 V s−1 at 450 °C for up to 10 000 cycles.

discharge, solvent evaporation, and loss of electrolyte at elevated temperatures.37,38 Here, we demonstrate an all solidstate symmetric supercapacitor, using SiC NW arrays as the electrodes and YSZ as the electrolyte. The SiC NW electrodes are coated with a YSZ film via a sol−gel method. A stacked symmetric supercapacitor based on SiCNWs/YSZ/SiCNWs is assembled and demonstrated to exhibit excellent thermal stability and capacitive performance at temperatures up to 500 °C. This represents the highest operating temperature microsupercapacitor to date. The novel combination of the YSZ electrolyte and the SiC NWs electrode in this study holds promises for high-temperature microsupercapacitor applications.

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EXPERIMENTAL METHODS

Preparation of SiC NWs. The SiC NWs are grown by a Nicatalyzed chemical vapor deposition (CVD) process similar to that reported by Alper et al.42 More specifically, a SiC film is first deposited on a silicon wafer in a low pressure CVD (LPCVD) reactor. The deposition proceeds for an hour at 1200 °C under flow rates of 70 and 0.7 sccm of H2 and methyltrichlorosilane (MTS) precursor, respectively, resulting in a SiC fim thickness of 0.8 μm. A thin layer of nickel (10 nm) is deposited on the SiC coated silicon wafer by ebeam evaporation. This Ni layer acts as the catalyst for the later SiC NWs growth. The Ni deposited samples are placed inside the LPCVD reactor, and the temperature is increased to 950 °C at a rate of about 55 °C min−1 under a flow of 10 sccm of H2. Once the growth temperature is reached, MTS precursor and ammonia (5% in H2) are introduced into the reactor at flow rates of 0.5 and 0.015 sccm, respectively. The NW growth proceeds for 30 min. The pressure is maintained at approximately 4.5−5 Torr throughout the growth process. At the end of the growth, the H2 flow rate is maintained at 10 sccm while the MTS and NH3 flows are stopped and samples are then cooled to room temperature. Preparation of YSZ Films by Sol−Gel Deposition Method. The preparation of YSZ precursor follows the sol−gel procedures detailed in ref 43. Zirconium oxychloride (ZrOCl2·8H2O, Acros Organics, > 98%) and yttrium nitrate (Y(NO3)3·6H2O, Sigma-Aldrich, > 99.8%) are dissolved in a citric acid aqueous solution with citric acid/[ZrOCl2·8H2O]/[Y(NO3)3·6H2O] molar ratio of 108:92:16. For 10 mL of deionized (DI) water, this corresponds to 0.454 g (2.16 mmol) of citric acid monohydrate, 0.593 g (1.84 mmol) of ZrOCl2· 8H2O and 0.123 g (0.32 mmol) of Y(NO3)3·6H2O. The solution is then evaporated at 80 °C to obtain a viscous YSZ precursor. The obtained YSZ precursor liquid (80 μg) is dropped on the prepared SiC NW electrode, wherein it can penetrate between the SiC nanowires. The SiC NWs film/YSZ precursor composites are subsequently dried using a constant temperature hot plate at 40 °C. Afterward, samples are placed into the APCVD reactor and heated in air at a heating rate

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RESULTS AND DISSCUSSION Two substrates have been investigated as electrodes. Smooth Si(100) substrate is studied to focus on the YSZ electrolyte characteristics. High surface area SiC nanowire array grown on SiC-coated Si(100) is studied to examine the effect of enhanced surface area and high-temperature stability. Figure 2a shows the optical image of the YSZ film deposited on SiC nanowire substrate after one cycle of sol−gel treatment. A discontinuous film with cracks is obtained which would lead to electrical short circuiting when the supercapacitor device is assembled. To achieve a continuous YSZ film on the flat substrate, we conduct multiple cycles of the sol−gel treatment, resulting in thicker YSZ films with better substrate-coverage (Figure 2b−d). After the fourth cycle, a continuous YSZ film is obtained (Figure 2d). B

DOI: 10.1021/acsami.5b08423 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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Figure 2. Optical images of YSZ-covered SiC NWs substrates after (a) one, (b) two, (c) three, and (d) four cycles of sol−gel deposition.

This is confirmed by scanning electron micrographs, shown in Figure 3. The cross-sectional SEM images reveal a dense forest of SiC nanowires (Figure 3a). High-resolution transmission electron micrographs of the nanowires grown via the same synthesis method have already been published and indicate that the nanowires grow along the ⟨111⟩-3C axis with a high density of stacking faults. 14 The average length of the NWs is approximately 3 μm. Figure 3b,c shows the morphologies of the YSZ covered SiC NWs substrates, clearly distinguishing the SiC thin film, SiC NWs, and YSZ film. A thick YSZ layer (about 8 μm) is achieved by repeating the sol−gel deposition four times. The YSZ appears to contact much of the SiC NW surface area although some voids are still apparent. All subsequent analyses are carried out employing products obtained from four YSZ deposition cycles. Figure 4 shows the X-ray diffraction spectrum obtained on YSZ/SiC NWs film after 1 h annealing at 1000 °C. The spectrum shows pronounced diffraction peaks at the 2θ values of 30.4, 35.2, 50.5, and 60.2°, indicating crystallization of the YSZ during heat treatment. The diffraction pattern is in good agreement with the database for YSZ (JCPDS 301468), matching well with that of the cubic fluorite-type phase (space group Fm3m) commonly found for fully yttria-stabilized zirconia.39 However, with XRD alone, it is difficult to distinguish between cubic and tetragonal YSZ phases as they share common diffraction patterns.41 Thus, Raman spectroscopy is used as a complementary characterization to confirm the crystalline nature of Y2O3−ZrO2. Figure 5 shows the Raman spectrum recorded for the YSZ films deposited on the SiC NWs grown substrate. The spectrum obtained on the YSZ-deposited Si substrate is essentially the same and, thus, is not shown. There are five dominant peaks, located at 144, 250, 328, 475, and 620 cm−1,

Figure 4. X-ray diffraction pattern of YSZ-covered SiC NWs substrate calcined at 1000 °C in air for 1 h. Red line is based on database XRD pattern of YSZ (JCPDS 301468).

Figure 5. Raman spectrum of YSZ film deposited on SiC NWs grown substrate.

present in the spectrum. These characteristic peaks can be assigned to relevant Raman active modes proposed by Bouvier et al.40 The single peak at 620 cm−1 is due to the F2g symmetric O−Zr−O stretching mode, characteristic of the cubic modification of zirconia,39 whereas the bands located at 143, 250, 328, 475, 603, and 640 cm−1 represent the tetragonal phase. The low symmetry of the tetragonal phase of zirconia results in a large number of Raman-active modes (i.e., Eg, B1g, and A1g). On the basis of the Raman spectrum, it is evident that

Figure 3. Cross-sectional SEM images of as-prepared (a) SiC NWs grown on Si(100) substrate, (b) substrate with one cycle of YSZ deposition, and (c) substrate with four cycles of YSZ deposition. C

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of Si and the degradation of the Si/YSZ interface or Si/Ni contacts. The appreciable difference in thermal expansion coefficients of Si (2.56 × 10−6 K−1) and YSZ (10 × 10−6 K−1) domains might lead to poor adhesion between them with increasing temperature. Nevertheless, the Si/YSZ/Si device is shown to be workable at temperatures up to 500 °C. With the growth of SiC NWs and a subsequent deposition of YSZ on the SiC NWs grown substrate, a stacked SiCNWs/ YSZ/SiCNWs device is fabricated, as described in the Experimental Section. The integration of the SiC NWs is expected to significantly increase the contact area between the electrode and electrolyte, enhancing the magnitude of the electric double layer and thus the areal capacitance. Figure 7a

the deposited and annealed YSZ is a mixture of the tetragonal and cubic phases.39,40 It should be noted that the peaks due to SiC substrates are not observed in the spectrum. As evident from the SEM images (Figure 3), the deposited YSZ films are several microns thick, thus explaining the absence of any contributions from SiC in the Raman spectrum because of the limited sampling depth of the Raman spectroscopy. Cyclic voltammetry (CV) measurements of the stacked Si/ YSZ/Si device at various temperatures are shown in Figure 6a.

Figure 6. (a) Cyclic voltammograms of assembled symmetric capacitor Si/YSZ/Si at different temperatures in a potential window of −1 to 1 V scanned at 100 mV s−1 and (b) areal capacitance vs temperature.

The area enclosed by the CV loops increases as the temperature increases, resulting in an increase in capacitance. The areal capacitance (C) can be calculated via Equation 1, i 1 C= × (1) dV /dt A

Figure 7. (a) Cyclic voltammograms of SiCNWs/YSZ/SiCNWs device at different temperatures at a scan rate of 100 mV s−1 and (b) areal capacitance vs temperature.

where i is the current at V = 0 V during the positive sweep, dV/ dt is the scan rate used for the measurement, and A is the apparent electrode area of 1 × 1 cm. The positive effect of the temperature on the areal capacitance of the Si/YSZ/Si device is clearly illustrated in Figure 6b. This positive temperature effect can be attributed to the increasing ionic conductivity of the YSZ electrolyte with increasing temperature. A maximum areal capacitance of ∼4.7 μF cm−2 is obtained at 500 °C. However, the CV loop of the device becomes somewhat skewed and shows a peak during the negative sweep for temperatures above 450 °C. This behavior may be caused by the possible oxidation

shows the cyclic voltammograms of the device at varied temperatures. The areal capacitance of the SiCNWs/YSZ/ SiCNWs supercapacitor is measured to be roughly 30 times that of the Si/YSZ/Si supercapacitor. The capacitances generated in the present system are due to the electric double layer formation, and thus, the values are proportional to the electrode surface area. One can estimate the total surface area offered by the SiC NWs from the cross-sectional SEM images, as shown in Figure 3a. The nanowire number density, nNW, is estimated to be ∼6.4 × 109 per cm2 chip area. Additionally, the average NW diameter, d, and length, h, based on the crossD

DOI: 10.1021/acsami.5b08423 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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constant temperature of 450 °C. Quasi-linear and quasisymmetric charge/discharge curves are observed for all tested cases, and an average Coulombic efficiency of 98% is obtained from these measurements. The equivalent series resistance (ESR) of the device can be obtained by estimating the IR drop at the beginning of the discharging. The average ESR for all cases tested at 450 °C is about 47 kΩ cm2, for current densities ranging from 0.2 to 1.2 μA cm−2. The ESR is large enough to lead to a significant decline in capacitance with increasing current densities. Figure 8b shows the galvanostatic charge/ discharge curves for the Si/YSZ/Si device measured at varied temperatures. It is evident that as the operation temperature increases, the discharge time increases and the IR drop decreases and hence the ESR of the device decreases. The estimated ESR values are 490, 85, and 50 kΩ cm2 for the operation temperatures of 300, 400, and 450 °C, respectively, at a current density of 0.5 μA cm−2. The result demonstrates that the ion diffusion rate is enhanced at high temperatures, allowing for increased charge storage. Galvanostatic charge/discharge curves of the SiCNWs/YSZ/ SiCNWs device at 450 °C under increasing current densities are presented in Figure 9a. The curves under high current densities are quite linear, an expected characteristic for a good capacitor. At the current density of 50 μA cm−2, the charge/ discharge curve shows excellent symmetry and exhibits Coulombic efficiency of essentially 100%. The galvanostatic charge/discharge curves recorded at varied temperatures under a current density of 10 μA cm−2 are shown in Figure 9b. The discharge time increases and IR drop decreases with increasing temperature (ESR = 76, 25, and 12 kΩ cm2 for 300, 400, and 450 °C, respectively, at a current density of 10 μA cm−2). Thus, the areal capacitance values increase. This result can be attributed again to the high charge conductivity acquired at high temperatures for the YSZ electrolyte. Electrochemical impedance spectroscopy is also conducted to investigate the impedance of the devices. The result is shown in Figure S1. Evidently, with increasing operation temperature, the electrochemical impedance spectra approach the characteristics of a simple RC circuit, a vertical line intercepting the real axis, Z′, at R. A simple RC circuit is an ideal capacitor circuit, containing no interfacial impedances in the system. This phenomenon agrees well with the trend we observe in ESR with increasing operation temperature. The average equivalent series resistance at 450 °C is about 12 kΩ cm2 for current densities ranging from 5 to 50 μA cm−2. Such a large ESR value leads to a significant decrease in capacitance with increasing current densities, as shown in Figure 9c. For practical energy storage devices, high energy and power densities are desired. The areal energy density, E (J cm−2), and power density, P (W cm−2), are calculated from the discharge curve according to eqs 3 and 4, respectively:

sectional SEM images are 0.05 and 3 μm, respectively. The total surface area of the SiC NW electrode, Atotal, is then estimated by eq 2, A total = πdh × nNW

(2)

yielding the value of ∼30 cm2 per square centimeter (cm2) of chip area. This estimated surface area is consistent with the increased capacitance reported with the integration of the SiC NWs. The CV loops exhibit an increase in loop area with increasing temperature, attributable to higher conductivities of the YSZ at high temperatures (≥300 °C). Figure 7b shows that the areal capacitance of the SiCNWs/YSZ/SiCNWs device exhibits a considerable increase as the operation temperature is increased, corresponding to more than 35 times increase from room temperature (20 °C) to 500 °C. The areal capacitance of 147 μF cm−2 at 500 °C compares well to the values (∼240 μF cm−2) obtained on SiC NWs electrodes in aqueous electrolyte at room temperature using three-electrode geometry.16 This further confirms good coverage of the SiC NWs with the YSZ electrolyte. Figure 8a shows the galvanostatic charge/discharge curves for the Si/YSZ/Si device under varied current densities at a

E=

1 2 CV 2

(3)

P=

E Δt

(4)

where C is the areal capacitance (F cm−2) calculated from the galvanostatic charge/discharge tests, V is the maximum voltage window (V), and Δt is the discharge time (s). For comparison to the literature, the areal energy density is converted to be in the units of Wh cm−2. A Ragone plot of the specific energy density versus specific power density for the SiCNWs/YSZ/

Figure 8. Galvanostatic charge/discharge curves for Si/YSZ/Si devices: (a) under increasing current densities from 0.2 to 1.5 μA cm−2 at 450 °C, (b) under increasing temperatures from 300 to 450 °C at constant current density of 0.5 μA cm−2. E

DOI: 10.1021/acsami.5b08423 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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Figure 10. (a) Ragone plot of SiCNWs/YSZ/SiCNWs devices at 300, 400, and 450 °C. (b) Ragone plot of both Si/YSZ/Si and SiCNWs/ YSZ/SiCNWs devices at 450 °C.

NWs can be clearly seen from Figure 10b. Both energy and power densities are improved by more than 1 order of magnitude because of the integration of the SiC NWs. Long cycle life is one key advantage of supercapacitors over batteries. To test the cycling stability of an electrode material or device, we performed repetitive charge/discharge cycles using CV scans over the full 2 V voltage window at a scan rate of 0.2 V s−1 and at a temperature of 450 °C (Figure 11). The SiCNWs/YSZ/SiCNWs devices retain 60% of their initial capacitance after 10 000 cycles, revealing excellent stability of the electrode material and YSZ electrolyte, considering the high operation temperature of 450 °C. The performance appears to degrade and then stabilize toward the end of the cycling test. Referring to literature,3 the capacitance retention is also ∼60% when using a 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsuphonyl)imide electrolyte and reduced graphene oxide electrodes. However, the result from the literature is achieved at a temperature of 200 °C, while this work demonstrates a similar capacitance retention at 450 °C. The inset shows the CV loops recorded at the first and 10 000th cycles, clearly illustrating that even though only 60% of the areal capacitance remains after 10 000 cycles, a more rectangular and less skewed CV loop is obtained. On the basis of the similarity between the irreversible peaks at the extrema of the initial cycle CV in the current work and in ref 3,

Figure 9. Galvanostatic charge/discharge curves for SiCNWs/YSZ/ SiCNWs devices (a) with increasing current densities from 8 to 50 μA cm−2 at 450 °C and (b) with increasing temperatures from 300 to 450 °C under a current density of 10 μA cm−2. (c) Capacitance as a function of current density at 450 °C normalized to the capacitance at 10 μA cm−2.

SiCNWs device operated at 300, 400, and 450 °C is shown in Figure 10a. Generally, there is a trade-off between the energy density and power density in electrochemical energy storage devices, as evident from Figure 10a. Also evident from Figure 10a is that both energy and power densities are improved when the operation temperature increases. Furthermore, the effect of the enlarged electrode surface through the incorporation of SiC F

DOI: 10.1021/acsami.5b08423 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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Research Article

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is financially supported by National Science Foundation under grant DMR-1207053 and DARPA Science and Technology Centre, CIEMS. B.H. and L.E.L. acknowledge additional support through NSF graduate fellowships. The work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC0205CH11231. C.H.C. acknowledges the National Tsing-Hua University, Taiwan, for sponsoring her one-year visit at the Department of Chemical and Biomolecular Engineering, University of California, Berkeley, in Berkeley, CA.

Figure 11. Cycling stability test of SiCNWs/YSZ/SiCNWs at 450 °C at scan rate of 200 mV s−1 for 10 000 cycles by cyclic voltammetry measurements.

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we conclude that electrochemical degradation is the cause of capacitance fade during the initial cycles in this device as well. The absence of large irreversible peaks in the CV after 10 000 cycles and the stabilizing of the capacitance are further evidence for this conclusion.

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CONCLUSIONS

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ASSOCIATED CONTENT

REFERENCES

(1) Kötz, R.; Carlen, M. Principles and Applications of Electrochemical Capacitors. Electrochim. Acta 2000, 45, 2483−2498. (2) Masarapu, C.; Zeng, H. F.; Hung, K. H.; Wei, B. Effect of Temperature on the Capacitance of Carbon Nanotube Supercapacitors. ACS Nano 2009, 3, 2199−2206. (3) Borges, R. S.; Reddy, A. L. M.; Rodrigues, M. T. F.; Gullapalli, H.; Balakrishnan, K.; Silva, G. G.; Ajayan, P. M. Supercapacitor Operating at 200 Degrees Celsius. Sci. Rep. 2013, 3, 2572. (4) Hibino, T.; Kobayashi, K.; Nagao, M.; Kawasaki, S. HighTemperature Supercapacitor with a Proton-Conducting Metal Pyrophosphate Electrolyte. Sci. Rep. 2015, 5, 7903. (5) Pan, H.; Li, J.; Feng, Y. P. Carbon Nanotubes for Supercapacitor. Nanoscale Res. Lett. 2010, 5, 654−668. (6) Hsia, B.; Marschewski, J.; Wang, S.; In, J. B.; Carraro, C.; Poulikakos, D.; Maboudian, R.; Grigoropoulos, C. P. Highly Flexible, All Solid-State Micro-Supercapacitors from Vertically Aligned Carbon Nanotubes. Nanotechnology 2014, 25, 055401. (7) Hsia, B.; Kim, M. S.; Vincent, M.; Carraro, C.; Maboudian, R. Photoresist-Derived Porous Carbon for On-Chip Micro-Supercapacitors. Carbon 2013, 57, 395−400. (8) Chmiola, J.; Largeot, C.; Taberna, P. L.; Simon, P.; Gogotsi, Y. Monolithic Carbide-Derived Carbon Films for Micro-Supercapacitors. Science 2010, 328, 480−483. (9) Pech, D.; Brunet, M.; Durou, H.; Huang, P.; Mochalin, V.; Gogotsi, Y.; Simon, P.; Taberna, P.-L. Ultrahigh-Power MicrometreSized Supercapacitors based on Onion-like Carbon. Nat. Nanotechnol. 2010, 5, 651−654. (10) Hsia, B.; Kim, M. S.; Luna, L. E.; Mair, N. R.; Kim, Y.; Carraro, C.; Maboudian, R. Templated 3D Ultrathin CVD Graphite Networks with Controllable Geometry: Synthesis and Application as Supercapacitor Electrodes. ACS Appl. Mater. Interfaces 2014, 6, 18413− 18417. (11) Fu, C.; Kuang, Y.; Huang, Z.; Wang, X.; Yin, Y.; Chen, J.; Zhou, H. Supercapacitor based on Graphene and Ionic Liquid Electrolyte. J. Solid State Electrochem. 2011, 15, 2581−2585. (12) Maboudian, R.; Carraro, C.; Senesky, D. G.; Roper, C. S. Advances in Silicon Carbide Science and Technology at the Microand-Nanoscales. J. Vac. Sci. Technol., A 2013, 31, 050805. (13) Senesky, D. G.; Jamshidi, B.; Cheng, K. B.; Pisano, A. P. Harsh Environment Silicon Carbide Sensors for Health and Performance Monitoring of Aerospace Systems: A Review. IEEE Sens. J. 2009, 9, 1472−1478. (14) Xie, S.; Guo, X. N.; Jin, G. Q.; Tong, X. L.; Wang, Y. Y.; Guo, X. Y. In Situ Grafted Carbon on Sawtooth-like SiC Supported Ni for

In summary, a high temperature all solid-state supercapacitor has been successfully fabricated using YSZ as the electrolyte and SiC NWs as the electrode. The SiNWs/YSZ/SiNW supercapacitor has been demonstrated to be operational up to 500 °C and exhibits excellent thermal stability and good capacitive performances at temperatures above 300 °C. A high areal capacitance of 147 μF cm−2 is obtained at 500 °C with integration of the high surface area SiC NWs in the electrode. While this capacitance value may be modest when compared to other nanowire-based microsupercapacitor electrodes mentioned above, as the highest temperature stable configuration to date, it shows promise in fulfilling the niche energy needs of extreme environment remote sensors, as desired in deep oil well drilling, military operations, and other applications.2−4,13 Furthermore, as capacitance scales linearly with electrode− electrolyte interfacial area, work is ongoing to optimize techniques to achieve conformal YSZ coverage over longer SiC NW arrays. The stability of the device is also reflected in its long-term cycling test, surviving up to 10 000 cycles at 450 °C. This novel combination of SiC NWs electrode and solid-state YSZ electrolyte achieves a drastic boost in operation temperature of the supercapacitor, and demonstrates promising potential for high temperature supercapacitor applications.

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.5b08423. Electrochemical impedance spectroscopy conducted for SiCNWs/YSZ/SiCNWs devices operated at 400, 450, and 500 °C. (PDF) G

DOI: 10.1021/acsami.5b08423 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

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DOI: 10.1021/acsami.5b08423 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX