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International Edition: DOI: 10.1002/anie.201713029 German Edition: DOI: 10.1002/ange.201713029
Natural Gas Purification
Achieving Simultaneous CO2 and H2S Conversion via a Coupled SolarDriven Electrochemical Approach on Non-Precious-Metal Catalysts Weiguang Ma, Hong Wang, Wei Yu, Xiaomei Wang, Zhiqiang Xu, Xu Zong,* and Can Li* Abstract: Carbon dioxide (CO2) and hydrogen sulfide (H2S) are generally concomitant with methane (CH4) in natural gas and traditionally deemed useless or even harmful. Developing strategies that can simultaneously convert both CO2 and H2S into value-added products is attractive; however it has not received enough attention. A solar-driven electrochemical process is demonstrated using graphene-encapsulated zinc oxide catalyst for CO2 reduction and graphene catalyst for H2S oxidation mediated by EDTA-Fe2+/EDTA-Fe3+ redox couples. The as-prepared solar-driven electrochemical system can realize the simultaneous conversion of CO2 and H2S into carbon monoxide and elemental sulfur at near neutral conditions with high stability and selectivity. This conceptually provides an alternative avenue for the purification of natural gas with added economic and environmental benefits.
Natural gas is consumed in large qualities as fuel and chemical feedstock in modern society. Although it consists primarily of methane (CH4), various gases are concomitantly present. For example, it was reported that the Puguang natural gas field, the biggest natural gas field in China, contains of up to 8.6 % carbon dioxide (CO2) and 14.1 % hydrogen sulfide (H2S), respectively.[1] Similarly, CO2 and H2S account for ca. 10 % and 15 % of the total gases in some fields of the Middle East.[2] These gases, which are enormous in quality and traditionally deemed useless or even harmful, have to be pretreated for further processing.[3] However, if they can be used to produce value-added products, more economic and environmental benefits will be obtained. The catalytic conversion of CO2 into valuable products such as fuels and chemicals is a global challenge owing to the high energy barrier for the activation of stable CO2 molecules.[4] Various approaches have been reported for the transformation of CO2.[5] Among all the approaches under investigation, the electrocatalytic or photoelectrochemical [*] Dr. W. G. Ma, H. Wang, Dr. W. Yu, X. M. Wang, Z. Q. Xu, Prof. X. Zong, Prof. C. Li State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian National Laboratory for Clean Energy, The Collaborative Innovation Center of Chemistry for Energy Materials (iChEM) Zhongshan Road 457, Dalian 116023 (China) E-mail:
[email protected] [email protected] H. Wang, X. M. Wang, Z. Q. Xu University of Chinese Academy of Sciences Beijing 100049 (China) Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.org/10.1002/anie.201713029. Angew. Chem. Int. Ed. 2018, 57, 3473 –3477
conversion of CO2 is attractive as they can proceed at ambient conditions by utilizing renewable energy resources such as solar energy.[6] Although noble metal-based catalysts, such as Au,[7] Ag,[8] and Pd,[9] have been investigated for catalyzing the reduction of CO2, developing inexpensive, selective, and stable catalysts operating at low overpotentials is attractive. As for H2S, several approaches such as Claus process have been used commercially to dispose H2S,[10] and we also proposed a more attractive photoelectrochemical–chemical loop strategy for the remediation of H2S recently.[11] However, although the conversion of CO2 and H2S has been investigated separately, to the best of our knowledge, there is still no report on the simultaneous conversion of CO2 and H2S into value-added chemicals with electrochemical or photoelectrochemical approaches. Ideally, this will provide an attractive landscape for producing valuable chemicals by consuming negative value waste products. Herein, we present a solar-driven electrochemical approach that can realize the simultaneous conversion of CO2 and H2S into value-added products. By integrating the CO2 reduction and H2S oxidation reactions with the aid of redox couples, CO2 and H2S can be converted into carbon monoxide (CO) and sulfur (S) with high activity and stability on non-precious catalysts. To the best of our knowledge, this is the first report of using photoelectrochemical processes for the simultaneous conversion of CO2 and H2S into valueadded chemicals. This conceptually provides an alternative avenue for the purification and utilization of concomitant gases in natural gas with added economic and environmental benefits. Our approach of converting CO2 and H2S into CO and S is consisted of two integrated steps (see Scheme 1). In the first step, CO is produced through CO2 reduction reaction in the cathodic compartment and EDTA-Fe2+ is oxidized to EDTAFe3+ in the anodic compartment through photovoltaic– electrolysis reactions. In the second step, the chemical energy stored in EDTA-Fe3+ is liberated to convert H2S selectively into elemental sulfur and protons via a simple and fast chemical reaction, and EDTA-Fe3+ is restored to EDTAFe2+. Protons generated from H2S oxidation in the anodic compartment transfer to the cathodic compartment through a Nafion membrane and act as the proton source for CO2 reduction in the cathodic compartment. Therefore, CO2 and H2S were continuously converted into CO and S via the coupled electrochemical transformation process. As a proof-of-concept study, the catalytic transformation of CO2 and H2S were first investigated individually. To realize the electrochemical CO2 reduction reaction, zinc oxide nanoparticles encapsulated by a graphene layer (ZnO@G) were synthesized according to a reported procedure.[12] X-ray
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Scheme 1. Illustration of coupled electrochemical transformation of CO2 and H2S on non-precious metal catalysts.
diffraction (XRD) analysis indicates that the diffraction peaks for ZnO can be well indexed to those of the standard ZnO (Figure 1 a). As for ZnO@G, two new diffraction peaks at 25.888 and 43.588 were observed, which correspond to the (002) and (100) planes of graphene. In the Raman spectra, three peaks at 475 cm@1, 1592.7 cm@1, and 1566.6 cm@1 were observed, which correspond to ZnO and graphene, respectively (Figure 1 b).[13] These results clearly indicate the successful preparation of ZnO@G composites. To obtain more clear information on the morphology of ZnO@G, transmission electron microscopy (TEM) analysis was conducted. As shown in Figure 1 c, ZnO@G composites are consisted of finely dispersed nanoparticles with a size of ca. 15 nm. A close examination with high-resolution TEM (HRTEM) indicates that the as-prepared ZnO@G catalysts have a core–shell structure (Figure 1 c). The shell is highly disordered with a thickness of approximately 2.2 nm. The
Figure 1. a) XRD patterns of ZnO and ZnO@G. b) Raman spectra of ZnO and ZnO@G. c) TEM image of ZnO@G. d),e) HRTEM images of ZnO@G.
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core can be assigned to ZnO with good crystallinity. Other detailed information for the structural properties of the asprepared catalysts is presented in the Supporting Information, Figures S1–S4. The electrochemical performances of ZnO and ZnO@G were then evaluated in CO2-saturated 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid containing water (EMIM-BF4/H2O (V/V) = 7/1, IL). As a comparison, ZnO/ graphene composite (denoted as ZnO/G) was also prepared. Prior to test, ZnO@G, ZnO/G, and ZnO were electrochemically reduced in Ar-saturated electrolytes (Supporting Information, Figure S5). There is no substantial change in the morphology of the three catalysts after electrochemical reduction treatment (Supporting Information, Figure S6). However, both XRD and XPS characterizations indicate that ZnO was partially reduced to Zn (Supporting Information, Figures S7, S8), which is in good agreement with reported work.[14] The resulting catalysts were denoted as rZnO@G, rZnO/G, and rZnO, respectively. As shown in Figure 2 a, rZnO@G catalyst exhibits an onset potential of
Figure 2. a) LSV curves for three catalysts in CO2-saturated EMIM-BF4/ H2O IL. b) The FECO of three catalysts at different applied potentials. c) The TOFCO of three catalysts at overpotential range from 0.508 to 0.908 V. d) The stability of three catalysts for CO2 reduction at @0.813 V in CO2-saturated EMIM-BF4/H2O IL.
@0.40 V (overpotential @0.29 V), which is more positive relative to rZnO/G (@0.62 V, overpotential @0.51 V) and rZnO (@0.67 V, overpotential @0.56 V). Additionally, a current density of @5.2 mA cm@2 was achieved for rZnO@G catalyst at @0.813 V, which were ca. 2.5 and 2.8 times those of rZnO/G and rZnO catalysts at the same potential. The electrochemical results with IR correction are also shown in the Supporting Information, Figure S9. The electroreduction products were identified and quantified with gas chromatograph and 1H nuclear magnetic resonance spectroscopy. H2 and CO were observed to be the major gas products (Supporting Information, Figure S10) and no products were detected in the aqueous solution (Supporting Information, Figure S11). Moreover, rZnO@G showed much higher Faradaic efficiency for CO formation (FECO) than rZnO/G and rZnO in the whole applied potentials (Figure 2 b). At the potential of @0.813 V, rZnO@G obtained a maximum FECO
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Communications of 83 %, which was about 3.1 and 3.7 times higher than those of rZnO/G and rZnO catalysts. We also investigated the turnover frequency for CO formation (TOFCO) over the three catalysts. As shown in Figure 2 c, The TOFCO of rZnO@G is approximately two orders of magnitude higher than those of rZnO/G and rZnO over a potential range from @0.618 to @1.018 V. Of note, rZnO@G exhibits a TOFCO as high as 0.024 s@1 at @0.813 V, which is comparable with that obtained on noble catalysts in previous works.[9a, 15] The electrochemical stability of rZnO@G was also evaluated with chronopotentiometry at @0.813 V. The current density did not show any obvious decay and the FECO remained about 96 % of the initial value during the test, indicative of its good stability at operation conditions (Figure 2 d). On the contrary, both rZnO/G and rZnO exhibited relatively poor long-term stability. The good stability of rZnO@G should be partially attributed to the encapsulation of ZnO core with graphene shell, which could prevent the agglomerations of ZnO nanoparticles (Supporting Information, Figure S12). Therefore, the encapsulation of ZnO with thin graphene layer was found to be beneficial to promote the electrocatalytic CO2 reduction performance. Furthermore, the encapsulation strategy can not only decrease the interfacial charge-transfer resistance (Supporting Information, Figure S13) but also stabilize the intermediate of CO2 reduction reaction (Supporting Information, Figures S14, S15), which are supposed to be the other reasons for the drastically enhanced CO2 reduction performance. After establishing that CO2 can be selectively converted into CO in the cathodic side of the as-proposed approach on the rZnO@G catalyst, we then focused on the conversion of H2S into S in the anodic side. Fe2+/Fe3+ redox couples were applied to convert H2S into S in our previous work through a simple chemical reaction.[11c] However, the serious crossover of Fe2+/Fe3+ species through Nafion membrane significantly impaired the long-term stability of the system. Moreover, Fe2+/Fe3+ can only exist in strongly acidic condition, which seriously limits their applications. Therefore, seeking alternative mediators to Fe2+/Fe3+ is crucial for the establishment of a more stable system working under environmentally benign conditions. In the present study, EDTA-Fe2+/EDTAFe3+ with a large molecular size was tentatively used. We found that the permeation rate for EDTA-Fe2+/EDTA-Fe3+ across the Nafion membrane is about 182 times slower than that of Fe2+/Fe3+ during a 70 h testing (Figure 3 a). Furthermore, EDTA-Fe2+/EDTA-Fe3+ is stable in neutral solution, which is more suitable than Fe2+/Fe3+ in practical applications. Commercially available graphite carbon sheet (GCS), which was previously used for electrochemical Fe2+ oxidation,[11c] was then used for the oxidation of EDTA-Fe2+. As shown in Figure 3 b, a current density of only 8 mA cm2 was obtained at 0.8 V for EDTA-Fe2+ oxidation. After modification with graphene (Supporting Information, Figure S16), the asobtained G/GCS delivered about 4 times higher current density for EDTA-Fe2+ oxidation at 0.8 V than the pristine GCS (Figure 3 b). Furthermore, the G/GCS electrode exhibited enhanced stability for the EDTA-Fe2+ oxidation reaction (Supporting Information, Figure S17). The Faradaic efficiency for EDTA-Fe2+ oxidation on the G/GCS electrode Angew. Chem. Int. Ed. 2018, 57, 3473 –3477
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Figure 3. a) The crossover of FeCl3 and EDTA-Fe3+ species through Nafion membrane in an “H” type electrolytic cell. b) LSV curves of GCS and G/GCS electrodes in 0.1 m EDTA-Fe2+ in a three-electrode configuration. c) The effect of different anodic reactions on CO2 reduction in a two-electrode configuration. d) The stability of rZnO@G modified electrode for CO2 reduction in CO2-saturated EMIM-BF4/H2O IL in a two-electrode configuration.
was calculated to be about 100 % by analyzing the EDTAFe3+ product in the anodic compartment during reaction, again demonstrating the excellent performance of G/GCS electrode for EDTA-Fe2+ oxidation. The electrochemical results with IR correction were also shown in the Supporting Information, Figure S18. We then slowly bubbled H2S gas into the electrolytes containing EDTA-Fe3+. The solution turned yellow turbid rapidly owing to the facile chemical reaction between H2S and EDTA-Fe3+(Supporting Information, Figure S19). The yellowish precipitate was collected via a simple filtration process and identified to be a-S by XRD and Raman analysis (Supporting Information, Figures S20, S21), indicating the successful production of S by chemically treating H2S with the solution obtained in the electrochemical reaction. Therefore, the electrochemical oxidation of EDTA-Fe2+ to EDTA-Fe3+ can be well coupled to the oxidative conversion of H2S into S and H+ under neutral conditions. After achieving the electrochemical conversion of CO2 and H2S, respectively, a two-electrode electrochemical system based on rZnO@G and G/GCS catalysts was established towards the target of simultaneous H2S and CO2 conversion. As shown in Figure 3 c, an applied potential of only about @1.0 V is required to initiate the CO2 reduction and EDTAFe2+ oxidation. Moreover, the polarization curve of the twoelectrode system did not show obvious change after a 6 h chronopotentiometric test, suggesting the excellent stability of the system (Figure 3 d). The amount of CO and EDTAFe3+ produced in the cathodic and anodic compartment were analyzed by gas chromatography and UV/Vis spectroscopy and are shown in the Supporting Information, Figure S22. As a comparison, if EDTA-Fe2+ oxidation was replaced by the water oxidation reaction that generally occurs in the conventional CO2 electroreduction cycle, up to @1.6 V is needed to initiate the overall reaction even iridium oxide catalyst was used. Therefore, the integration of CO2 reduction and H2S oxidation (through EDTA-Fe2+ oxidation) can significantly
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Communications reduce the energy input besides producing value-added products by consuming negative value waste. Finally, a solar-driven electrochemical system was established for the simultaneous conversion of CO2 and H2S. A single three-junction commercial planar silicon (Si) solar cell, with an open-circuit voltage of 1.72 V and a photoconversion efficiency of 10.1 %, was used to convert the solar energy into electrical energy (Figure 4 a). By connecting the Si solar cell
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Sciences (No. XDB17000000), the China Postdoctoral Science Foundation (No. 2016M590237). X.Z. acknowledges the support from Young Thousand Talents Program of China.
Conflict of interest The authors declare no conflict of interest. Keywords: CO2 reduction · H2S splitting · natural gas purification · noble-metal-free catalysts · solar energy conversion How to cite: Angew. Chem. Int. Ed. 2018, 57, 3473 – 3477 Angew. Chem. 2018, 130, 3531 – 3535
Figure 4. a) J–V curves of the single three-junction Si solar cell under dark and simulated AM 1.5 G 100 mWcm@2 illumination, overlaid with the matched J–V characteristic of the rZnO@G and G/GCS electrodes in a two-electrode configuration. b) Chronoamperometric measurement of a solar-driven electrochemical system under chopped simulated sunlight (AM 1.5 G).
with rZnO@G and G/GCS electrodes in series (Supporting Information, Figure S23), we were able to obtain a current density of 8.5 mA cm@2 corresponding to a solar-to-chemical (STC) conversion efficiency of ca. 7.5 % under AM 1.5 G illumination at 100 mW cm2 intensity (Figure 4 b). The STC efficiency increases to ca. 8.3 %, if hydrogen produced from CO2 reduction is considered together. The STC efficiency can be further increased by using better solar cells and optimizing operation conditions.[16] Finally, simulated nature gas (Ar:CH4 :CO2 :H2S 60:20:19:1 % v/v) was bubbled into the solar-driven electrochemical system according to the Supporting Information, Scheme S1. As expected, CO and S were also obtained by consuming CO2 and H2S in simulated natural gas. This conceptually provides an economic and environmentally benign avenue for the purification of natural gas. In summary, we demonstrated a solar-driven electrochemical approach for the coupled conversion of CO2 and H2S into value-added products at neutral conditions. CO2 and H2S can be simultaneously converted into CO and S with high activity and stability on non-precious ZnO@G and graphene catalysts at low energy input. This conceptual design of producing value-added chemicals by consuming negative value waste products in nature gas is solely based on lowcost materials and a simple system configuration, which provides an attractive avenue for the purification of natural gas with added economic and environmental benefits.
Acknowledgements This work was financially supported by the National Natural Science Foundation of China (No. 21573219), National Key R&D Program of China (No. 2017YFA0204804), the Strategic Priority Research Program of Chinese Academy of
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[1] Y. Yu, H. Mao, A. Pei, Nat. Gas Ind. 2011, 31, 22 – 25. [2] C. J. Orme, F. F. Stewart, J. Membr. Sci. 2005, 253, 243 – 249. [3] a) H. S. Roh, K. W. Jun, J. Y. Kim, J. W. Kim, D. R. Park, J. D. Kim, S. S. Yang, J. Ind. Eng. Chem. 2004, 10, 511 – 515; b) P. K. Thallapally, R. K. Motkuri, C. A. Fernandez, B. P. McGrail, G. S. Behrooz, Inorg. Chem. 2010, 49, 4909 – 4915; c) A. de Angelis, Appl. Catal. B 2012, 113, 37 – 42; d) S. Rezaei, A. Tavana, J. A. Sawada, L. Wu, A. S. M. Junaid, S. M. Kuznicki, Ind. Eng. Chem. Res. 2012, 51, 12430 – 12434; e) V. M. Berdnikov, Y. N. Lebedev, K. V. Baklashov, B. I. Belinskii, E. M. Prokhorov, T. M. Zaitseva, Chem. Technol. Fuels Oils 2001, 37, 167 – 171. [4] E. V. Kondratenko, G. Mul, J. Baltrusaitis, G. O. Larrazabal, J. Perez-Ramirez, Energy Environ. Sci. 2013, 6, 3112 – 3135. [5] a) S. Bontemps, L. Vendier, S. Sabo-Etienne, J. Am. Chem. Soc. 2014, 136, 4419 – 4425; b) J. Kothandaraman, A. Goeppert, M. Czaun, G. A. Olah, G. K. S. Prakash, J. Am. Chem. Soc. 2016, 138, 778 – 781; c) J. Wu, X.-D. Zhou, Chin. J. Catal. 2016, 37, 999 – 1015. [6] a) R. J. Lim, M. Xie, M. A. Sk, J.-M. Lee, A. Fisher, X. Wang, K. H. Lim, Catal. Today 2014, 233, 169 – 180; b) D. D. Zhu, J. L. Liu, S. Z. Qiao, Adv. Mater. 2016, 28, 3423 – 3452; c) Y. Oh, X. Hu, Chem. Soc. Rev. 2013, 42, 2253 – 2261; d) Z. P. Jovanov, H. A. Hansen, A. S. Varela, P. Malacrida, A. A. Peterson, J. K. Norskov, I. E. L. Stephens, I. Chorkendorff, J. Catal. 2016, 343, 215 – 231; e) X. Sun, Q. Zhu, X. Kang, H. Liu, Q. Qian, Z. Zhang, B. Han, Angew. Chem. Int. Ed. 2016, 55, 6771 – 6775; Angew. Chem. 2016, 128, 6883 – 6887; f) M. Schreier, L. Curvat, F. Giordano, L. Steier, A. Abate, S. M. Zakeeruddin, J. Luo, M. T. Mayer, M. Graetzel, Nat. Commun. 2015, 6, 7326; g) M. Schreier, F. Heroguel, L. Steier, S. Ahmad, J. S. Luterbacher, M. T. Mayer, J. Luo, M. Gratzel, Nat. Energy 2017, 2, 17087. [7] a) Y. Chen, C. W. Li, M. W. Kanan, J. Am. Chem. Soc. 2012, 134, 19969 – 19972; b) C. Rogers, W. S. Perkins, G. Veber, T. E. Williams, R. R. Cloke, F. R. Fischer, J. Am. Chem. Soc. 2017, 139, 4052 – 4061. [8] a) S. Liu, H. Tao, L. Zeng, Q. Liu, Z. Xu, Q. Liu, J.-L. Luo, J. Am. Chem. Soc. 2017, 139, 2160 – 2163; b) B. A. Rosen, A. SalehiKhojin, M. R. Thorson, W. Zhu, D. T. Whipple, P. J. A. Kenis, R. I. Masel, Science 2011, 334, 643 – 644; c) W. Luc, C. Collins, S. Wang, H. Xin, K. He, Y. Kang, F. Jiao, J. Am. Chem. Soc. 2017, 139, 1885 – 1893; d) M. Ma, B. J. Trzesniewski, J. Xie, W. A. Smith, Angew. Chem. Int. Ed. 2016, 55, 9748 – 9752; Angew. Chem. 2016, 128, 9900 – 9904. [9] a) D. Gao, H. Zhou, J. Wang, S. Miao, F. Yang, G. Wang, J. Wang, X. Bao, J. Am. Chem. Soc. 2015, 137, 4288 – 4291; b) S. Ma, M. Sadakiyo, M. Heima, R. Luo, R. T. Haasch, J. I. Gold, M. Yamauchi, P. J. A. Kenis, J. Am. Chem. Soc. 2017, 139, 47 – 50; c) H. Huang, H. Jia, Z. Liu, P. Gao, J. Zhao, Z. Luo, J. Yang, J.
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Angew. Chem. Int. Ed. 2018, 57, 3473 –3477
Angewandte
Communications [10]
[11]
[12] [13] [14]
Zeng, Angew. Chem. Int. Ed. 2017, 56, 3594 – 3598; Angew. Chem. 2017, 129, 3648 – 3652. a) W. D. Monnery, K. A. Hawboldt, A. E. Pollock, W. Y. Svrcek, Ind. Eng. Chem. Res. 2001, 40, 144 – 151; b) A. K. Gupta, S. Ibrahim, A. Al Shoaibi, Prog. Energy Combust. Sci. 2016, 54, 65 – 92. a) X. Zong, H. Chen, B. Seger, T. Pedersen, M. S. Dargusch, E. W. McFarland, C. Li, L. Wang, Energy Environ. Sci. 2014, 7, 3347 – 3351; b) X. Zong, J. Han, B. Seger, H. Chen, G. Lu, C. Li, L. Wang, Angew. Chem. Int. Ed. 2014, 53, 4399 – 4403; Angew. Chem. 2014, 126, 4488 – 4492; c) W. Ma, J. Han, W. Yu, D. Yang, H. Wang, X. Zong, C. Li, ACS Catal. 2016, 6, 6198 – 6206. D. I. Son, B. W. Kwon, D. H. Park, W.-S. Seo, Y. Yi, B. Angadi, C.-L. Lee, W. K. Choi, Nat. Nanotechnol. 2012, 7, 465 – 471. Z. Protich, P. Wong, K. S. V. Santhanam, ACS Sustainable Chem. Eng. 2016, 4, 6177 – 6185. a) J. Rosen, G. S. Hutchings, Q. Lu, R. V. Forest, A. Moore, F. Jiao, ACS Catal. 2015, 5, 4586 – 4591; b) D. H. Won, H. Shin, J.
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Koh, J. Chung, H. S. Lee, H. Kim, S. I. Woo, Angew. Chem. Int. Ed. 2016, 55, 9297 – 9300; Angew. Chem. 2016, 128, 9443 – 9446. [15] a) W. Zhu, Y.-J. Zhang, H. Zhang, H. Lv, Q. Li, R. Michalsky, A. A. Peterson, S. Sun, J. Am. Chem. Soc. 2014, 136, 16132 – 16135; b) Q. Lu, J. Rosen, Y. Zhou, G. S. Hutchings, Y. C. Kimmel, J. G. Chen, F. Jiao, Nat. Commun. 2014, 5, 3242. [16] a) M. Gong, W. Zhou, M. J. Kenney, R. Kapusta, S. Cowley, Y. Wu, B. Lu, M.-C. Lin, D.-Y. Wang, J. Yang, B.-J. Hwang, H. Dai, Angew. Chem. Int. Ed. 2015, 54, 11989 – 11993; Angew. Chem. 2015, 127, 12157 – 12161; b) J. Jia, L. C. Seitz, J. D. Benck, Y. Huo, Y. Chen, J. W. D. Ng, T. Bilir, J. S. Harris, T. F. Jaramillo, Nat. Commun. 2016, 7, 13237. Manuscript received: December 18, 2017 Revised manuscript received: January 27, 2018 Accepted manuscript online: February 7, 2018 Version of record online: February 27, 2018
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