Controlled Self-Assembled NiFe Layered Double Hydroxides

Subscriber access provided by Drexel University Libraries

Functional Nanostructured Materials (including low-D carbon)

Controlled Self-assembled NiFe-Layered Double Hydroxides/Reduced Graphene Oxide Nanohybrids Based on Solid Phase Exfoliation Strategy as an Excellent Electrocatalyst for the Oxygen Evolution Reaction Jia Shen, Ping Zhang, Ruishi Xie, Lin Chen, Mengting Li, Jiapeng Li, Bingqiang Ji, Zongyue Hu, Jiajun Li, Lixian Song, Yeping Wu, and Xiuli Zhao ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b22260 • Publication Date (Web): 20 Mar 2019 Downloaded from http://pubs.acs.org on March 21, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 39 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

ACS Applied Materials & Interfaces

Controlled Self-assembled NiFe-Layered Double Hydroxides/Reduced Graphene Oxide Nanohybrids Based on Solid Phase Exfoliation Strategy as an Excellent Electrocatalyst for the Oxygen Evolution Reaction Jia Shen a, Ping Zhang a, , Ruishi Xie a, Lin Chen a, Mengting Li a, Jiapeng Li a , Bingqiang Ji a , Zongyue Hu a , Jiajun Li a , Lixian Song a , Yeping Wu b, Xiuli Zhao b, a



National Engineering Technology Center for Insulation materials & State Key

Laboratory of Environmental-friendly Energy Materials, Southwest University of Science and Technology, Mianyang, 621010, PR China b

Institute of Chemical Materials, China Academy of Engineering Physics (CAEP),

Mianyang, 621900, PR China

KEYWORDS: Layered Double Hydroxides, Graphene Oxide, Solid Phase Exfoliation, Controllable Self-assembly, Oxygen Evolution Reaction ABSTRACT: Layered double hydroxides (LDHs), as an effective oxygen evolution reaction (OER) electrocatalyst, face many challenges in the practical application. The main obstacle is that bulk materials limit the exposure of active sites. At the same time, the poor conductivity of LDHs is also an important factor. Exfoliation is one of the

 Corresponding author. Fax: +86-816-2419245

E-mail address: [email protected] (Ping Zhang)  Corresponding author. Fax: +86-816-2485312 E-mail address: [email protected] 1 ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 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 2 of 39

most direct and effective strategy to increase the electrocatalytic properties of LDHs due to the exposure of more active sites. However, developing an efficient exfoliation strategy to exfoliate LDHs into stable monolayer nanosheets is still challenging. Therefore, we report a new and efficient solid phase exfoliation strategy to exfoliate NiFe-LDH and graphene oxide (GO) into monolayer nanosheets, and the exfoliating ratio of NiFe-LDH and GO can reach up to 10 wt% and 5 wt%, respectively. Based on the solid phase exfoliation strategy, we accidentally discovered that there is a dynamic evolution process between NiFe-LDH nanosheets (NiFe-LDH-NS) and GO nanosheets (GO-NS) to assemble a new NiFe-LDH/GO nanohybrids, i, e. NiFe-LDH-NS could be horizontal bespreading on GO-NS, or NiFe-LDH-NS are well-organized standing on GO-NS, or simultaneously. Electrocatalytic OER property test results show that NiFeLDH/RGO-3 (NFRG-3) nanohybrids obtained by reduction treatment of NiFeLDH/GO-3 (NFGO-3) nanohybrids, which NiFe-LDH-NS are well-organized standing on GO-NS, have excellent electrocatalytic properties for OER in an alkaline solution (with a small overpotential of 273 mV and Tafel slope of 49 mV dec-1 at the current density of 30 mA cm-2). The excellent electrocatalytic properties for OER of NFRG-3 nanohybrids could be attributed to the unique three-dimensional array-like structure with more active sites. At the same time, reduced graphene oxide (RGO) with excellent conductivity can improve the charge transfer efficiency, and synergistically improve OER properties of nanohybrids. INTRODUCTION Oxygen evolution reaction (OER), as a crucial part of the energy conversion reaction, 2 ACS Paragon Plus Environment

Page 3 of 39 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


has a wide range of applications in renewable energy technologies such as water splitting and rechargeable metal/air batteries, and it has led to many studies in recent years1-3. However, OER at the anode has been regarded as the main bottleneck due to the sluggish kinetics and large overpotential4,5. So it is necessary to construct and design an OER electrocatalyst with a lower overpotential to improve the energy conversion efficiency. Current research indicates that Iridium dioxide (IrO2) and ruthenium dioxide (RuO2) are considered to be the best OER electrocatalysts6, but the high cost and poor resources limit their further applications7-11. Therefore, researchers are devoted to developing non-precious metal OER electrocatalysts with high catalytic activity12, 13. Layered double hydroxides (LDHs) have attracted the interest of researchers due to their unique two-dimensional lamellar structure and high catalytic activity14-17, and NiFe-LDHs as a currently reported most effective class of OER electrocatalysts under alkaline conditions have been extensively studied recently18-22. It is frustrating that bulk NiFe-LDHs with poor conductivity and lack of electrocatalytic active sites limit their further application as an electrocatalyst in OER23, 24. Numerous strategies have been developed to enhance the intrinsic activity of LDHs electrocatalysts for the OER, such as exfoliation25, 26, anion intercalation27-30, element doping31-35, construction of special nanostructures36, defect engineering37-39, forming nanohybrids with conductive substrates (graphene40-42, carbon nanotubes43, 19, MXenes44, etc.) and so on. Compared with bulk LDHs, monolayer LDH nanosheets (LDH-NS) with large specific surface area can expose more electrocatalytic active sites and thus show higher electrocatalytic OER properties45 and exfoliation is an easy way to obtain monolayer nanosheets. Liquid 3 ACS Paragon Plus Environment


Page 4 of 39

exfoliation as a typical exfoliation strategy has been widely used in exfoliation of 2D materials in recent years46, 47. Song et al.48 dispersed NiFe LDH-ClO4- in degassed formamide under ultrasonic treatment and then mechanically stirred under a N2 atmosphere for 24h to obtain an exfoliated single LDHs layers. Ge et al.49 mixed Ni– Al LDH with formamide and then vigorously shaken on a mechanical shaker for 60 hours to achieve exfoliation of Ni-Al LDH. However, liquid exfoliation of LDHs as the most typical exfoliation strategy is time-consuming, inefficient and incomplete. At the same time, toxic solvents are required, and the exfoliated LDH-NS cannot be stored for long periods of time because LDH-NS tend to restack into bulk LDHs when the solvent molecules have been removed. Based on liquid exfoliation, Wang et al.50 described the successful exfoliation of bulk CoFe LDHs into ultrathin LDH nanosheets through Ar plasma etching. This kind of method of dry exfoliation is time-saving, non-toxic and avoids the adsorption of solvent molecules. However, the exfoliated LDH obtained by this method is difficult to form composite materials with other materials, such as graphene. Our research team previously reported a new strategy for solid phase exfoliation51, which used Polylactic acid (PLA) to destroy the interlaminar forces of 2D materials to achieve exfoliation of MgAl-LDH and Montmorillonite (MMT), and the combination of MgAl-LDH and MMT was achieved by hydrolysis of PLA under hydrothermal conditions. Therefore, it is of vital importance to develop new and efficient exfoliation strategies of LDHs and other 2D materials. Herein, we have developed a new solid phase exfoliation material (SPEM) and the monolayer NiFe-LDH nanosheets (NiFe-LDH-NS) and graphene oxide nanosheets 4 ACS Paragon Plus Environment

Page 5 of 39 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


(GO-NS) were obtained by inserting SPEM molecules into the layers of 2D materials to break the interlaminar forces. Compared with traditional liquid exfoliation, this kind of solid phase exfoliation strategy is time-saving, high efficiency and no toxic solvent molecules adsorption. NiFe-LDH and GO can reach a very considerable exfoliating efficiency of 10 wt% and 5 wt%, respectively. At the same time, it can keep LDH-NS and GO-NS stable for long periods of time. Surprisingly, SPEM is a kind of material with excellent water solubility, which means that NiFe-LDH-NS and GO-NS with two types of opposite charges can be electrostatically self-assembled to construct

Scheme 1. Preparation of NiFe-LDH/GO nanohybrids based on solid phase exfoliationliquid phase assembly strategy.

nanohybrids in the aqueous phase at room temperature. Therefore, we propose a solid phase exfoliation-liquid phase assembly strategy to design a highly active OER electrocatalyst. These kind of nanohybrids with heterostructure are obtained by electrostatic self-assembly of two types of oppositely charged NiFe-LDH-NS and GONS. We also unexpectedly found that NiFe-LDH/GO hybrids with different 5 ACS Paragon Plus Environment


Page 6 of 39

heterogeneous structures can be obtained by adjusting the mass ratio of NiFe-LDH-NS to GO-NS. We unambiguously proposed that NiFe-LDH-NS are horizontal bespreading on GO-NS, or NiFe-LDH-NS are well-organized standing on GO-NS, or simultaneously, combined with the characterization results of XRD and HRTEM. This is different from previous reports that LDH-NS and GO-NS merely constitute a faceto-face and layer by layer superlattice structure52, 24, 49. The NFRG-3 catalyst with threedimensional array-like heterostructure exhibits the best OER catalytic activity (with a small overpotential of 273 mV and Tafel slope of 49 mV dec-1 at the current density of 30 mA cm-2) than that of bulk NiFe-LDH and NFGO nanohybrids, which can be ascribed to the exposure of active sites in exfoliated NiFe-LDH and rapid transfer of interlayer charge generated by stacking LDH-NS and RGO-NS. EXPERIMENTAL SECTION Materials. Nickel(II) nitrate hexahydrate (Ni(NO3)2·6H2O, AR) and Iron(III) nitrate nonahydrate (Fe(NO3)3·9H2O, AR) were purchased from Tianjing Fuchen Chemical Reagents Factory, China. Natural flake graphite (99.99 wt% purity, average particle diameter of 20 μm) was purchased from Yingshida Graphite Co. Ltd., China. Hydrated hydrazine (N2H4·H2O, 85%, AR) and Sodium hydroxide (NaOH, AR) was purchased from Chengdu Kelong Chemical Reagent Company, China. Preparation of NiFe-LDH and GO. The preparation of NiFe-LDH followed hydrothermal method53. A mixture solution was prepared by adding 0.06 mol Ni(NO3)2·6H2O and 0.02 mol Fe(NO3)3·9H2O to 100 ml of deionized water (the ratio of Ni2+ and Fe3+ were 3:1). Then mix the solution evenly by sonicating for 30 min. After 6 ACS Paragon Plus Environment

Page 7 of 39 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


that, the pH of the solution was adjusted to 10 using 1M NaOH solution with magnetic stirring at room temperature. The above solution was transferred to a stainless-steel Teflon-lined autoclave. After being kept in a preheated oven at 150 oC for 10 h, the autoclave was cooled down naturally to room temperature. Finally, the reaction product was collected and washed repeatedly and dried in a vacuum oven at 60 oC. GO was prepared from a modified Hummers method54. Solid phase exfoliation of NiFe-LDH and GO. In our experience, a series polyhydroxy materials (SPEM) with appropriate proportion are used as an exfoliated material to achieve the exfoliation of 2D materials. The NiFe-LDH powders (0.3 g) was gradually incorporated into melting solid phase exfoliating material (SPEM) by mixing roll (XSS-300), the temperature, viscosity, shearing rate of SPEM system were contantly regulated and controlled, simultaneously. Different exfoliation ratios of NiFeLDH/SPEM composites could be obtained by changing the quality of NiFe-LDH powders. The exfoliation of GO was similar to NiFe-LDH excepted that a certain amount of deionized water was added and ultrasonically dispersed for 30 minutes in the early stage. Preparation

of

NiFe-LDH/GO

(NFGO)

and

NiFe-LDH/RGO

(NFRG)

nanohybrids. Self-assembly of GO-NS and LDH-NS under liquid phase conditions were shown in Scheme 1. First, 0.2 g of GO/SPEM (1wt%) composite was dissolved in 100 ml of deionized water to form a colloidal dispersion of GO-NS. Then NiFeLDH/SPEM (1wt%) composite was added at different mass ratio under magnetic stirring. The NiFe-LDH-NS gradually dispersed in the solution and self-assembled with 7 ACS Paragon Plus Environment


Page 8 of 39

GO-NS under the action of electrostatic attraction to obtain floc-like precipitated NFGO nanohybrids. Finally, NFGO nanohybrids were washed with deionized water repeatedly to remove SPEM and dried in a vacuum oven at 60 oC. NFRG nanohybrids were obtained from the reduction treatment of NFGO nanohybrids. Frist, Hydrated hydrazine (85%, 500 μL) was placed in a teflon-lined autoclaved, with no direct contact with NFGO nanohybrids, and a separate vessel containing NFGO nanohybrids (50 mg) was put in same container, then the container was sealed and kept at 90 oC for 12 h. Finally, the NFRG nanohybrids was washed by deionized water for several times and and dried in a vacuum oven at 60 oC. According to the different structure assembled by NiFe-LDH and GO, NiFe-LDH : GO=3 : 1, NiFe-LDH : GO=8 : 1 and NiFe-LDH : GO=14: 1 are recorded as NFGO-1, NFGO-2 and NFGO-3, respectively, and the corresponding reduction products are recorded as NFRG-1, NFRG-2 and NFRG-3, respectively. Preparation of samples for OER electrocatalysis. The homogeneous catalyst ink was obtained by dispersing 5 mg of the active material, 2 mg of acetylene black and 20 µL of PTFE solution in a 400 µL of N-Methyl pyrrolidone (NMP) by sonication for 30 min. In order to prepare the working electrode, 210 µL catalyst ink was uniformly placed onto the 1 cm2 of area on a piece of 1×2 cm Ni foam electrode and dried in vacuum at 65 oC for 24 h with the final mass loading of 2.5 mg cm-2. Structural characterization. The X-ray diffraction (XRD) patterns of the obtained samples were taken on a PANalytical X’Pert PRO X-ray diffractometer equipped with a copper anode (Cu Kα radiation, λ = 1.54187 Å). The X-ray source was operated at 40 8 ACS Paragon Plus Environment

Page 9 of 39 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


kV and 40 mA. The measurements were performed using a θ−2θ scan. The morphology of all electrocatalysts was investigated by field emission scanning electron microscope (FESEM, UItra55, Carl zeissNTS GmbH, Germany) and transmission electron microscope (TEM, Libra200, Carl zeiss irts Co., Germany). The X-ray photoelectron spectroscopy (XPS) was carried out with a VG Escalab Mark II spectrometer (ThermoVG Scientific Ldt, UK), using Al Kα excitation radiation (hv = 1486.6 eV). The Infared spectrum tests were performed at the Fourier transformation infrared spectrometer (FTIR, Spectrum one autoima, PerkinElmer Co., USA). The Raman spectrum tests were performed at the Raman spectroscopy (in Via, Renishaw Co., UK). The tomographic particle image measurement is studied by building a simulated particle imaging platform. This platform is consist of double pulse laser (Vlite-500 PIV, Beamtech Optronics Co., Ltd.) and four Nikon stereo lenses and synchronizer (SMMicroPulse725, Beijing Cube Tiandi Technology Development Co., Ltd.). Signal acquisition is achieved by MicroVec 3.3.1 software (Beijing Cube Tiandi Technology Development Co., Ltd.). The normalized particle images were obtained by 3D reconstruction from MATLAB 2016 (Figure S12). Electrochemical characterizations. Electrochemical studies for OER were carried out in a standard three electrode system controlled by a CHI760E electrochemistry workstation. Catalysts loaded on Ni foam was used as the working electrode, platinum wire used as the counter electrode and saturated calomel electrode (SCE) as the reference electrode. All electrochemical tests were performed in 1 M KOH electrolyte at room temperature and the reference was calibrated against and converted to 9 ACS Paragon Plus Environment


Page 10 of 39

reversible hydrogen electrode (RHE). The catalysts were cycled about 20 times of cyclic voltammetry (CV) until a stable CV curve was developed before measuring polarization curves of catalysts. Linear sweep voltammetry (LSV) was carried out from 0 to 0.8 V vs SCE with a scan rate of 5 mV s-1 for the polarization curves, and the measured potentials were normalized considering RHE as the reference according to the following equation: E(RHE) = E(SCE) + 0.059pH + 0.244 V. The overpotentials were calculated as E (overpotential, η) = E (j= 30 mA cm-2) − 1.23 V. All LSV polarization curves were not corrected with iR compensation before measurements. The Tafel slopes were obtained by plotting the overpotential η against log (j) from LSV curves. The electrochemical active surface area (ECSA) was determined from the CV data with a potential window of 0.05−0.2 V vs SCE (the non-Faradic region) at different scan rates (20, 40, 60, 80, 100 and 120 mV s-1). When plotting the ∆j (= ja - jc) vs RHE against the scan rate, a linear slope that was twice of the double layer capacitance (Cdl) was used to obtain the ECSA55, and the ECSA can be calculated as: ECSA =

Cdl Cs

Cs is the specific capacitance value for a flat standard with 1 cm2 of real surface area, and the general value for is Cs between 20 μF cm-2 and 60 μF cm-2. Here we use 40 μF cm-2 as the average value56. The Turnover frequency (TOF) calculation values of the catalysts are calculated from the equation: TOF =

j×A 4×F×n 10

ACS Paragon Plus Environment

Page 11 of 39 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


j is the current density at overpotential of 300 mV and 400 mV. A is the area of the electrode. F is the faraday constant (96485 C mol-1). n is the number of moles of active materials that are loaded on the electrodes. In our case, all metal elements (Ni and Fe) are assumed to be catalytically active no matter whether or not they are accessible to the electrolyte. Therefore, the calculated TOF value represents the lowest limit, because not every metal atom has catalytic activity57.The electrochemical impedance spectroscopy (EIS) data were collected in the frequency region of 0.1−100000 Hz at the overpotential of 270 mV. Time-dependent current density (i-t) curve was recorded under a static overpotential of 250 mV. Chrompotentiometry (CP) was carried out under a constant current density of 10 mA cm-2. RESULTS AND DISCUSSION X-ray diffraction (XRD) is one of the most important technique to estimate the exfoliating degree of NiFe-LDH and GO, and the evolution of self-assembled heterostructures of NFGO nanohybrids. As shown in Figure S1 (see the Supporting Information for details), it can be seen from the diffraction pattern of XRD that the bulk NiFe-LDHs had been successfully synthesized because all of the diffraction peaks of the bulk NiFe-LDHs could be well indexed to PDF#40-0215. The two strong and sharp diffraction peaks appearing at 2θ=11.24° and 2θ=22.90° correspond to the typical (003) and (006) planes of LDHs, respectively, and the interlayer distance in bulk NiFe-LDHs is 0.78 nm. The typical (001) plane diffraction peak appearing at 2θ=9.80° indicates 11 ACS Paragon Plus Environment


Page 12 of 39

that GO was also successfully synthesized, and the interlayer distance in GO is 0.9 nm. The field emission scanning electron microscopy (FESEM) images of the NiFe-LDHs and GO (Figure S3) both show a typical 2D nanosheet like structure, and GO has a large lamellar area. The typical (003) plane diffraction peak of LDHs and the typical (002) plane diffraction peak of GO disappeared in NiFe-LDH/SPEM and GO/SPEM composites, indicating that the host sheets of LDHs and GO are not interrelated and not in parallel, i.e., NiFe-LDH and GO achieved complete exfoliation in SPEM (Figure 1a, b). The maximum exfoliation of NiFe-LDH and GO in SPEM is further considered and the different exfoliation ratios were obtained by changing the amount of NiFe-LDH or GO added in SPEM (Figure S2). The XRD pattern of NiFe-LDH/SPEM with different exfoliation ratio (1 wt%, 2 wt%, 10 wt% and 15 wt%) is shown in Figure S1(c). A weak and wide-ranging XRD diffraction peak corresponding to the typical (003) crystal plane of NiFe-LDH begins to appear in NiFe-LDH/SPEM (15 wt%), indicating that NiFeLDH failed to reach complete exfoliation at this ratio. Therefore, NiFe-LDH can achieve at least 10 wt% exfoliation efficiency in the SPEM system, which proves that this is a very efficient and complete exfoliation strategy compared with liquid phase exfoliation (Table S4). Figure S1(d) is the XRD pattern of GO/SPEM with different exfoliation ratio (1 wt%, 2 wt%, 5 wt% and 10 wt%). The layer spacing of GO in GO/SPEM (10 wt%) was increased from 0.90 nm to 1.41 nm, indicating that GO can only be expanded in GO/SPEM (10 wt%), and cannot be exfoliated completely. It also proves that GO can achieve at least 5 wt% complete exfoliation in this SPEM system. We believe that the hydrogen bonding between the polyhydroxyl-SPEM and the surface 12 ACS Paragon Plus Environment

Page 13 of 39 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


functional groups of the 2D material (NiFe-LDH and GO) and the external shear force are the main driving forces for the exfoliation process. Since SPEM has excellent water solubility, NiFe-LDH-NS or GO-NS can be released from NiFe-LDH/SPEM or GO/SPEM composites as SPEM is gradually dissolved in deionized water. The typical (003) and (006) planes of NiFe-LDHs and the typical (002) plane diffraction peak of GO had disapeared, further indicating the successful exfoliation of NiFe-LDHs and GO

Figure 1. XRD patterns of (a) bulk NiFe-LDH, NiFe-LDH/SPEM (1wt%). (b) GO, GO/SPEM (1wt%). (c) NiFe-LDH-NS and GO-NS. (d-e) NFGO nanohybrids with mass ratio from NiFe-LDH-NS: GO-NS=1:2 to 14:1. (f) The pictures of GO-NS, NiFeLDH-NS and NFGO nanohybrids.

into monolayers nanosheets (Figure 1c). Furtherly, a clear Tyndall effect is observed upon laser irradiation for the GO-NS and NiFe-LDH-NS colloidal suspension (Figure 1(f)), which illustrates that the NiFe-LDH-NS and GO-NS are well dispersed in 13 ACS Paragon Plus Environment


Page 14 of 39

water25,48. It can be clearly seen from Figure S3 that GO has a larger planar size than NiFe-LDH, so there is also a difference in layer size and planar size between NiFeLDH-NS and GO-NS. In theory, LDH-NS and GO-NS with two opposite charges will attract each other and assemble as much as possible, and a GO-NS with a larger planar size can often attract dozens of LDH-NS. Therefore, the mass ratio between LDH-NS and GO-NS will become an important factor affecting the self-assembly structure of NFGO nanohybrids. Based on this theory and the complete exfoliation of NiFe-LDH and GO, we consider exploring the changes in the structure of NiFe-LDH/GO nanohybrids by adjusting the mass ratio of NiFe-LDH-NS to GO-NS. As shown in Figure 1(d-e), the mass ratio of NiFe-LDH-NS to GO-NS ranges from 1:2 to 10:1, and a new diffraction peak appears at 2θ=7.40°. However, this diffraction peak is different from the (001) plane (2θ=9.80°) of GO and the (003) plane (2θ=11.24°) of NiFe-LDH (Figure S1), so we believe that the XRD diffraction peak at 2θ=7.40° is caused by the well-ordered heterogeneous superlattice structure that formed by LDH-NS and GO-NS. And the new diffraction peak position is lower than the peak positions of the original GO and LDH, reflecting the remarkable expansion of interlayer spacing upon hybridization. As the mass ratio of NiFe-LDH-NS increases gradually, the intensity of this diffraction peak decreases and widens gradually until it disappears at the mass ratio of NiFe-LDH-NS to GO-NS is 11:1. As the LDH-NS content in the assembly system increases, the NiFe-LDH-NS with the same charge will mutually exclusive, this kind of repulsion can decrease or even destroy the crystallinity of the ordered superlattice structure formed by NiFe-LDH-NS and GO-NS. Therefore, the intensity of the 14 ACS Paragon Plus Environment

Page 15 of 39 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


diffraction peak at 2θ=7.40° decreases and widens gradually, until it disappears. When the mass ratio of NiFe-LDH-NS to GO-NS is 4:1, a new diffraction peak appears at 2θ=11.40°, which corresponds to the typical (003) planes of LDHs. The change of the diffraction peak indicates that there is a dynamic evolution process of the assembled structure of NiFe-LDH and GO. In the first stage (the mass ratio of NiFe-LDH to GO is from 1:2 to 3:1), the GO-NS in the solution system is in excess. Under the action of electrostatic attraction, the positively charged NiFe-LDH-NS is adsorbed by the negatively charged GO-NS and tends to face-to-face assembly58. In the second stage, when the NiFe-LDH-NS content in the solution system increases (the mass ratio of NiFe-LDH to GO is from 4:1 to 10:1), the NiFe-LDH-NS with the same charge will mutually exclusive, some NiFe-LDH-NS on GO-NS tend to stand up regularly to reduce electrostatic repulsion between the positively charged of NiFe-LDH laminates. In the third stage, as the NiFe-LDH-NS content in the solution system continues to increase (the mass ratio of NiFe-LDH to GO is from 11:1 to 14:1), all the NiFe-LDHNS on GO-NS will be standing up regularly because of this repulsion. That is to say, it becomes possible to obtain a specific heterostructure of NFGO nanohybrids by controlling the mass ratio of NiFe-LDH-NS to GO-NS.

15 ACS Paragon Plus Environment


Page 16 of 39

Figure 2. Tomographic Particle Image Velocimetry images of NiFe-LDH and GO-NS mixed solution over time. (Magenta arrow: NiFe-LDH-NS; Green arrow: GO-NS) The dispersion and self-assembly of GO-NS and NiFe-LDH-NS in aqueous solution were intuitively observed by using Tomographic Particle Image Velocimetry (Tomo-PIV) measurement. The images of the assembly process of NiFe-LDH-NS and GO-NS were obtained by tracer particle imaging and the three-dimensional reconstruction through MATLAB 2016. As shown in Figure S4A, NiFe-LDH-NS and GO-NS can be stably and uniform dispersed in solution. The self-assembly process of NiFe-LDH-NS and GO-NS are shown in Figure 2. When NiFe-LDH-NS and GO-NS are uniformly mixed, the oppositely charged LDH-NS and GO-NS attract each other to cause migration under the action of electrostatic attraction (Figure 2(a) & (b)), and further self-assembly occurs (Figure 2(c) & (d)). NFGO nanohybrids obtained by selfassembly will settle gradually under the action of gravity over time. Figure S4B is a normalized particle image of NFGO nanohybrid at t = 5 min. It can be seen from the figure that NFGO-1, NFGO-2 and NFGO-3 nanohybrids show different sedimentation 16 ACS Paragon Plus Environment

Page 17 of 39 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


rates at the same time, and NFGO-3 nanohybrids exhibits the fastest sedimentation velocity, further indicate that NFGO-1, NFGO-2 and NFGO-3 nanohybrids have different assembly structures. Finally, NFGO nanohybrids completely settle at t = 10 min. The FESEM images of NFGO nanohybrids are shown in Figure 3(a-c). Under aqueous conditions, the oppositely charged NiFe-LDH-NS and GO-NS will attract each other under electrostatic attraction and then assemble. It can be seen that there is a smaller layer of LDH-NS on the large-sized GO-NS (Figure 3(a-c)). NiFe-LDH-NS and GO-NS form nanostructures stacked on each other under the electrostatic attraction,

Figure 3. FESEM images of (a) NFGO-1, (b) NFGO-2 and (c) NFGO-3 nanohybrids (the yellow arrows point at small LDH nanosheets and the red arrows point at GO nanosheets). (d) FESEM images and X-ray Energy dispersive spectroscopy (EDS) of NFGO-3 nanohybrids. (e) C maps of the area labeled by the yellow rectangle in (d), (f) O map of the labeled area in (d), (g) Ni map of the labeled area in (d), (h) Fe map of 17 ACS Paragon Plus Environment


Page 18 of 39

the labeled area in (d).

and this kind of stacked structure could effectively prevent LDH-NS or GO-NS from re-stacking into bulk materials. X-ray energy dispersive spectrometry (EDS)−elemental mapping analyses show the uniform hybridization of NiFe-LDH and GO. The TEM images of NFGO nanohybrids show that exfoliated NiFe-LDH-NS are uniformly loaded on GO-NS due to the result of electrostatic attraction, and the diffraction rings of both NiF-LDH and GO are presented in the SAED pattern of NFGO nanohybrids (Figure 4(a-c)). Figure 4(g) illustrates a typical XRD pattern of NFGO-1 nanohybrids with an interlayer spacing of 1.2 nm, which is basically equal to the value of the

Figure 4. TEM and selected area electron diffraction (SAED) images of (a) NFGO-1, 18 ACS Paragon Plus Environment

Page 19 of 39 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


(b) NFGO-2 and (c)NFGO-3 nanohybrids. High-resolution TEM (HRTEM) images of (d) NFGO-1, (e) NFGO-2 and (f) NFGO-3 nanohybrids. XRD patterns of (g) NFGO1, (h) NFGO-2 and (i) NFGO-3 nanohybrids.

HRTEM result (Figure 4(d), d=0.44 nm + (0.5 nm + 1.0 nm)/2=1.19 nm), the crystallographic thickness of the LDH and GO host layers is about 0.50 nm59 and 1.0 nm60, and the thickness of the interlayer spacing is equal to the sum of the thickness of one host layer and one interplanar spacing (d(003) =d(host

61, 62.

layer)+d(interplanar spacing))

Figure 4(h) illustrates two XRD peaks of flocculation NFGO-2 nanohybrids with an interlayer spacing of 1.2 nm and 0.78 nm, which are confirmed by the value of HRTEM results (Figure 4(e), d= 0.47 nm + (0.5 nm + 1.0 nm)/2=1.22 nm). The layer spacing is 0.78 nm, which corresponds to the NiFe-LDH (003) crystal plane due to the regular standing of the NiFe-LDH-NS on the GO-NS. If all the NiFe-LDH-NS are standing up regularly on GO-NS, in the NFGO-3 nanohybrids, only one diffraction peak corresponding to the typical (003) crystal plane of LDH appears in the XRD pattern (Figure 4(i)), and it matches the results of HRTEM (Figure 4(f)). The consistency of XRD and HRTEM results further proves that there is a dynamic evolution process of electrostatic self-assembly of NiFe-LDH-NS and GO-NS. That is to say, we can obtain the NFGO nanohybrids with different heterostructures by changing the mass ratio of NiFe-LDH-NS to GO-NS. More importantly, this process is completely controllable.



Page 20 of 39

Figure 5. XPS spectra of (a) NiFe-LDH and (b) NFGO-3 nanohybrids. High resolution of Ni 2p spectra derived from XPS spectrum of (c) NiFe-LDH and (d) NFGO-3 nanohybrids. High resolution of Fe 2p spectra derived from XPS spectrum of (e) NiFeLDH and (f) NFGO-3 nanohybrids.

The chemical valence state of the elements of NiFe LDH and NFGO-3 have been characterized by X-ray photoelectron spectroscopy (XPS) (Fig 5). The survey spectra of NiFe-LDH and NFGO-3 nanohybrids confirmed the existence of C, O, Fe and Ni elements of the samples (Fig 5a-b), and the shifts in the XPS peaks after hybridization are summarized in Table S163, 20. For NFGO-3 nanohybrids, the two strong peaks at 873.66 and 855.95 eV corresponding to Ni 2p1/2 and Ni 2p3/2, accompanying with two shakeup satellites at 879.73 and 861.78 eV (Fig 5d), demonstrating that Ni is in the Ni2+ oxidation state. The binding energies at 725.41 and 712.83 eV corresponded to Fe 2p1/2 and Fe 2p3/2 of Fe3+ (Fig 5f), respectively64. Figure S5 shows the C 1s core level spectrum together with the deconvolution analysis result of NFGO-3 nanohybrids. The 20 ACS Paragon Plus Environment

Page 21 of 39 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


binding energies at at around 284.65, 288.09 and 286.35 eV corresponded to C-C/C=C, C=O and C-O groups of GO-NS, respectively.

Figure 6. (a) FT-IR spectra of NiFe-LDH, GO, NFGO-3 and NFRG-3 nanohybrids. (b) Raman spectra of the NFGO-3 and NFRG-3 nanohybrids.

The FT-IR spectra of NiFe-LDH, GO, NFGO-3 and NFRG-3 nanohybrids are shown in Figure 6(a), the pristine NiFe-LDH displayed a strong and sharp IR absorption peak at 1387 cm−1 corresponding to the ν3 vibration mode of the nitrate (NO3−) ions, which indicated that the nitrate ions are stabilized in the interlayer space of this material65. The FT-IR absorption peak in NFGO and NFRG nanohybrids can correspond to the infrared absorption peaks of GO and NiFe-LDH (seeing in Figure S6 a-b), indicating an effective recombination of GO and NiFe-LDH. Moreover, the FTIR absorption peaks of NFRG nanohybrids hardly changed compared with NFGO nanohybrids after the reduction treatment, because most oxygen-containing functional groups are still present on the RGO surface. NFGO and NFRG nanohybrids show two Raman absorption peaks corresponding to D band and G band of graphene63 at 1351 cm-1 and 1588 cm-1 (Figure 6(b), Figure S6, indicating the presence of GO or RGO in 21 ACS Paragon Plus Environment


Page 22 of 39

nanohybrids). The widening and blue shift of the G band of NFGO nanohybrids indicate that the defect of GO-NS were increased due to the recombination of NiFe-LDH-NS and GO-NS. It also should be noted that the ID/IG ratio of the NFRG nanohybrids is higher than that of NFGO nanohybrids (Table S2), suggesting the presence of more defect sites on the NFRG nanohybrids. This is because the reduction of hydrazine hydrate increases the defects of GO-NS and increases the topological disorder. The electrocatalytic properties of the different heterostructures of NFRG nanohybrids electrocatalysts were investigated with respect to OER in a typical threeelectrode configuration in 1M KOH aqueous solution (pH=13.6), and Ni foam uniformly covered with the bulk NiFe-LDHs and NFGO and NFRG nanohybrids are directly used as the working electrode (2.5 mg cm-2). Figure 7(a) exhibits representative linear sweep voltammetry (LSV) curves of Ni foam loading various catalysts at a scan rate of 5 mV/s, and the Ni foam itself is also determined under the same conditions for

Figure 7. (a) The polarization curves, (b) Tafel plots, (c) Overpotential and (d) Nyquist plots (at an overpotential of 270 mV) of Ni foam, RGO, NiFe-LDH, NFRG-1, NFRG22 ACS Paragon Plus Environment

Page 23 of 39 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


2 and NFRG-3 nanohybrids (inset: the equivalent RC circuit model and the fitting Nyquist plots of RGO, NiFe-LDH and NFRG-3 nanohybrids). (e) LSV curves of NFRG-3 nanohybrids before and after i-t test for OER at an overpotential of 250 mV for 10 h.

comparison. Bare Ni foam, RGO and bulk NiFe-LDHs exhibit the poor OER catalytic activity with the overpotential of 460 mV, 396 mV and 336 mV, respectively, at the current density of 30 mA cm-2 (Figure 7(c)). The corresponding Tafel slope of 114 mV mV dec-1, 109 mV mV dec-1 and 80 mV mV dec-1 also indicate the sluggish kinetics (Figure 7(b)). Noticeably, NFRG-1, NFRG-2 and NFRG-3 nanohybrids with a lower overpotential of 305 mV, 291 mV and 273 mV at the current density of 30 mA cm-2 respectively than that of bulk NiFe-LDHs. It also shows a faster kinetics, with a corresponding Tafel slope of 74 mV dec-1, 58 mV dec-1 and 49 mV dec-1. The improvement in OER performance may be due to several reasons: (1) completed exfoliation of NiFe-LDH can expose more active sites; (2) RGO-NS has a positive effect on preventing the restack of NiFe-LDH-NS and it can be verified from XRD and TEM; (3) the introduction of RGO-NS improves the electrical conductivity of NFRG nanohybrids; (4) strong chemical and electronic coupling between NiFe-LDH-NS and RGO-NS. In addition, we have found that NFRG nanohybrids with different heterostructures exhibit different electrocatalytic properties. NFRG-3 nanohybrids, which NiFe-LDH-NS are well-organized standing on GO-NS, show the optimal OER performance because of the unique three-dimensional array-like structure with more 23 ACS Paragon Plus Environment


Page 24 of 39

active sites. The LSV curves of the NFGO nanohybrids are shown in Figure S7(a). The overpotential of NFGO-1, NFGO-2 and NFGO-3 are 303 mV, 297 mV and 298 mV at the current density of 30 mA cm-2 respectively, while the overpotential of NFRG-1, NFRG-2 and NFRG-3 are 305 mV, 291 mV and 273 mV. We discovered that the electrocatalytic OER properties of NFRG nanohybrids obtained by NFGO nanohybrids after hydrazine hydrate reduction treatment had been further improved. This is because RGO has better conductivity than GO, which is beneficial to the rapid migration of charges66. However, recent reports indicate that the choice of surface area will have a greater impact on the evaluation of electrocatalytic activity67, 68. The Current densities normalized by geometric surface area, electrochemical (EC) surface area and Brunauer−Emmett−Teller (BET) surface area are usually different. Therefore, the influence of different surface areas on evaluation in a catalyst was studied in Figure S11 (The BET specific surface areas of NFRG-3 nanohybrids was measured with an Quantachrome Autosorb-IQ surface area, nitrogen gas is used as the probe gas. And the specific surface area of NFRG-3 nanohybrids is 55.9 m2/g according to BET measurements.). It can be seen from Figure S11 that the Tafel slope of NFRG-3 nanohybrids which are normalized by the three surface areas as mentioned above are different and the Tafel slope obtained with respect to the geometric surface area is larger than the Tafel slope obtained by the EC surface area and the BET surface area. However, since the actual surface area is larger than the geometric surface area, it generally overestimates the electrochemical performance of the catalyst. This indicates that the applied active surface area is quite important for determining the performance of the 24 ACS Paragon Plus Environment

Page 25 of 39 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


catalyst. Electrochemical impedance spectroscopy measurements (EIS) were performed to confirm the hypothesis of the enhanced electron transfer (Figure 7(d)). The inset figures in Figure 7(d) are the Nyquist plots of RGO, NiFe-LDH and NFRG3 nanohybrids and the equivalent electrical circuit. The charge-transfer resistance (Rct) of NFRG-3 nanohybrids (0.8 Ω) is smaller than that of NiFe-LDH (2.0 Ω) and RGO (13.2 Ω), which shows a much lower mass transfer resistance, and it is highly accordant with the result of the Tafel slope. This is due to the strong interaction between exfoliated NiFe-LDH-NS and RGO-NS and enhanced electrical conductivity with RGO-NS. The electrochemical active surface area (ECSA) of catalyst plays a crucial role in the reactions. The double-layer capacitances (Cdl) of the Ni foam, bulk NiFe-LDH and the NFRG-3 nanohybrids were determined by cyclic voltammetry (CV) (Figure S8). As the Cdl is linearly proportional to the ECSA, the linear slope, equivalent to twice the doublelayer capacitance, was used to represent the ECSA. Therefore, the ECSA of Ni foam, bulk NiFe-LDH and the NFRG-3 nanohybrids can be compared by comparing the slope value. As shown in Figure S8(d), the slope of Ni foam was much less than that of NiFeLDH and NFRG-3 nanohybrids. This might be due to the surface of Ni foam was relatively smooth exposing less active sites. In addition, the surface of catalyst electrode was totally covered by NiFe-LDH or NFRG-3 nanohybrids, so the contribution of Ni foam substrate to the ECSA could be ignored. The slope of the NFRG-3 nanohybrids is much higher than that of the bulk NiFe-LDHs, indicating that the NFRG-3 nanohybrids have larger active surface areas than the bulk NiFe-LDHs. The increased ECSA was attributed to the complete exfoliation of NiFe-LDH leads to exposure of 25 ACS Paragon Plus Environment


Page 26 of 39

more active sites for OER. The Turnover frequency (TOF) calculation values of the catalysts at different overpotentials were calculated and plotted in Figure S9. The TOF of NFRG-3 nanohybrids show a clear increase that was higher than that of NiFe-LDH and NFGO-3 nanohybrids under the same overpotentials, indicating an increase intrinsic activity towards OER. In addition, we evaluated the durability of NFRG-3 nanohybrids at a current density of 10 mA cm-2 (Figure S10), and the Chronopotentiometry measurement result of the NFRG-3 nanohybrids indicate that NFRG-3 nanohybrids have good stability. The LSV curve of NFRG-3 nanohybrids for the OER showed negligible degradation after i-t test at an overpotential of 250 mV for 10 h, which indicated that the NFRG-3 nanohybrids had superior operational stability (Figure 7(e)). The low overpotential, low Tafel slope and superior stability indicate that the NFRG-3 nanohybrids are an ideal electrocatalyst for the OER.

Conclusion In summary, we have adopted a new solid phase exfoliation strategy to obtain the monolayer of NiFe-LDH-NS and GO-NS. This exfoliation strategy is efficient, timesaving, non-toxic and environmental-friendly compared with the traditional liquid exfoliation, and NiFe-LDH and GO can reach a very considerable exfoliating efficiency of 10 wt% and 5 wt%, respectively. NFRG nanohybrids electrocatalysts with different heterostructures (NiFe-LDH-NS are horizontal bespreading on GO-NS, or NiFe-LDHNS are well-organized standing on GO-NS) were obtained by electrostatic self26 ACS Paragon Plus Environment

Page 27 of 39 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


assembly of NiFe-LDH-NS and GO-NS and subsequent hydrated hydrazine reduction treatment. The as-prepared NFRG-3 nanohybrids exhibits the best electrocatalytic activity and stability for OER than that of bulk NiFe-LDHs and NFGO nanohybrids in an alkaline solution. The overpotential of catalytic OER is 273mV at the current density of 30 mA cm-2 and the Tafel slope is 49 mV dec-1. We believe that this kind of artificially assembled unique three-dimensional array-like heterostructure can expose more active sites, thus improving the catalytic performance of NiFe-LDHs. In addition, the rapid transfer of electrons caused by the strong coupling between NiFe-LDH-NS and RGO-NS also plays a positive role in improving the catalytic properties. Further investigations are being carried out to apply this solid phase exfoliation strategy for other 2D materials and to explore multifunctional hybrid materials with different heterostructures applicable for hydrogen evolution reaction (HER), CO2 reduction, supercapacitors and Li-/Na- ion batteries.

Acknowledgments This study was supported by National Natural Science Foundation of China (No. 51503173), Longshan academic talent research supporting program of SWUST (17LZX636, 18LZX629) and Graphene Engineering Technology Research Center of Sichuan (2018SCGCZX05). The above fundings were all obtained by the Corresponding author, Ping Zhang.

Associated content 27 ACS Paragon Plus Environment


Page 28 of 39

Supporting Information available: The Supporting Information includes XRD patterns and optical pictures of NiFe-LDH, GO, NiFe-LDH/SPEM (with different exfoliation ratio) and GO/SPEM (with different exfoliation ratio), FESEM images of NiFe-LDH and GO, normalized particle image of GO-NS, NiFe-LDH-NS and NFGO nanohybrids, XPS spectra and the corresponding elemental compositions, FT-IR spectra and Raman spectra of NFGO and NFRG nanohybrids, the polarization curves and overpotential of NFGO nanohybrids, cyclic voltammetry curves obtained in non-Faradic region and the derived ECSA, turnover frequency (TOF) values, chronopotentiometry curves, tafel plots, tracer particle imaging schematic, the table containing evolution of the binding energies of XPS peaks upon hybridization, the table containing Raman spectra parameters of NFGO and NFRG nanohybrids, the table containing recently reported literatures and our material for comparison, the table containing the comparison of exfoliation efficiency between solid phase exfoliation and liquid phase exfoliation.

Reference [1] Qin, Q.; Jang, H.; Chen, L. L.; Nam, G.; Liu, X.; Cho, J. Low Loading of RhxP and RuP on N, P Codoped Carbon as Two Trifunctional Electrocatalysts for the Oxygen and Hydrogen Electrode Reactions. Adv. Energy. Mater. 2018, 8, 1801478. [2] Wang, T. Y.; Nam, G.; Jin, Y.; Wang, X. Y.; Ren, P. J.; Kim, M. G.; Liang, J. S.; Wen, X. D.; Jang, H.; Han, J. T.; Huang, Y. H.; Li, Q.; Cho, J. NiFe(Oxy) Hydroxides Derived from NiFe Disulfides as an Efficient Oxygen Evolution Catalyst for 28 ACS Paragon Plus Environment

Page 29 of 39 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


Rechargeable Zn–Air Batteries: The Effect of Surface S Residues. Adv. Mater. 2018, 30, 1800757. [3] Zhu, W. X.; Liu, L. Z.; Yue, Z. H.; Zhang, W. T.; Yue, X. Y.; Wang, J.; Yu, S. X.; Wang, L.; Wang, J. L. Au Promoted Nickel-Iron Layered Double Hydroxide Nanoarrays: A Modular Catalyst Enabling High-Performance Oxygen Evolution. ACS Appl. Mater. Interfaces. 2017, 9, 19807-19814. [4] Hu, E. L.; Feng, Y. F.; Nai, J. W.; Zhao, D.; Hu, Y.; (David) Lou, X. W. Construction of Hierarchical Ni-Co-P Hollow Nanobricks with Oriented Nanosheets for Efficient Overall Water Splitting. Energ. Environ. Sci. 2018, 11, 872-880. [5] Zhang, H. J.; Li, X. P.; Hähnel, A.; Naumann, V.; Lin, C.; Azimi, S.; Schweizer, S. L.; Maijenburg, A. W.; Wehrspohn, R. B. Bifunctional Heterostructure Assembly of NiFe LDH Nanosheets on NiCoP Nanowires for Highly Efficient and Stable Overall Water Splitting. Adv. Funct. Mater. 2018, 28, 1706847. [6] Wang, X.; Zhuang, L. Z.; Jia, Y.; Liu, H. L.; Yan, X. C.; Zhang, L. Z.; Yang, D. J.; Zhu, Z. H.; Yao, X. D. Plasma-Triggered Synergy of Exfoliation, Phase Transformation, and Surface Engineering in Cobalt Diselenide for Enhanced Water Oxidation. Angew. Chem. Int. Ed. 2018, 57, 16421-16425. [7] Yu, L.; Zhou, H. Q.; Sun, J. Y.; Qin, F.; Yu, F.; Bao, J. M.; Yu, Y.; Chen, S.; Ren, Z. F. Cu Nanowires Shelled with NiFe Layered Double Hydroxide Nanosheets as Bifunctional Electrocatalysts for Overall Water Splitting. Energ. Environ. Sci. 2017, 10, 1820-1827. [8] Ni, Y. M.; Yao, L. H.; Wang, Y.; Liu, B.; Cao, M. H.; Hu, C. W. Construction of 29 ACS Paragon Plus Environment


Page 30 of 39

Hierarchically Porous Graphitized Carbonsupported NiFe Layered Double Hydroxides with Core-shell Structure as an Enhanced Electrocatalyst for Oxygen Evolution Reaction. Nanoscale. 2017, 9, 11596-11604. [9] Anantharaj, S.; Karthick, K.; Venkatesh, M.; Simha, T. V. S. V.; Salunke, A. S.; Ma, L.; Liang, H.; Kundu, S. Enhancing Electrocatalytic Total Water Splitting at Few Layer Pt-NiFe Layered Double Hydroxide Interfaces. Nano. Energy. 2017, 39, 30-43. [10] Zhong, H. H.; Tian, R.; Gong, X. M.; Li, D. Q.; Tang, P. G.; Alonso-Vante, N.; Feng, Y. J. Advanced Bifunctional Electrocatalyst Generated Through Cobalt Phthalocyanine Tetrasulfonate Intercalated Ni2Fe-Layered Double Hydroxides for A Laminar Flow Unitized Regenerative Micro-cell. J. Power. Sources. 2017, 361, 21-30. [11] Dou, S.; Wang, X.; Wan, S. Y. Rational Design of Transition Metal-Based Materials for Highly Efficient Electrocatalysis. Small. Methods. 2018, 3, 1800211. [12] Song, F.; Hu, X. L. Ultrathin Cobalt-manganese Layered Double Hydroxide is an Efficient Oxygen Evolution Catalyst. J. Am. Chem. Soc. 2014, 136, 16481-16484. [13] Zhang, Y. K.; Wu, C. Q.; Jiang, H. L.; Lin, Y. X.; Liu, H. J.; He, Q.; Chen, S. G.; Duan, T.; Song, L. Atomic Iridium Incorporated in Cobalt Hydroxide for Efficient Oxygen Evolution Catalysis in Neutral Electrolyte. Adv. Mater. 2018, 30, 1707522. [14] Gunjakar, J. L.; Kim, T. W.; Kim, H. N.; Kim, I. Y.; Hwang, S. J. Mesoporous Layer-by-Layer Ordered Nanohybrids of Layered Double Hydroxide and Layered Metal Oxide: Highly Active Visible Light Photocatalysts with Improved Chemical Stability. J. Am. Chem. Soc. 2011, 133, 14998–15007. [15] Wang, Q.; Hare, D. O. Recent Advances in the Synthesis and Application of 30 ACS Paragon Plus Environment

Page 31 of 39 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


Layered Double Hydroxide (LDH) Nanosheets. Chem. Rev. 2012, 112, 4124−4155. [16] Liu, P. F.; Yang, S.; Zhang, B.; Yang, H. G. Defect-Rich Ultrathin Cobalt-Iron Layered Double Hydroxide for Electrochemical Overall Water Splitting. ACS Appl. Mater. Interfaces. 2016, 8, 34474-34481. [17] Zeng, Y. F.; Wang, Y. Y.; Huang, G.; Chen, C.; Huang, L. L.; Chen, R.; Wang, S. Y. Porous CoP Nanosheets Converted from Layered Double Hydroxides with Superior Electrochemical Activity for Hydrogen Evolution Reactions at Wide pH Ranges. Chem. Commun. 2018, 54, 1465-1468. [18] Yu, L.; Yang, J. F.; Guan, B. Y.; Lu, Y.; (David) Lou, X. W. Hierarchical Hollow Nanoprisms Organized by Ultrathin Ni-Fe Layered Double Hydroxide Nanosheets with Enhanced Electrocatalytic Activity Toward Oxygen Evolution. Angew. Chem. Int. Ed. 2018, 57, 172-176. [19] Gong, M.; Li, Y. G.; Wang, H. L.; Liang, Y. Y.; Wu, J. Z.; Zhou, J. G.; Wang, J.; Regier, T.; Wei, F.; Dai, H. J. An Advanced Ni−Fe Layered Double Hydroxide Electrocatalyst for Water Oxidation. J. Am. Chem. Soc. 2013, 135, 8452−8455. [20] Long, X.; Li, J. K.; Xiao, S.; Yan, K. Y.; Wang, Z. L.; Chen, H. N.; Yang, S. H. A Strongly Coupled Graphene and FeNi Double Hydroxide Hybrid as an Excellent Electrocatalyst for the Oxygen Evolution Reaction. Angew. Chem. Int. Ed. 2014, 53, 7584-7588. [21] Dionigi, F.; Strasser, P. NiFe-Based (Oxy)hydroxide Catalysts for Oxygen Evolution Reaction in Non-Acidic Electrolytes. Adv. Energy. Mater. 2016, 6, 1600621. [22] Xiang, Q.; Li, F.; Chen, W. L.; Ma, Y. L.; Wu, Y.; Gu, X.; Qin, Y.; Tao, P.; Song, 31 ACS Paragon Plus Environment


Page 32 of 39

C. Y.; Shang, W.; Zhu, H.; Deng, T.; Wu, J. B. In-Situ Vertical Growth of Fe-Ni Layered Double Hydroxide Arrays on Fe-Ni Alloy Foil: Interfacial Layer Enhanced Electrocatalyst with Small Overpotential for Oxygen Evolution Reaction. ACS Energy. Lett. 2018, 3, 2357-2365. [23] 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. [24] Ma, W.; Ma, R. Z.; Wang, C. X.; Liang, J. B.; Liu, X. H.; Zhou, K. C.; Sasaki, T. A Superlattice of Alternately Stacked Ni-Fe Hydroxide Nanosheets and Graphene for Efficient Splitting of Water. ACS Nano. 2015, 9, 1977-1984. [25] Wang, Q.; L. Chen, F.; S. Guan, L.; Zhang, X.; Wang, B.; Cao, X. Z.; Yu, Z.; He, Y. F.; Evans, D. G.; Feng, J. T.; Li, D. Q. Ultrathin and Vacancy-rich CoAl-Layered Double Hydroxide/Graphite Oxide Catalysts: Promotional Effect of Cobalt Vacancies and Oxygen Vacancies in Alcohol Oxidation. ACS Catal. 2018, 8, 3104-3115. [26] Liang, H.F.; Meng, F.; Acevedo, M. C.; Li, L. S.; Forticaux, A.; Xiu, L. C.; Wang, Z. C.; Jin, S. Hydrothermal Continuous Flow Synthesis and Exfoliation of NiCo Layered Double Hydroxide Nanosheets for Enhanced Oxygen Evolution Catalysis. Nano. Lett. 2015, 15, 1421-1427. [27] Dang, L. N.; Liang, H. F.; Zhuo, J. Q.; Lamb, B. K.; Sheng, H. Y.; Yang, Y.; Jin, S. Direct Synthesis and Anion Exchange of Noncarbonate-Intercalated NiFe-Layered Double Hydroxides and the Inﬂuence on Electrocatalysis. Chem. Mater. 2018, 30, 4321−4330. 32 ACS Paragon Plus Environment

Page 33 of 39 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] Hunter, B. M.; Hieringer, W.; Winkler, J. R.; Gray, H. B.; Müller, A. M. Effect of Interlayer

Anions on [NiFe]-LDH Nanosheet

Water

Oxidation

Activity .

Energ. Environ. Sci. 2016, 9, 1734-1743. [29] Zhou, D. J.; Cai, Z.; Bi, Y. G.; Tian, W. L.; Luo, M.; Zhang, Q.; Zhang, Q.; Xie, Q. X.; Wang, J. D.; Li, Y. P.; Kuang, Y.; Duan, X.; Bajdich, M.; Siahrostami, S.; Sun, X. M. Effects of Redox-active Interlayer Anions on the Oxygen Evolution Reactivity of NiFe-Layered Double Hydroxide Nanosheets. Nano. Res. 2018, 11, 1358-1368. [30] Li, X. M.; Hao, X. G.; Wang, Z. D.; Abudula, A.; Guan, G. Q. In-situ Intercalation of NiFe LDH Materials: An Efficient Approach to Improve Electrocatalytic Activity and Stability for Water Splitting. J. Power. Sources. 2017, 347, 193-200. [31] Li, P. S.; Duan, X. X.; Kuang, Y.; Li, Y. P.; Zhang, G. X.; Liu, W.; Sun, X. M. Tuning Electronic Structure of NiFe Layered Double Hydroxides with Vanadium Doping Toward High Efficient Electrocatalytic Water Oxidation. Adv. Energy. Mater. 2018, 8, 1703341. [32] Yang, Y.; Dang, L. N.; Shearer, M. J.; Sheng, H. Y.; Li, W. J.; Chen, J.; Xiao, P.; Zhang, Y. H.; Hamers, R. J.; Jin, S. Highly Active Trimetallic NiFeCr Layered Double Hydroxide Electrocatalysts for Oxygen Evolution Reaction. Adv. Energy. Mater. 2018, 8, 1703189. [33] Chen, G. B.; Wang, T.; Zhang, J.; Liu, P.; Sun, H. J.; Zhuang, X. D.; Chen, M. W.; Feng, X. L. Accelerated Hydrogen Evolution Kinetics on NiFe-Layered Double Hydroxide Electrocatalysts by Tailoring Water Dissociation Active Sites. Adv. Mater. 2018, 30, 1706279. 33 ACS Paragon Plus Environment


Page 34 of 39

[34] Liu, H. X.; Wang, Y. R.; Lu, X. Y.; Hu, Y.; Zhu, G. Y.; Chen, R. P.; Ma, L. B.; Zhu, H. F.; Tie, Z. X.; Liu, J.; Jin, Z. The Effects of Al Substitution and Partial Dissolution on Ultrathin NiFeAl Trinary Layered Double Hydroxide Nanosheets for Oxygen Evolution Reaction in Alkaline Solution. Nano. Energy. 2017, 35, 350-357. [35] 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. 2017, 28, 1703363. [36] Li, Haoy. Y.; Chen, S. M.; Zhang, Y.; Zhang, Q. H.; Jia, X. F.; Zhang, Q.; Gu, L.; Sun, X. M.; Song, L.; Wang, X. Systematic Design of Superaerophobic Nanotubearray Electrode Comprised of Transition-metal Sulﬁdes for Overall Water Splitting. Nat. Commun. 2018, 9, 2452. [37] Yan, D. F.; Li, Y. X.; Huo, J.; Chen, R.; Dai, L. M.; Wang, S. Y. Defect Chemistry of Nonprecious-Metal Electrocatalysts for Oxygen Reactions. Adv. Mater. 2017, 29, 1606459. [38] Wang, Y. Y.; Yan, D. F.; Hankari, S. E.; Zou, Y. Q.; Wang, S. Y. Recent Progress on Layered Double Hydroxides and Their Derivatives for Electrocatalytic Water Splitting. Adv. Sci. 2018, 5, 1800064. [39] Wang, Y. Y.; Qiao, M.; Li, Y. F.; Wang, S. Y. Tuning Surface Electronic Configuration of NiFe LDHs Nanosheets by Introducing Cation Vacancies (Fe or Ni) as Highly Efficient Electrocatalysts for Oxygen Evolution Reaction. Small. 2018, 14, 1800136. [40] Qin, K. Q.; Wang, L.P.; Wen, S. W.; Diao, L. C.; Liu, P.; Lia, J. J.; Ma, L. Y.; Shi, 34 ACS Paragon Plus Environment

Page 35 of 39 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


C. S.; Zhong, C.; Hu, W. B.; Liu, E. Z.; Zhao, N. Q. Designed Synthesis of NiCo-LDH and Derived Sulfide on Heteroatoms Doping Edge-enriched 3D Rivet Graphene Films for High-performance Asymmetric Supercapacitor and Efficient OER. J. Mater. Chem. A. 2018, 6, 8109-8119. [41] Zhou, D. J.; Cai, Z.; Lei, X. D.; Tian, W. L.; Bi, Y. M.; Jia, Y.; Han, N. N.; Gao, T. F.; Zhang, Q.; Kuang, Y.; Pan, J. Q.; Sun, X. M.; 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, 1701905. [42] Zhan, T. R.; Zhang, Y. M.; Liu, X. L.; Lu, S. S.; Hou, W. G. NiFe Layered Double Hydroxide/Reduced Graphene Oxide Nanohybrid as an Efficient Bifunctional Electrocatalyst for Oxygen Evolution and Reduction Reactions. J. Power. Sources. 2016, 333, 53-60. [43] Xu, H. J.; Wang, B. K.; Shan, C. F.; Xi, P. X.; Liu, W. S.; Tang, Y. Ce-Doped NiFe-Layered-double-hydroxide

Ultrathin

Nanosheets/Nanocarbon

Hierarchical

Nanocomposite as Efficient Oxygen Evolution Catalyst. ACS Appl. Mater. Interfaces. 2018, 10, 6336-6345. [44] Yu, M. Z.; Zhou, S.; Wang, Z. Y.; Zhao, J. J.; Qiu, J. H. Boosting Electrocatalytic Oxygen Evolution by Synergistically Coupling Layered Double Hydroxide with MXene. Nano. Energy. 2018, 44, 181-190. [45] Zhao, Y. F.; Zhang, X.; Jia, X. D.; Waterhouse, G. I. N.; Shi, R.; Zhang, X. R.; Zhan, F.; Tao, Y.; Wu, L. Z.; Tung, C. H.; O’Hare, D.; Zhang, T. R. Sub-3 nm Ultrafine 35 ACS Paragon Plus Environment


Page 36 of 39

Monolayer Layered Double Hydroxide Nanosheets for Electrochemical Water Oxidation. Adv. Energy. Mater. 2018, 8, 1703585. [46] Wang, Q.; O’Hare, D. Recent Advances in the Synthesis and Application of Layered Double Hydroxide (LDH) Nanosheets. Chem. Rev. 2012, 112, 4124−4155. [47] Biccai, S.; Barwich, S.; Boland, D.; Harvey, A.; Hanlon, D.; Mcevoy, N.; Colemanl, J. N. Exfoliation of 2D Materials by High Shear Mixing. 2D Mater. 2019, 6, 015008. [48] Song, F.; Hu, X. L. Exfoliation of Layered Double Hydroxides for Enhanced Oxygen Evolution Catalysis. Nat. Commun. 2014, 5, 4477. [49] Ge, X.; Gu, C. D.; Yin, Z. Y.; Wang, X. L.; Tu, J. P.; Li, J. Periodic Stacking of 2D Charged Sheets: Self-assembled Superlattice of Ni–Al Layered Double Hydroxide (LDH) and Reduced Graphene Oxide. Nano. Energy. 2016, 20, 185-193. [50] Wang, Y. Y.; Zhang, Y. Q.; Liu, Z. J.; Xie, C.; Feng, S.; Liu, D. D.; Shao, M. F.; Wang, S. Y. Layered Double Hydroxide Nanosheets with Multiple Vacancies Obtained by Dry Exfoliation as Highly Efficient Oxygen Evolution Electrocatalysts. Angew. Chem. Int. Ed. 2017, 56, 5867-5871. [51] Hu, Z. Y.; Zhang, P.; Xie, R. S.; Li, M. T.; Lu, Z. Y.; Xu, X.; Song, L. X.; Zhou, L.; Wu, Y. P.; Chen, M.; Zhao, X. L. Controlled Synthesis of Train-structured Montmorillonite/Layered Double Hydroxide Nanocomposites by Regulating the Hydrolysis of Polylactic Acid. J. Mater. Sci. 2018, 53, 15859-15870. [52] Sun, P. Z.; Ma, R. Z.; Ma, W.; Wu, J. H.; Wang, K. L.; Sasaki, T.; Zhu, H. W. 36 ACS Paragon Plus Environment

Page 37 of 39 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


Highly Selective Charge-guided Ion Transport Through a Hybrid Membrane Consisting of Anionic Graphene Oxide and Cationic Hydroxide Nanosheet Superlattice Units. NPG Asia. Mater. 2016, 8, e259. [53] Zhang, J. F.; Liu, J. Y.; Xi, L. F.; Yu, Y. F.; Chen, N.; Sun, S. H.; Wang, W. C.; Lange, K. M.; Zhang, B. Single-Atom Au/NiFe Layered Double Hydroxide Electrocatalyst: Probing the Origin of Activity for Oxygen Evolution Reaction. J. Am. Chem. Soc. 2018, 140, 3876-3879. [54] Chen, J.; Yao, B. B.; Li, C.; Shi, G. Q. An Improved Hummers Method for Ecofriendly Synthesis of Graphene Oxide. Carbon. 2013, 64, 225-229. [55] Wu, Z. C.; Zou, Z. X.; Huang, J. S.; Gao, F. NiFe2O4 Nanoparticles/NiFe Layered Double Hydroxide Nanosheets Heterostructure Array for Efficient Overall Water Splitting at Large Current Densities. ACS Appl. Mater. Interfaces. 2018, 10, 2628326292. [56] Kibsgaard, J.; Jaramillo, T. F., Molybdenum Phosphosulfide: An Active, AcidStable, Earth-Abundant Catalyst for the Hydrogen Evolution Reaction. Angew. Chem. Int. Ed. 2014, 53, 14433-14437. [57] Wang, X., Zhuang, L.Z., He, T. W., Jia, Y., Zhang, L. Z., Yan, X. C., Gao, M. R., Du, A. J., Zhu, Z. H., Yao, X. D., Yu, S. H. Grafting Cobalt Diselenide on Defective Graphene for Enhanced Oxygen Evolution Reaction. iScience. 2018, 7, 145–153. [58] Wang, L.; Wang, D.; Dong, X. Y.; Zhang, Z. J.; Pei, X. F.; Chen, X. J.; Chen, B.; Jin, J., Layered Assembly of Graphene Oxide and Co-Al Layered Double Hydroxide Nanosheets as Electrode Materials for Supercapacitors. Chem. Commun. 2011, 47, 37 ACS Paragon Plus Environment


Page 38 of 39

3556-3558. [59] Jia, Y.; Zhang, L. Z.; Gao, G. P.; Chen, H.; Wang, B.; Zhou, J. Z.; Soo, M. T.; Hong, M.; Yan, X. C.; Qian, G. G.; Zou, J.; Du, A. J.; Yao, X. D. A Heterostructure Coupling of Exfoliated Ni–Fe Hydroxide Nanosheet and Defective Graphene as a Bifunctional Electrocatalyst for Overall Water Splitting. Adv. Mater. 2017, 29, 1700017. [60] Stankovich, S.; Dikin, D. A.; Piner, R. D.; Kohlhaas, K. A.; Kleinhammes, A.; Jia, Y.; Wu, Y.; Nguyen, S. T.; Ruoff, R. S. Synthesis of Graphene-based Nanosheets Via Chemical Reduction of Exfoliated Graphite Oxide. Carbon. 2007, 45, 1558–1565. [61] Lu, Z. Y.; Qian, L.; Xu, W. W.; Tian, Y.; Jiang, M.; Li, Y. P.; Sun, X. M.; Duan, X. Dehydrated Layered Double Hydroxides: Alcohothermal Synthesis and Oxygen Evolution Activity. Nano. Res. 2016, 9, 3152-3161. [62] Naseem, S., Gevers, B., Boldt, R., Labuschagné, F. J. W. J., Leuteritz, A. Comparison of Transition Metal (Fe, Co, Ni, Cu, and Zn) Containing Tri-metal Layered Double Hydroxides (LDHs) Prepared by Urea Hydrolysis. RSC Adv. 2019, 9, 3030– 3040. [63] Yu, C.; Han, X. T.; Liu, Z. B.; Zhao, C. T.; Huang, H. W.; Yang, J.; Niu, Y. Y.; Qiu, J. S. An Effective Graphene Confined Strategy to Construct Active Edge Sitesenriched Nanosheets with Enhanced Oxygen Evolution. Carbon. 2018, 126, 437-442. [64] Liu, C. Y.; Ma, H.; Yuan, M. W.; Yu, Z. H.; Li, J.; Shi, K. R.; Liang, Z. P.; Yang, Y.; Zhu, T. J.; Sun, G. B.; Li, H. F.; Ma, S. L. (NiFe)S2 nanoparticles Grown on Graphene as an Efficient Electrocatalyst for Oxygen Evolution Reaction. Electrochim. 38 ACS Paragon Plus Environment

Page 39 of 39 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


Acta. 2018, 286, 195-204. [65] Islam, M. S.; Kim, M.; Jin, X.Y.; Oh, S. M.; Lee, N.; Kim, H.; Hwang, S. Bifunctional 2D Superlattice Electrocatalysts of Layered Double HydroxideTransition Metal Dichalcogenide Active for Overall Water Splitting. ACS Energy. Lett. 2018, 3, 952-960. [66] Chen, D.; Wang, X. Y.; Liu, T. X.; Wang, X. D.; Li, J. Electrically Conductive Poly(vinyl alcohol) Hybrid Films Containing Graphene and Layered Double Hydroxide Fabricated via Layer-by-Layer Self-Assembly. ACS Appl. Mater. Interfaces. 2010, 2, 2005-2011. [67] Sun, S. N.; Li, H. Y.; Xu, Z. C. J. Impact of Surface Area in Evaluation of Catalyst Activity. Joule. 2018, 2, 1–4. [68] Wang, Z.; Long, X.; Yang, S. H. Effects of Metal Combinations on the Electrocatalytic Properties of Transition-Metal-Based Layered Double Hydroxides for Water Oxidation: A Perspective with Insights. ACS Omega. 2018, 3, 16529-16541.


Controlled Self-Assembled NiFe Layered Double Hydroxides

Recommend Documents