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Article

Time Evolution Characterization of Atmospheric-Pressure Plasma Jet (APPJ)-Synthesized Pt-SnOx Catalysts

by
Chia-Chun Lee
1,
Tzu-Ming Huang
1,2,
I-Chun Cheng
3,4,*,
Cheng-Che Hsu
5,* and
Jian-Zhang Chen
1,2,*
1
Graduate Institute of Applied Mechanics, National Taiwan University, Taipei 10617, Taiwan
2
Advanced Research Center for Green Materials Science and Technology, National Taiwan University, Taipei 10617, Taiwan
3
Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei 10617, Taiwan
4
Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan
5
Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan
*
Authors to whom correspondence should be addressed.
Metals 2018, 8(9), 690; https://doi.org/10.3390/met8090690
Submission received: 17 August 2018 / Revised: 29 August 2018 / Accepted: 29 August 2018 / Published: 1 September 2018
(This article belongs to the Special Issue Plasmas Processes Applied on Metals and Alloys)
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Abstract

:
We characterize the time evolution (≤120 s) of atmospheric-pressure plasma jet (APPJ)-synthesized Pt-SnOx catalysts. A mixture precursor solution consisting of chloroplatinic acid and tin(II) chloride is spin-coated on fluorine-doped tin oxide (FTO) glass substrates, following which APPJ is used for converting the spin-coated precursors. X-ray photoelectron spectroscopy (XPS) indicates the conversion of a large portion of metallic Pt and a small portion of metallic Sn (most Sn is in oxidation states) from the precursors with 120 s APPJ processing. The dye-sensitized solar cell (DSSC) efficiency with APPJ-synthesized Pt-SnOx CEs is improved greatly with only 5 s of APPJ processing. Electrochemical impedance spectroscopy (EIS) and Tafel experiments confirm the catalytic activities of Pt-SnOx catalysts. The DSSC performance can be improved with a short APPJ processing time, suggesting that a DC-pulse nitrogen APPJ can be an efficient tool for rapidly synthesizing catalytic Pt-SnOx counter electrodes (CEs) for DSSCs.

Graphical Abstract

1. Introduction

Atmospheric-pressure plasma (APP) technology is operated without using a vacuum chamber and associated pumping system. It is therefore considered a cost-effective manufacturing tool. Recent developments have resolved stability and arcing problems, making APP technology promising for industrial applications. Traditional APP sources include transferred arc, corona discharge, dielectric barrier discharge, and atmospheric pressure plasma jet (APPJs) [1,2]. APPs with various heavy particle temperatures and charge densities can be produced by using different excitation methods and electrode configuration designs. The synergy between the reactive plasma species and heat can promote rapid chemical reactions during material processing [3,4,5,6]. APPs have been used for processing various types of materials, such as carbon nanotubes [3,7,8] and reduced graphene oxides [9,10,11]. Applications of APPs for surface cleaning or modification [12,13,14], deposition of metal oxides [15,16], and syntheses of metal compounds from liquid precursors [6,17,18] have been extensively investigated. Metals and metal oxides are common catalysts [19,20,21,22,23,24]. APPs also have been used for syntheses and post-treatments of catalysts [25].
In 1991, Grätzel et al. reported a great breakthrough of DSSCs [26], and since then, dye-sensitized solar cells (DSSCs) have been extensively investigated. A conventional DSSC consists of a dye-adsorbed photoanode, an electrolyte, and a counter electrode (CE). A catalytic CE is used for reducing triiodide into iodine in the electrolyte. Generally, Pt is the most commonly used CE material in DSSC, owing to its high catalytic activity and stability [27]. Various alternative CE materials such as carbon-based materials, metal oxides or chalcogenides, and alloys or intermetallics have been studied extensively [3,5,28,29,30,31,32,33,34,35,36]. Composites containing Pt and Sn have been used as electrocatalysts for CEs of DSSCs [36,37], methanol or ethanol oxidation [38,39,40,41,42,43,44], aqueous phase oxidation [45], and gas sensing [46]. The addition of metal oxides has been reported to improve the catalytic activity [40,47]. Pt:SnO2 electrocatalytic films were used as CEs of DSSCs [48]. Dao et al. fabricated DSSCs with a PtSn alloy supported by reduced graphene oxides via dry plasma reduction [36]. In the present study, Pt-SnOx composites were synthesized by mixing chloroplatinic acid and tin(II) chloride that were processed using a DC-pulse nitrogen APPJ. X-ray photoelectron spectroscopy (XPS) results showed that the majority of Sn was in the oxidation state. The DSSC efficiency can be improved rapidly through 5 s APPJ processing of the chloroplatinic acid and tin(II) chloride mixture precursor; no metallic Pt was converted within such a short processing time. This suggests the catalytic effect of oxidized Pt and Sn compounds. A DSSC with a 120 s APPJ-processed Pt-SnOx CE shows efficiency comparable to that of a cell with a furnace-processed Pt CE.

2. Materials and Methods

2.1. Preparation of Pt-SnOx CEs

25-mM chloroplatinic acid (H2PtCl6) (purity: 99.95%, Uniregion Biotech, Taipei, Taiwan) and 25-mM tin(II) chloride (SnCl2) isopropanol solutions were separately stirred for 24 h. These two solutions were mixed with the same volume ratios and were stirred using a magnetic stirrer (PC-420D, Corning Inc., Corning, NY, USA)for another 24 h. Next, 60 μL of the mixture precursor was spin-coated onto fluorine-doped tin oxide (FTO) substrates with an area of 1.5 cm × 1.5 cm at a speed of 1000 rpm for 15 s. The spin-coated precursors were then processed by a nitrogen APPJ for 5, 15, 30, 60, and 120 s. Figure 1a shows the APPJ setup. The operation parameters are as follows: nitrogen flow of 46 standard liter per minute (slm), power supply voltage of 275 V, and ON/OFF duty cycle of 7/33 μs. The temperature evolution of the substrates, shown in Figure 1b, was measured using a K-type thermocouple (OMEGA Engineering, Norwalk, CT, USA). The temperature rapidly increased to ~510 °C, and it dramatically decreased after the APPJ was turned off. Because our process is conducted at ~510 °C, we use FTO glass substrates (Sigma-Aldrich, St. Louis, MO, USA) which can tolerate a higher processing temperature.

2.2. Preparation of TiO2 Photoanode and Assembly of DSSCs

The photoanode consists of a TiO2 compact layer and a TiO2 nanoporous layer for dye adsorption. First, a 0.23-M titanium isopropoxide solution (Fluka, St. Louis, MO, USA) was spin-coated on a FTO substrate and then baked at 200 °C for 10 min to form a TiO2 compact layer to prevent electron recombination. Then, 1.6 g of TiO2 nanoparticles (diameter: ~21 nm), 8 mL of ethanol, 6.49 g of terpineol (anhydrous, #86480, Fluka, St. Louis, MO, USA), 4.5 g of 10 wt % ethyl cellulose ethanolic solution (5–15 mPa·s, #46070, Fluka, St. Louis, MO, USA), and 3.5 g of 10 wt % ethyl cellulose ethanolic solution (30–50 mPa·s, #46080, Fluka, St. Louis, MO, USA) were mixed together. Next, a 0.4 g mixture containing TiO2 was mixed with 500 μL of ethanol and stirred using a magnetic stirrer for 24 h. The mixed solution was baked at 53 °C until its weight became 0.175 g, thus completing the preparation of the TiO2 pastes. The TiO2 pastes were screen-printed onto the TiO2 compact layer coated FTO substrate with a printed area of 0.5 cm × 0.5 cm. The screen-printed pastes were calcined at 510 °C for 15 min in a conventional furnace to form the TiO2 photoanode. Next, the TiO2 photoanode was immersed in a 0.3-mM N719 solution, which is mixed with acetonitrile and tertbutyl alcohol in a 1:1 volume ratio for 24 h. This completed the preparation of the dye-anchored nanoporous TiO2 photoanodes.
The Pt-SnOx CEs and dye-anchored TiO2 photoanodes were assembled with a 25-μm-thick spacer to form sandwich-structure DSSCs. Then, a commercial electrolyte (E-Solar EL 200, Everlight Chemical Industrial Co., Taipei, Taiwan) was injected into the solar cells.
Counterpart DSSC with furnace-processed Pt CE was fabricated for comparison. In this case, 60 μL of 25-mM H2PtCl6 isopropanol solution was spin-coated on the FTO substrate and calcined at 400 °C for 15 min using a tube furnace. The assembly procedure of DSSC with furnace-processed Pt CE is the same as that of DSSC with APPJ-processed Pt-SnOx CE.

2.3. Characterization of Materials and DSSCs

During the APPJ reduction processes, a spectrometer (USB4000, Ocean Optics, Largo, FL, USA) was used for monitoring the plasma optical emission spectra (OES). Pt-SnOx nanoparticles were inspected using a scanning electron microscope (SEM, JSM-7800F Prime, JEOL, Tokyo, Japan) with an energy-dispersive spectroscopy (EDS) attachment. To investigate the chemical configuration of Pt-SnOx, XPS (Thermo K-Alpha, VGS, Waltham, MA, USA was used for analyzing the binding status. The C1s core level was centered at 284.6 eV to calibrate the binding energy scale. XPSPEAK 4.1 software (was used for fitting binding energy positions. XPS samples were prepared with Corning glass substrates instead of FTO glass ones to avoid the interference of Sn signals emitted from FTO substrates. To examine the electrochemical catalytic activities of Pt-SnOx CEs, electrochemical impedance spectroscopy (EIS) and Tafel measurements were performed using an electrochemical workstation (PGSTAT204, Metrohm Autolab, Herisau, Switzerland). EIS measurements were performed with a sinusoidal amplitude of 10 mV with frequencies of 0.1‒105 Hz, and the data were fitted using Z-view 3.1 software. Tafel curves were recorded from −0.6 V to 0.6 V at a scan rate of 50 mV/s. Both measurements were performed on a symmetrical cell with two equal Pt-SnOx CEs. A solar simulator (WXS-155S-L2, WACOM, Saitama, Japan) with an AM 1.5 filter equipped with an electrometer (Keithley 2440, Tektronix, Beaverton, OR, USA) was used for measuring the photocurrent-voltage characteristics of the DSSCs.

3. Results and Discussion

Figure 2a shows the plasma OES evolution during APPJ processing of the mixed H2PtCl6/SnCl2 precursor. NOγ, NOβ, N2 1st positive, and N2 2nd positive emissions were observed clearly during 120 s APPJ processes. Figure 2b shows the plasma spectra when processing H2PtCl6, SnCl2, and mixed H2PtCl6/SnCl2 precursors on the FTO substrates. The NOγ system (A2Σ+-X2Π) is located at wavelengths lower than 280 nm. The NOβ system (B2Π-X2Π) is located from around 260 to 500 nm, and it partially overlaps the NOγsystem. The other emissions at 357, 385, and 389 nm were attributed to the N2 2nd positive system (C3Πu-B3Πg); these overlap with the NOβ system. The N2 1st positive system (B3Πg-A3Σu+) was located at wavelengths higher than 530 nm.
Figure 3a–e shows the SEM images of Pt-SnOx nanoparticles converted from mixed H2PtCl6/SnCl2 precursors on the FTO glass substrates using various APPJ processing times. The nanoparticle size and morphology remained similar for APPJ processing times of 5‒120 s. Figure 3f shows EDS results for the 120 s and APPJ-processed sample. Pt and Sn signals indicate the presence of two elements in the nanoparticles. Both of Sn and O signals could result from the nanoparticles and the FTO substrates.
To identify the chemical states of Pt-SnOx compounds, Figure 4a,b shows the XPS spectra of Pt4f and Sn3d for samples. The Pt4f spectrum can be deconvoluted into three components including Pt, Pt2+, and Pt4+. The metallic peaks of Pt are located at 71.30 and 74.65 eV, Pt(II) components are located at 72.70 and 76.50 eV, and Pt(IV) components are located at 73.80 and 77.15 eV [49,50]. In Figure 4a, the major peaks belong to Pt2+ and Pt4+ for as-deposited and 5 and 15 s APPJ-processed samples. These results indicate that most of the H2PtCl6/SnCl2 precursor was not converted to metallic Pt by APPJ processing for less than 15 s. As the APPJ processing time increases, increased conversion of precursors into metallic Pt was clearly observed. The Pt2+ signal is noted as the oxidation state of Pt, and it could indicate PtO [51,52] or Pt(OH)2 [53]. The presence of Pt oxidation states, due to the interaction with the Pt-support, is attributed to an electronic effect or oxygen absorption from air [54,55]. Figure 4b shows the oxidation state of Sn3d under various APPJ processing times. The binding energy of Sn3d can be deconvoluted into two categories: one at 485.8 and 494.2 eV for the zero-valent state of Sn, and the other at 487.3 and 495.7 eV for Sn(II/IV) components [56]. The major peak is attributed to the oxidation state of Sn for up to 120 s, and the percentage of metallic Sn increased only slightly increased with the APPJ processing time. Sn(II) and Sn(IV) species are difficult to distinguish from XPS measurements because of the small difference between their binding energies [57,58]. Table 1 and Table 2 show the percentages of Pt and Sn species, respectively. The Pt-support interaction may influence charge transfer from Pt to oxygen species on the surface and improve the electrochemical catalytic abilities and catalyst stability [47].
Figure 5a,b shows the EIS Nyquist and Bode phase plots to evaluate the catalytic activities of APPJ-processed Pt-SnOx CEs. The inset of Figure 5a shows the equivalent circuit for Nyquist curve fitting [59]. The series resistance (Rs) and charge-transfer resistance (Rct) can be described as the resistance of substrates and the catalytic effect of the electrode-reducing triiodide ions, respectively. Rs can be obtained from the high-frequency intercept on the real axis and Rct, from the radius of the real semi-circle [60]. Table 3 shows the EIS parameters including Rs, Rct, and constant phase element (CPE1) [29]. A higher catalytic effect and lower charge-transfer resistance would improve the DSSC performance. For all cases, Rs of Pt-SnOx CEs remained similar. Rct generally decreased (i.e., semi-circle became smaller) as the APPJ processing time increased, indicating that APPJ processing can enhance the catalytic activity. Rct was comparable for APPJ processing times of 60 s (4.72 Ω) and 120 s (4.69 Ω). Lower Rct results in a higher electrocatalytic activity at the interface between the CEs and the electrolytes [61]. CPE1, which represents the interfacial capacitance between the electrode and the electrolyte, is also a good indicator of the surface activity of CEs [62,63,64]. The 120 s APPJ-processed CEs had a higher CPE1-T (105.5 μF/cm2), indicating larger surface reaction between the CE and the electrolyte. Bode phase plots show the electron lifetime for recombination in devices; the electron lifetime is expressed as τe = 1/(2πfpeak), where fpeak is the frequency of the highest peak. Shorter electron lifetime indicates faster charge transfer at the interface between the CE and the electrolyte [64,65]. In Figure 5b, the trend of the electron lifetime follows the EIS results. The 5 s APPJ-processed CE has the smallest peak frequency, indicating the largest electron lifetime with slower charge transfer. Furthermore, electron lifetimes are comparable in 60 s and 120 s APPJ-processed CEs, and this is consistent with the results for Rct.
To further clarify the catalytic activities of Pt-SnOx CEs, Tafel polarization experiments were conducted and the results are shown in Figure 6. The exchange current density (J0) was measured by the intercept of the Y-axis (zero voltage) from the tangential line of the curve [66,67]. The 120 s APPJ-processed CEs had a large J0, indicating better electrocatalyic activity and lower charge-transfer resistance at the interface of the CE and the electrolyte. Table 3 shows that J0 increases with the APPJ processing time. APPJ processes enhanced the triiodide reduction reaction [60]. The exchange current density is also proportional to Rct obtained from the EIS measurement. It can be described as J0 = RT/nFRct, where R is a gas constant; T is temperature; n is the number of electrons involved in the redox reaction; and F is the Faraday’s constant [68]. EIS and Tafel measurements both indicate that APPJ-processed Pt-SnOx elecrodes show suitable catalytic performance for use as the CEs of DSSCs. J0 increases with the APPJ processing time, indicating that APPJ processing can enhance the catalyst activity of Pt-SnOx.
Figure 7 shows the IV curves of DSSCs with APPJ-processed Pt-SnOx CEs. Table 4 shows the photovoltaic parameters, including the open-circuit voltage (Voc), short-circuit current (Jsc), fill factor (FF), and efficiency (EFF) with their standard deviations. The power conversion efficiencies (PCEs) of DSSCs with 5 s and 15 s APPJ-processed Pt-SnOx CEs are 3.87 ± 0.58% and 3.86 ± 0.28%, respectively, indicating that APPJ processing for a short duration can improve the DSSC performance. XPS results show that almost no metallic Pt was converted with 5 s and 15 s APPJ processing, indicating the catalytic effect of oxidized Pt and Sn compound CEs in DSSCs, and this agrees with previous reported findings [30,32]. As the APPJ treatment time increases, the PCE of DSSCs with 30 s, 60 s, and 120 s APPJ-processed CEs reaches 4.01 ± 0.34%, 4.20 ± 0.41%, and 4.46 ± 0.29%, respectively. The performance of DSSC with a 120 s APPJ-processed Pt-SnOx CE was comparable to that with a conventional furnace-processed Pt CE (4.42 ± 0.26%). Figure 8 shows the statistics of the DSSC parameters. APPJ processing gradually increased the FFs and PCEs of DSSCs, consistent with the results obtained from EIS and Tafel measurement. The improved FF and efficiency with APPJ processing time could result from the better conversion of metallic Pt from the precursor solution.

4. Conclusions

We analyze the time evolution of Pt-SnOx nanoparticle catalysts that are converted from a mixture of chloroplatinic acid and tin(II) chloride using DC-pulse nitrogen APPJ. XPS analyses indicate the conversion of a large portion of the metallic Pt and tin oxide. EIS and Tafel measurements indicate improved electrochemical catalytic effects. The synthesized Pt-SnOx nanoparticles on FTO glass substrates are used as the CEs of DSSCs. The I-V curve shows that the performance of DSSCs with APPJ-processed Pt-SnOx CEs is comparable to that of DSSCs with conventional furnace-processed Pt CEs. As the APPJ processing time is increased, the FF and efficiency of DSSCs gradually increase. Our results show that a DC-pulse nitrogen APPJ is an efficient tool for synthesizing Pt-SnOx catalysts from a mixture precursor solution consisting of chloroplatinic acid and tin(II) chloride.

Author Contributions

C.-C.L. performed the experiments, analyzed the data, and wrote the paper draft. T.-M.H. assisted in conducting experiments. I.-C.C. and C.-C.H. assisted in instructing the research and analyzing the data. J.-Z.C. directed the research direction, analyzed the data, and revised the paper. All authors commented on the manuscript.

Funding

This work is supported by the “Advanced Research Center for Green Materials Science and Technology” from The Featured Area Research Center Program of the Higher Education Sprout Project by the Ministry of Education (107L9006) and the Ministry of Science and Technology in Taiwan (MOST 105-2221-E-002-047-MY3, MOST 106-2221-E-002-193-MY2 & MOST 107-3017-F-002-001).

Acknowledgments

The cleanroom facility is provided by the Nano-Electro-Mechanical-Systems (NEMS) Research Center at National Taiwan University. Yuan-Tzu Lee of the Instrumentation Center at National Taiwan University helps with the SEM operation.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. (a) Schematic of APPJ setup; (b) Temperature evolution of substrate during APPJ treatment.
Figure 1. (a) Schematic of APPJ setup; (b) Temperature evolution of substrate during APPJ treatment.
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Figure 2. (a) OES evolution during APPJ processing of mixed H2PtCl6/SnCl2 precursors. (b) OES when processing H2PtCl6, SnCl2, and mixed H2PtCl6/SnCl2 precursors using nitrogen APPJ.
Figure 2. (a) OES evolution during APPJ processing of mixed H2PtCl6/SnCl2 precursors. (b) OES when processing H2PtCl6, SnCl2, and mixed H2PtCl6/SnCl2 precursors using nitrogen APPJ.
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Figure 3. Scanning electron microscope (SEM) images of samples processed by APPJ for various durations: (a) 5 s, (b) 15 s, (c) 30 s, (d) 60 s, and (e) 120 s. (f) Energy-dispersive spectroscopy (EDS) spectrum of nanoparticles converted from H2PtCl6/SnCl2 precursors on FTO glass substrates using 120 s APPJ processing.
Figure 3. Scanning electron microscope (SEM) images of samples processed by APPJ for various durations: (a) 5 s, (b) 15 s, (c) 30 s, (d) 60 s, and (e) 120 s. (f) Energy-dispersive spectroscopy (EDS) spectrum of nanoparticles converted from H2PtCl6/SnCl2 precursors on FTO glass substrates using 120 s APPJ processing.
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Figure 4. X-ray photoelectron spectroscopy (XPS) spectra of (a) Pt4f and (b) Sn3d for samples processed by APPJ for various durations.
Figure 4. X-ray photoelectron spectroscopy (XPS) spectra of (a) Pt4f and (b) Sn3d for samples processed by APPJ for various durations.
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Figure 5. (a) Nyquist curves of symmetric cells with two Pt-SnOx CEs. The inset shows the equivalent circuit diagram. (b) Bode phase plots of symmetric cells with two Pt-SnOx CEs.
Figure 5. (a) Nyquist curves of symmetric cells with two Pt-SnOx CEs. The inset shows the equivalent circuit diagram. (b) Bode phase plots of symmetric cells with two Pt-SnOx CEs.
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Figure 6. Tafel curves of symmetric cells with various Pt-SnOx CEs.
Figure 6. Tafel curves of symmetric cells with various Pt-SnOx CEs.
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Figure 7. Photocurrent density-voltage curves of DSSCs with various CEs.
Figure 7. Photocurrent density-voltage curves of DSSCs with various CEs.
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Figure 8. Statistics of DSSC parameters based on APPJ-processed Pt-SnOx CEs and furnace-processed Pt CE (reference).
Figure 8. Statistics of DSSC parameters based on APPJ-processed Pt-SnOx CEs and furnace-processed Pt CE (reference).
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Table
Table 1. Percentage of Pt species obtained from XPS analysis.
Table 1. Percentage of Pt species obtained from XPS analysis.
APPJ Pt4f (%)Pt 7/2Pt 5/2Pt(II) 7/2Pt(II) 5/2Pt(IV) 7/2Pt(IV) 5/2
0 s--39.1932.3417.9010.58
5 s--46.1737.9410.904.99
15 s--48.8736.2910.873.97
30 s3.724.3839.1628.5214.399.82
60 s1.8714.3438.0435.641.808.31
120 s22.6628.7220.4615.212.6910.26
Table
Table 2. Percentage of Sn species obtained from XPS analysis.
Table 2. Percentage of Sn species obtained from XPS analysis.
APPJ Sn3d (%)Sn 5/2Sn 3/2Sn(II/IV) 5/2Sn(II/IV) 3/2
0 s--60.1939.81
5 s1.130.3658.3340.19
15 s2.211.3156.9539.53
30 s4.171.7255.3538.76
60 s3.721.1456.2738.87
120 s6.722.9353.5136.84
Table
Table 3. EIS parameters of Pt-SnOx CEs.
Table 3. EIS parameters of Pt-SnOx CEs.
Counter ElectrodeRs (Ω)Rct (Ω)CPE1-T (μF/cm2)CPE1-PW1J0 a (mA/cm2)J0 b (mA/cm2)
W1-R(Ω)W1-T(s)W1-P
Pt-SnOx APPJ5 s18.815.7435.60.8353.232.130.50.821.04
15 s18.28.1883.10.8082.821.990.51.581.39
30 s17.555.8950.752.732.250.52.231.67
60 s18.254.721050.8155.043.150.52.741.85
120 s19.284.69105.50.842.211.80.52.752.08
a J0: Exchange current density is calculated from Rct. b J0: Exchange current density is calculated from Tafel curve.
Table
Table 4. Photovoltaic parameters of DSSCs with different CEs.
Table 4. Photovoltaic parameters of DSSCs with different CEs.
ConditionVoc (V)Jsc (mA/cm2)FF (%)EFF (%)
Pt0.70 ± 0.0210.34 ± 0.4761.27 ± 1.914.42 ± 0.26
Pt-SnOx APPJ5 s0.70 ± 0.0110.76 ± 0.8251.65 ± 6.033.87 ± 0.58
15 s0.69 ± 0.0210.30 ± 0.7854.43 ± 2.653.86 ± 0.28
30 s0.69 ± 0.0210.26 ± 0.8056.38 ± 2.374.01 ± 0.34
60 s0.69 ± 0.0210.47 ± 0.9457.91 ± 2.044.20 ± 0.41
120 s0.70 ± 0.0210.72 ± 0.7559.41 ± 1.084.46 ± 0.29

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Lee, C.-C.; Huang, T.-M.; Cheng, I.-C.; Hsu, C.-C.; Chen, J.-Z. Time Evolution Characterization of Atmospheric-Pressure Plasma Jet (APPJ)-Synthesized Pt-SnOx Catalysts. Metals 2018, 8, 690. https://doi.org/10.3390/met8090690

AMA Style

Lee C-C, Huang T-M, Cheng I-C, Hsu C-C, Chen J-Z. Time Evolution Characterization of Atmospheric-Pressure Plasma Jet (APPJ)-Synthesized Pt-SnOx Catalysts. Metals. 2018; 8(9):690. https://doi.org/10.3390/met8090690

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Lee, Chia-Chun, Tzu-Ming Huang, I-Chun Cheng, Cheng-Che Hsu, and Jian-Zhang Chen. 2018. "Time Evolution Characterization of Atmospheric-Pressure Plasma Jet (APPJ)-Synthesized Pt-SnOx Catalysts" Metals 8, no. 9: 690. https://doi.org/10.3390/met8090690

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