Subscriber access provided by Binghamton University | Libraries
Letter
A novel micro-MEA design to precisely measure the in-situ activity of ORR electrocatalysts for PEMFC Zhi Long, Yankai Li, Guangrong Deng, Changpeng Liu, Junjie Ge, Shuhua Ma, and Wei Xing Anal. Chem., Just Accepted Manuscript • Publication Date (Web): 24 May 2017 Downloaded from http://pubs.acs.org on May 24, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Analytical Chemistry 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 5 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
Analytical Chemistry
A novel micro-MEA design to precisely measure the in-situ activity of ORR electrocatalysts for PEMFC Zhi Long,†, ‡ Yankai Li,‡ Guangrong Deng, †, ║, Changpeng Liu, †, §Junjie Ge *,†, §ÈShuhua Ma*, ‡, Wei Xing*, †, § † State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, Jilin, China ‡ Shandong Provincial Key Laboratory of Fluorine Chemical Materials, School of Chemistry and Chemical Engineering, University of Jinan, Jinan 250022, Shandong, China §Laboratory of Advanced Power Sources, Changchun Institute of Applied Chemistry, 5625 Renmin Street, Changchun 130022, Jilin, China ║Graduate School of the Chinese Academy of Sciences, Beijing 100039, China Supporting Information Placeholder
ABSTRACT: An in-situ micro-MEA technique, which could precisely measure the performance of ORR electrocatalyst using Nafion as electrolyte, was designed and compared with regular thin-film rotating-disk electrode (TFRDE) (0.1 M HClO4) and normal in-situ membrane electrode assembly (MEA) tests. Compared to the traditional TFRDE method, the micro-MEA technique makes the acquisition of catalysts’ behavior at low potential values easily achieved without being limited by the solubility of O2 in water. At the same time, it successfully mimics the structure of regular MEAs and obtains similar results to a regular MEA, thus providing a new technique to simply measure the electrode activity without being bothered by complicated fabrication of regular MEA. In order to further understand the importance of in-situ measurement, Fe-N-C as a typical oxygen reduction reaction (ORR) free-Pt catalyst was evaluated by TFRDE and micro-MEA. The results show that the half wave potential of Fe-N-C only shifted negatively by -135 mV in comparison with state-of-the-art Pt/C catalysts from TFRDE tests. However, the active site density, mass transfer of O2, and the proton transfer conductivity are found strongly influence the catalysts activity in the micro-MEA, thereby resulting in much lower limiting current density than Pt/C (8.7 times lower). Hence, it is suggested that the micro-MEA is better in evaluating the in-situ ORR performance, where the catalysts are characterized more thoroughly in terms of intrinsic activity, active site density, proton transfer and mass transfer properties.
Proton exchange membrane fuel cell (PEMFC), a device efficiently converting chemical energy into electricity through electrochemical reactions, is considered ideal power sources for future mobile and stationary applications due to their high energy efficiency, high power density, as well as zero emissions of pollutant1, 2. However, several challenges have been identified for the commercialization of PEMFCs, among which the very low abundance of platinum is a very important
one due to the heavy dependency of sluggish oxygen reduction reaction (ORR) kinetics on the Pt-based catalysts3-5. In order to tackle the above issues, numerous research groups are dedicated to lowering Pt loading or even making Pt-free catalysts. Precise evaluation of ORR electrocatalysts is necessary for effective development of new electrocatalysts for application4.
ACS Paragon Plus Environment
Analytical Chemistry 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
The electrocatalyst activity for ORR is currently mainly evaluated by an ex-situ thin-film rotating-disk electrode (TFRDE) or an in-situ fuel cell testing procedures. TFRDE using HClO4 solution as the electrolyte is more frequently used due to the ease in testing, however, the information collected are deviated from that obtained through the in-situ testing conditions due to the differed properties in mass and proton transfers. In HClO4 solution, O2 transfers to TFRDE by dissolution in the electrolyte and approaches the electrode through forced convection and diffusion so that the information at lower current densities is collected only. In fuel cell, however, O2 is directly fed to the cathode electrode to form gas diffusion electrode. Furthermore, proton transfers freely in HClO4 solution, with no problem in approaching any sites of the electrode surface as long as the electrode is sufficiently wetted. However, proton transfers in a more complex way in Nafion, with clustering tunnel works in the membrane and a totally different, yet to understand model in catalyst layer. Therefore, the in-situ measurement is more desirable to evaluate the true applicability of a catalyst. However, the evaluation is limited by the complication in synthesis technique of a membrane electrode assembly (MEA) and the high demand in testing equipment. Therefore, developing an easy testing technique, which can successfully mimicking the working condition of an in-situ fuel cell without being complicated by MEA fabrication and complex testing procedures is rather meaningful. In this letter, an in situ micro-MEA testing approach was developed to measure the ORR activity. It successfully mimics the structure of regular MEAs with Nafion as the electrolyte, thereby avoids being bothered by the differed proton transfer and mass transfer property. The effectiveness of such novel design in catalyst evaluation is clearly revealed by comparing the TFRDE and micro-MEA results of a Fe-N-C catalyst.
EXPERIMENT
Figure 1. The preparation of micro-MEAs
Micro-MEA was prepared through a newly developed technique shown in Figure 1. A three layer composite film was made through hot pressing 2 layers of PTFE films with Nafion membrane sandwiched in the middle. Two 5×5 mm2 holes were carved on both PTFE membranes prior to the hot pressing process. Therefore, the Nafion membrane is exposed for drop casting the catalyst layers. On the one side of composite film, the catalyst ink of working electrode (WE) was dropped onto the bare Nafion membrane area and the ink consisted of
Page 2 of 5
Pt/C + 20wt.% Nafion was dropped onto bare Nafion membrane areas on the other side of composite film to form the reference and counter electrode (CE), with CE facing WE. The detailed preparation and measurements of micro-MEA, TFRDE and MEA are shown in Supporting Information (SI).
RESULTS AND DISCUSSION Comparison of ESA results of Pt/C through TFRDE and micro-MEA. The electrochemical surface area (ESA) of Pt/C in the TFRDE and micro-MEA electrodes were measured to compare the Pt utilization (uPt) in different working conditions through calculating the charge of HUPD in a cyclic voltammetry (CV) curve, and the results are shown in Figure S3 and Table 1. The ESA is calculated using Equation 1, where S(m2) is electrochemical surface area corresponding to mass of platinum (m(gPt)) on the WE, QH-desorption(A mV) and ν(mV s-1) are respectively the hydrogen desorption charge and the scan rate and 210(µC cm-2) which is the charge of full coverage for clean polycrystalline Pt which is used as the conversion factor16, after correction for double-layer charging. ESA
g
$ "#
∙"# % & %' () *"
+
& 10.
(1)
The ESA results acquired in 0.1 M HClO4 is at 67.19 m2 gPt-1, a normal value for commercial JM Pt/C catalysts. However, the ESA results from micro-MEA are much lower due to the insufficient protons available6. The ESAs increases from 3.52 to 41.08 m2 gPt-1 with increase in Nafion content, and the ESA micro-MEA/ESA0.1M HClO is referred as Pt utilization (UPt), as shown in Table 1. The reason for the low UPt is further illustrated by testing the micro-MEA in water and in 0.1 M HClO4. With distilled water fed to WE, the ECA of N30 increases to 44.09 m2 gPt-1, thus demonstrating UPt value at 65.5%, suggesting that the complete thin water film on the surface of Pt could improve proton conductivity of CL so that more Pt NPs are in contact with the proton pathway. The micro-MEA testing results in the presence of 0.1M HClO4 demonstrates ESA at 60.8 m2 gPt-1, which exhibits UPt at 90.5%, suggesting that the lower ESA in micro-MEA can mainly be ascribed to the deficiency in proton conducting capability of Nafion ionomer in comparison with liquid electrolyte. Thus, the micro-MEA test is highly necessary in order to truly understand the ORR behavior in real fuel cell. ORR results of the Pt/C catalysts. In order to validate the effectiveness of micro-MEA technique in mimicking regular MEA, the ORR polarization curve of micro-MEA is compared with results from regular MEA, as shown in Figure 2(a). According to our previous report17 and references18, 19, CL with 30wt.% Nafion (N30) is the optimal content for ORR, consequently, 30wt.% Nafion was used for both electrodes. As shown clearly, the micro-MEA performs slightly better than the regular MEA, which is probably due to the overcome of mass-transfer issue at low catalyst loading. Therefore, it is confirmed that the micro-MEA successfully mimics the working condition of an in-situ fuel cell, which makes it very much appealing for catalysts performance evaluation. As shown in Fig. 2b, the electrocatalytic activities for the ORR process were evaluated by both ex-situ TFRDE and microMEA. Two clear differences are observed for the two different techniques: (i) The diffusion limiting current of the TFRDE is
ACS Paragon Plus Environment
4
Page 3 of 5 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
Analytical Chemistry
limited by the solubility of O2 in water and the rotation speed of the RDE (determines the diffusion layer thickness), where Table 1. The ESAs of Pt/C through micro-MEA and TFRDE. Electrolyte
N10
N30
N50
N30 in water
N30 in 0.1 HClO4
0.1M HClO4
ESA / (m2 gPt-1)
3.52
24.74
41.08
44.09
60.8
67.19
uPt / %
5.24
36.8
61.1
65.5
90.5
100
the maximum current density at 1600 rpm is acquired at 5.5 mA cm-2, within 10% of the theoretical value. Therefore, the catalytic behavior at lower potentials cannot be obtained through the RDE measurement, which significantly limits the information obtained. However, micro-MEA results are not limited by such effect, which makes the acquisition of data at low potential values easily achieved (up to 400 mA/cm2 compared to 5.5 mA/cm2 for RDE). This feature is of significant importance for testing the behavior of non-platinum groups, as shown in the following section; (ii) The ORR current at 2.75mA/cm2 for the micro-MEA electrode is shifted negatively by -65mV in comparison with the regular RDE results, suggesting the deviation of the RDE results from the true fuel cell performance. Fig. 2(c) shows the Tafel plots, where the overpotentials are plotted against logarithm of kinetic current densities log(Jk). The kinetic current densities (Jk) can generally be obtained from Equation 2, where J is the measured current density, Jk is the kinetic current density and Jl is the diffusionlimited current density20. /
/0
1
/2
TFRDE and in Nafion fed 2 slpm O2 into WE chamber for microMEA with 30wt.% Nafion.
Two Tafel slopes of ~60 mV dec-1 at the low current density and ~120 mV dec-1 at the high current density were observed, suggesting the change from Temkin to Langmuir adsorption behavior due to the change in the OHad surface coverage 21-24. The micro-MEA technique allows the successful acquisition of Tafel slope at much higher currents, and the results show that the Langmuir adsorption is validate at large current densities until reaching the mass transfer region. Higher polarization loss of the micro-MEA electrode was also observed from Tafel plots, in comparison with the RDE test, which was probably due to the limited of proton accessibility to the Pt electrode and the varied mass transport feature of the former, as suggested in the ESA results acquired from CV tests.
(2)
Figure 2. Pt/C performances for ORR measured through TFRDE, micro-MEA and regular MEA. (a) ORR IR-free polarization curves by micro-MEA and regular MEA under 100% O2 for 30wt.% Nafion in the electrodes (b) ORR polarization curves corrected-IR in O2-saturated 0.1 M HClO4 with scan rate of 50 mV s-1 and rotation speed of 1600 rpm for TFRDE and in Nafion fed 2 slpm O2 into WE chamber for micro-MEA with 30wt.% Nafion. (c) Tafel plots for ORR polarization curves extracted from figure (b). (d) EIS of ORR at 0.9V from 10k-0.1Hz in O2saturated 0.1 M HClO4 with rotation speed of 1600 rpm for
Figure 3. Structure and condition optimization of micro-MEA measurement. (a) IR-free polarization curves of varied Nafion content from N0 to N50 is measured with 100% O2 fed to WE and the scan rate of 50 mV s-1. Upper and lower right are EIS at 0.4 and 0.6 V from 10k-0.1Hz, respectively. (b) IR-free polarization curves of varied O2 concentration from 0.5% to 100% is measured for N30 micro-MEA with the scan rate of 50 mV s-1. Upper and lower right are EIS at 0.4 and 0.6 V from 10k-0.1Hz, respectively. Room temperature; Humidifica-
ACS Paragon Plus Environment
Analytical Chemistry 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
tion at 35 ; Pt loading = 20 µgPt cm-2; 2 slpm mixture of N2 and O2. EIS data at 0.9 V was further acquired to compare the difference in charge transfer resistance (Rct), as shown in Figure 2(d). The Rct of micro-MEA (~1900 Ω) is 3 times that of the TFRDE in 0.1M HClO4 (~650 Ω), which is well corresponding to the 36.8% utilization of Pt in the micro-MEA. All these results imply the imprecise measurement results of the TFRDE, making it unable to completely evaluate catalytic behaviors for the application. In contrast, micro-MEA is a more appropriate technique for such evaluation. Structure and work condition optimization of micro-MEA measurement. The electrode structure and working condition was further optimized in order to ensure precise results from micro-MEA, parameters including Nafion content and O2 concentration were studied. As is known, increase in Nafion ionomer content leads to improvement in proton conductivity of WE, however, it also leads to the higher coverage of catalysts and blocks the Pt surface from the reactants25, 26. Therefore, an optimized Nafion content is often observed due to the trade-off effect from the two. As is shown in Figure 3 (a), IR-free polarization curves with Nafion contents varying from N0 to N50 for 100% O2 were measured by LSV at a scan rate of 50 mV s-1. Among all the contents, N30 is found the optimal value, as suggested by the lower polarization loss and the lower Rct.18, 19Another merit of the micro-MEA is its easily tuned O2 concentration. As shown in Figure 3(b), with O2 concentration varies from 0.5% to 100%, significant increase in ORR performance is observed from both LSV and impedance results. The diffusion limiting current increases from 15.7 mA/cm2 at 0.5% O2 to as high as 428.7 mA cm-2 at 0.383 V for 100% O2, thus making it easy to evaluate the kinetic and mass transfer properties at high current densities. This feature is extremely valuable in evaluating the true performance of non-precious catalysts, where the active site density is low and the mass transfer issue may be an important problem. ORR performance of FeNC by micro-MEA. Fe-N-C is the most promising non-precious metal catalyst for ORR and has been paid much attention. The Fe-N-C, which was designed and synthesized with similar method as our previous report27, is evaluated by micro-MEA and TFRDE. As shown in Figure 4(a), using TFRDE measurement, the Fe-N-C catalyst exhibits an outstanding ORR activity, where the half wave potential only negatively shifted by -135 mV in comparison with stateof-the-art Pt/C catalysts. However, the micro-MEA results present a totally different story. A much lower ORR performance has been gained through the micro-MEA electrode due to the lowered capability in proton transfer, lower active site density, and therefore higher mass transfer demand at single active site in order to achieve high current density, as shown in Figure 4(b). First, proton transfer at the surface of Fe-N-C depends more heavily on Nafion than Pt, as Pt is known to transfer H+ with the help of thin water film on the surface while Fe-N-C is not. As a result, the optimized Nafion content is 40wt.% for Fe-N-CÈhigher than Pt/C(30wt.%), as shown in Figure S5. Second, the deficiency of Fe-N-C is clearly demonstrated compared to Pt/C through the micro-MEA
Page 4 of 5
measurement, as shown in Figure 4(c). For the Pt/C catalysts, the current density easily goes to 428.7 mA cm-2 at 0.645V; on the contrary, the Fe-N-C catalyst shows much inferior activity, where the current increases much slower than that of Pt/C and only reaches 49.3mA cm-2 at 0.07V (vs. RHE). The much lower current (8.7 times lower than that of Pt/C) achieved for Fe-N-C at much lower potential clearly demonstrating its deficiency in terms of both active site density and mass transfer of O2. The results obtained with the micro-MEA on Fe-N-C electrocatalysts is compared with the results obtained with a real MEA, shown in the Figure 4(d), indicating that micro-MEA is able to mimic MEA and decrease diffusion-limited barriers. In addition, as shown in Figure S6(a), the Tafel plots obtained from the micro-MEA results of Fe-N-C is 247.1 mV dec-1, which is much higher than the results from RDE tests and the Pt/C (Micro-MEA), clearly suggesting the influence of proton and mass transfer. Rct for Fe-N-C is 36 times higher (360 Ω) than Pt/C (10 Ω) at 0.6 V and 25 times higher (90 Ω) than Pt/C (3.6 Ω) at 0.4 V, shown in Figure S6(b-c), also clearly demonstrating its deficiency in terms of both active site density and mass transfer of O2. However, these features of Fe-N-C are not successfully revealed by the TFRDE tests due to the limitation of the technique itself. Therefore, the micro-MEA is more reliable in gaining overall information of the electrocatalysts in terms of intrinsic activity, active site density, proton transfer and mass transfer properties.
Figure 4. (a) IR-free polarization curve of Fe-N-C and Pt/C in 0.1 M HClO4 by RDE with 1600 rpm and the scan rate of 50 mV s-1. (b) Fe-N-C polarization curves corrected-IR in O2-saturated 0.1 M HClO4 with scan rate of 50 mV s-1 and rotation speed of 1600 rpm for TFRDE and in Nafion fed various O2 concentration into WE chamber for micro-MEA with 30wt.% Nafion. (c) IR-free polarization curve of Fe-N-C and Pt/C in Nafion by micro-MEA with 100% O2 fed to WE and the scan rate of 50 mV s-1. (d) ORR IRfree polarization curves by micro-MEA and regular MEA under 100% O2 for 30wt.% Nafion in the electrodes for FeNC. The loadings of Fe-N-C and 20% Pt/C for micro-MEA are 200µg cm-2 and 100µg cm-2 (Pt loading is 20µg cm-2), respectively. The loading of Fe-N-C for MEA is 3.5mg cm-2.
CONCLUSION
4 ACS Paragon Plus Environment
Page 5 of 5 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
Analytical Chemistry
An in situ approach, which could measure the performance of ORR electrocatalyst in the polymer electrolyte Nafion, was designed and compared with regular TFRDE in 0.1 M HClO4 and MEA. The micro-MEA successfully overcomes the solubility limitation of O2 in water due to the similar design in structure to the regular MEAs in term of the gas diffusion electrode. The ORR results obtained from micro-MEA are highly consistent with the regular MEA, thus making it a precise yet simple measurement method in evaluating the true behavior of an ORR catalyst. In order to elucidate the importance of the micro-MEA method, Fe-N-C as a typical ORR free-Pt catalyst was evaluated by TFRDE and micro-MEA. Its half wave potential only negatively shifted by -135 mV in comparison with state-of-the-art Pt/C catalysts from TFRDE, however, its limiting current density is 8.7 times lower than Pt/C in the micro-MEA test due to the deficiency in active sites and the strong dependency of proton transfer capability on Nafion. From our investigation, it is evident that microMEA is a good design to evaluate in-situ ORR performance.
ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. The detailed preparations and measurements of micro-MEA, TFRDE and MEA; CV about ESA of micro-MEA; optimization of O2 concentration for Pt/C; optimization of Nafion content for Fe-N-C (PDF)
AUTHOR INFORMATION Corresponding Author * E-mail:
[email protected] * E-mail:
[email protected] * E-mail:
[email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.
Notes
(3) Scofield ME, Liu H, Wong SS. Chem. Soc. Rev. 2015, 44 (16), 5836-5860. (4) Nie Y, Li L, Wei Z. Chem Soc Rev. 2015, 44 (8), 2168-2201. (5) Ng JWD, Tang M, Jaramillo TF. Energy Environ. Sci. 2014, 7 (6), 2017. (6) Gasteiger HA, Kocha SS, Sompalli B, Wagner FT. Appl. Catal. B. 2005, 56 (1-2), 9-35. (7) Kolics A, Wieckowski A. J. Phys. Chem. B. 2001, 105 (13), 2588-2595. (8) Attard GA, Brew A, Hunter K, Sharman J, Wright E. Phys. Chem. Chem. Phys. 2014, 16 (27), 13689-13698. (9) Iwasita T, Xia X. J. Electroanal. Chem. 1996, 411 (1), 95-102. (10) Yano H, Uematsu T, Omura J, Watanabe M, Uchida H. J. Electroanal. Chem. 2015, 747, 91-96. (11) Omura J, Yano H, Tryk DA, Watanabe M, Uchida H. Langmuir. 2014, 30 (1), 432-439. (12) Omura J, Yano H, Watanabe M, Uchida H. Langmuir. 2011, 27 (10), 6464-6470. (13) Ferreira-Aparicio P. ACS Appl. Mater. Interfaces. 2009, 1 (9), 1946-1957. (14) Hongsirikarn K, Mo X, Liu Z, Goodwin JG. J Power Sources. 2010, 195 (17), 5493-5500. (15) Mauritz KA, Moore RB. Chem Rev. 2004, 104 (10), 45354586. (16) Garsany Y, Baturina OA, Swider-Lyons KE, Kocha SS. Anal Chem. 2010, 82 (15), 6321-6328. (17) Long Z, Deng G, Liu C, Ge J, Xing W, Ma S. Chinese Journal of Catalysis. 2016, 37 (7), 988-993. (18) Mu S, Tian M. Electrochim Acta. 2012, 60, 437-442. (19) Passalacqua E, Lufrano F, Squadrito G, Patti A, Giorgi L. Electrochim Acta. 2001, 46 (6), 799-805. (20) Paulus UA, Wokaun A, Scherer GG, Schmidt TJ, Stamenkovic V, Markovic NM, et al. Electrochim Acta. 2002, 47 (22–23), 3787-3798. (21) Holewinski A, Linic S. J Electrochem Soc. 2012, 159 (11), H864-H870. (22) Liu L, Samjeske G, Nagamatsu S-i, Sekizawa O, Nagasawa K, Takao S, et al. J. Phys. Chem. C. 2012, 116 (44), 23453-23464. (23) Stamenković V, Schmidt TJ, Ross PN, Marković NM. J. Phys. Chem. B. 2002, 106 (46), 11970-11979. (24) Bonnet N, Otani M, Sugino O. J. Phys. Chem. C. 2014, 118 (25), 13638-13643. (25) Soboleva T, Malek K, Xie Z, Navessin T, Holdcroft S. ACS Appl. Mater. Interfaces. 2011, 3 (6), 1827-1837. (26) Soboleva T, Zhao X, Malek K, Xie Z, Navessin T, Holdcroft S. ACS Appl. Mater. Interfaces. 2010, 2 (2), 375-384. (27) Zhu J, Xiao M, Liu C, Ge J, St-Pierre J, Xing W. J. Mater. Chem. A. 2015, 3 (43), 21451-21459.
The authors declare no competing financial interest.
ACKNOWLEDGMENT The work is supported by the National Natural Science Foundation of China (21673221, 21633008), the Strategic priority research program of CAS (XDA09030104), Jilin Province Science and Technology Development Program (20150101066JC, 20160622037JC), the Hundred Talents Program of Chinese Academy of Sciences and the Recruitment Program of Foreign Experts (WQ20122200077).
REFERENCES (1) Chen Z, Higgins D, Yu A, Zhang L, Zhang J. Energy Environ. Sci. 2011, 4 (9), 3167-3192. (2) Zhang S, Shao Y, Yin G, Lin Y. J. Mater. Chem. A. 2013, 1 (15), 4631.
5 ACS Paragon Plus Environment
