Amorphous Boron Oxide Coated NiCo-LDHs Nanoarrays for Highly

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Amorphous Boron Oxide Coated NiCo-LDHs Nanoarrays for Highly Efficient Oxygen Evolution Reaction Zemin Sun, Liu Lin, Caiyun Nan, Huifeng Li, Genban Sun, and Xiaojing Yang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b02893 • Publication Date (Web): 25 Sep 2018 Downloaded from http://pubs.acs.org on September 25, 2018

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ACS Sustainable Chemistry & Engineering

Amorphous Boron Oxide Coated NiCo-LDHs Nanoarrays for Highly Efficient Oxygen Evolution Reaction Zemin Sun,†,§ Liu Lin,†,§ Caiyun Nan, † Huifeng Li, † Genban Sun†,‡,* Xiaojing Yang†,* †

Beijing Key Laboratory of Energy Conversion and Storage Materials, College of Chemistry,

Beijing Normal University, Xinjiekouwaidajie 19, Haidian District, Beijing 100875, China ‡

State Key Laboratory for Advanced Metals and Materials, School of Materials Science and

Engineering, University of Science and Technology Beijing, Xueyuan Road 30, Haidian District, Beijing, 100083, China *Corresponding Authors E-mail address: [email protected] (G. S.); yang.xiaojing@ bnu.edu.cn (X. Y.) ABSTRACT Amorphous boron oxide layer has been deposited in-situ on the NiCo-LDHs nanosheet arrays via the simple chemical vapor deposition. The overpotential of the NiCo-LDHs@B2O3/Carbon paper (NiCo-LDHs@B2O3/CP) electrode is only 213 mV at the current density of 10 mA cm-2 in 1M KOH, which is 123 mV less than that of NiCo-LDHs/CP and slightly better than noble metal catalyst RuO2/CP (230 mV). What’s more, at 50 mA cm-2 in 1.0 M KOH ， the overpotential of NiCo-LDHs@B2O3/CP is still kept at a low value of 320 mV much better than that of NiCo-LDHs /CP (441 mV) and RuO2/CP (373 mV). Importantly, it showed long-term electrochemical stability. The introduction of amorphous boron oxide layers can promote to form borate interface, it can effectively enhance reactivity of active species. The boron oxide shell on the surface of LDHs can protect active species stability to enhance cycling stability. This work may inspire the development 1

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of low-cost and efficient OER electrocatalysts for energy conversion with NiCo-LDHs@B2O3/CP. KEYWORDS：NiCo-LDHs nanoarrays; in-situ deposition; amorphous boron oxide layer; oxygen evolution reaction INTRODUCTION Under the situation of increasing domestic energy demand and rapidly growing greenhouse gas emissions, there are urgent demands to find clean and long-term sustainable energy, alternative energy conversion and storage systems.1-4 Hydrogen, as a clean energy source, holds the prospect as an ideal fuel in the future.5,6 Electrocatalytic water splitting into hydrogen and oxygen is an appealing and promising way to store renewable energy.7-9 There are two half reactions during the process of electrochemical water splitting: on one hand, the hydrogen evolution reaction (HER) occurs on cathode; on the other hand, the oxygen evolution reaction (OER) takes place on anode. 10-12 However, compared with cathodic HER process, the anodic OER would suffer from sluggish kinetics due to the four electron transfer process to form O−O bond, leading to a high overpotential, which becomes a critical bottleneck to improve the water-splitting technologies.13-16 Thus, it is essential to adopt appropriate catalyst to achieve low overpotential and realize high efficiency of water electrolysis. Up to now, the most active OER catalysts, Ru and Ir based materials, have low overpotential and Tafel slope.17-21 The large-scale utilization of noble metals, however, cannot be expected due to their high cost and earth scarcity. In consideration of realistic application, it is highly attractive to develop noble metal-free OER catalysts. In order to resolve the above-mentioned problems, tremendous efforts are focused on exploring new low-cost catalysts.22-24 Layered double hydroxide (LDHs) is an important member of noble metal-free OER catalysts,25-30 which has attracted increasing attention due to cost-effectiveness, 2


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environmental-friendly nature and excellent catalytic activities.30,31 Especially Co- and Ni-based LDHs materials have been discovered to exhibit good electrocatalytic activity towards OER in alkaline solution.32-40 Both theoretical and experimental studies proved that LDHs have abundant catalytic area and exposed active sites.35,41,42 Nonmetallic elements doping become an effective method to improve the amount of active sites to enhance electric catalytic properties. Recently, Nocera group has been reported borate anions in the electrolyte as a dopant can enhance OER performance.43 Herein, a simple and facile strategy is applied to effectively enhance the oxygen evolution reaction (OER) performance of non-noble-metal electrocatalysts in alkaline media. NiCo-LDHs grow on carbon paper (NiCo-LDHs/CP) via in situ hydrothermal method as a binder-free catalyst for OER. In this process, the carbon paper as a high surface area and low-cost 3D electrode can become a current collector which can avoid the binder introduced and realize rapid electron transportation to enhance electrochemical performance.44-46 Then, an amorphous boron oxide layer is formed on the surface of NiCo-LDHs nanoarray (NiCo-LDHs@B2O3/CP) by chemical vapor deposition at 200 ˚C. The NiCo-LDHs@B2O3/CP nanoarray shows high catalytic activity. It achieves excellent OER performance with low overpotential of 213 mV at catalytic current density of 10 mA cm -2 in 1 M KOH solution, which is 123 mV less than that of NiCo-LDHs/CP. And when the current density is 50 mA cm-2, the overpotential is only 320 mV. The low Tafel slope is 61 mV dec-1 in 1 M KOH solution. Importantly, this electrode also shows strong long-term electrochemical durability which maintained for more than 28 hours. EXPERIMENTAL SECTION Chemicals and Materials: 3



.

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.

Ni(NO3)2 6H2O (Beijing Chemical Reagent Co., Ltd.,99.5%), Co(NO3)2 6H2O (Beijing Chemical Reagent Co., Ltd, 97.0%), Hexamethylenetetramine (HMT, Beijing Chemical Reagent Co., Ltd.,99.5%), acetone (Beijing Chemical Reagent Co., Ltd, 99.0%), ethanol (Beijing Chemical Reagent Co., Ltd, 99.0%), potassium hydroxide (KOH, Beijing Chemical Reagent Co., Ltd, 82.0%), Nafion solution (Sigma-Aldrich Co., 5 wt%) and RuO2 (Shanghai Macklin Biochemical Co., Ltd, 99.9%). All the materials in this experiment were used directly without any purification. Material Synthesis Pre-treatment of carbon paper (CP) The CP was cut into slices (~0.5 cm *1.0 cm), and then ultrasonicated in acetone, ethanol and deionized water with 30 min, respectively. After that, the CP was treated with H2SO4 and H2O2 100 ml（V(H2SO4 3mol/L) : V(H2O2 30%) = 2:1) for 3 h, followed ultrasonicated in water. Finally, it dried at 80 ˚C to get the carbon paper. Synthesis of NiCo-LDHs /CP electrode The NiCo-LDHs/CP electrode was prepared via a facile .

.

hydrothermal method. Firstly, 0.65 mmol Ni(NO3)2 6H2O, 0.325 mmol Co(NO3)2 6H2O (the molar radio of Ni:Co=2:1), 7.5 mmol hexamethylenetetramine (HMT), and the CP were added into a mixed solution of water (80 mL) in order to ultrasonic treatment for 30 min. Then, the solution and substrate were transferred into a 100 ml Teflon-lined stainless steel autoclave to maintain at 120 ˚C for 12 h. After the autoclave was cooled to room temperature, the electrode was ultrasonicated with ethanol to remove the weak bonds of NiCo-LDHs on CP. Subsequently, the as-made sample was rinsed with deionized water and ethanol respectively, and then dried at 80 ˚C. Synthesis of NiCo-LDHs-200 /CP electrode The preparation of NiCo-LDHs /CP was took place at the tube furnace and the samples are heated at 200 ˚C for 120 min with Ar gas flowing at 200 s.c.c.m. Finally,

the

NiCo-LDHs-200

/CP

electrode

was

obtained.

4


Like

NiCo-LDHs-200/CP,

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NiCo-LDHs-150/CP is heated the NiCo-LDHs /CP at 150˚C and NiCo-LDHs-100/CP is heated the NiCo-LDHs /CP at 100˚C with other conditions unchanged. Synthesis of NiCo-LDHs@B2O3 /CP electrode The H3BO3 (2.0 g) is placed at the upstream side of the tube furnace and the corresponding NiCo-LDHs /CP are placed at the downstream side, thenthe samples are heated at 200 °C for 120 min with Ar gas flowing at 200 s.c.c.m. Finally, the obtained was named NiCo-LDHs@B2O3/CP. Synthesis of RuO2 /CP electrode 5 mg of RuO2 was dispersed in a 1 mL mixed solution containing 490 μL of water, 15 μL of 5 wt% Nafion solution, and 495 μL of ethanol, followed by sonication to obtain a homogeneous catalyst ink. Then, the catalyst ink was loaded on the surfaces of CP. 2.2. Microstructural characterizations Crystal structure of catalysts has been confirmed via X-ray powder diffraction on a Phillips X’pert ProMPD diffractometer (CuKα, λ=1.54056 Å). The generator setting was 40 kV and 40 mA. The morphologies of the products were measured using field emission scanning electronic microscope (FESEM, an acceleration voltage of 10 kV, S-8010, Hitachi) and a high-resolution transmission electronmicroscope (HRTEM, an acceleration voltage of 200 kV, JEM-2010, JEOL and FEI Technai G2 F20). ESCALAB 250Xi spectrometer (Thermo Fisher) with Al Kα radiation as the X-ray source for excitation was used to collect the X-ray photoelectron spectra (XPS) data. 2.3. Electrochemical measurements Electrochemical measurements were measured via an electrochemical workstation which was named Zennium IM6 station and came from Germany. Use a conventional three-electrode setup (a 5



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platinum foil as the counter electrode, Hg/HgO electrode as the reference electrode, and glassy carbon electrode holders with as-prepared working electrode. The OER performances were tested in 1.0 M KOH using linear sweep voltammetry (LSV) with a scan rate of 2 mV s -1. The measured potentials were converted to the reversible hydrogen electrode (RHE) and calculated based on the following formula: ERHE = EHg/HgO + 0.098 + 0.0591 * pH (1) and the overpotentials (η) for OER is calculated based on the following formula: η= ERHE−1.23 V (2).8,47 Electrochemical impedance spectra (EIS) measured by AC impedance with an amplitude of 5 mV over the frequency range from 105 to 0.01 Hz in a solution of 1.0 M KOH. To estimate the catalytically active sites of the materials, using a conventional three-electrode setup (a platinum foil as the counter electrode, Saturated calomel electrode (SCE) as the reference electrode, and glassy carbon electrode holders with as-prepared working electrode. The electrochemical double layer capacitance (Cdl) was measured by cyclic voltammetry curves at a potential range of 0.24-0.34 V (V vs. SCE) with scanning rates of 10, 20, 40, 60, 80, and 100 mV s−1. RESULTS AND DISCUSSIONS The X-ray powder diffraction (XRD) of CP, NiCo-LDHs/CP, NiCo-LDHs-200/CP and NiCo-LDHs@B2O3/CP were showed in Figure 1, respectively. The XRD file showed peaks at 26.2o and 54.2o indicated the CP introduced in Figure 1a. According to the previously reported NiCo-LDHs,48-51 NiCo-LDHs has diffraction peaks at 11.2o, 33.2o, 34.8o, 42.6ºand 59.4ºwhich were indexed to (003), (101), (012), (018) and (110) characteristic diffraction of the hydrotalcite-like structure. According to the XRD profile, the peaks position of the NiCo-LDHs/CP (Figure 1b), NiCo-LDHs-200/CP (Fig. 1c) and NiCo-LDHs@B2O3/CP (Figure 1d) were shown almost the same diffraction peaks and the peaks included both the peaks of CP at 26.2o and 54.2o and NiCo-LDHs at 6


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1.2o, 33.2o, 34.8o, 42.6ºand 59.4º. And From the XRD of NiCo-LDHs-200/CP (Figure 1c and d), the (003) peaks were slightly weaker and broader compared with NiCo-LDHs/CP (Figure 1b) which might loss absorbed water and part of crystalline water molecules and make the crystallinity of NiCo-LDHs decrease. The results agreed with TGA results Figure S1, which can been seen the mass loss at different temperature has been demonstrate that the first weight loss before 250 °C can be attributed to the removal of adsorbed and crystalline water molecules not the removal of OH. Furthermore, the peaks of B2O3 were not detected from NiCo-LDHs@B2O3/CP in Figure 1d. It might be related to the amorphous boron oxide layer formation on NiCo-LDHs nanoarrays. The typical scanning electron microscopy (SEM) images of NiCo-LDHs/CP were shown in Figure 2a. It showed that NiCo-LDHs were vertically oriented nanoarrays on the CP surface. After the boron oxide shell introduced via chemical vapor deposition, the NiCo-LDHs@B2O3/CP still remained its nanoarrays feature not only from details but also from overall structures presented in different magnification SEM images in Figure 2b and S2, respectively. The energy-dispersive X-ray (EDX) spectrum was carried on to confirm NiCo-LDHS@B2O3/CP in order to determine the existence of Ni, Co, and B elements in the product. It can be showed that the Ni, Co, B, and O elements were evenly distributed throughout the full coverage of the NiCo-LDHS@B2O3/CP in Figure 2c-g. The high-resolution

transmission

electron

microscopy

(HRTEM)

images

took

from

the

NiCo-LDHS@B2O3/CP as shown in Figure 2h, it can be clearly showed that the amorphous shell was formed on the surface of NiCo-LDHs compared with NiCo-LDHs/CP (Figure S3a) which was consistent with the result of XRD. Furthermore, the Fast Fourier Transformation (FFT) insert of Figure 2h indicated the core of NiCo-LDHs@B2O3/CP was well-defined hexagonal phase of NiCo-LDHs.50,52,53 Beyond that, the core of NiCo-LDHS@B2O3/CP showed well-resolved lattice 7



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fringes with a lattice spacing value of 0.257 nm indexed to (012) plane of NiCo-LDHs in Figure 2I,50,51 which was in accordance with the NiCo-LDHs/CP in Figure S3b. The X-ray photoelectron spectra (XPS) were carried out in order to probe the surface composition and chemical states of samples. The Ni 2p, Co 2p, B 1s and O 1s spectrum on the surface of NiCo-LDHs@B2O3/CP were showed in Figure 3a-d, respectively. In Figure 3a, the Ni 2p spectrum shows two peaks at 855.7 and 873.1 eV which can be assigned to Ni 2p 3/2 and Ni 2p1/2 signals of Ni2p, respectively, suggesting the existence of Ni2+ were bound to oxygen. And the two obvious shakeup satellites (identified as “Sat.”) at 862.0 and 880.0 eV were according with the Ni2+ which were bound to oxygen.50,51, 54,55 From Figure 3b, the peaks at 782.1 and 795.2 eV in the Co 2p region are consistent with Co 2p3/2 and Co 2p1/2, respectively, indicating that the co-existence of Co2+ or Co3+.48,51,56 The Ni 2p and Co 2p spectrum are consistent with the previously reported NiCo-LDHs.50,51, 54, 55 The XPS of B 1s region was showed in Figure 3c, a peaks at 191.0 eV is corresponding to B 1s, which indicated a typical of three-coordinated borate species.57, 58 And O 1s region was showed in Figure 3d, at the peaks at 530.6 eV is corresponding to O 1s. 57,58 These results can be confirmed that B−O species exist on the shell of NiCo-LDHs nanosheets array. Above-stated analyses verify that the amorphous layer is boron oxide in nature which came from boric acid thermal decomposition. The core−shell structured NiCo-LDHs@B2O3 nanoarrays can be obtained via chemical vapor deposition. The electrochemical performances of a series of electrodes were evaluated in 1 M KOH aqueous electrolyte, in order to obtain accurate RHE value, the potentials have been calibrated, as shown in Figure S4. The LSV results were shown in Figure 4a and S5a and b. Interestingly, from the LSV of NiCo-LDHs/CP and NiCo-LDHs-200/CP, it can be seen that the oxidation peak shifted to high 8


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potential in Figure 4a. And other temperature also has been measured in Figure S5b, it can be seen that the oxidation peak shifted to high potential with temperature rising. The oxidation peak shifted to high potential might cause by the decrease of crystallinity (Figure 1) due to the dehydration in NiCo-LDHs as the temperature rises (Figure S1). What’s more, the oxidation peak of NiCo-LDHs@B2O3/CP has disappeared compared with NiCo-LDHs/CP and NiCo-LDHs-200/CP. It might relate to the Ni-Co borate which was existed in the interface between amorphous boron oxide layer and NiCo-LDHs. Meantime, under the protection of B2O3 layer, the electron deficiency of borate might suppress NiCo-LDHs oxidation peak appear. For comparison, the catalytic activities of CP, CP@ B2O3, NiCo-LDHs/CP, NiCo-LDHs-200/CP, NiCo-LDHs@B2O3/CP and the state-of-the art RuO2/CP were measured. As observed, bare CP (760 mV) and CP@B2O3 (746 mV) had poor OER activity, whereas the OER catalytic activity of the NiCo-LDHs@B2O3/CP is delivered 213 mV at a current density of 10 mA cm-2 much better than that of NiCo-LDHs/CP( 336 mV ), NiCo-LDHs /CP-200 (318 mV ) and slightly better RuO2 (230 mV), which was listed in the Figure 4a and S5a. The LSV results indicated that amorphous boron oxide were not directly provide the active sites for catalyst and the interface between NiCo-LDHs and amorphous boron oxide could benefit to provide the active site for OER. In addition, at a current density of 50 mA cm-2, The OER catalytic activity of the NiCo-LDHs@B2O3/CP (320 mV) is also much better than that of NiCo-LDHs/CP (441 mV), NiCo-LDHs-200/CP (427 mV) and RuO2/CP (373 mV). Note that it also rivalled the performances of most reported Ni-based and Co-based catalysts. A detailed comparison can be seen in Table S1. In order to get further insight into the electrocatalytic activity of catalysts for OER, EIS measurement was conducted as shown in Figure S6. The Nyquist semicircle loop diameter in the high-frequency region corresponded to the charge-transfer resistance. The Nyquist semicircle of the NiCo-LDHs/CP, 9



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NiCo-LDHs-200/CP and NiCo-LDHs@B2O3/CP cathode was much lower than that of the carbon paper. Meantime, among NiCo-LDHs/CP, NiCo-LDHs-200/CP and NiCo-LDHs@B2O3/CP cathode, the Nyquist semicircle of NiCo-LDHs@B2O3/CP was the lowest indicting the lower charge transfer impedance and the faster reaction kinetics during the process of OER. Tafel plots derived from polarization curves were also important parameters for the evaluation of OER kinetics. It is found that of the NiCo-LDHs@B2O3/CP delivered the lowest Tafel slope (61 mV dec-1) in Figure 4c, which is much smaller than NiCo-LDHs/CP (137 mV dec-1), NiCo-LDHs-200/CP (131 mV dec-1) and even the RuO2 ( 91 mV dec-1). It suggested NiCo-LDHs@B2O3/CP was more favourable OER kinetics. In order to evaluate performance of stability is the critical for practical applications of catalysts, and then we probed the stability of the NiCo-LDHs@B2O3/CP electrode by the means of continuous CV. The LSV curve after 2000 cycles were showed that there was insignificant current loss compared with the initial state in Figure 4d. The LSV curves of initial and 3000th, 4000th and 5000th cycles of NiCo-LDHs@B2O3/CP nanosheets have been tested in Figure S7a. As a result, the overpotential was increased and the catalyst activities were decreased at the higher cycling number. After 4000 cycles, the oxidation peak appeared again. And the catalysts which tested after 4000 cycles were measured via HRTEM, it can be seen that the amorphous boron oxide layer have been destroyed in Figure S7b. This result can prove that the disappeared oxidation peak of NiCo-LDHs@B2O3/CP compared with NiCo-LDHs/CP might relate to Ni-Co borate which was under the protection of B2O3 layer. Meantime, the overpotential was increased and the catalyst activities were decreased due to the deamorphous boron oxide layer. It also could demonstrate that the interface between NiCo-LDHs and amorphous boron oxide could benefit to provide the active site for OER. To further assess the durability of the NiCo-LDHs@B2O3/CP electrode in an alkaline medium. The chronopotentiometry 10


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experiment was measured at fixed overpotentials of 230 mV. Compared with NiCo-LDHs-200/CP (Figure S8), it can demonstrate that NiCo-LDHs@B2O3/CP showed superior in long-term electrochemical durability as showed in Figure 4e, which were no obvious loss of current densities. The SEM, HRTEM, XPS and XRD datas of NiCo-LDHs-200/CP and NiCo-LDHs@B2O3/CP after the electrochemical stability test have been measured as presented in Figures S9-S11. There were no obvious changes for the morphology of NiCo-LDHs@B2O3/CP which was observed via SEM in Figure S9a after stability test for 28 h in 1.0 M KOH, however, there were many nanoparticles aggregation on the NiCo-LDHs-200/CP (Figure S9c). Meantime, the NiCo-LDHs@B2O3 still kept well-crystalline and core-shell structure (Figure S9b), by comparison, the substantial lattice structure of NiCo-LDHs-200 has been erosive (Figure S9d). Through boron oxide coated, it can well maintain structural stability. Furthermore, according to the XPS and XRD in Figure S10 and S11 respectively, it also can be seen that the composition and structure of NiCo-LDHs@B2O3/CP almost no changed after chronopotentiometry experiment compared with the uncoated NiCo-LDHs-200. All the results demonstrate it can maintain stable structure and strong long-term electrochemical durability via coating amorphous boron oxide layer. The electrochemical surface area (ECSA) is also one of the most important factors that reflect the electrocatalytic activity of catalysts. Electrochemical double layer capacitances (Cdl) are tested via CV scans to compare the electrochemically active surface area.39,49,52,54 The cyclic voltammograms were collected in the region of 0.24 - 0.34 V versus the saturated calomel electrode (SCE), where the current responses should only be owing to the charging of the double layer. The C dl and CVs of CP was showed in Figure S12a and 12b, And the Cdl was calculated as 0.06 mF cm-2. It indicated that there was almost no electrochemically active surface area of CP. Obviously, The C dl of 11



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NiCo-LDHs@B2O3/CP (Figure S13a) and NiCo-LDHs/CP (Figure S13 b) are calculated as 80.5 and 3.5 mF cm−2, respectively (Figure 5). The increased ECSA is ascribed to the introduced of amorphous boron oxide layer effectively enhanced the reactivity of active species on the surface for OER process. The excellent OER activities could be mainly originated from the introduction of amorphous boron oxide layers. Nonmetallic elements introduced can enhance electric catalytic properties.59-61 On one hand, due to electron-deficient effect of boron,62 the boron oxide of interface was coordinated directly to the metal and then formed the borate in the interface between boron oxide and NiCo-LDHs. It can improve the amount of active sites which was in accordance with ECSA. On the other hand, the boron oxide nanoshell on the surface of LDHs can protect active species stability to enhance cycling stability. CONCLUSION In conclusion, we develop a simple and facile strategy to synthesis NiCo-LDHs@B2O3/CP via hydrothermal

growth

and

then

chemical

vapor deposition.

The overpotential

of the

NiCo-LDHs@B2O3/CP electrode is only 213 mV at the current density of 10 mA cm-2 in 1M KOH, which is 123 mV less than that of NiCo-LDHs/CP and slightly better RuO2/CP (230 mV). What’s more, at 50 mA cm-2 in 1.0 M KOH，the overpotential of NiCo-LDHs@B2O3/CP is still kept at a low value of 320 mV much better than that of NiCo-LDHs /CP (441 mV) and RuO2/CP (373 mV). Notably, this electrode also showed strong long-term electrochemical durability. The superior activity is ascribed to the introduced of amorphous boron oxide shell, which effectively enhance catalysis reactivity. This work opens an exciting new way for developing high-performance and economic OER catalyst materials. 12


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Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.******.TGA profile of NiCo-LDHs powder; SEM, TEM and HRTEM of NiCo-LDHs /CP; the LSV curves of hydrogen electrode reactions on Pt wire; the polarization curves of CP@B2O3, NiCo-LDHs-T/CP; Nyquist plots of the electrodes; the LSV curves of different cycles and HRTEM image; Chronoamperometric response of NiCo-LDHs-200/CP; SEM, TEM, XPS and XRD of catalysts after Chronoamperometric response; CVs curves; comparison of alkaline OER performance. AUTHOR INFORMATION Author contributions: *Corresponding Authors E-mail address: [email protected] (Genban Sun); yang.xiaojing@ bnu.edu.cn (Xiaojing Yang) §

Zemin Sun and Liu Lin are equally contribution. All authors have given approval to the final

version of the manuscript.

Acknowledgements This work was supported by the National Science Foundations of China (21771024, 21471020, 21271028 and 21421003)

REFERENCES 1. Walter, M. G.; Warren, E. L.; McKone, J. R.; Boettcher, S. W.; Mi, Q.; Santori, E. A.; Lewis, N. S., Solar water splitting cells. Chem. Rev. 2010, 110 (11), 6446-6473. DOI 10.1021/cr1002326. 2. Chow, J.; Kopp, R. J.; Portney, P. R., Energy resources and global development. Science 2003, 302 (5650), 1528-1531. DOI 10.1126/science.1091939. 13



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3. Cook, T. R.; Dogutan, D. K.; Reece, S. Y.; Surendranath, Y.; Teets, T. S.; Nocera, D. G., Solar energy supply and storage for the legacy and nonlegacy worlds. Chem. Rev. 2010, 110 (11), 6474-6502. DOI 10.1021/cr100246c. 4. Nocera, D. G., The artificial leaf. Accounts Chem. Res. 2012, 45 (5), 767-776. DOI 10.1021/ar2003013. 5. Dresselhaus, M. S.; Thomas, I. L., Alternative energy technologies. Nature 2001, 414 (6861), 332-337. DOI 10.1038/35104599. 6. Li, Y.; Wang, H.; Xie, L.; Liang, Y.; Hong, G.; Dai, H., MoS2 nanoparticles grown on graphene: an advanced catalyst for the hydrogen evolution reaction. J. Am. Chem. Soc. 2011, 133 (19), 7296-7299. DOI 10.1021/ja201269b. 7. Joya, K. S.; Joya, Y. F.; Ocakoglu, K.; van de Krol, R., Water-splitting catalysis and solar fuel devices: artificial leaves on the move. Angew. Chem., Int. Ed. 2013, 52 (40), 10426-10437. DOI 10.1002/anie.201300136. 8. Li, W.; Gao, X.; Xiong, D.; Xia, F.; Liu, J.; Song, W. G.; Xu, J.; Thalluri, S. M.; Cerqueira, M. F.; Fu, X.; Liu, L., Vapor-solid synthesis of monolithic single-crystalline CoP nanowire electrodes for efficient and robust water electrolysis. Chem. Sci. 2017, 8 (4), 2952-2958. DOI 10.1039/c6sc05167g. 9. Zhang, Y.; Ouyang, B.; Xu, J.; Jia, G.; Chen, S.; Rawat, R. S.; Fan, H. J., Rapid Synthesis of Cobalt Nitride Nanowires: Highly Efficient and Low-Cost Catalysts for Oxygen Evolution. Angew. Chem., Int. Ed. 2016, 55 (30), 8670-8674. DOI 10.1002/anie.201604372. 10. Fominykh, K.; Chernev, P.; Zaharieva, I.; Sicklinger, J.; Stefanic, G.; Doblinger, M.; Muller, A.; Pokharel, A.; Bocklein, S.; Scheu, C.; Bein, T.; Fattakhova-Rohlfing, D., Iron-doped nickel oxide nanocrystals as highly efficient electrocatalysts for alkaline water splitting. ACS Nano 2015, 9 (5), 5180-5188. DOI 10.1021/acsnano.5b00520. 11. Cobo, S.; Heidkamp, J.; Jacques, P. A.; Fize, J.; Fourmond, V.; Guetaz, L.; Jousselme, B.; Ivanova, V.; Dau, H.; Palacin, S.; Fontecave, M.; Artero, V., A Janus cobalt-based catalytic material for electro-splitting of water. Nat. Mater. 2012, 11 (9), 802-807. DOI 10.1038/nmat3385. 14


Page 15 of 26 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


12. McCrory, C. C.; Jung, S.; Peters, J. C.; Jaramillo, T. F., Benchmarking heterogeneous electrocatalysts for the oxygen evolution reaction. J. Am. Chem. Soc. 2013, 135 (45), 16977-16987. DOI 10.1021/ja407115p. 13. McEvoy, J. P.; Brudvig, G. W., Water-splitting chemistry of photosystem II. Chem.Rev. 2006, 106 (11), 4455-4483. DOI 10.1021/cr0204294. 14. Chen, P.; Zhou, T.; Xing, L.; Xu, K.; Tong, Y.; Xie, H.; Zhang, L.; Yan, W.; Chu, W.; Wu, C.; Xie, Y., Atomically Dispersed Iron-Nitrogen Species as Electrocatalysts for Bifunctional Oxygen Evolution and Reduction Reactions. Angew. Chem. Int. Ed. 2017, 56 (2), 610-614. DOI 10.1002/anie.201610119. 15. McCrory, C. C.; Jung, S.; Ferrer, I. M.; Chatman, S. M.; Peters, J. C.; Jaramillo, T. F., Benchmarking hydrogen evolving reaction and oxygen evolving reaction electrocatalysts for solar water splitting devices. J. Am. Chem. Soc. 2015, 137 (13), 4347-4357. DOI 10.1021/ja510442p. 16. Zhu, Y. P.; Qiao, S. Z., Unprecedented carbon sub-microspheres with a porous hierarchy for highly efficient oxygen electrochemistry. Nanoscale 2017, 9 (47), 18731-18736. DOI 10.1039/c7nr06801h. 17. Cherevko, S.; Geiger, S.; Kasian, O.; Kulyk, N.; Grote, J.-P.; Savan, A.; Shrestha, B. R.; Merzlikin, S.; Breitbach, B.; Ludwig, A.; Mayrhofer, K. J. J., Oxygen and hydrogen evolution reactions on Ru, RuO2 , Ir, and IrO2 thin film electrodes in acidic and alkaline electrolytes: A comparative study on activity and stability. Catal. Today 2016, 262, 170-180. DOI 10.1016/j.cattod.2015.08.014. 18. Grimaud, A.; Demortière, A.; Saubanère, M.; Dachraoui, W.; Duchamp, M.; Doublet, M.-L.; Tarascon, J.-M., Erratum: Activation of surface oxygen sites on an iridium-based model catalyst for the oxygen evolution reaction. Nat. Energy 2017, 2 (2), 17002. DOI 10.1038/nenergy.2016.189. 19. Lee, Y.; Suntivich, J.; May, K. J.; Perry, E. E.; Shao-Horn, Y., Synthesis and Activities of Rutile IrO2 and RuO2 Nanoparticles for Oxygen Evolution in Acid and Alkaline Solutions. J. Phys. Chem. Lett. 2012, 3 (3), 399-404. DOI 10.1021/jz2016507. 20. Pagliaro, M.; Campestrini, S.; Ciriminna, R., Ru-based oxidation catalysis. Chem. Soc. Rev. 15



Page 16 of 26

2005, 34 (10), 837-845. DOI 10.1039/b507094p. 21. Windle, C. D.; Perutz, R. N., Advances in molecular photocatalytic and electrocatalytic CO2 reduction. Coordin. Chem. Rev. 2012, 256 (21-22), 2562-2570. DOI 10.1016/j.ccr.2012.03.010. 22. Han, L.; Yu, X. Y.; Lou, X. W., Formation of Prussian-Blue-Analog Nanocages via a Direct Etching Method and their Conversion into Ni-Co-Mixed Oxide for Enhanced Oxygen Evolution. Adv. Mater. 2016, 28 (23), 4601-4605. DOI 10.1002/adma.201506315. 23. Lu, X. F.; Gu, L. F.; Wang, J. W.; Wu, J. X.; Liao, P. Q.; Li, G. R., Bimetal-Organic Framework Derived CoFe2O4/C Porous Hybrid Nanorod Arrays as High-Performance Electrocatalysts for Oxygen Evolution Reaction. Adv. Mater. 2017, 29 (3), 1604437. DOI 10.1002/adma.201604437. 24. Wang, X.; Yu, L.; Guan, B. Y.; Song, S.; Lou, X. W. D., Metal-Organic Framework Hybrid-Assisted Formation of Co3O4 /Co-Fe Oxide Double-Shelled Nanoboxes for Enhanced Oxygen Evolution. Adv. Mater. 2018, 30 (29), 1801211. DOI 10.1002/adma.201801211. 25. Ma, W.; Ma, R.; Wang, C.; Liang, J.; Liu, X.; Zhou, K.; Sasaki, T., A superlattice of alternately stacked Ni-Fe hydroxide nanosheets and graphene for efficient splitting of water. ACS Nano 2015, 9 (2), 1977-1984. DOI 10.1021/nn5069836. 26. Long, X.; Ma, Z.; Yu, H.; Gao, X.; Pan, X.; Chen, X.; Yang, S.; Yi, Z., Porous FeNi oxide nanosheets as advanced electrochemical catalysts for sustained water oxidation. J. Mater. Chem. A 2016, 4 (39), 14939-14943. DOI 10.1039/c6ta05907d. 27. Tang, C.; Wang, H. S.; Wang, H. F.; Zhang, Q.; Tian, G. L.; Nie, J. Q.; Wei, F., Spatially Confined Hybridization of Nanometer-Sized NiFe Hydroxides into Nitrogen-Doped Graphene Frameworks Leading to Superior Oxygen Evolution Reactivity. Adv. Mater. 2015, 27(30), 4516-4522. DOI 10.1002/adma.201501901. 28. Xie, C.; Wang, Y.; Hu, K.; Tao, L.; Huang, X.; Huo, J.; Wang, S., In situ confined synthesis of molybdenum oxide decorated nickel–iron alloy nanosheets from MoO42− intercalated layered double hydroxides for the oxygen evolution reaction. J. Mater. Chem. A 2017, 5 (1), 87-91. DOI 10.1039/c6ta08149e. 29. Cao, L.-M.; Wang, J.-W.; Zhong, D.-C.; Lu, T.-B., Template-directed synthesis of sulphur 16


Page 17 of 26 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


doped NiCoFe layered double hydroxide porous nanosheets with enhanced electrocatalytic activity for the oxygen evolution reaction. J. Mater. Chem. A 2018, 6 (7), 3224-3230. DOI 10.1039/c7ta09734d. 30. Yu, L.; Yang, J. F.; Guan, B. Y.; Lu, Y.; Lou, X. W. D., Hierarchical Hollow Nanoprisms Based on Ultrathin Ni-Fe Layered Double Hydroxide Nanosheets with Enhanced Electrocatalytic Activity towards Oxygen Evolution. Angew. Chem. Int. Ed. 2018, 57 (1), 172-176. DOI 10.1002/anie.201710877. 31. Song, F.; Hu, X., Ultrathin cobalt-manganese layered double hydroxide is an efficient oxygen evolution catalyst. J. Am. Chem. Soc. 2014, 136 (47), 16481-16484. DOI 10.1021/ja5096733. 32. Wang, Q.; O'Hare, D., Recent advances in the synthesis and application of layered double hydroxide (LDH) nanosheets. Chem. Rev. 2012, 112 (7), 4124-4155. DOI 10.1021/cr200434v. 33. Abellán, G.; Carrasco, J. A.; Coronado, E.; Prieto-Ruiz, J. P.; Prima-García, H., In-Situ Growth of Ultrathin Films of NiFe-LDHs: Towards a Hierarchical Synthesis of Bamboo-Like Carbon Nanotubes. Adv. Mater. Interfaces 2014, 1 (6), 1400184. DOI 10.1002/admi.201400184. 34. Abellán, G.; Carrasco, J. A.; Coronado, E.; Romero, J.; Varela, M., Alkoxide-intercalated CoFe-layered double hydroxides as precursors of colloidal nanosheet suspensions: structural, magnetic and electrochemical properties. J. Mater. Chem. C 2014, 2 (19), 3723-3731. DOI 10.1039/c3tc32578d. 35. Chen, W.; Wang, T.; Xue, J.; Li, S.; Wang, Z.; Sun, S., Cobalt-Nickel Layered Double Hydroxides Modified on TiO2 Nanotube Arrays for Highly Efficient and Stable PEC Water Splitting. Small 2017, 13 (10), 1602420. DOI 10.1002/smll.201602420. 36. Diaz-Morales, O.; Ledezma-Yanez, I.; Koper, M. T. M.; Calle-Vallejo, F., Guidelines for the Rational Design of Ni-Based Double Hydroxide Electrocatalysts for the Oxygen Evolution Reaction. ACS Catal. 2015, 5 (9), 5380-5387. DOI 10.1021/acscatal.5b01638. 37. Li, Y.; Zhang, L.; Xiang, X.; Yan, D.; Li, F., Engineering of ZnCo-layered double hydroxide nanowalls toward high-efficiency electrochemical water oxidation. J. Mater. Chem. A 2014, 2 (33), 13250-13258. DOI 10.1039/c4ta01275e. 17



Page 18 of 26

38. Qian, M.; Cui, S.; Jiang, D.; Zhang, L.; Du, P., Highly Efficient and Stable Water-Oxidation Electrocatalysis with a Very Low Overpotential using FeNiP Substitutional-Solid-Solution Nanoplate Arrays. Adv. Mater. 2017, 29 (46), 1704075. DOI 10.1002/adma.201704075. 39. Song, F.; Hu, X., Exfoliation of layered double hydroxides for enhanced oxygen evolution catalysis. Nat. Commun. 2014, 5, 4477. DOI 10.1038/ncomms5477. 40. Wu, J.; Ren, Z.; Du, S.; Kong, L.; Liu, B.; Xi, W.; Zhu, J.; Fu, H., A highly active oxygen evolution electrocatalyst: Ultrathin CoNi double hydroxide/CoO nanosheets synthesized via interface-directed assembly. Nano Res. 2016, 9 (3), 713-725. DOI 10.1007/s12274-015-0950-4. 41. Zhou, D.; Cai, Z.; Lei, X.; Tian, W.; Bi, Y.; Jia, Y.; Han, N.; Gao, T.; Zhang, Q.; Kuang, Y.; Pan, J.; Sun, X.; Duan, X., NiCoFe-Layered Double Hydroxides/N-Doped Graphene Oxide Array Colloid Composite as an Efficient Bifunctional Catalyst for Oxygen Electrocatalytic Reactions. Adv. Energy Mater. 2017, 8 (9),1701905. DOI 10.1002/aenm.201701905. 42. Zou, X.; Goswami, A.; Asefa, T., Efficient noble metal-free (electro)catalysis of water and alcohol oxidations by zinc-cobalt layered double hydroxide. J. Am. Chem. Soc. 2013, 135 (46), 17242-17245. DOI 10.1021/ja407174u. 43. 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 (9), 3662-3674. DOI 10.1021/ja3126432. 44. Kargar, A.; Yavuz, S.; Kim, T. K.; Liu, C. H.; Kuru, C.; Rustomji, C. S.; Jin, S.; Bandaru, P. R., Solution-Processed CoFe2O4 Nanoparticles on 3D Carbon Fiber Papers for Durable Oxygen Evolution

Reaction.

ACS

Appl.

Mater.

Interfaces

2015,

7

(32),

17851-6.

DOI

10.1021/acsami.5b04270 45. Yang, Y.; Dang, L.; Shearer, M. J.; Sheng, H.; Li, W.; Chen, J.; Xiao, P.; Zhang, Y.; Hamers, R. J.; Jin, S., Highly Active Trimetallic NiFeCr Layered Double Hydroxide Electrocatalysts for Oxygen

Evolution

Reaction.

Adv.

Energy

Mater.

2018,

8

(15),

1703189.

DOI

10.1002/aenm.201703189. 46. Zhu, Y. P.; Jing, Y.; Vasileff, A.; Heine, T.; Qiao, S.-Z., 3D Synergistically Active Carbon 18


Page 19 of 26 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


Nanofibers for Improved Oxygen Evolution. Adv. Energy Mater. 2017, 7 (14), 1602928. DOI 10.1002/aenm.201602928. 47. He, P.; Yu, X. Y.; Lou, X. W., Carbon-Incorporated Nickel-Cobalt Mixed Metal Phosphide Nanoboxes with Enhanced Electrocatalytic Activity for Oxygen Evolution. Angew. Chem., Int. Ed. 2017, 56 (14), 3897-3900. DOI 10.1002/anie.201612635. 48. Li, R.; Hu, Z.; Shao, X.; Cheng, P.; Li, S.; Yu, W.; Lin, W.; Yuan, D., Large Scale Synthesis of NiCo Layered Double Hydroxides for Superior Asymmetric Electrochemical Capacitor. Sci. Rep-UK 2016, 6, 18737. DOI 10.1038/srep18737. 49. Li, X.; Shen, J.; Sun, W.; Hong, X.; Wang, R.; Zhao, X.; Yan, X., A super-high energy density asymmetric

supercapacitor

based

on

3D

core–shell

structured

NiCo-layered

double

hydroxide@carbon nanotube and activated polyaniline-derived carbon electrodes with commercial level mass loading. J. Mater. Chem. A 2015, 3 (25), 13244-13253. DOI 10.1039/c5ta01292a. 50. Wang, X.; Li, X.; Du, X.; Ma, X.; Hao, X.; Xue, C.; Zhu, H.; Li, S., Controllable Synthesis of NiCo LDH Nanosheets for Fabrication of High-Performance Supercapacitor Electrodes. Electroanal. 2017, 29 (5), 1286-1293. DOI 10.1002/elan.201600602. 51. Yu, C.; Liu, Z.; Han, X.; Huang, H.; Zhao, C.; Yang, J.; Qiu, J., NiCo-layered double hydroxides vertically assembled on carbon fiber papers as binder-free high-active electrocatalysts for water oxidation. Carbon 2016, 110, 1-7. DOI 10.1016/j.carbon.2016.08.020. 52. Fan, K.; Chen, H.; Ji, Y.; Huang, H.; Claesson, P. M.; Daniel, Q.; Philippe, B.; Rensmo, H.; Li, F.; Luo, Y.; Sun, L., Nickel-vanadium monolayer double hydroxide for efficient electrochemical water oxidation. Nat. Commun. 2016, 7, 11981. DOI 10.1038/ncomms11981. 53. Li, X.; Xin, M.; Guo, S.; Cai, T.; Du, D.; Xing, W.; Zhao, L.; Guo, W.; Xue, Q.; Yan, Z., Insight of synergistic effect of different active metal ions in layered double hydroxides on their electrochemical

behaviors.

Electrochim.

Acta

2017,

253,

302-310.

DOI

10.1016/j.electacta.2017.09.075 54. Lee, J. W.; Ahn, T.; Soundararajan, D.; Ko, J. M.; Kim, J. D., Non-aqueous approach to the preparation of reduced graphene oxide/alpha-Ni(OH)2 hybrid composites and their high capacitance 19



Page 20 of 26

behavior. Chem. Commun. 2011, 47 (22), 6305-6307. DOI 10.1039/c1cc11566a. 55. N. S. McIntyre, and M. G. Cook, X-ray photoelectron studies on some oxides and hydroxides of cobalt, nickel, and copper. Anal. Chem., 1975, 47 (13), 2208–2213. DOI 10.1021/ac60363a034. 56. Nai, J.; Yin, H.; You, T.; Zheng, L.; Zhang, J.; Wang, P.; Jin, Z.; Tian, Y.; Liu, J.; Tang, Z.; Guo, L., Efficient Electrocatalytic Water Oxidation by Using Amorphous Ni-Co Double Hydroxides Nanocages. Adv. Energy Mater. 2015, 5 (10), 1401880. DOI 10.1002/aenm.201401880. 57. Wang, Y. J.; Trenary, M., Surface-Chemistry of Boron Oxidation .2. The Reactions of B2O2 and B2O3 with Boron Films Grown on Ta(110). Chem. Mater. 1993, 5 (2), 199-205. DOI 10.1021/cm00026a008. 58. Raskar, D.; Rinke, M. T.; Eckert, H., The mixed-network former effect in phosphate glasses: NMR and XPS studies of the connectivity distribution in the glass system (NaPO3)1-x(B2O3)x. J. Phys. Chem. C 2008, 112 (32), 12530-12539. DOI 10.1021/jp8035549. 59. Jiang, W. J.; Niu, S.; Tang, T.; Zhang, Q. H.; Liu, X. Z.; Zhang, Y.; Chen, Y. Y.; Li, J. H.; Gu, L.; Wan, L. J.; Hu, J. S., Crystallinity-Modulated Electrocatalytic Activity of a Nickel(II) Borate Thin Layer on Ni3 B for Efficient Water Oxidation. Angew. Chem., Int. Ed. 2017, 56 (23), 6572-6577. DOI 10.1002/anie.201703183. 60. Dinca, M.; Surendranath, Y.; Nocera, D. G., Nickel-borate oxygen-evolving catalyst that functions under benign conditions. P. Natl. Acad. Sci. USA 2010, 107 (23), 10337-10341. DOI 10.1073/pnas.1001859107. 61. Xuan, C.; Wang, J.; Xia, W.; Zhu, J.; Peng, Z.; Xia, K.; Xiao, W.; Xin, Huolin L.; Wang, D., Heteroatom (P, B, or S) incorporated NiFe-based nanocubes as efficient electrocatalysts for the oxygen evolution reaction. J. Mater. Chem. A 2018, 6 (16), 7062-7069. DOI 10.1039/c8ta00410b. 62. Power, P. P.; Woods, W. G., The chemistry of boron and its speciation in plants. Plant Soil 1997, 193 (1), 1-13. DOI 10.1023/A:1004231922434.

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Figure 1. XRD patterns of Carbon paper (a), NiCo-LDHs/CP (b), NiCo-LDHs-200/CP (c) and NiCo-LDHs@B2O3/CP (d) (the XRD peaks of CP and NiCo-LDHs were remarked with □ and ○， respectively).

21



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Figure 2. SEM images for (a) NiCo-LDHs/CP and inset is partial enlargement (b) NiCo-LDHs@B2O3/CP and inset is partial enlargement. EDX elemental mapping images of (d) Ni, (e) Co, (f) B, (g) for (c) NiCo-LDHs@B2O3/CP. (h) TEM and (I) HRTEM of NiCo-LDHs@B2O3/CP and the insert of (h) is the FFT

22


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Figure 3. X-ray photoelectron spectra (XPS) images of (a) Ni 2p, (b) Co 2p, (c) B 1s, (d) O 1s for NiCo-LDHs@B2O3/CP

23



Figure

4

(a)

The

polarization

curves

of

CP,

NiCo-LDHs/CP,

Page 24 of 26

NiCo-LDHs-200/CP,

NiCo-LDHs@B2O3/CP and RuO2/CP for the OER in 1.0 M KOH solution (scan rate 2 mV s-1) and (b) a bar graph of the corresponding overpotential (η) at 10 mA cm-2 of the differents samples. (c) Tafel plots of NiCo-LDHs/CP, NiCo-LDHs-200/CP, NiCo-LDHs@B2O3/CP and RuO2/CP. (d) the LSV

curves

of

initial

and

2000th

cycles

of

NiCo-LDHs@B2O3/CP

Chronoamperometric response at a fixed overpotential of 230 mV.

24


nanosheets.

(e)

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Figure 5. The capacitive currents at 0.30 V vs. SCE as a function of scan rate for NiCo-LDHs/CP and NiCo-LDHs@B2O3/CP. The determined double-layer capacitance of the system is taken as the average of the absolute value of the slope for the linear fits to the data.

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Table of Content

Synopsis: A core-shell structure of NiCo-LDHs@B2O3/CP was prepared via hydrothermal and chemical vapor deposition. It exhibit excellent OER catalytic activity.

26


Amorphous Boron Oxide Coated NiCo-LDHs Nanoarrays for Highly

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