Lewis-Basic Lanthanide Metal-Organic Framework Derived Versatile

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Energy, Environmental, and Catalysis Applications

Lewis-Basic Lanthanide Metal-Organic Framework Derived Versatile Multi-Active-Site Synergistic Catalysts for Oxygen Reduction Reaction Zhong Zhang, Shumei Liu, Xiaohui Li, Tao Qin, Ling Wang, Xiangjie Bo, Yiwei Liu, Li Xu, Shuang Wang, Xiuwei Sun, Ying Lu, Fang Luo, and Shuxia Liu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b03742 • Publication Date (Web): 11 Jun 2018 Downloaded from http://pubs.acs.org on June 11, 2018

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ACS Applied Materials & Interfaces

Lewis-Basic Lanthanide Metal-Organic Framework Derived Versatile Multi-Active-Site Synergistic Catalysts for Oxygen Reduction Reaction Zhong Zhang,† Shumei Liu,† Xiaohui Li,† Tao Qin,† Ling Wang,† Xiangjie Bo*, † Yiwei Liu,† Li Xu,† Shuang Wang,† Xiuwei Sun, † Ying Lu,† Fang Luo,† Shuxia Liu*, † †

Key Laboratory of Polyoxometalate Science of the Ministry of Education, College of

Chemistry, Northeast Normal University, Jilin 130024, P. R. China. KEYWORDS: lanthanide metal-organic framework; synergistic catalysts; oxygen reduction reaction; La-doped ceria; N-doped porous carbon

ABSTRACT: Oxygen reduction reaction (ORR) underpins the development of the whole fuel cell field, where there is strong impetus to develop efficient and stable catalysts that can replace the precious metal Pt/C. Herein, a series of excellent catalysts for ORR derived from Ce/La dual lanthanide metal-organic framework (MOF) with functional Lewis-basic (LB) sites were synthesized for the first time. The synergistic effect of high concentration of oxygen vacancies from La-embedded CeO2 and Fe-Nx sites as well as porous structure endow the catalyst superior performance to Pt/C, with half-wave potential (E1/2) of 0.870 V and current density (j) of 5.43 mA/cm2. Furthermore, the catalysts are also effective for other non-electrocatalytic reactions. It is expected that this research will contribute to synthesis of an excellent nonplatinum

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electrocatalyst for fuel-cell applications and the oxygen vacancies stabilized in carbon matrix offer a method for versatile catalyst design for other reactions.

INTRODUCTION As a new form of energy conversion, fuel cells are considered as highly promising technology to solve energy and environmental problems1-2. To this end, optimization of the core of fuel cells - cathodic ORR - has attracted much attention3-5. Although the commercial Pt/C catalyst demonstrates excellent performance for ORR, its low earth abundance, high cost, ease of poisoning and poor stability limit further development6-9. Therefore, the demand for nonprecious metal catalysts with efficient and stable ORR is imminent. In recent years, numerous studies have demonstrated that functionalized porous carbon-based material derived from MOFs exhibits exceptional activity and stability for ORR catalysis10-13, owing to the distinctive features of MOF with crystalline porous structure and large surface area built from metal ions or clusters and suitable organic linkers. These features include rich composition, atomic level dispersion, tunable pre-modification/post-synthesis performance and unique template as well as precursor effect14-16. At present, MOF derived functionalized carbonbased catalysts are mainly manufactured by three strategies. In the first strategy, MOFs are pyrolyzed directly, leading to limited active sites of the resulting catalysts17-18. In the second, functionalization of MOF with metal ions19-21, small molecules22-25 and other carbon sources26-30 such as graphene oxide (GO) through adsorption or host-guest interaction, can greatly expand the types of active sites and enhance the performance of final material. The last one is through the construction of isomorphic MOFs to optimize the composition and structure of the final catalyst after pyrolysis, like the most typical ZIF-8 and ZIF-67 pairs31-33. It is noted that M-N/C (such as


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Fe, Co) catalysts obtained have shown much higher activity and stability than the commercial Pt/C catalyst among all the non-precious metal catalysts34. In addition, ceria (CeO2), as an important oxygen storage material used in the three way catalysts (TWCs), possesses unique oxygen storage capacity (OSC) and exhibits reversible transformation between Ce3+/Ce4+, properties beneficial for CO oxidation, NOx reduction35 and ORR36-39 etc. Furthermore, the doping of aliovalent ions (La3+, Gd3+, Cu2+, etc.) results in oxygen vacancies40-41 and thus induce more attractive properties, including enhanced sintering resistance42, electron transfer and adsorption of reactant species37, which can greatly improve performance of CeO2. Our group has reported a series of isomorphic fluorescent lanthanide MOFs (Ln-BTPCA) with multiple Lewis basic sites based on rare earth metal ions and nitrogen-containing carboxylic acid ligands, which exhibit superior performance in metal ion sensing (especially Fe3+ ions) and tunable white light emission43-44. Inspired by previous research, herein, we synthesized a series of Fe/N doped porous carbon in collaboration with La embedded CeO2 catalysts (xLa-CeNC-Fe. Here x stands for the atomic ratio of La in original MOF-Ce/La, the same in MOF-Ce/La-x, see below) derived from Ce/La dual rare earth metal MOF (MOF-Ce/La-x). Due to the synergistic effect of Fe/N doped porous carbon with massive oxygen vacancies in La embedded CeO2 nanoparticles, the catalyst 0.5La-CeNC-Fe shows the best performance for ORR catalysis among the catalysts evaluated in this study. EXPERIMENTAL SECTION Chemical Reagents and Materials. Except the ligand of 1,1’,1’’-(benzene-1,3,5-triyl) tripiperidine-4-carboxylic acid (H3BTPCA) was synthesized referring to the previous literature43-


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, all other reagents were commercially available and used without further purification. The

Cerium(III) acetate hydrate [(CH3CO2)3Ce·xH2O wm: 317.25 g/mol] and Lanthanum(III) acetate hydrate [(CH3CO2)3La·xH2O wm: 316.04 g/mol] were purchased from Macklin Biochemical Co., Ltd (Shanghai, China). Deionized water was used for all experiments. Synthesis of MOF-Ce/La-x. Typically, the Cerium(III) acetate hydrate and Lanthanum(III) acetate hydrate with the different ratios of Ce3+/La3+ were dissolved in 10 ml deionized water (the total molar amounts of La3+ and Ce3+ were 0.4 mmol). H3BTPCA (0.4 mmol, 0.93g) was dissolved in 10 ml N, N-Dimethylformamide (DMF) and added dropwise to the earth metal acetate solution with continuous stirring at room temperature. The precipitate was washed with alcohol and distilled water several times and followed by drying in an oven at 60 °C for 10 h. Preparation of xLa-CeNC-Fe electrocatalysts. Typically, 400 mg of MOF-Ce/La-x was immersed in 8 ml of 0.05 M FeCl3 DMF solution for 20 h (Fe3+/MOF-Ln=0.6, mole ratio), then washed with ethanol three times. Drying process as above. The prepared MOF-Ce/La-x@Fe3+ was heated to 900 °C for 2 h under high-purity N2 (99.999%) atmosphere with a heating rate of 5 °C min-1. The prepared carbon material (denoted as xLa-CeNC-Fe NAE, NAE represents the sample without acid etching treatment) was immersed in 1M HCl solution for 10 h, then centrifuged, washed and dried. Preparation of xLa-CeNC. 400 mg of MOF-Ce/La-x was directly pyrolyzed as above without introduction of Fe3+ as well as acid etching treatment. RESULTS AND DISCUSSION


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The Ce/La bimetal MOFs were synthesized by a simple co-precipitation method between the corresponding acetate hydrate with different Ce/La ratios and ligand (Scheme 1). Several lines of evidence suggest that acetate probably form some precursor fragment structure45-46 with metal ions in solution, and acetate ions can accelerate the deprotonation of the ligand47-48 at the same time. The rapid nucleation rate resulted in nanometer dimension MOFs with uniform size about 200 nm (Figure S1). In order to determine the phase purity of the obtained powder, XRD patterns of MOF-Ce/La-x were obtained (Figure S2). XRD patterns are in good agreement with the simulated ones. However, sharp peaks broaden with increasing ratios of La3+, which can probably be attributed to the incorporation of La3+ with a larger radius, leading to poor crystallinity. The element content of Ce and La in all MOF-Ce/La-x was determined by energy dispersive X-ray (EDAX) data (Table S1).

Scheme 1. Illustrated preparation process of xLa-CeNC-Fe from MOF-Ce/La-x. Then, Fe3+-modified MOF-Ce/La-x (designated as MOF-Ce/La-x@Fe3+) were collected by immersing MOF-Ce/La-x in DMF solutions containing FeCl3. This was further confirmed by the fluorescence quenching experiment (Figure S3). After pyrolysis in an inert atmosphere followed by a simple one-step acid etching, the corresponding catalysts were obtained (designated as xLaCeNC-Fe). The phase constitution was confirmed by powder X-ray diffraction (PXRD). The


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characteristic diffraction peaks were assigned to the bulk CeO2 (PDF# 34-0394). Both before and after acid etching, the diffraction peaks of the correlative Fe phase were not found (Figure 1a, Figure S4a, b). The diffraction peaks of Ce-NC-Fe without La3+ incorporation did not shift, indicating that Fe3+ wasn’t doped into the ceria lattice (Figure 1a). As expected, with increasing ratios of La3+ in the MOF-Ce/La-x, the diffraction peaks of CeO2 gradually shifted towards lower 2θ values, suggesting that the doping amount of La3+ gradually increased due to the larger ionic radius of La3+ (0.116 nm) than Ce4+ (0.097 nm)49-50. However, when the content of La3+ increased to x=0.6, no CeO2 diffraction and scattering peaks existed in the corresponding sample of 0.6La-CeNC-Fe, indicating excessive doping and unstable crystal structure (Figure S4c, d), which was also corroborated by EDAX data (Figure S5) and XPS survey spectra (Figure S6). Unexpectedly, when MOF-Ce/La-x without Fe3+ was pyrolyzed, almost no diffraction peak for the corresponding La oxide was observed (Figure S4a). However, the characteristic diffraction peaks of La2O3 (PDF# 05-0602) were clearly observed when Fe3+ was immersed (Figure S4b). We speculate that trace iron could apparently catalyze crystallization of La2O3 during pyrolysis. The unexpected formation of La2O3 could be advantageous, in that the catalyst’s surface area and porosity can be improved after these nanoparticles were etched, as verified by N2 sorption/desorption experiments. The obvious characteristics of micropore were shown for CeNC-Fe, while other xLa-CeNC-Fe samples showed typical typed-Ⅳ isotherms, suggesting the coexistence of micropores and mesopores51-52 (Figure 1b). BET surface areas of xLa-CeNC-Fe (corresponding x = 0, 0.2, 0.5 and 1) were determined to be 218.23 m2/g, 280.49m2/g, 418.55m2/g and 561.72m2/g which increased rapidly in line with the hypothesis above (Figure S7). Such a high BET surface area is critical to adequate exposure of the catalytic active sites. At the same time, the size distribution of 0.5La-CeNC-Fe is in the mesoporous range, and primarily


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within 2-8 nm range, which is highly beneficial for mass transfer during the reaction (Figure 1c). On the other hand, after the La2O3 nanoparticles being removed, the carbon content was also increased which also contributed to large surface area and high conductivity of catalysts (Figure S7, Table S2).

Figure 1. (a) PXRD patterns of xLa-CeNC-Fe (The vertical purple line represents bulk CeO2 PDF#34-0394). (b, c) N2 adsorption/desorption isotherms and pore size distribution of xLaCeNC-Fe. To further investigate the composition and morphology of catalysts, scanning electron microscopy (SEM) and transmission electron microscope (TEM) images (Figure 2a-j, Figure S8 and S9) were acquired. Due to the catalytic graphitization effect of Fe53-55, a large amount of carbon nanotubes (CNTs) with about 20 nm wide and several micrometers long appeared in the 0.5La-CeNC-Fe (Figure 2a-h, Figure S8f). This may be because volatilized organic fragments assemble to form carbon nanotubes under the catalysis of Fe. Besides CNTs, graphene-wrapped three-dimensional porous carbon (GWPC) was also presented (Figure 2i, j, Figure S8e). TEM images showed that small La-doped CeO2 nanoparticles with sizes of 5-10 nm were homogeneously embedded in the CNTs/GWPC structure (Figure 2i, j). On the contrary, as for other samples of La3+ incorporation, significant agglomeration of material (Figure S8a-d)


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occurred with the appearance of large-size ceria nanoparticles (Figure S9a-d). The La3+ in MOF facilitated the dispersion of Ce3+ and effectively hindered the agglomeration of CeO2 particles.

Figure 2. (a-d) SEM images and (e-j) TEM&HRTEM images of 0.5La-CeNC-Fe. (k-r) Corresponding element mapping of 0.5La-CeNC-Fe. On the other hand, removal of the produced La2O3 nanoparticles after acid treating greatly improved the surface area and permeability of the catalyst, consistent with the N2 adsorption/desorption experiment results. Furthermore, the fact that pure porous CNTs were collected after pyrolysis of MOF-La also confirmed the effect of La3+ (Figure S8g, h and S9e, f). High-resolution TEM (HRTEM) images further showed the homogeneous distribution of nanoparticles (Figure 2j). Corresponding lattice space (Figure 2g, j) are identical with the (200) planes of graphitized carbon and doped-CeO2, in consistent with the calculation results by


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Bragg's law based on PXRD data (Figure 1a). The crystal facet spacing value 0.271 nm of (200) plane for bulk CeO2 (PDF#34-0394) is smaller than the experimental data (0.279 nm, Figure 2j) which are in accord with the left shift of diffraction peaks of CeO2 (Figure 1a), indicating the successful incorporation of La3+.49-50 The mapping images of 0.5La-CeNC-Fe revealed that as prepared catalyst was with homogeneous N/Fe doping, and La-doped CeO2 nanoparticles were uniformly distributed (Figure 2k-r). The exact content La-doped CeO2 were 21.02 wt%, according to elemental analysis experiment (Table S3 and S4). To gain more information about the surface of catalyst on atomic level, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were performed. As can be concluded from the G band (about 1580 cm-1) in the Raman spectrum56-57, all the catalysts held an extraordinary degree of graphitization due to the catalysis effect of Fe53-55 (Figure 3a). In addition, all catalysts except La-NC-Fe showed a peak at about 465 cm-1, which was attributed to the F2g vibration of CeO2 with fluorite structure58(Figure 3a). Nonetheless, the peak intensity of 465 cm-1 weakened with increasing the amount of La3+, which is ascribed to the reduction of CeO2 content and decrease of symmetry. F2g bands of the 0.2 and 0.5La-CeNC-Fe shifted slightly towards lower wave numbers probably because the presence of La3+ affected the vibrational frequency of the Ce-O bonds49 (Figure 3a). The band at about 570 cm-1 indicates the formation of oxygen vacancies (Vo··) which acted as the active site for binding and activating oxygen molecules during the reactions36, 58. With increasing ratios of La3+, the concentration of oxygen vacancies increased as shown in Figure 3a. High-resolution XPS spectra of C 1s for the 0.5La-CeNC-Fe showed a predominant peak at 284.7 eV which was assigned to sp2 hybrid carbon59-60 (Figure 3b). The result is in accordance with the strong carbon (200) diffraction peak in XRD (Figure 1a) and graphitic carbon layers with well-defined lattice spacing (Figure 2g). Highly sp2 hybridized


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carbon is extremely crucial for rapid electron transfer for fast ORR kinetics21. The large amount of graphitic nitrogen (Gr-N) and pyridinic nitrogen (Py-N) appearing at 401.2 and 398.2 eV in the high-resolution N 1s XPS spectrum (Figure 3c) are important active sites to adsorb and activate O2 because of the N doping-induced charge redistribution stemmed from the different electronegativity between C and N61. In addition, the high content of graphitic nitrogen benefits from the large amount of the aromatic N present in the ligand of MOF-Ce/La-x16. Other types of N also appeared, such as pyrrolic N (Py-N) and oxidized N (Ox-N) (Figure 3c, Figure S10a). The corresponding possible C-N bond also appeared in Fourier Transform Infrared (FT-IR) spectrum62 (Figure S11). The Fe signal was present in the prepared catalyst by the identification of possible satellite peak (about 718 eV) in the high-resolution Fe 2p XPS spectrum59, 63 (Figure S10b) and possible Fe-N peak (399.4 eV)19, 21 in the N 1s spectrum (Figure 3c). Fe content is found to be ca. 1.42 wt% (Table S3). The O 1s high-resolution spectrum was deconvoluted into three typical peaks at 529.1 (Oα), 531.7(Oβ), and 533.16 eV (Oγ) (Figure 3d). Oα is ascribed to lattice oxygen while Oβ is attributable to chemisorbed oxygen which serves as reactive oxygen species to promote ORR36. The Oγ located on 533.2 eV is identical with C-O, suggesting that CeO2 particles with high vacancy were stabilized by the surrounding carbon substrate64. Red peaks in the high-resolution Ce 3d spectrum of catalysts were assigned to be Ce3+37-39 (Figure 3e, Figure S12a, c). Based on the peak area quantification, the Ce3+ content is shown in Figure 3f with various La3+ ratios. On the basis of previous reports, the content of Ce3+ is another manifestation of the concentration of oxygen vacancies because of charge balance in the final material37, 39. And then ceria nanoparticles with high concentrations of oxygen vacancies hold excellent oxygen storage capacity (OSC), which is extremely beneficial for enhancing the ORR rate by increasing the concentration of local O235, 38, 65.


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Figure 3. (a) Raman spectrum of xLa-CeNC-Fe. High-resolution XPS spectra of (b) C 1s, (c) N 1s, (d) O 1s and (e) Ce 3d in the 0.5La-CeNC-Fe. (f) The content of Ce3+ based on XPS data of xLa-CeNC-Fe and xLa-CeNC-Fe-Ad. O2 adsorption/desorption measurement was performed to further probe the oxygen vacancies of the catalyst (Figure 4). As expected, 0.5La-CeNC-Fe reached the maximum O2 adsorption capacity at 1 bar due to the synergistic effect between more oxygen vacancies and higher surface area than other samples. Under the same conditions, O2 adsorption capacity of CeNC-Fe is higher than 0.2La-CeNC-Fe, suggesting that ceria is crucial for O2 adsorption. The O2 desorption isotherms of La-doped CeNC-Fe catalysts showed significant hysteresis during the low-pressure section, indicating the strong interactions between the adsorbed oxygen and the catalysts66-67. While the desorption isotherm of La-NC-Fe is almost completely closed, the slight hysteresis may be attributed to Fe-Nx and the other corresponding nitrogen sites61. These results suggest that the oxygen vacancies of catalysts could bind O2 effectively. 0.5La-CeNC-Fe was


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characterized with XPS after oxygen adsorption/desorption experiment (designated as xLaCeNC-Fe-Ad) (Figure S13). The percentage of chemisorbed oxygen improved significantly while the Ce3+ content decreased (Figure 3f and S13) which indicated that oxygen vacancies could bind and activate O238, 65 to promote ORR.

Figure 4. O2 adsorption/desorption isotherms of (a) CeNC-Fe, (b) 0.2La-CeNC-Fe, (c) 0.5LaCeNC-Fe and (d) La-NC-Fe (P0=1 bar). Filled symbols-adsorption; open symbols-desorption. All ORR measurements were investigated with a three-electrode system (detailed in supporting information). Cyclic voltammetry (CV) measurements of xLa-CeNC-Fe were performed which implied that these catalysts are ORR active because of the appearance of welldefined cathodic reduction peaks (Figure 5a and Figure S14). The sample of 0.5La-CeNC-Fe is superior to other catalysts, even Pt/C (0.875 V and 2.36 mA/cm2), with the most positive peak potential (0.886 V) and the largest current density (2.72 mA/cm2). The linear sweep voltammetry (LSV) polarization curves obtained by the rotating disk electrodes (RDE) of the catalysts and Pt/C were displayed in Figure 5b and Figure S15. The catalyst of 0.5La-CeNC-Fe with half-wave


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potential (E1/2) of 0.870V exhibits a significantly better ORR activity than other catalysts and is slightly better than Pt/C with E1/2 of 0.862V. Meanwhile, the ORR activity of 0.5La-CeNC-Fe is also better than that of most CeO2-based and Fe-N-C-based catalysts reported recently (Table S5 and Table S6). Compared with CeNC-Fe and La-NC-Fe, the oxygen vacancies played an extremely important role during ORR, in consistency with the analysis above. As for the sample without and with low-content Fe, they also showed poor ORR activity, which may be attributed to the poor conductivity and absent Fe-Nx sites (Figure S15 and S16). When a high amount of Fe was used for experiments, unexpected unknown phases were produced (Figure S17). To gain further understanding of the ORR mechanism, LSV polarization curves were collected at different rotation speeds (Figure 5c) and used for Koutecky-Levich (K-L) plots, upon which the electron transfer numbers were calculated (Figure 5d, e, Figure S18). At all potentials, the calculated electron transfer number of 0.5La-CeNC-Fe is about 3.94, which indicated a fourelectrons pathway during ORR like Pt/C (3.96). However, there are obvious two-electron and four-electrons mixing processes for other catalysts which indicated poor selectivity during electrochemical catalysis59 (Figure S18). As showed in Figure 5f, the Tafel slope of 0.5LaCeNC-Fe (86.8 mV/dec) is much smaller than that of Pt/C (125.7 mV/dec), indicating a faster electron transfer rate68, which is attributed to the high crystalline carbon layer and oxygen vacancies in ceria37, 49.


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Figure 5. (a) CV curves for 0.5La-CeNC-Fe and Pt/C (20 wt%) at a scan rate of 20 mV s-1. (b) LSV curves for xLa-CeNC-Fe and Pt/C with the rotation rate of 1600 rpm. (c) LSV curves for 0.5La-CeNC-Fe with different rotation rates at a scan rate of 5 mV s-1. (d) K-L plots for 0.5LaCeNC-Fe at different electrode potentials from 0.20 V to 0.70 V. (e) The calculated electron transfer number from K-L plots data under various potentials and (f) Tafel plots of 0.5La-CeNCFe and Pt/C catalysts. All the tests were conducted in O2-saturated 0.1 M KOH solution. Besides the role of oxygen vacancies played in ORR, probable Fe-Nx is also the important catalysis sites for ORR. LSV curves were obtained with and without 0.01M SCN- in O2 saturated 0.1 M KOH solution (Figure S19a). Because of SCN- poisoning22, E1/2 of 0.5La-CeNC-Fe decreased by 53 mV, which showed the important role of Fe-Nx for promoting ORR. Compared with Pt/C (20 mV), catalyst 0.5La-CeNC-Fe exhibited excellent cycle stability with only a 7mV loss after 1000 cycles (Figure S19b, c). Durability tests lasting 20h (72000s) for 0.5La-CeNC-Fe and commercial Pt/C catalysts further demonstrated the excellent stability of the catalyst with


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only 10.0% attenuation of current (Figure S19d) by using current-time (i-t) chronoamperometry technology. The crossover effect caused by methanol (MeOH) was interrogated by LSV in O2 saturated 0.1 M KOH solution with 3 M MeOH. The introduction of MeOH lead to a decrease of current density with Pt/C system due to the accompanied MeOH oxidation, a process not observed with 0.5La-CeNC-Fe, indicating a strong tolerance to MeOH crossover of this new catalyst (Figure S19e). The rotating ring-disk electrode (RRDE) experiment was performed to confirm the ORR kinetics and monitor the formation of intermediate peroxide species (Figure S20). The HO2- yield (HO2- %) of 0.5La-CeNC-Fe is 2.26-5.55% over a wide potential range from -0.2 V to -0.8 V (vs. Ag/AgCl) which is comparable to that of the Pt/C catalyst (Figure S20b). A range of the electron-transfer number of 3.90-3.96 suggests of a four-electrons pathway dominated ORR process16, 18 (Figure S20c). CONCLUSION A series of Fe/N doped porous carbon and La embedded CeO2 composite catalysts derived from Ce/La dual rare earth metal MOF were synthesized for the first time. Impressively, 0.5LaCeNC-Fe stands out with the best ORR catalytic activity arising from a synergistic effect of Fe/N doped porous carbon with La-embedded CeO2 nanoparticles. On the one hand, the introduction of La3+ improves the surface area and porosity of the catalyst, which is conducive to the mass transfer during reaction. On the other hand, La3+ embedded into the lattice of CeO2 results in high concentration of oxygen vacancies and effectively activated the oxygen molecules. In addition, this versatile catalyst is demonstrated to be suitable for the efficient activation of other oxygen species, showcasing their potential in other non-electrochemical reactions (Figure S21).


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We are also trying out the use of this catalyst for other reactions using oxygen as the oxidant, and we think oxygen vacancies stabilized by the carbon substrate played an extremely important role during the catalytic reaction, which paved the way for constructing the catalyst with a high concentration of oxygen vacancies for other practical application. ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website. Electrochemistry measurements details and additional characterizations of all materials (PDF). AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] *E-mail: [email protected] ORCID Shuxia Liu: 0000-0003-0235-8594 Xiangjie Bo: 0000-0002-0407-0976 Notes The authors declare no competing financial interests. ACKNOWLEDGMENT


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This work was financially supported by the National Natural Science Foundation of China (Grant No. 21231002, 21371029, 21671033, 21571030 and 91622108), and the Open Research Fund of the State Key Laboratory of Inorganic Synthesis and Preparative Chemistry (Jilin University, Grant No. 2015-01).

REFERENCES

(1) Liu, M.; Zhang, R.; Chen, W. Graphene-Supported Nanoelectrocatalysts for Fuel Cells: Synthesis, Properties, and Applications. Chem. Rev. 2014, 114, 5117-5160. (2) Nasef, M. M. Radiation-Grafted Membranes for Polymer Electrolyte Fuel Cells: Current Trends and Future Directions. Chem. Rev. 2014, 114, 12278-12329. (3) Xia, W.; Mahmood, A.; Liang, Z.; Zou, R.; Guo, S. Earth-Abundant Nanomaterials for Oxygen Reduction. Angew. Chem. Int. Ed. 2016, 55, 2650-2676. (4) Shao, M.; Chang, Q.; Dodelet, J.-P.; Chenitz, R. Recent Advances in Electrocatalysts for Oxygen Reduction Reaction. Chem. Rev. 2016, 116, 3594-3657. (5) Zhou, M.; Wang, H.-L.; Guo, S. Towards High-efficiency Nanoelectrocatalysts for Oxygen Reduction through Engineering Advanced Carbon Nanomaterials. Chem. Soc. Rev. 2016, 45, 1273-1307. (6) Han, Y.; Wang, Y.-G.; Chen, W.; Xu, R.; Zheng, L.; Zhang, J.; Luo, J.; Shen, R.-A.; Zhu, Y.; Cheong, W.-C.; Chen, C.; Peng, Q.; Wang, D.; Li, Y. Hollow N-Doped Carbon Spheres with Isolated Cobalt Single Atomic Sites: Superior Electrocatalysts for Oxygen Reduction. J. Am. Chem. Soc. 2017, 139, 17269-17272.


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(7) Jiang, W.-J.; Gu, L.; Li, L.; Zhang, Y.; Zhang, X.; Zhang, L.-J.; Wang, J.-Q.; Hu, J.-S.; Wei, Z.; Wan, L.-J. Understanding the High Activity of Fe-N-C Electrocatalysts in Oxygen Reduction: Fe/Fe3C Nanoparticles Boost the Activity of Fe-Nx. J. Am. Chem. Soc. 2016, 138, 3570-3578. (8) Yao, Z.; Nie, H.; Yang, Z.; Zhou, X.; Liu, Z.; Huang, S. Catalyst-Free Synthesis of IodineDoped Graphene via a Facile Thermal Annealing Process and Its use for Electrocatalytic Oxygen Reduction in an Alkaline Medium. Chem. Commun. 2012, 48, 1027-1029. (9) Jin, Z.; Nie, H.; Yang, Z.; Zhang, J.; Liu, Z.; Xu, X.; Huang, S. Metal-Free Selenium Doped Carbon Nanotube/Graphene Networks as a Synergistically Improved Cathode Catalyst for Oxygen Reduction Reaction. Nanoscale 2012, 4, 6455-6460. (10) Fu, S.; Zhu, C.; Song, J.; Du, D.; Lin, Y. Metal-Organic Framework-Derived Non-Precious Metal Nanocatalysts for Oxygen Reduction Reaction. Adv. Energy Mater. 2017, 7, 17003631700381. (11) Zhang, H.; Osgood, H.; Xie, X.; Shao, Y.; Wu, G. Engineering Nanostructures of PGM-Free Oxygen-Reduction Catalysts Using Metal-Organic Frameworks. Nano Energy 2017, 31, 331350. (12) Dang, S.; Zhu, Q.-L.; Xu, Q. Nanomaterials Derived From Metal-Organic Frameworks. Nat. Rev. Mater. 2017, 3, 17075. (13) Qian, Y.; Khan, I. A.; Zhao, D. Electrocatalysts Derived from Metal-Organic Frameworks for Oxygen Reduction and Evolution Reactions in Aqueous Media. Small 2017, 13, 17011431701164.


18

Page 19 of 27 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


(14) Lee, K. J.; Lee, J. H.; Jeoung, S.; Moon, H. R. Transformation of Metal-Organic Frameworks/Coordination Polymers into Functional Nanostructured Materials: Experimental Approaches Based on Mechanistic Insights. Acc. Chem. Res. 2017, 50, 2684-2692. (15) Shen, K.; Chen, X.; Chen, J.; Li, Y. Development of MOF-Derived Carbon-Based Nanomaterials for Efficient Catalysis. ACS Catal. 2016, 6, 5887-5903. (16) Zhang, L.; Su, Z.; Jiang, F.; Yang, L.; Qian, J.; Zhou, Y.; Li, W.; Hong, M. Highly Graphitized Nitrogen-Doped Porous Carbon Nanopolyhedra Derived from ZIF-8 Nanocrystals as Efficient Electrocatalysts for Oxygen Reduction Reactions. Nanoscale 2014, 6, 6590-6602. (17) Meng, J.; Niu, C.; Xu, L.; Li, J.; Liu, X.; Wang, X.; Wu, Y.; Xu, X.; Chen, W.; Li, Q.; Zhu, Z.; Zhao, D.; Mai, L. General Oriented Formation of Carbon Nanotubes from Metal-Organic Frameworks. J. Am. Chem. Soc. 2017, 139, 8212-8221. (18) Zhang, L.; Wang, X.; Wang, R.; Hong, M. Structural Evolution from Metal-Organic Framework to Hybrids of Nitrogen-Doped Porous Carbon and Carbon Nanotubes for Enhanced Oxygen Reduction Activity. Chem. Mater. 2015, 27, 7610-7618. (19) Lai, Q.; Zheng, L.; Liang, Y.; He, J.; Zhao, J.; Chen, J. Metal-Organic-Framework-Derived Fe-N/C Electrocatalyst with Five-Coordinated Fe-Nx Sites for Advanced Oxygen Reduction in Acid Media. ACS Catal. 2017, 7, 1655-1663. (20) Fang, X.; Jiao, L.; Yu, S.-H.; Jiang, H.-L. Metal-Organic Framework-Derived FeCo-NDoped Hollow Porous Carbon Nanocubes for Electrocatalysis in Acidic and Alkaline Media. ChemSusChem 2017, 10, 3019-3024. (21) Zhang, H.; Hwang, S.; Wang, M.; Feng, Z.; Karakalos, S.; Luo, L.; Qiao, Z.; Xie, X.; Wang, C.; Su, D.; Shao, Y.; Wu, G. Single Atomic Iron Catalysts for Oxygen Reduction in Acidic


19


Page 20 of 27

Media: Particle Size Control and Thermal Activation. J. Am. Chem. Soc. 2017, 139, 1414314149. (22) Chen, Y.; Ji, S.; Wang, Y.; Dong, J.; Chen, W.; Li, Z.; Shen, R.; Zheng, L.; Zhuang, Z.; Wang, D.; Li, Y. Isolated Single Iron Atoms Anchored on N-Doped Porous Carbon as an Efficient Electrocatalyst for the Oxygen Reduction Reaction. Angew. Chem. Int. Ed. 2017, 56, 6937-6941. (23) Ye, Y.; Cai, F.; Li, H.; Wu, H.; Wang, G.; Li, Y.; Miao, S.; Xie, S.; Si, R.; Wang, J.; Bao, X. Surface Functionalization of ZIF-8 with Ammonium Ferric Citrate Toward High Exposure of Fe-N Active Sites for Efficient Oxygen and Carbon Dioxide Electroreduction. Nano Energy 2017, 38, 281-289. (24) Park, J.; Lee, H.; Bae, Y. E.; Park, K. C.; Ji, H.; Jeong, N. C.; Lee, M. H.; Kwon, O. J.; Lee, C. Y. Dual-Functional Electrocatalyst Derived from Iron-Porphyrin-Encapsulated Metal-Organic Frameworks. ACS Appl. Mater. Interfaces 2017, 9, 28758-28765. (25) Aijaz, A.; Fujiwara, N.; Xu, Q. From Metal-Organic Framework to Nitrogen-Decorated Nanoporous Carbons: High CO2 Uptake and Efficient Catalytic Oxygen Reduction. J. Am. Chem. Soc. 2014, 136, 6790-6793. (26) Liu, Y.; Jiang, H.; Hao, J.; Liu, Y.; Shen, H.; Li, W.; Li, J. Metal-Organic FrameworkDerived Reduced Graphene Oxide-Supported ZnO/ZnCo2O4/C Hollow Nanocages as Cathode Catalysts for Aluminum-O2 Batteries. ACS Appl. Mater. Interfaces 2017, 9, 31841-31852. (27) Jiao, L.; Zhou, Y.-X.; Jiang, H.-L. Metal-Organic Framework-Based CoP/Reduced Graphene Oxide: High-Performance Bifunctional Electrocatalyst for Overall Water Splitting. Chem. Sci. 2016, 7, 1690-1695.


20

Page 21 of 27 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


(28) Hou, Y.; Wen, Z.; Cui, S.; Ci, S.; Mao, S.; Chen, J. An Advanced Nitrogen-Doped Graphene/Cobalt-Embedded Porous Carbon Polyhedron Hybrid for Efficient Catalysis of Oxygen Reduction and Water Splitting. Adv. Funct. Mater. 2015, 25, 872-882. (29) Hou, Y.; Huang, T.; Wen, Z.; Mao, S.; Cui, S.; Chen, J. Metal-Organic Framework-Derived Nitrogen-Doped Core-Shell-Structured Porous Fe/Fe3C@C Nanoboxes Supported on Graphene Sheets for Efficient Oxygen Reduction Reactions. Adv. Energy Mater. 2014, 4, 14003371400344. (30) Zhong, H.-X.; Wang, J.; Zhang, Y.-W.; Xu, W.-L.; Xing, W.; Xu, D.; Zhang, Y.-F.; Zhang, X.-B. ZIF-8 Derived Graphene-Based Nitrogen-Doped Porous Carbon Sheets as Highly Efficient and Durable Oxygen Reduction Electrocatalysts. Angew. Chem. Int. Ed. 2014, 53, 14235-14239. (31) Wang, J.; Huang, Z.; Liu, W.; Chang, C.; Tang, H.; Li, Z.; Chen, W.; Jia, C.; Yao, T.; Wei, S.; Wu, Y.; Li, Y. Design of N-Coordinated Dual-Metal Sites: A Stable and Active Pt-Free Catalyst for Acidic Oxygen Reduction Reaction. J. Am. Chem. Soc. 2017, 139, 17281-17284. (32) Yin, P.; Yao, T.; Wu, Y.; Zheng, L.; Lin, Y.; Liu, W.; Ju, H.; Zhu, J.; Hong, X.; Deng, Z.; Zhou, G.; Wei, S.; Li, Y. Single Cobalt Atoms with Precise N-Coordination as Superior Oxygen Reduction Reaction Catalysts. Angew. Chem. Int. Ed. 2016, 55, 10800-10805. (33) Chen, Y.-Z.; Wang, C.; Wu, Z.-Y.; Xiong, Y.; Xu, Q.; Yu, S.-H.; Jiang, H.-L. From Bimetallic

Metal-Organic

Framework

to

Porous

Carbon:

High

Surface

Area

and

Multicomponent Active Dopants for Excellent Electrocatalysis. Adv. Mater. 2015, 27, 50105016. (34) Singh, K.; Razmjooei, F.; Yu, J.-S. Active Sites and Factors Influencing Them for Efficient Oxygen Reduction Reaction in Metal-N Coordinated Pyrolyzed and Non-Pyrolyzed Catalysts: a Review. J. Mater. Chem. A 2017, 5, 20095-20119.


21


Page 22 of 27

(35) Montini, T.; Melchionna, M.; Monai, M.; Fornasiero, P. Fundamentals and Catalytic Applications of CeO2-Based Materials. Chem. Rev. 2016, 116, 5987-6041. (36) Yu, Y.; Gao, L.; Liu, X.; Wang, Y.; Xing, S. Enhancing the Catalytic Activity of Zeolitic Imidazolate Framework-8-Derived N-Doped Carbon with Incorporated CeO2 Nanoparticles in the Oxygen Reduction Reaction. Chem. Eur. J. 2017, 23, 10690-10697. (37) Yu, Y.; Wang, X.; Gao, W.; Li, P.; Yan, W.; Wu, S.; Cui, Q.; Song, W.; Ding, K. Trivalent Cerium-Preponderant CeO2/Graphene Sandwich-Structured Nanocomposite with Greatly Enhanced Catalytic Activity for the Oxygen Reduction Reaction. J. Mater. Chem. A 2017, 5, 6656-6663. (38) Liu, K.; Huang, X.; Wang, H.; Li, F.; Tang, Y.; Li, J.; Shao, M. Co3O4-CeO2/C as a Highly Active Electrocatalyst for Oxygen Reduction Reaction in Al-Air Batteries. ACS Appl. Mater. Interfaces 2016, 8, 34422-34430. (39) Chen, J.; Zhou, N.; Wang, H.; Peng, Z.; Li, H.; Tang, Y.; Liu, K. Synergistically Enhanced Oxygen Reduction Activity of MnOx-CeO2/Ketjenblack composites. Chem. Commun. 2015, 51, 10123-10126. (40) Schmitt, R.; Spring, J.; Korobko, R.; Rupp, J. L. M. Design of Oxygen Vacancy Configuration for Memristive Systems. ACS Nano 2017, 11, 8881-8891. (41) Liyanage, A. D.; Perera, S. D.; Tan, K.; Chabal, Y.; Balkus, K. J. Synthesis, Characterization, and Photocatalytic Activity of Y-Doped CeO2 Nanorods. ACS Catal. 2014, 4, 577-584. (42) Fu, Q.; Saltsburg, H.; Flytzani-Stephanopoulos, M. Active Nonmetallic Au and Pt Species on Ceria-Based Water-Gas Shift Catalysts. Science 2003, 301, 935-938.


22

Page 23 of 27 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


(43) Tang, Q.; Liu, S.; Liu, Y.; He, D.; Miao, J.; Wang, X.; Ji, Y.; Zheng, Z. Color Tuning and White Light Emission via in Situ Doping of Luminescent Lanthanide Metal-Organic Frameworks. Inorg. Chem. 2014, 53, 289-293. (44) Tang, Q.; Liu, S.; Liu, Y.; Miao, J.; Li, S.; Zhang, L.; Shi, Z.; Zheng, Z. Cation Sensing by a Luminescent Metal-Organic Framework with Multiple Lewis Basic Sites. Inorg. Chem. 2013, 52, 2799-2801. (45) Schlesinger, M.; Schulze, S.; Hietschold, M.; Mehring, M. Evaluation of Synthetic Methods for Microporous Metal-Organic Frameworks Exemplified by the Competitive Formation of [Cu2(btc)3(H2O)3] and [Cu2(btc)(OH)(H2O)]. Microporous Mesoporous Mater. 2010, 132, 121127. (46) Diring, S.; Furukawa, S.; Takashima, Y.; Tsuruoka, T.; Kitagawa, S. Controlled Multiscale Synthesis of Porous Coordination Polymer in Nano/Micro Regimes. Chem. Mater. 2010, 22, 4531-4538. (47) Liu, Y.; Liu, S.; Liu, S.; Liang, D.; Li, S.; Tang, Q.; Wang, X.; Miao, J.; Shi, Z.; Zheng, Z. Facile Synthesis of a Nanocrystalline Metal-Organic Framework Impregnated with a Phosphovanadomolybdate and Its Remarkable Catalytic Performance in Ultradeep Oxidative Desulfurization. ChemCatChem 2013, 5, 3086-3091. (48) Guo, H.; Zhu, Y.; Wang, S.; Su, S.; Zhou, L.; Zhang, H. Combining Coordination Modulation with Acid-Base Adjustment for the Control over Size of Metal-Organic Frameworks. Chem. Mater. 2012, 24, 444-450. (49) Zhou, X.; Ling, J.; Sun, W.; Shen, Z. Fabrication of Homogeneously Cu2+/La3+-doped CeO2 Nanosheets and Their Application in CO Oxidation. J. Mater. Chem. A 2017, 5, 9717-9722.


23


Page 24 of 27

(50) Reddy, B. M.; Katta, L.; Thrimurthulu, G. Novel Nanocrystalline Ce1-xLaxO2-δ (x = 0.2) Solid Solutions: Structural Characteristics and Catalytic Performance. Chem. Mater. 2010, 22, 467-475. (51) Tang, F.; Lei, H.; Wang, S.; Wang, H.; Jin, Z. A Novel Fe-N-C Catalyst for Efficient Oxygen Reduction Reaction Based on Polydopamine Nanotubes. Nanoscale 2017, 9, 1736417370. (52) Wang, H.; Wang, W.; Asif, M.; Yu, Y.; Wang, Z.; Wang, J.; Liu, H.; Xiao, J. Cobalt IonCoordinated Self-Assembly Synthesis of Nitrogen-Doped Ordered Mesoporous Carbon Nanosheets for Efficiently Catalyzing Oxygen Reduction. Nanoscale 2017, 9, 15534-15541. (53) Wang, Q.; Lei, Y.; Chen, Z.; Wu, N.; Wang, Y.; Wang, B.; Wang, Y. Fe/Fe3C@C Nanoparticles Encapsulated in N-Doped Graphene-CNTs Framework as an Efficient Bifunctional Oxygen Electrocatalyst for Robust Rechargeable Zn-Air Batteries. J. Mater. Chem. A 2018, 6, 516-526. (54) Su, P.; Xiao, H.; Zhao, J.; Yao, Y.; Shao, Z.; Li, C.; Yang, Q. Nitrogen-Doped Carbon Nanotubes Derived from Zn-Fe-ZIF Danospheres and Their Application as Efficient Oxygen Reduction Electrocatalysts with In Situ Generated Iron Species. Chem. Sci. 2013, 4, 2941-2946. (55) Li, J.-S.; Li, S.-L.; Tang, Y.-J.; Han, M.; Dai, Z.-H.; Bao, J.-C.; Lan, Y.-Q. Nitrogen-Doped Fe/Fe3C@Graphitic Layer/Carbon Nanotube Hybrids Derived from MOFs: Efficient Bifunctional Electrocatalysts for ORR and OER. Chem. Commun. 2015, 51, 2710-2713. (56) Sadezky, A.; Muckenhuber, H.; Grothe, H.; Niessner, R.; Pöschl, U. Raman Microspectroscopy of Soot and Related Carbonaceous Materials: Spectral Analysis and Structural Information. Carbon 2005, 43, 1731-1742.


24

Page 25 of 27 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


(57) Li, P.; Yang, Z.; Shen, J.; Nie, H.; Cai, Q.; Li, L.; Ge, M.; Gu, C.; Chen, X. a.; Yang, K.; Zhang, L.; Chen, Y.; Huang, S. Subnanometer Molybdenum Sulfide on Carbon Nanotubes as a Highly Active and Stable Electrocatalyst for Hydrogen Evolution Reaction. ACS Appl. Mater. Interfaces 2016, 8, 3543-3550. (58) Pu, Z.-Y.; Liu, X.-S.; Jia, A.-P.; Xie, Y.-L.; Lu, J.-Q.; Luo, M.-F. Enhanced Activity for CO Oxidation over Pr- and Cu-Doped CeO2 Catalysts: Effect of Oxygen Vacancies. J. Phys. Chem. C 2008, 112, 15045-15051. (59) Zhang, C.; Liu, J.; Ye, Y.; Aslam, Z.; Brydson, R.; Liang, C. Fe-N-Doped Mesoporous Carbon with Dual Active Sites Loaded on Reduced Graphene Oxides for Efficient Oxygen Reduction Catalysts. ACS Appl. Mater. Interfaces 2018, 10, 2423-2429. (60) Cheng, Q.; Yang, L.; Zou, L.; Zou, Z.; Chen, C.; Hu, Z.; Yang, H. Single Cobalt Atom and N Codoped Carbon Nanofibers as Highly Durable Electrocatalyst for Oxygen Reduction Reaction. ACS Catal. 2017, 7, 6864-6871. (61) Gong, K.; Du, F.; Xia, Z.; Durstock, M.; Dai, L. Nitrogen-Doped Carbon Nanotube Arrays with High Electrocatalytic Activity for Oxygen Reduction. Science 2009, 323, 760-764. (62) Amiinu, I. S.; Liu, X.; Pu, Z.; Li, W.; Li, Q.; Zhang, J.; Tang, H.; Zhang, H.; Mu, S. From 3D ZIF Nanocrystals to Co-Nx/C Nanorod Array Electrocatalysts for ORR, OER, and Zn-Air Batteries. Adv. Funct. Mater. 2018, 28, 1704638-1704646. (63) Huang, Z.; Pan, H.; Yang, W.; Zhou, H.; Gao, N.; Fu, C.; Li, S.; Li, H.; Kuang, Y. In Situ Self-Template Synthesis of Fe-N-Doped Double-Shelled Hollow Carbon Microspheres for Oxygen Reduction Reaction. ACS Nano 2018, 12, 208-216.


25


Page 26 of 27

(64) Kong, L.; Wei, W.; Zhao, Q.; Wang, J.-Q.; Wan, Y. Active Coordinatively Unsaturated Manganese Monoxide-Containing Mesoporous Carbon Catalyst in Wet Peroxide Oxidation. ACS Catal. 2012, 2, 2577-2586. (65) Xia, W.; Li, J.; Wang, T.; Song, L.; Guo, H.; Gong, H.; Jiang, C.; Gao, B.; He, J. The Synergistic Effect of Ceria and Co in N-Doped Leaf-Like Carbon Nanosheets Derived from a 2D MOF and Their Enhanced Performance in the Oxygen Reduction Reaction. Chem. Commun. 2018, 54, 1623-1626. (66) Yoon, J. W.; Jhung, S. H.; Hwang, Y. K.; Humphrey, S. M.; Wood, P. T.; Chang, J. S. GasSorption Selectivity of CUK-1: A Porous Coordination Solid Made of Cobalt(II) and Pyridine2,4- Dicarboxylic Acid. Adv. Mater. 2007, 19, 1830-1834. (67) Zhang, W.; Banerjee, D.; Liu, J.; Schaef, H. T.; Crum, J. V.; Fernandez, C. A.; Kukkadapu, R. K.; Nie, Z.; Nune, S. K.; Motkuri, R. K.; Chapman, K. W.; Engelhard, M. H.; Hayes, J. C.; Silvers, K. L.; Krishna, R.; McGrail, B. P.; Liu, J.; Thallapally, P. K. Redox-Active MetalOrganic Composites for Highly Selective Oxygen Separation Applications. Adv. Mater. 2016, 28, 3572-3577. (68) Yang, W.; Zhang, Y.; Liu, X.; Chen, L.; Jia, J. In Situ Formed Fe-N Doped Metal Organic Framework@Carbon Nanotubes/Graphene Hybrids for a Rechargeable Zn-Air Battery. Chem. Commun. 2017, 53, 12934-12937.


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Lewis-Basic Lanthanide Metal-Organic Framework Derived Versatile

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