Enhancing Oxygen Evolution Electrocatalysis via the Intimate

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Enhancing Oxygen Evolution Electrocatalysis via the Intimate Hydroxide-Oxide Interface Dandan Zhao, Yecan Pi, Qi Shao, Yonggang Feng, Ying Zhang, and Xiaoqing Huang ACS Nano, Just Accepted Manuscript • DOI: 10.1021/acsnano.8b03141 • Publication Date (Web): 15 May 2018 Downloaded from http://pubs.acs.org on May 15, 2018

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Enhancing Oxygen Evolution Electrocatalysis via the Intimate Hydroxide-Oxide Interface Dandan Zhao, Yecan Pi, Qi Shao*, Yonggang Feng, Ying Zhang, and Xiaoqing Huang* College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Jiangsu, 215123, China. *

Address correspondence to: [email protected]; [email protected].

ABSTRACT: The development of electrocatalysts with highly activity and stability for oxygen evolution reaction (OER) is critically important, the one being regarded as the bottleneck process of overall water splitting. Herein, we fulfil significant OER improvement in both activity and stability by constructing a class of Ni(OH)2-CeO2 supported on carbon paper (NixCey@CP) with intimate hydroxide(Ni(OH)2)-oxide(CeO2) interface. Such interface largely promotes the OER activity with a low

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overpotential of 220 mV at 10 mA cm-2 and a small Tafel slope of 81.9 mV dec-1 in 1 M KOH. X-ray photoelectron spectroscopy (XPS) analysis shows that the intimate interface induced by the strong electronic interactions between Ni(OH)2 and CeO2 intrigues the modulation of binding strength between intermediates and catalysts, making great contribution to the OER enhancement. Importantly, such intimate interface structures can be largely maintained even after a long time stability test. We have further demonstrated that, when pairing with the Ni4Ce1@CP after phosphorization (P-Ni4Ce1@CP), the Ni4Ce1@CP and P-Ni4Ce1@CP assembly is highly active and stable for overall water splitting with a low voltage of 1.68 V at 25 mA cm-2 and negligible stability delay over 30 h continuous operation, which are much better than the commercial Ir/C and Pt/C.

KEYWORDS: nickel(II) hydroxide, cerium(IV) oxide, interfacial effect, oxygen evolution reaction, overall water splitting

Electrochemical water splitting is recognized as a green and sustainable route to convert water into the useful hydrogen (H2) and oxygen (O2).1-8 From the kinetic view, the oxidative half reaction-oxygen evolution reaction (OER) is regarded as the biggest obstacle since it is a multiple electron transfer process, requiring large overpotentials.9-12 The pursuit of efficient OER electrocatalyst has thus become an important frontier in the practical development of overall water splitting. IrO2 and RuO2 are employed as the most active OER electrocatalysts, while their widely practical applications are largely hindered by their limited reservoir and high costs.13-15 To this end, particular emphases have been placed on the development of the earth-abundant non-precious 3d transition metals for OER, whereas their activity and stability are still far from desirable.16-21


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Oxide decorated catalyst is regarded as a promising candidate for OER benefiting from the large oxygen storage capacity of oxide and the electron interaction between different components. 22-25 For instance, CeO2 cluster doped NiO shows larger OER enhancement than CeO2 cluster surface loaded NiO due to the promoted oxygen storage capacity and optimized electronic structure of the active sites. 26 Unfortunately, those two catalysts are unstable with more than 23% activity loss within only short electrocatalysis. This may due to the fact that the lack of intimate oxide/catalyst interface, which results in the easy active site loss in the corrosive condition. To improve the electrochemcial stability, another work has been represented by depositing a protective thin CeO2 layer on NiFeOx, which leads to the enhanced stability by preventing the ions from leaching.27 However, hardly activity enhancement is observed since a large area of the coating layer also prevents the contact between the active sites and the electrolyte. Therefore, the rational design of the structure for achieving both activity and stability enhancements would be of paramount importance for OER. Herein, we report a class of NixCey@CP electrocatalysts, which are constructed by abundant intimate hydroxide (Ni(OH)2)-oxide(CeO2) interfaces supported on carbon paper (CP). Benefit from the strong interactions between the intimate Ni(OH)2 and CeO2 interface that desirably modified the binding energy of intermediates on the Ni(OH)2, the optimized Ni4Ce1@CP delivered efficient OER performance with the lowest overpotential of 220 mV at 10 mA cm-2 and Tafel slope of 81.9 mV dec-1 in alkaline electrolyte. Significantly, the Ni4Ce1@CP exhibited the best stability with a small potential shift after 20 h chronopotentiometry test and largely maintained intimate interfaces. During the overall water splitting, the combination of Ni4Ce1@CP with Ni4Ce1@CP after phosphorization achieves the current density of 25 mA cm-2 with applying a low voltage of 1.68 V and excellent stability for 30 h continuous electrocatalysis. RESULTS AND DISCUSSION


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The OER electrocatalysts (Ni8Ce1@CP, Ni4Ce1@CP and Ni2Ce1@CP) were synthesized through a one-pot wet-chemical process (Supporting information). The scanning electron microscopy (SEM) images (Figure 1a&Figure S1) show that NixCey nanosheets homogeneously grow on CP with three dimensional (3D) open structure. The EDX confirms the presences of Ni, Ce and O in the NixCey@CP (Figure S2). With increasing the Ce concentration, the atomic ratio of Ni to Ce changes from 8:1, 4:1 to 2:1. The XRD patterns show two separated strong pattern diffraction peaks comprised of .-Ni(OH)2 (JCPDS card No.38-0715) and CeO2 (JCPDS card No.75-0076) (Figure 1b&Figure S3). The STEMEDX and SEM-EDX mapping images (Figure 1c&Figure S4) show that the Ni and Ce are homogeneously mixed with each other. As shown in Figure 1d, the HAADF-STEM image with high magnification reveals that the CeO2 nanoparticles, marked with white arrows, with higher contrast homogeneously coat on the .-Ni(OH)2 nanosheet, highlighted by white arrows. To gain better view about the distribution of Ni(OH)2 and CeO2, high-resolution transmission electron microscopy (HRTEM) was carried out (Figure 1e-g). It revealed that CeO2 with the size of around 4.5 nm was evenly dispersed on .-Ni(OH)2. More interestingly, the intimate Ni(OH)2-CeO2 interface was clearly displayed, where two different sets of lattice fringes with the interplanar spacings of 0.156 nm and 0.315 nm indexed to the (110) phase of .-Ni(OH)2 and (111) phase of CeO2, respectively, were observed, indicating the successful fabrication of the intimate CeO2-Ni(OH)2 interface. For comparison, the pure Ni(OH)2 nanosheet grown on CP (Ni@CP) was also synthesized by the same method without the use of Ce precursors (Figure S5).


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Figure 1. (a) SEM image, (b) XRD pattern and (c) HAADF-STEM image and the corresponding STEM-EDX mappings of Ni4Ce1@CP. (d) HAADF-STEM image of Ni4Ce1@CP, in which CeO2 nanoparticles are pointed by white arrows. (e) HRTEM and (f, g) enlarged HRTEM images of Ni4Ce1@CP. The OER performance was first evaluated in the alkaline electrolyte (1 M KOH) at room


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temperature. As shown in Figure 2a, with increasing the atomic ratio of Ni to Ce, the OER activity shows a volcano-like fashion, in which the Ni4Ce1@CP endows the best OER performance among the tested catalysts. Figure 2b exhibits the Tafel slopes of different catalysts, where Ni4Ce1@CP shows a low Tafel slope of 81.9 mV dec-1. More detailed information can be founded in Figure 2c, in which Ni4Ce1@CP achieves the lowest overpotential of 220 mV at 10 mA cm-2 and the lowest Tafel slope of 81.9 mV dec-1, making it among the best OER catalysts (Table S1). To understand the excellent OER activity, the electrochemical impedance spectroscopy (EIS) was tested at the potential of 1.55 V. As shown in Figure 2d, the charge transfer resistance (Rct) is decreased with introducing Ce to Ni(OH)2 and the Rct of Ni4Ce1@CP is smaller than those of Ni@CP, Ni8Ce1@CP and Ni2Ce1@CP under the same condition, suggesting that Ni4Ce1@CP possesses the fast electron transport ability for OER. Furthermore, the Ni4Ce1@CP exhibits the best stability with a very small shift during the 20 h chronopotentiometry test, in which the OER polarization curve, morphology and composition showed limited changes after a prolonged chronopotentiometry test at the current density of 5 mA cm-2 (Figures S6-S8). The chronopotentiometry test of Ni4Ce1@CP was further carried out at higher current densities of 10 mA cm-2 and 20 mA cm-2 for 20 h, both of which show negligible changes in potential and morphology (Figure 2e&Figure S9).


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Figure 2. OER performances of Ni@CP, Ni8Ce1@CP, Ni4Ce1@CP, Ni2Ce1@CP and the commercial Ir/C. (a) OER polarization curves. (b) Tafel slopes. (c) Comparisons of Tafel slopes (up) and overpotentials at 10 mA cm-2 (bottom). (d) Nyquist plots of different electrocatalysts recorded at 1.55 V vs. RHE. (e) Chronopotentiometry curves of Ni4Ce1@CP at 5 mA cm-2, 10 mA cm-2 and 20 mA cm-2, respectively. (f) The OER polarization curves of CeO2&Ni@CP and CeO2. Now, it is of major essential to encode the reason behind the enhanced OER activity since OER is regarded as the bottleneck reaction in water splitting reaction. As shown in Figure 2f, compared with


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Ni@CP, CeO2 delivered negligible OER activity, indicating that Ni(OH)2 provide the active sites for OER. In addition, a reference electrocatalyst was prepared by mechanically mixing Ni@CP and CeO 2 (Figure S10). However, such eletrocatalyst exhibits an overpotential of 380 mV at the current density of 10 mA cm-2, which is much higher than that of the in-situ synthesized Ni4Ce1@CP (Figure 2f), suggesting the intimate interface between Ni(OH)2 and CeO2 boosts the OER. Based on the above discussion, XPS was used to analyze the surface chemical states of NixCey@CP. XPS spectra of NixCey@CP in O 1s, Ce 3d and Ni 2p regions are first measured (Figure 3a&Figures S11, 12). In Figure S11, the fitting analyses reveal that the peaks at about 529.19 eV and 531.3 eV correspond to the Ce-O and OH- bonds, respectively.28,29 With raising the atomic ratio of Ce to Ni, the intensities of the peak of Ce-O are also increased. As shown in Figure S12, the XPS demonstrates that the element Ce mainly exists as CeO2, which are composed of 3d5/2 (vn) and 3d3/2 (un) spin-orbit components.28 For Ce 3d of CeO2, the spectra can be deconvoluted into ten peaks, which consist of two pairs of doublets (v 0/u0 DQG Y¶ X¶ DVVLJQHG WR &H3+ DQG WKUHH SDLUV RI GRXEOHWV GRXEOHWV Y X Y¶¶ X¶¶ DQG Y¶¶¶ X¶¶¶ DVVLJQHG WR Ce4+, indicating that the coexistences of Ce3+ and Ce4+ in the Ni8Ce1@CP, Ni4Ce1@CP and [email protected],31 Figure 3a shows the Ni 2p spectra of NixCey@CP and the fitting analyses reveal that all catalysts can be deconvoluted into eight peaks.32 The major peaks can be assigned to Ni2+ and Ni3+ peaks. If we have a closer view about the XPS peak locations, all the Ni peaks of different catalysts shift to the lower binding energies compared with those of Ni@CP, in which Ni4Ce1@CP exhibit the largest peak shift. This result suggests that a strong electronic interaction formed between Ni(OH)2 and CeO2. In addition, Ni3+ is generally believed to provide the active site for OER reaction. As shown in Figure 3b&Table S2, the molar ratio of Ni2+/Ni3+ are calculated to be 1.77 to 0.96, 0.78, and 0.87 in Ni@CP, Ni8Ce1@CP, Ni4Ce1@CP and Ni2Ce1@CP, suggesting that the highest concentration of Ni3+ formed in Ni4Ce1@CP, in good agreement with the trend of the OER activity.


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Figure 3. (a) Ni 2p XPS spectra and (b) molar ratios of Ni2+/Ni3+ (up) and the current densities at 1.53 V (vs. RHE) (bottom) of NixCey@CP and Ni@CP. (c) Ni 2p XPS spectra of Ni4Ce1@CP, CeO2&Ni@CP and Ni@CP. To understand the intrinsic effect of the interface on the OER performance, XPS result of CeO2&Ni@CP was also analyzed. Figure 3c compares the Ni 2p spectra of Ni4Ce1@CP, CeO2&Ni@CP and Ni@CP. By choosing the Ni@CP as a reference, no obvious peak shift of Ni 2p was detected in CeO2&Ni@CP, indicating the negligible electronic interaction between Ni(OH)2 and CeO2 via mechanically mixing. However for the Ni4Ce1@CP, the binding energy of Ni 2p is negatively shifted about 0.4 eV, confirming the strong interaction between Ni(OH)2 and CeO2. In general, the OER mechanism in alkaline conditions can be expressed as following steps: OH-

: +2

HO* + OH- : 2

H+2O + e-

(1) (2)


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O* + OH- : +22 HOO* + OH- :

H22 + H2O + e-

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(3) (4)

The * denotes the active sites at the catalyst surface.33 The OER performance largely depends on the binding energies between catalyst surface and intermediates (O*, HO* and HOO*), where an appropriate binding strength leads to the optimal OER performance.34

Scheme 1. The schemes of the OER processes in different catalysts: (a) Ni@CP and (b) Ni4Ce1@CP with the intimate Ni(OH)2-CeO2 interfaces. For the real catalysts, the binding energy of the intermediate O* species is generally used to describe the OER activity.35 Ni is regarded as the active site for OER, while its major limitation is due to


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its strong binding strength to O*. This also can be derived from the OER volcano plot based on the DFT calculation, whereas NiOX is located at the stronger binding energy.36,37 According to the above discussion, the differences in the OER processes of Ni4Ce1@CP and Ni@CP can be illustrated by Scheme 1. Compared to Ni@CP, the Ni 2p peak of Ni4Ce1@CP shifts to the lower binding energy, indicating the chemical state of Ni3+ changes to Ni3- , caused by the electron transferred from CeO2 to Ni(OH)2 via the intimate interfaces.38 Therefore the binding energy of the intermediate O* on the Ni4Ce1@CP is expected to be weaker than that on the Ni@CP. This change leads to the weaker absorption O* on the Ni surface of Ni4Ce1@CP and the shift of binding strength to the optimal one, all of which can facilitate to generate the intermediates OOH* and thus accelerate the O2 production. One thing should be noted that such promotion on OER performance can not achieved by the weak interaction in the CeO2&Ni@CP, evidenced by no obvious peak shift of Ni 2p peak.

Figure 4. (a) HAADF-STEM and (b) HRTEM images of Ni4Ce1@CP after stability test. The inset in (a) is XRD pattern of Ni4Ce1@CP after stability test.


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Considering the negligible activity loss after the stability tests, particular emphasis has been placed on exploring the reasons behind the enhanced stability. As shown in Figure 4a, after stability test the CeO2 nanoparticles still keep the homogeneous distribution on the Ni(OH)2 with .-Ni(OH)2 and CeO2 phases largely presented. As evidenced by the HRTEM image (Figure 4b), the intimate interfaces between Ni(OH)2 and CeO2 can be clearly observed with clear crystal lattice. These results confirm that the intimate interface is stable under the long term corrosion condition. In order to improve the feasibility of Ni4Ce1@CP, the development of overall water splitting is extremely necessary. The HER electrocatalysts were created by converting the NixCey@CP into PNixCey@CP via phosphorization at high temperature (Figure S13). The EDX analysis confirms that the presences of P, Ni and Ce in the P-Ni4Ce1@CP (Figure S14). And the SEM-EDX mappings revealed that the elements O, Ni, Ce and P were uniformly distributed in P-Ni4Ce1@CP (Figure S15). Furthermore, XPS is employed to understand the phosphorization condition of the P-Ni4Ce1@CP. In Figure S16a, the high-resolution XPS spectrum of Ni 2p3/2 can be deconvolved into three separated peaks. The peaks at 853.16, 856.92 and 861.3 eV are assigned to Ni/ species in the Ni-P compound, Ni2+ in nickel oxide and the satellite peak, respectively.39 In Figure S16b, as for the P 2p, the peak can be deconvoluted into three peaks. The peaks at the 129.32 eV and 129.92 eV are assigned to P3-, and the predominate peak located at the 134.11 eV represents the oxidized phosphate species, due to the air exposure.40 The high-resolution XPS spectra of Ce 3d peak can be deconvoluted into six peaks, where the peaks located at 880-890 eV and 900-910 eV are referred to the 3d5/2 and 3d3/2 spin-orbit components, respectively. The peaks at the 881.71 eV, 888.45 eV, 900.50 eV and 907.05 eV are assigned to Ce4+, while the peaks at the 885.01 eV and 903.65 eV are attributed to Ce3+ (Figure S16c).30,31 All the above results prove the successful phosphorization of NixCey@CP. The HER activities of P-NixCey@CP were then measured in 1 M KOH electrolyte. As shown in Figures 5a,


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5b&S17, P-Ni4Ce1@CP exhibits the lowest overpotential of 180 mV at the current density of 10 mA cm-2 and Tafel slope of 90.1 mV dec-1, among the best performance of non-precious metal HER catalysts (Table S3). We further conceived the optimized Ni4Ce1@CP and P-Ni4Ce1@CP as the anode and the cathode to split water molecules to H2 and O2 in 1 M KOH. As shown in Figure 5c, the PNi4Ce1@CP || Ni4Ce1@CP proceeds the current density of 25 mA cm-2 at the potential of 1.68 V, and exhibits low Tafel slope of 264.2 mV dec-1, which is superior to those of commercial Pt/C || Ir/C and many other bifunctional catalysts (Table S4). Furthermore, the P-Ni4Ce1@CP || Ni4Ce1@CP couple also exhibits fairly stable durability towards the overall water splitting reaction of 30 h, while the Pt/C || Ir/C shows a relatively short time stability (Figures 5d&S18). As shown in Figure 5e, after the stability test, the elements O, Ni and Ce distribute homogeneously in the catalysts. The similar element distributions are observed in the P-Ni4Ce1@CP (Figure 5f). Both the superior electrocatalytic activity and the prolonged stability indicate the promising potential of P-Ni4Ce1@CP || Ni4Ce1@CP in practical applications.


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Figure 5. (a) HER polarization curves and (b) comparisons of Tafel slopes (up) and overpotentials at 10 mA cm-2 (bottom) of P-NixCey@CP. (c) LSVs of P-Ni4Ce1@CP || Ni4Ce1@CP and Pt/C || Ir/C for overall water splitting system in 1 M KOH and the corresponding Tafel slope curves (inset). (d) The chronopotentiometry curve of P-Ni4Ce1@CP || Ni4Ce1@CP at a current density of 10 mA cm-2 and a photograph of the water splitting (inset). SEM images and the corresponding EDX mappings of (e) Ni4Ce1@CP and (f) P-Ni4Ce1@CP after the water splitting stability test.

CONCLUSIONS


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In summary, we have described the intimate hydroxide-oxide interface enhanced OER catalyst, which shows an outstanding activity and stability for OER with affording a low overpotential of 220 mV at the current density of 10 mA cm-2. XPS analysis reveals that the excellent performance can be attributed to strong electronic interaction formed by the intimate Ni(OH)2-CeO2 interfaces, which favorably modulate the interaction between intermediate and catalyst. In addition, this interesting structure can be largely remained after a long time stability tests, providing a vital support for the excellent stability. Consequently, the P-Ni4Ce1@CP || Ni4Ce1@CP assembly shows efficient performance for overall water splitting, which is far better than that of the Pt/C || Ir/C. The present work highlights precisely designing of high-performance electrocatalysts for OER and overall water splitting. EXPERIMENTAL SECTION Chemicals. 1LFNHO ,, DFHW\ODFHWRQDWH 1L DFDF &HULXP ,,, QLWUDWH KH[DK\GUDWH &H 12

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ASSOCIATED CONTENT Supporting Information. Figures S1-S18&Tables S1-4. This material is available free of charge via the Internet at http://pubs.acs.org. Detailed analyses of SEM images, EDX results, XRD patterns, SEM-EDX mappings, XPS spectra, electrochemical measurements, tables for the surface molar ratios of Ni2+/Ni3+ and electroactivity comparison for OER, HER and overall water splitting and associated references (PDF). Corresponding Authors *Email: [email protected]; [email protected]. ORCID


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Qi Shao: 0000-0002-9858-0458 Xiaoqing Huang: 0000-0003-3219-4316 Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was financially supported by Ministry of Science and Technology (2016YFA0204100, 2017YFA0208200), the National Natural Science Foundation of China (21571135), Young Thousand Talented Program, the start-up supports from Soochow University, the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), Jiangsu Province Natural Science Fund for Distinguished Young Scholars (BK20170003) and Natural Science Foundation of Jiangsu Higher Education Institutions (17KJB150032).

REFERENCES (1) Yin, Q. S.; Tan, J. M.; Besson, C.; Geletii, Y. V.; Musaev, D. G.; Kuznetsov, A. E.; Luo, Z.; Hardcastle, K. I.; Hill, C. L. In Pursuit of Water Oxidation Catalysts for Solar Fuel Production. Science 2010, 328, 315316. (2) Dresselhaus, M. S.; Thomas, I. L. Alternative Energy Technologies. Nature 2001, 414, 332-337. (3) Yue, X.; Huang, S. L.; Cai, J. J.; Jin, Y. S.; Shen, P. K. Heteroatoms Dual Doped Porous Graphene Nanosheets As Efficient Bifunctional Metal-Free Electrocatalysts for Overall Water-Splitting. J. Mater. Chem. A, 2017, 5, 7784-7790. (4) Helm, M. L.; Stewart, M. P.; Bullock, R. M.; DuBois, M. R.; DuBois, D. L. A Synthetic Nickel Electrocatalyst with a Turnover Frequency above 100,000 s-1 for H2 Production. Science 2011, 333, 863-866.


18

Page 19 of 22 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

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(5) Shu, C.; Kang, S.; Jin, Y. S.; Yue, X.; Shen, P. K. Bifunctional Porous Non-Precious Metal WO2 Hexahedral Networks As an Electrocatalyst for Full Water Splitting. J. Mater. Chem. A, 2017, 5, 9655-9660. (6) Chen, D. J.; Chen, C.; Baiyee, Z. M.; Shao, Z. P.; Ciucci, F. Nonstoichiometric Oxides As Low-Cost and Highly-Efficient Oxygen Reduction/Evolution Catalysts for Low-Temperature Electrochemical Devices. Chem. Rev. 2015, 115, 9869-9921. (7) Jin, Y. S.; Wang, H. T.; Li, J. J.; Yue, X.; Han, Y. J.; Shen, P. K.; Cui, Y. Porous MoO 2 Nanosheets As Non-Noble Bifunctional Electrocatalysts for Overall Water Splitting. Adv. Mater. 2016, 28, 3785-3790. (8) Xiao, Z. H.; Wang, Y.; Huang, Y. C.; Wei, Z. X.; Dong, C. L.; Ma, J. M.; Shen, S. H.; Li, Y. F.; Wang, S. Y. Filling the Oxygen Vacancies in Co3O4 with Phosphorus: An Ultra-Efficient Electrocatalyst for Overall Water Splitting. Energy Environ. Sci. 2017, 10, 2563-2569. (9) Bediako, D. K.; Surendranath, Y.; Nocera, D. G. Mechanistic Studies of the Oxygen Evolution Reaction Mediated by a Nickel-Borate Thin Film Electrocatalyst. J. Am. Chem. Soc. 2013, 135, 3662-3674. (10) Gupta, A.; Chemelewski, W. D.; Mullins, C. B.; Goodenough, J. B. High-Rate Oxygen Evolution Reaction on Al-Doped LiNiO2. Adv. Mater. 2015, 27, 6063-6067. (11) Suen, N. T.; Hung, S. F.; Quan, Q.; Zhang, N.; Xu, Y. Y.; Chen, H. M. Electrocatalysis for the Oxygen Evolution Reaction: Recent Development and Future Perspectives. Chem. Soc. Rev. 2017, 46, 337-365. (12) Chen, P. Z.; Xu, K.; Zhou, T. P.; Tong, Y.; Wu, J. C.; Cheng, H.; Lu, X. L.; Ding, H.; Wu, C. Z.; Xie, Y. Strong-Coupled Cobalt Borate Nanosheets/Graphene Hybrid As Electrocatalyst for Water Oxidation Under Both Alkaline and Neutral Conditions. Angew. Chem. Int. Ed. 2016, 55, 2488-2492. (13) Wang, J.; Zhong, H. X.; Qin, Y. L.; Zhang, X. B. An Efficient Three-Dimensional Oxygen Evolution Electrode. Angew. Chem. Int. Ed. 2013, 125, 5356-5361. (14) Seitz, L. C.; Dickens, C. F.; Nishio, K.; Hikita, Y.; Montoya, J.; Doyle, A.; Kirk, C.; Vojvodic, A.; Hwang, H. Y.; Norskov, J. K. et al. A Highly Active and Stable IrOx/SrIrO3 Catalyst for the Oxygen Evolution Reaction. Science 2016, 353, 1011-1014.


19

ACS Nano 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

Page 20 of 22

(15) Danilovic, N.; Subbaraman, R.; Chang, K. C.; Chang, S. H.; Kang, Y. J.; Snyder, J.; Paulikas, A. P.; Strmcnik, D.; Kim, Y. T.; Myers, D. et al. Using Surface Segregation to Design Stable Ru-Ir Oxides for the Oxygen Evolution Reaction in Acidic Environments. Angew. Chem. Int. Ed. 2014, 53, 14016-14021. (16) Hunter, B. M.; Gray, H. B.; Müller, A. M. Earth-Abundant Heterogeneous Water Oxidation Catalysts. Chem. Rev. 2016, 116, 14120-14136. (17) Ma, Y. Y.; Wu, C. X.; Feng, X. J.; Tan, H. Q.; Yan, L. K.; Liu, Y.; Kang, Z. H.; Wang, E. B.; Li, Y. G. Highly Efficient Hydrogen Evolution from Seawater by a Low-Cost and Stable CoMoP@C Electrocatalyst Superior to Pt/C. Energy Environ. Sci. 2017, 10, 788-798. (18) Wang, Y. Y.; Xie, C.; Zhang, Z. Y.; Liu, D. D.; Chen, R.; Wang, S. Y. In Situ Exfoliated, N-Doped, and Edge-Rich Ultrathin Layered Double Hydroxides Nanosheets for Oxygen Evolution Reaction. Adv. Funct. Mater. 2018, 28, 1703363. (19) Jin, Y. S.; Huang, S. L.; Yue, X.; Du, H. Y.; Shen, P. K. Mo-and Fe-Modified Ni(OH)2/NiOOH Nanosheets as Highly Active and Stable Electrocatalysts for Oxygen Evolution Reaction. ACS Catal. 2018, 8, 2359-2363. (20) Liu, R.; Wang, Y. Y.; Liu, D. D.; Zou, Y. Q.; Wang, S. Y. Water-Plasma-Enabled Exfoliation of Ultrathin Layered Double Hydroxide Nanosheets with Multivacancies for Water Oxidation. Adv. Mater. 2017, 29, 1701546. (21) Jin, Y. S.; Yue, X.; Du, H. Y.; Wang, K.; Huang, S. L.; Shen, P. K. One-Step Growth of NitrogenDecorated Iron-Nickel Sulfide Nanosheets for the Oxygen Evolution Reaction. J. Mater. Chem. A, 2018, 6, 5592-5597. (22) Xu, X.; Song, F.; Hu, X. L. A Nickel Iron Diselenide-Derived Efficient Oxygen-Evolution Catalyst. Nat. Commun. 2016, 7, 12324. (23) Fan, K.; Chen, H.; Ji, Y. F.; Huang, H.; Claesson, P. M.; Daniel, Q.; Philippe, B.; Rensmo, H.; Li, F. S.; Luo, Y. et al. Nickel-Vanadium Monolayer Double Hydroxide for Efficient Electrochemical Water Oxidation. Nat. Commun. 2016, 7, 11981.


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ACS Nano

(24) Pi, Y. C.; Shao, Q.; Wang, P. T.; Lv, F.; Guo, S. J.; Guo, J.; Huang, X. Q. Trimetallic Oxyhydroxide Coralloids for Efficient Oxygen Evolution Electrocatalysis. Angew. Chem. Int. Ed. 2017, 129, 4573-4577. (25) Zhang, P. L.; Li, L.; Nordlund, D.; Chen, H.; Fan, L. Z.; Zhang, B. B.; Sheng, X.; Daniel, Q.; Sun, L. C. Dendritic Core-Shell Nickel-Iron-Copper Metal/Metal Oxide Electrode for Efficient Electrocatalytic Water Oxidation. Nat. Commun. 2018, 9, 381. (26) Gao, W.; Xia, Z. M.; Cao, F. X.; Ho, J. C.; Jiang, Z.; Qu, Y. Q. Comprehensive Understanding of the Spatial Configurations of CeO2 in NiO for the Electrocatalytic Oxygen Evolution Reaction: Embedded or Surface-Loaded. Adv. Funct. Mater. 2018, 28, 1706056. (27) Obata, K.; Takanabe, K. A Permselective CeOx Coating Improves the Stability of Oxygen Evolution Electrocatalysts. Angew. Chem. Int. Ed. 2018, 130, 1632-1636. (28) Feng, J. X.; Ye, S. H.; Xu, H.; Tong, Y. X.; Li, G. R. Design and Synthesis of FeOOH/CeO 2 Heterolayered Nanotube Electrocatalysts for the Oxygen Evolution Reaction. Adv. Mater. 2016, 28, 46984703. (29) Li, H. X.; Hao, W. L.; Hu, J. C.; Wu, H. Y. A Photoelectrochemical Sensor Based on Nickel HydroxylOxide Modified n-Silicon Electrode for Hydrogen Peroxide Detection in an Alkaline Solution. Biosens. Bioelectron. 2013, 47, 225-230. (30) Hardacre, C.; Roe, G. M.; Lambert, R. M. Structure, Composition and Thermal Properties of Cerium Oxide Films on Platinum {111}. Surf. Sci. 1995, 326, 1-10. (31) Lin, B. Y.; Liu, Y.; Heng, L.; Ni, J.; Lin, J. X.; Jiang, L. L. Effect of Ceria Morphology on the Catalytic Activity of Co/CeO2 Catalyst for Ammonia Synthesis. Catal. Commun. 2017, 101, 15-19. (32) Chen, C. C.; Kang, Y. J.; Huo, Z. Y.; Zhu, Z. W.; Huang, W. Y.; Xin, H. L.; Snyder, J. D.; Li, D. G.; Herron, J. A.; Mavrikakis, M. et al. Highly Crystalline Multimetallic Nanoframes with Three-Dimensional Electrocatalytic Surfaces. Science 2014, 343, 1339-1343. (33) Lu, F.; Zhou, M.; Zhou, Y. X.; Zeng, X. H. First-Row Transition Metal Based Catalysts for the Oxygen Evolution Reaction under Alkaline Conditions: Basic Principles and Recent Advances. Small 2017, 13,


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Page 22 of 22

1701931. (34) McCrory, C. C. L.; Jung, S.; Peters, J. C.; Jaramillo, T. F. Benchmarking Heterogeneous Electrocatalysts for the Oxygen Evolution Reaction. J. Am. Chem. Soc. 2013, 135, 16977-16987. (35) Rossmeisl, J.; Qu, Z. W.; Zhu, H.; Kroes, G. J.; Norskov, J. K. Electrolysis of Water on Oxide Surfaces. J. Electroanal. Chem. 2007, 607, 83-89. (36) Friebel, D.; Louie, M. W.; Bajdich, M.; Sanwald, K. E.; Cai, Y.; Wise, A. M.; Cheng, M. J.; Sokaras, D.; Weng, T. C.; Mori, R. A. et al. Identification of Highly Active Fe Sites in (Ni, Fe)OOH for Electrocatalytic Water Splitting. J. Am. Chem. Soc. 2015, 137, 1305-1313. (37) Seh, Z. W.; Kibsgaard, J.; Dickens, C. F.; Chorkendorff, I.; Nørskov, J. K.; Jaramillo, T. F. Combining Theory and Experiment in Electrocatalysis: Insights into Materials Design. Science 2017, 355, eaad4998. (38) Gao, M. R.; Xu, Y. F.; Jiang, J.; Zheng, Y. R.; Yu, S. H. Water Oxidation Electrocatalyzed by an Efficient Mn3O4/CoSe2 Nanocomposite. J. Am. Chem. Soc. 2012, 134, 2930-2933. (39) Tang, C.; Zhang, R.; Lu, W. B.; Wang, Z.; Liu, D. N.; Hao, S.; Du, G.; Asiri, A. M.; Sun, X. P. EnergySaving Electrolytic Hydrogen Generation: Ni 2P Nanoarray As a High-Performance Non-Noble-Metal Electrocatalyst. Angew. Chem. Int. Ed, 2017, 56, 842-846. (40) Pu, Z. H.; Liu, Q.; Tang, C.; Asiri, A. M.; Sun, X. P. Ni2P Nanoparticle Films Supported on a Ti Plate As an Efficient Hydrogen Evolution Cathode. Nanoscale 2014, 6, 11031-11034.


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