Formation of yolk-shelled nickel-cobalt selenide dodecahedral

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Formation of yolk-shelled nickel-cobalt selenide dodecahedral nanocages from metal-organic frameworks for efficient hydrogen and oxygen evolution Kelong Ao, Jiancheng Dong, Chonghui Fan, Di Wang, Yibing Cai, Dawei Li, Fenglin Huang, and Qufu Wei ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/acssuschemeng.8b02343 • Publication Date (Web): 09 Jul 2018 Downloaded from http://pubs.acs.org on July 11, 2018

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ACS Sustainable Chemistry & Engineering

Formation of yolk-shelled nickel-cobalt selenide dodecahedral nanocages from metal-organic frameworks for efficient hydrogen and oxygen evolution Kelong Ao, Jiancheng Dong, Chonghui Fan, Di Wang, Yibing Cai, Dawei Li, Fenglin Huang and Qufu Wei* Key Laboratory of Eco-Textiles, Ministry of Education, Jiangnan University, 1800 Lihu Avenue, Wuxi, Jiangsu Province, Wuxi 214122, PR China

*Corresponding authors. Tel.: +86-510-85913536. E-mail addresses: [email protected] (Q. Wei).

ABSTACT: Developing cost-effective electrocatalysts for both hydrogen and oxygen evolution reaction (HER and OER) in alkaline media is crucial in renewable energy conversion technologies. Metal-organic frameworks (MOFs) can act as precursors to design and construct varied nanostructured materials which may be difficult to produce in other ways. Herein, we put forward a serial ion-exchange reaction and selenation strategy to prepare novel yolk-shelled Ni-Co-Se dodecahedral nanocages on carbon fiber paper (Y-S Ni-Co-Se/CFP). ZIF-67@LDH/CFP was firstly synthesized by a simple ion-exchange reaction, followed by a hydrothermal selenation process to form Y-S Ni-Co-Se/CFP. Moreover, the composition of the as-prepared 1

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yolk-shelled Ni-Co-Se nanocages were the mixture of Co0.85Se and Ni0.85Se (Co/Ni atomic ratio of about 2.42). Due to their structural and compositional merits, the as-prepared Y-S Ni-Co-Se/CFP exhibited remarkable electrocatalytic activity and long-term stability (over 80% current retention for at least 18 h) for both HER and OER. For HER, it required an overpotential of 250 mV to attain current density of 10 mA cm-2, which was 162 mV less than that of the Y-S Co0.85Se/CFP counterpart. The catalyst also efficiently catalyzed OER with a current density of 10 mA cm-2 at an overpotential of 300 mV, which was lower than other reported Co-based catalysts. KEYWORDS: yolk-shell structure, hydrogen evolution reaction, oxygen evolution reaction, metal-organic frameworks, nickel-cobalt selenide INTRODUCTION Hydrogen has been regarded as a clean energy to displace diminishing fossil fuels.1, 2 Water electrolysis is an effective commercial technology, which converts intermittent renewable energy (wind energy, solar energy) to chemical energy stored in hydrogen energy.3 Although water electrolysis is an efficient way to evolve hydrogen with high purity, the high energy consumption (1.8-2.0 V commercially) still restricts its vast hydrogen production.4, 5 To make the process of water electrolysis more economical, active electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are supposed to reduce the large water-splitting overpotntials.6 Noble-metal materials such as Ir-, Ru-, and Pt-based are still the most efficient OER and HER catalysts,7-9 respectively, but the high cost limits their extensive applications. It’s greatly necessary to design bifunctional non-noble 2


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metal-based catalysts towards HER and OER, which will simplify electrolytic system and cut the cost. Since acidic water splitting utilizes acid-insoluble noble-metal materials as OER catalysts with reasonable activity mostly,10 alkaline water splitting is a powerful candidate for vast hydrogen production commercially. It’s thus attractive to fabricate bifunctional noble-metal-free catalysts towards HER and OER in strong alkaline media. As a type of highly active transition metal chalcogenides (TMCs), cobalt diselenide (CoSe2) has drawn extensive attention due to its high conductivity, low cost, high catalytic activity and chemical stability.11, 12 Compared with largely reported CoSe2 for various applications in dye-sensitized solar cell (DSSC),13 HER in acid medium,14 and oxygen reduction reaction (ORR) in alkaline medium,15 the compound Co0.85Se has been seldom reported for both HER and OER in alkaline medium.8, 16 Then, as a kind of TMCs, Ni0.85Se shows promising electrocatalytic potential because of its abundant unsaturated atoms and special electronic structure.17,

18

Moreover,

there are synergetic effects between the nanoscale interfaces of different TMCs. And the effects will farther enrich structural deficiencies and motivate some inert sites, thus increasing the activities of both TMCs.19 Therefore, it is interesting to combine nanoscale Co0.85Se with Ni0.85Se and probe into whether it’s an efficient bifunctional catalyst towards HER and OER even overall water splitting. Recently, studies of metal-organic frameworks (MOFs) in electrochemical energy storage and conversion have been expanding, including metal-air battery,20,

21

Li/Na-ion battery,22,

28

23

supercapacitor,24-26 as well as water splitting device.27,

3



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Among them, MOFs usually act as precursors and templates to construct many novel structures such as hollow structures due to their well-tunable properities.29 Presently, zeolitic imidazolate framework-67 (ZIF-67) as a common type of Co-based MOFs, has been used as the precursors or templates to prepare some hollow electrocatalysts, such as C/LDH/S hollow polyhedrons,30 hollow CeOx/CoS,31 yolk-shelled Co-C@Co9S8,32 and NiCoP/C hollow nanoboxes.33 These hollow structures with porous thin walls and massive cavities, e.g., single-shelled, yolk-shelled and multi-shelled nanocages, will allow ions and electrolytes to enter easily, thus exposing more electrochemical active sites and favoring reaction kinetics.32, 34, 35 Heretofore, as far as we know, nickel-cobalt selenide with yolk-shelled structures transformed from ZIF as a catalyst has rarely been reported. Enlightened by synergetic effects between different TMCs and merits of hollow structures above, we designed a facile formation of nanocomposite dodecahedral nanocages involving yolk-shelled Ni-Co bimetallic selenides grown on carbon fiber paper (denoted as Y-S Ni-Co-Se/CFP) through a MOFs-based strategy. The Y-S Ni-Co-Se/CFP exhibited higher catalytic activity towards both HER and OER than the counterpart Y-S Co0.85Se/CFP, and performed better in alkaline medium than previously reported efficient Co-based HER or OER catalysts. We think the high performance can be attributed to two main aspects: (1) unique yolk-shell structure and chemical composition, and (2) high-concentration active sites in the Co0.85Se/Ni0.85Se catalyst system and its direct growth on three dimensional (3D) carbon material. The possible mechanisms for this high performance will be explored in this work. We 4


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believe that our work provides another way to design MOF-derived functional materials with interesting nanostructures for diversified applications. EXPERIMENTAL SECTION Material Synthesis Preparation of dodecahedron ZIF-67 on CFP: a methanol solution containing 2-Methylimidazole (2-MeIM) (50 mL, 1.64g) was rapidly poured into the methanol solution including Co(NO3)2·6H2O (50 mL, 1.455g), then a piece of cleaned CFP (2*6*0.019 cm3, TGP-H-060, from Toray Industries, Inc.) was dipped in the mixture for 24 h. The CFP was taken out, washed with ethanol for 3 times and vacuum dried at 60 ˚C overnight. Meanwhile, the mass loading of ZIF-67 was measured to ~0.47 mg cm-2. Preparation of core-shelled ZIF-67@LDH/CFP and ZIF-67@Co(OH)2/CFP: a piece of dodecahedron ZIF-67 on CFP was firstly immersed into 80 mL of ethanol, and then 20 mL of ethanol solution containing 400 mg of Ni(NO3)2·6H2O was quickly poured into the former dispersion. After ion exchange reaction for 1.5 h, the sample was cleaned with ethanol for 3 times and dried at 70 ºC for 10 h. Increasing the concentration of the latter Ni(NO3)2 solution to 200 mg mL-1 resulted in pure Ni-Co LDH cavity on CFP. The mass loading of ZIF-67@LDH was measured to ~0.64 mg cm-2. As for ZIF-67@Co(OH)2/CFP, the Ni(NO3)2 was replaced by 400 mg Co(NO3)2 with other conditions unchanged. Preparation of yolk-shelled Ni-Co-Se/CFP and Co0.85Se/CFP: prior to selenization, clear NaHSe solution should be prepared by adding Se powder (59 mg) 5



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into DI water (1.5 mL) containing NaBH4 (65 mg). After shaking for 5 min, the clear NaHSe solution was synthesized according to the following equation: NaBH4 + Se + H2O → NaHSe + Na2B4O7 + H2. A piece of ZIF-67@LDH/CFP was immersed into a N2-saturated ethanol solution (30 mL) containing the aforesaid NaHSe solution. The mixed solution was then poured into a 50 mL Teﬂon reaction kettle, and heated in an electric oven at 140 ºC for 6 h. After the kettle was cooled down to normal temperature, the sample was taken out and cleaned with ethanol for 3 times, and then vacuum dried at 50 ˚C. The mass loading of Ni-Co-Se was measured to ~0.65 mg cm-2. Decreasing the reaction time to 2 h resulted in insufficient selenization, while prolonging the reaction time to 10 h resulted in the collapse of dodecahedrons. As for Co0.85Se/CFP, the ZIF-67@LDH/CFP was replaced by ZIF-67@Co(OH)2/CFP with other conditions unchanged. The mass loading of Co0.85Se was measured to ~0.63 mg cm-2. Preparation of Co3O4@NiCo2O4/CFP: a piece of ZIF-67@LDH/CFP was calcined in air at 350 ˚C for 2 h with a heating rate of 2 ˚C min-1. Meanwhile, the mass loading of Co3O4@NiCo2O4 was measured to ~0.60 mg cm-2. Materials Characterization Scanning electron microscopy (SEM) images were taken on Hitachi SU1510, and the machine was equipped with an energy-dispersive X-ray spectroscopy (EDS). Transmission electron microscopic (TEM) and high-resolution TEM (HR-TEM) images were acquired using a JEOL JEM-2100F microscope at an acceleration voltage of 200 kV. The crystallographic and phase properties were investigated by 6


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X-ray diffraction (XRD) measurements performed with a GADDS XRD system by using the Cu-Kα radiation. X-ray photoelectron spectroscopy (XPS) measurements were conducted on Thermo ESCALAB 250XI X-ray photoelectron spectrometer with a monochromated Al-Kα radiation. The XPS binding energies were calibrated using the C1s level of 284.7 eV (Figure S5), which was taken as a reference. Fourier transform infrared spectroscopy (FTIR) was performed on a Thermo Fisher Nicolet is10 spectrophotometer. The weight of CFP electrodes was accurately recorded before and after reaction by a Shimadzu AUY120 electronic balance to calculate the actual mass loading. Electrochemical Characterization Electrochemical measurements were performed using CHI 660D electrochemical workstation (CH Instruments) at room temperature. The HER and OER catalytic activities were tested in a standard three-electrode system in 1.0 M KOH solution (PH=14), using a graphite rod and saturated calomel electrode (SCE) as the counter and reference electrode, respectively. Catalysts on CFP were directly used as the working electrode. The polarization curves were measured from 0 to 0.7 V (vs. SCE) for OER and -1.0 to -1.6 V (vs. SCE) for HER at 5 mV s-1 and iR compensated. All potentials here were converted to a reversible hydrogen electrode (RHE) reference scale

as

follows:

E(RHE)=E(SCE)+0.0592*pH+0.241.

Electrical

impedance

spectroscopy (EIS) was recorded under the following conditions: AC voltage amplitude 5 mV, frequency range 105 to 0.01 Hz and applied overpotential -0.20 V (RHE). The electrochemical stability was tested under constant voltage. Before tests, 7



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each working electrode was cycled 100 times at 100 mV s-1 until getting a reproducible CV. The double layer capacitance (Cdl) was used to assess the electrochemically active surface area (ECSA) and could be acquired by CV measurement within a non-Faradaic window of 0.10~0.20 V (RHE). The various scan rates were utilized, such as 10, 20, 40, 60, 80, 100, and 150 mV s-1. The Cdl was determined by plotting the half of ja - jc at 0.15 V (RHE) against the scan rate, in which the slope was the Cdl. RESULTS AND DISCUSSION Material Fabrication and Characterizations

Scheme 1. Schematic illustration for the formation process of yolk-shelled Ni-Co-Se/CFP.

The formation strategy for the yolk-shelled Ni-Co-Se dodecahedral nanocages on carbon fiber paper (Y-S Ni-Co-Se/CFP) is depicted in Scheme 1. Firstly, ZIF-67 nano dodecahedrons are grown on conductive CFP by a simple solvent method. In the second step, through a moderate ion-exchange reaction using Ni(NO3)2 in ethanol, the ZIF-67 would be wrapped by Ni-Co layered double-hydroxide (denoted as Ni-Co LDH), resulting in the formation of the core-shelled ZIF-67@LDH/CFP. During this 8


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process, the ZIF-67 diffuses out of the dodecahedrons partly to form shell LDH. Finally, the ZIF-67@LDH/CFP is chemically converted into Ni-Co mixed metal selenide by treatment with NaHSe in ethanol at 140 °C for 6 h. At the same time, the organic ligands in ZIF-67 partly decompose under the temperature. As a result, unique yolk-shelled Ni-Co-Se nanocages/CFP are obtained. The nanocomposite Y-S Ni-Co-Se/CFP can act as electrochemical electrodes directly and exhibits enhanced electrocatalytic performance for both HER and OER.

Figure 1. SEM and TEM of a,b;c) ZIF-67/CFP, d,e;f) ZIF-67@LDH/CFP, and g,h;i) yolk-shelled Ni-Co-Se nanocages/CFP. Inset (g): The corresponding yolk-shelled Ni-Co-Se/CFP electrode photograph.

The scanning electron microscope (SEM) observations in Figure 1a,b indicate that the ZIF-67 with a mean particle size of 700 nm covers uniformly on carbon fiber 9



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surface. From the transmission electron microscope (TEM) in Figure 1c, one can see the dodecahedral appearance of ZIF-67 with solid property. The XRD result of the ZIF-67 in Figure S2a identifies the formation of phase-pure ZIF-67 nano dodecahedrons,36 and the corresponding EDS result (Figure S2b) confirms the existence of C and N elements form the reagent 2-MeIM. Figure 1d,e show the typical morphology of ZIF-67 after the ion-exchange reaction in the presence of Ni(NO3)2. It can be observed that the dodecahedrons and uniform dispersion of them on the carbon fiber are still maintained. From the TEM in Figure 1f, we can see the surface of the ZIF-67 is assembled by a shell composed of numerous nanosheets. And the thickness of the shell is about 60 nm (Figure 1f). The XRD result of the sample is exactly similar with that of ZIF-67 (Figure S2a), indicating it still contains ZIF-67. EDS result (Figure S2c) shows the existence of Ni element, evidencing the incorporation of Ni into the nano dodecahedrons. The composition of the shell can be determined by removing the core ZIF-67 completely. When increasing the concentration of Ni(NO3)2 solution to 200 mg mL-1, the product presents the morphology of cavities (Figure S3a,b). From the XRD result (Figure S3c), the characteristic diffraction peaks detected at 2θ of 11.6°, 24.6°, 34.2°, and 60.3° are attributed to (003), (006), (009), and (110) lattice plane of hydrotalcite-like LDH phase (JCPDS No. 33-0429) and are also similar with the previously reported literature.37,

38

Therefore, the nano

dodecahedrons in Figure 1d-f are denoted as ZIF-67@LDH/CFP and the nanocavities without ZIF-67 (Figure S3) are denoted as LDH/CFP. Figure 1g and h show the typical morphology of ZIF-67@LDH/CFP after reacting with NaHSe for 6 h, from which 10


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one can see that the cages still maintain uniform coverage on the carbon fibers. From the TEM image in Figure 1i, nanocages with yolks can be observed clearly, indicating that

yolk-shell structures are formed. During the selenation reaction, the NaHSe reacts with both shell LDH and yolk ZIF-67. The disappearance of the ZIF-67 peaks from the XRD result (Figure S4b2) and absence of the N signal in the EDS result (Figure S4b3) indicate the successful selenizing of the ZIF-67@LDH. In fact, the reaction time would affect the morphologies and components of the products significantly. Short-time (2 h) selenizing process would result in maintained dodecahedral structure but insufficient selenizing (Figure S4a), while excess reaction time (10 h) could lead to the collapse of the structure and transformation into the Co(SeO3)(H2O)2 (JCPDS No. 80-1391) (Figure S4c).

Figure 2. a,b) XRD and EDS results of Y-S Ni-Co-Se. c) The representative FTIR spectra for 11



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ZIF-67, ZIF-67@LDH, and Y-S Ni-Co-Se. d) Elemental mapping of Y-S Ni-Co-Se for Ni, Co, and Se. e-g) TEM and HR-TEM images of Y-S Ni-Co-Se.

XRD and EDS measurements were performed to study the Y-S Ni-Co-Se/CFP electrode, as shown in Figure 2a and b. From the XRD result shown in Figure 2a, all the diffraction peaks of the Y-S Ni-Co-Se can be well indexed to the Co0.85Se phase (JCPDS No. 52-1008) and Ni0.85Se phase (JCPDS No. 18-0888).18, 39 The EDS result of Y-S Ni-Co-Se (Figure 2b) reveals the coexistence of C, Ni, Co, and Se elements. The atomic percentage of the elements for each sample is shown in Table S1, which suggests the Co/Ni in ZIF-67@LDH, Co3O4@NiCo2O4, and Y-S Ni-Co-Se are all around 2.5. Figure 2c shows the FTIR of the three materials. The FTIR spectrum of ZIF-67@LDH is extremely similar with that of ZIF-67 too, indicating it still contains ZIF-67. This is also consistent with the XRD results (Figure S2a). Meanwhile, ZIF-67 and ZIF-67@LDH spectra consist of two band at 1580 and 1384 cm-1 are associated with the C=N bonding in imidazole and N-O vibration mode in NO3-.38, 40, 41 The disappearance of the two peaks in Y-S Ni-Co-Se indicates the sufficient selenation reaction. The structural properties and chemical components of Y-S Ni-Co-Se was further clarified by TEM. After selenation, both the inner yolk and outer shell of the Y-S Ni-Co-Se nanocage possess dodecahedral structures (Figure 2e). A magnified observation on the shell reveals that the thickness of it is about 60 nm too(Figure 2f). HR-TEM images taken from the edge region of the Y-S Ni-Co-Se (Figure 2g) shows two lattice spacing of 2.69 and 2.7 Å, which is in agreement with the (101) planes of Co0.85Se (JCPDS No. 52-1008) and Ni0.85Se (JCPDS No. 18-0888), respectively. As 12


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revealed by elemental mapping images in Figure 2d, elements Ni, Co, and Se are homogeneously distributed in the Y-S Ni-Co-Se nanocage, meanwhile, the inner yolk is pure Co0.85Se42 and the outer shell is a mixture of Co0.85Se and Ni0.85Se.

Figure 3. a) XPS survey spectrum for Y-S Ni-Co-Se/CFP. XPS spectra in the b) Ni 2p, c) Co 2p, and d) Se 3d regions.

XPS was also used to detect the chemical states of elements in Y-S Ni-Co-Se/CFP. The XPS survey spectrum for Y-S Ni-Co-Se/CFP reveals the elements of C, O, Ni, Co, and Se without any other impurities (Figure 3a), which is consistent with the EDS result. As shown in the high-resolution XPS spectrum of Ni 2p in Figure 2b, the Ni 2p1/2 and Ni 2p3/2 centered at 873.6 and 856.0 eV correspond to Ni2+,2 and shakeup satellites (denoted as “Sat.”) are observed in the spectra. For the Co 2p spectra in Figure 3c, the binding energies of Co 2p3/2 and Co 2p1/2 are 780.9, 778.5, 797.2, and 13



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793.5 eV, respectively, indicating the coexistence of bivalent (+2) and trivalent (+3) Co species.8 Sat. are also observed in Co 2p spectra. Se species (Figure 3d) with the peak at 54.5 eV represents the Se 3d binding energy, and the peak at 58.9 eV suggests characteristic absorption peak of Co 3p species.43 In the XPS spectrum of C 1s (Figure S5), the peaks at 284.7 and 288.3 eV can be assigned to carbon fibers in the form of C-C and O-C=O,44 respectively.

Figure 4. a,b) SEM images, c,d) TEM images, e) HR-TEM image, f) XRD, and g) EDS results of Y-S Co0.85Se/CFP.

To further assess the electrocatalytic ability of Y-S Ni-Co-Se/CFP, similar loading of catalyst of Y-S Co0.85Se/CFP was also synthesized for comparison. After the solvothermal process, the dodecahedral structure can be well maintained (Figure 4a,b), and the nano dodecahedrons distribute on carbon fibers evenly. From the TEM image in Figure 4c and d, it can be seen that the particle size is about 700 nm and similar yolk-shell structures are formed. Form the HRTEM image in Figure 4e, the clear 14


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interlayer spacing of 2.69 Å is corresponding to the (101) plane of Co0.85Se (JCPDS No. 52-1008)45, which is also in line with the XRD pattern in Figure 4f. And the EDS result of Y-S Co0.85Se (Figure 4g) reveals the coexistence of C, Co, and Se elements. Hydrogen Evolution Reaction

Figure 5. a) Electrochemical performance of Pt Sheet, Y-S Ni-Co-Se, Y-S Co0.85Se, Co3O4@NiCo2O4, ZIF-67@LDH, and CFP electrodes for HER with iR correction. b) The corresponding Tafel plots. c) Polarization curves for Y-S Ni-Co-Se initially and after 1000 CV cycles. d) Chronoamperometry curve of Y-S Ni-Co-Se at -300 mV (RHE) over 18 h. e) Estimated Cdl and relative ECSA for Y-S Ni-Co-Se, Y-S Co0.85Se, Co3O4@NiCo2O4, ZIF-67@LDH, and CFP electrodes at 0.15 V (RHE). f) The corresponding Nyquist plots (100 kHz- 0.01 Hz) at -0.20 V (RHE). 15



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The Y-S Ni-Co-Se/CFP was directly used as an electrode to catalyze the HER in a typical three-electrode setup in 1.0 M KOH (Figure S7). For comparison, CFP, ZIF-67@LDH/CFP, Co3O4@NiCo2O4/CFP, Y-S Co0.85Se/CFP and commercial Pt Sheet were also tested under the same conditions. Potentials were recorded on the RHE scale. The representative polarization curves of the electrodes are shown in Figure 5a. Predictably, Pt Sheet shows the highest HER activity. Compared to other four electrodes, Y-S Ni-Co-Se/CFP requires a lower overpotential of 250 mV to drive the cathodic current density (J) of 10 mA cm-2. For ZIF-67@LDH/CFP, Co3O4@NiCo2O4/CFP, and Y-S Co0.85Se/CFP the overpotentials are 577, 436, and 412 mV respectively. The HER kinetics of the catalysts was further studied through the Tafel plots (Figure 5b). Compared to ZIF-67@LDH/CFP (118 mV dec-1), Co3O4@NiCo2O4/CFP (77 mV dec-1) and Y-S Co0.85Se/CFP (75 mV dec-1), Y-S Ni-Co-Se/CFP possesses the smallest slope of 72 mV dec-1, showing the highest electrocatalytic activity and kinetics toward HER in alkaline electrolyte. The value of Tafel slope of Y-S Ni-Co-Se/CFP electrode indicates that Volmer-Heyrovsky combination mechanism is operative for it in HER process.46,

47

That is, the

rate-limiting step of HER is Heyrovsky reaction with the electrochemical desorption: Had + H2O + e- → H2 + OH-. The electrocatalytic activity is also comparable to other reported Co-based catalysts (Table S3). Good catalytic activity and stability towards HER are both important for water electrolysis system. To investigate the stability, the polarization curves of Y-S Ni-Co-Se/CFP were carried out by taking continuous cyclic voltammetry (CV) cycles. 16


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As shown in Figure 5c, after 1000 cycles at 100 mV s-1 between the range of -0.20 to 0.20 V (RHE), the linear sweep voltammetry (LSV) curve has only a little decrease, suggesting the superior operational stability in alkaline solution. Besides, chronoamperometry curve was measured to further analyze the durability of Y-S Ni-Co-Se/CFP. Figure 5d shows the i-t curve of Y-S Ni-Co-Se/CFP at -300 mV (RHE), where the J can maintain 80.1 % over 18 h, suggesting the perfect durability of Y-S Ni-Co-Se/CFP catalyst. Furthermore, SEM and TEM images (Figure S10a-c) suggest that the yolk-shell structure of Ni-Co-Se compound is still retained after a long-time electrolysis.

The

prominent electrocatalytic

activity

and

stability

of

Y-S

Ni-Co-Se/CFP electrode would make it a useful HER catalyst for practical applications. Since the amount of active sites affect the catalytic activity, the ECSA of the electrodes are estimated by the Cdl.48 The CV of various scan rates (10- 150 mV s-1) for Y-S Ni-Co-Se/CFP, Y-S Co0.85Se/CFP, Co3O4@NiCo2O4/CFP, ZIF-67@LDH/CFP and CFP were obtained in the potential range from 0.10 to 0.20 V (RHE) (Figure S6). As shown in Figure 5e, the Cdl of the Y-S Ni-Co-Se/CFP, Y-S Co0.85Se/CFP, Co3O4@NiCo2O4/CFP, and ZIF-67@LDH/CFP are 8.00 mF cm-2, 3.85 mF cm-2, 1.61 mF cm-2, and 0.50 mF cm-2, respectively, revealing that the Y-S Ni-Co-Se/CFP has a much larger ECSA and more active sites for HER. Furthermore, the Nyquist plots (Figure 5f) also indicate that Y-S Ni-Co-Se/CFP possesses smallest semicircle diameter among the three test electrodes, manifesting a favorable charge-transfer resistance (Rct) for Y-S Ni-Co-Se/CFP (-0.20 V, Rct = 85.5 Ω). Whereas, the Y-S 17



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Co0.85Se/CFP, Co3O4@NiCo2O4/CFP and ZIF-67@LDH/CFP show higher Rct (201.9, 121.3 and 490.4 Ω) under the same condition (Table S2), suggesting the effective influence of selenation. Oxygen Evolution Reaction

Figure 6. a) Electrochemical performance of Y-S Ni-Co-Se, Y-S Co0.85Se, Co3O4@NiCo2O4, ZIF-67@LDH, and CFP electrodes for OER with iR correction. b) Corresponding overpotentials at a geometric J of 10 mA cm-2. c) The corresponding Tafel plots. d) Polarization curves for Y-S Ni-Co-Se initially and after 1000 CV cycles. e) Chronoamperometry curve of Y-S Ni-Co-Se at 1.63 V (RHE) over 20 h.

Afterwards, the catalytic activity of Y-S Ni-Co-Se/CFP for the OER in 1.0 M KOH (Figure S9) was tested. Figure 6a shows the LSV curves with iR correction, 18


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which suggests that the Y-S Ni-Co-Se/CFP exerts the lowest onset potential (245 mV) and highest J for OER. To achieve a J of 10 mA cm-2, the Y-S Ni-Co-Se/CFP needs an overpotential of 300 mV, which is superior to the performance of some representative Co-based OER electrocatalysts (Table S4) in 1.0 M KOH. Meanwhile, this overpotential is lower than that of Y-S Co0.85Se/CFP (359 mV), Co3O4@NiCo2O4/CFP (422 mV) and ZIF-67@LDH/CFP (372 mV) (Figure 6b). The anodic peaks of the four electrodes from 1.25 to 1.4 V (RHE) are observed, which are caused by the reaction of metallic

selenide, oxide and LDH with OH- in the alkaline solution.49 The

corresponding Tafel plots are shown in Figure 6c. The Tafel slope (87 mV dec-1) for Y-S Ni-Co-Se/CFP is close to 78 mV dec-1 for Co3O4@NiCo2O4/CFP and much lower than that of Y-S Co0.85Se/CFP (91 mV dec-1) and ZIF-67@LDH/CFP (97 mV dec-1), implying the advantageous OER kinetics for Y-S Ni-Co-Se/CFP. In the previous section, Y-S Ni-Co-Se/CFP with the highest ECSA has been proved (Figure 5e). The reusability test of Y-S Ni-Co-Se/CFP was further accomplished in 1.0 M KOH by 1000 CV cycles at 100 mV s-1 between the range of 1.00 to 1.40 V (RHE). The LSV curves (Figure 6d) show inappreciable change after 1000 cycles. Lastly, to investigate the durability of the catalyst, the Y-S Ni-Co-Se/CFP was operated at 1.63 V (RHE) (Figure 6e). Noticeably, 80.6% of the initial J is maintained over 20 h for Y-S Ni-Co-Se/CFP. Additionally, the yolk-shelled morphology also can be preserved after the long-time electrolysis (Figure S10d-f). Both reusability and durability tests manifest that the Y-S Ni-Co-Se/CFP has good stability towards OER. The OER mechanism of the Y-S Ni-Co-Se/CFP might be accord with the reported cobalt/nickel 19



selenide OER electrocatalysts.47,

50

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Co and Ni atoms on the surface are partially

oxidized into CoOOH and NiOOH at positive potential where the OER occurs. The oxide layers act as actual OER catalytic sites,2 underneath which the Co0.85Se (or Ni0.85Se) maintains the electroconductivity between carbon fibers and the active oxide layers, and thus boosts electrocatalytic activity. The enhanced catalytic activity of Y-S Ni-Co-Se/CFP for both HER and OER may be ascribed to the three aspects as follow. Primarily, a synergistic combination of Co0.85Se and Ni0.85Se in the nanocage might conduce to the boosted catalytic activity. Next, nanocomposites in situ grown on CFP substrate also assure sufficient catalyst-electrode contact, resulting in improved charge transfer and ion diffusion efficiency on electrode.51 Furthermore, unique yolk-shell structure with more exposed active sites endows larger electrolyte-catalyst contact area for the reactions, thereby reducing the overpotentials and favoring reaction kinetics. CONCLUSION In general, we reported a novel yolk-shelled Ni-Co-Se dodecahedral nanocages on CFP through a facile selenation strategy using ZIF-67@LDH as precursors. The yolk-shelled Ni-Co-Se nanocages/CFP electrode exhibited prominent bifunctional electrocatalytic performances towards HER and OER in alkaline condition. The needed overpotential was 250 mV for HER to reach the current density of 10 mA cm-2, 162 mV less than that of the Y-S Co0.85Se/CFP counterpart, and for OER the overpotential was 300 mV to drive 10 mA cm-2, meanwhile the electrode could keep superior durability for both HER and OER. The current work shed a new insight into 20


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the design and construction of TMCs-carbon electrodes with high activity, good durability and novel structure for direct electrocatalysis applications.

ASSOCIATED CONTENT Supporting Information XRD patterns, SEM images, TEM images, EDS chemical analysis, XPS spectra, capacitance study, optical images, durability test, and performance comparisons with various catalysts. AUTHOR INFORMATION Corresponding Author * [email protected]

Notes There are no conflicts to declare. ACKNOWLEDGEMENTS This research was financially supported by the National Natural Science Foundation of China (51641303), national first-class discipline program of Light Industry Technology and Engineering (LITE2018-21), the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), and the Fundamental Research Funds for the Central Universities (JUSRP51621A and JUSRP11701) and the Postgraduate Research & Practice Innovation Program of Jiangsu Province (KYCX18_1834).

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REFERENCES (1) Nocera, D. G. The Artificial Leaf. Accounts Chem. Res. 2012, 45, 767-776. (2) Tang, C.; Cheng, N.; Pu, Z.; Xing, W.; Sun, X. NiSe Nanowire Film Supported on Nickel Foam: An Efficient and Stable 3D Bifunctional Electrode for Full Water Splitting. Angew. Chem. Int. Ed. 2015, 54, 9351-9355. (3) Turner, J. A. Sustainable Hydrogen Production. Science 2004, 305, 972-974. (4) Zeng, K.; Zhang, D. Recent progress in alkaline water electrolysis for hydrogen production and applications. Prog. Energ. Combust. 2010, 36, 307-326. (5) Ao, K.; Li, D.; Yao, Y.; Lv, P.; Cai, Y.; Wei, Q. Fe-doped Co9S8 nanosheets on carbon fiber cloth as pH-universal freestanding electrocatalysts for efficient hydrogen evolution. Electrochim. Acta 2018, 264, 157-165. (6) Walter, M. G.; Warren, E. L.; McKone, J. R.; Boettcher, S. W.; Mi, Q.; Santori, E. A.; Lewis, N. S. Correction to Solar Water Splitting Cells. Chem. Rev. 2011, 111, 5815-5815. (7) Tian, J.; Liu, Q.; Asiri, A. M.; Sun, X. Self-Supported Nanoporous Cobalt Phosphide Nanowire Arrays: An Efficient 3D Hydrogen-Evolving Cathode over the Wide Range of pH 0-14. J. Am. Chem. Soc. 2014, 136, 7587-7590. (8) Hou, Y.; Lohe, M. R.; Zhang, J.; Liu, S.; Zhuang, X.; Feng, X. Vertically oriented cobalt selenide/NiFe layered-double-hydroxide nanosheets supported on exfoliated graphene foil: an efficient 3D electrode for overall water splitting. Energ. Environ. Sci. 2016, 9, 478-483. (9) Liu, Z.; Zhang, G.; Zhang, K.; Liu, H.; Qu, J. Facile Dispersion of Nanosized NiFeP for Highly Effective Catalysis of Oxygen Evolution Reaction. ACS Sustain. Chem. Eng. 2018, 6, 7206-7211. (10) Burke, M. S.; Kast, M. G.; Trotochaud, L.; Smith, A. M.; Boettcher, S. W. Cobalt-Iron (Oxy)hydroxide Oxygen Evolution Electrocatalysts: The Role of Structure and Composition on Activity, Stability, and Mechanism. J. Am. Chem. Soc. 2015, 137, 3638-3648. (11) Gao, M.-R.; Xu, Y.-F.; Jiang, J.; Yu, S.-H. Nanostructured metal chalcogenides: 22


Page 23 of 28 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


synthesis, modification, and applications in energy conversion and storage devices. Chem. Soc. Rev. 2013, 42, 2986-3017. (12) Wang, X.; Chen, Y.; Schmidt, O. G.; Yan, C. Engineered nanomembranes for smart energy storage devices. Chem. Soc. Rev. 2016, 45, 1308-1330. (13) Chiu, I. T.; Li, C.-T.; Lee, C.-P.; Chen, P.-Y.; Tseng, Y.-H.; Vittal, R.; Ho, K.-C. Nanoclimbing-wall-like CoSe2/carbon composite film for the counter electrode of a highly efficient dye-sensitized solar cell: A study on the morphology control. Nano Energy 2016, 22, 594-606. (14) Zou, X.; Zhang, Y. Noble metal-free hydrogen evolution catalysts for water splitting. Chem. Soc. Rev. 2015, 44, 5148-5180. (15) Feng, Y.; Alonso-Vante, N. Carbon-supported cubic CoSe2 catalysts for oxygen reduction reaction in alkaline medium. Electrochim. Acta 2012, 72, 129-133. (16) Meng, T.; Qin, J.; Wang, S.; Zhao, D.; Mao, B.; Cao, M. In situ coupling of Co0.85Se and N-doped carbon via one-step selenization of metal-organic frameworks as a trifunctional catalyst for overall water splitting and Zn-air batteries. J. Mater. Chem. A 2017, 5, 7001-7014. (17) Wu, X.; He, D.; Zhang, H.; Li, H.; Li, Z.; Yang, B.; Lin, Z.; Lei, L.; Zhang, X. Ni0.85Se as an efficient non-noble bifunctional electrocatalyst for full water splitting. Int. J. Hydrogen Energ. 2016, 41, 10688-10694. (18) Yu, B.; Hu, Y.; Qi, F.; Wang, X.; Zheng, B.; Liu, K.; Zhang, W.; Li, Y.; Chen, Y. Nanocrystalline Ni0.85Se as Efficient Non-noble-metal Electrocatalyst for Hydrogen Evolution Reaction. Electrochim. Acta 2017, 242, 25-30. (19) Hou, W.; Yu, B.; Qi, F.; Wang, X.; Zheng, B.; Zhang, W.; Li, Y.; Chen, Y. Scalable synthesis of graphene-wrapped CoSe2-SnSe2 hollow nanoboxes as a highly efficient and stable electrocatalyst for hydrogen evolution reaction. Electrochim. Acta 2017, 255, 248-255. (20) Wu, D.; Guo, Z.; Yin, X.; Pang, Q.; Tu, B.; Zhang, L.; Wang, Y. G.; Li, Q. Metal-organic frameworks as cathode materials for Li-O2 batteries. Adv. Mater. 2014, 26, 3258-3262. (21) Ma, T. Y.; Dai, S.; Jaroniec, M.; Qiao, S. Z. Metal-organic framework derived 23



Page 24 of 28

hybrid Co3O4-carbon porous nanowire arrays as reversible oxygen evolution electrodes. J. Am. Chem. Soc. 2014, 136, 13925-13931. (22) Xijun, X.; Jun, L.; Jiangwen, L.; Liuzhang, O.; Renzong, H.; Hui, W.; Lichun, Y.; Min, Z. A General Metal-Organic Framework (MOF)-Derived Selenidation Strategy for In Situ Carbon-Encapsulated Metal Selenides as High-Rate Anodes for Na-Ion Batteries. Adv. Funct. Mater. 2018, 28, 1707573. (23) Hu, H.; Zhang, J.; Guan, B.; Lou, X. W. Frontispiece: Unusual Formation of CoSe@carbon Nanoboxes, which have an Inhomogeneous Shell, for Efficient Lithium Storage. Angew. Chem. Int. Ed. 2016, 55, 9666-9670. (24) Wang, L.; Han, Y.; Feng, X.; Zhou, J.; Qi, P.; Wang, B. Metal-organic frameworks for energy storage: Batteries and supercapacitors. Coordin. Chem. Rev. 2015, 307, 361-381. (25) Hu, L.; Chen, Q. Hollow/porous nanostructures derived from nanoscale metal-organic frameworks towards high performance anodes for lithium-ion batteries. Nanoscale 2014, 6, 1236-1257. (26) Bai, X.; Liu, Q.; Lu, Z.; Liu, J.; Chen, R.; Li, R.; Song, D.; Jing, X.; Liu, P.; Wang, J. Rational Design of Sandwiched Ni-Co Layered Double Hydroxides Hollow Nanocages/Graphene Derived from Metal-Organic Framework for Sustainable Energy Storage. ACS Sustain. Chem. Eng. 2017, 5, 9923-9934. (27) Ai, L.; Tian, T.; Jiang, J. Ultrathin Graphene Layers Encapsulating Nickel Nanoparticles

Derived

Metal-Organic

Frameworks

for

Highly

Efficient

Electrocatalytic Hydrogen and Oxygen Evolution Reactions. ACS Sustain. Chem. Eng. 2017, 5, 4771-4777. (28) Ming, F.; Liang, H.; Shi, H.; Xu, X.; Mei, G.; Wang, Z. MOF-derived Co-doped nickel selenide/C electrocatalysts supported on Ni foam for overall water splitting. J. Mater. Chem. A 2016, 4, 15148-15155. (29) Wu, H. B.; Lou, X. Metal-organic frameworks and their derived materials for electrochemical energy storage and conversion: Promises and challenges. Sci. Adv. 2017, 3, eaap9252. (30) Yilmaz, G.; Yam, K. M.; Zhang, C.; Fan, H. J.; Ho, G. W. In Situ Transformation 24


Page 25 of 28 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


of MOFs into Layered Double Hydroxide Embedded Metal Sulfides for Improved Electrocatalytic and Supercapacitive Performance. Adv. Mater. 2017, 29, 1606814. (31) Huajie, X.; Jing, C.; Changfu, S.; Bingkai, W.; Pinxian, X.; Weisheng, L.; Yu, T. MOF-Derived Hollow CoS Decorated with CeOx Nanoparticles for Boosting Oxygen Evolution Reaction Electrocatalysis. Angew. Chem. Int. Ed. 2018, 130, 1-6. (32)

Hu,

H.;

Han,

L.;

Metal-organic-framework-engaged

Yu,

M.;

formation

Wang,

Z.;

of

nanoparticle-embedded

Co

Lou,

X.

W.

carbon@Co9S8 double-shelled nanocages for efficient oxygen reduction. Energ. Environ. Sci. 2016, 9, 107-111. (33) He, P.; Yu, X. Y.; Lou, X. W. D. Carbon-Incorporated Nickel-Cobalt Mixed Metal Phosphide Nanoboxes with Enhanced Electrocatalytic Activity for Oxygen Evolution. Angew. Chem. Int. Ed. 2017, 129, 3955-3958. (34) Lu, Y.; Yu, L.; Lou, X. W. Nanostructured Conversion-type Anode Materials for Advanced Lithium-Ion Batteries. Chem 2018, 4, 972-996. (35) Yu, B.; Qi, F.; Zheng, B.; Hou, W.; Zhang, W.; Li, Y.; Chen, Y. Self-assembled pearl-bracelet-like CoSe2-SnSe2/CNT hollow architecture as highly efficient electrocatalysts for hydrogen evolution reaction. J. Mater. Chem. A 2018, 6, 1655-1662. (36) Hu, H.; Guan, B. Y.; Lou, X. W. Construction of Complex CoS Hollow Structures with Enhanced Electrochemical Properties for Hybrid Supercapacitors. Chem 2016, 1, 102-113. (37) Li, T.; Li, G. H.; Li, L. H.; Liu, L.; Xu, Y.; Ding, H. Y.; Zhang, T. Large-Scale Self-Assembly of 3D Flower-like Hierarchical Ni/Co-LDHs Microspheres for High-Performance Flexible Asymmetric Supercapacitors. ACS Appl. Mater. Inter. 2016, 8, 2562-2572. (38) Nagaraju, G.; Raju, G. S.; Ko, Y. H.; Yu, J. S. Hierarchical Ni-Co layered double hydroxide nanosheets entrapped on conductive textile fibers: a cost-effective and flexible electrode for high-performance pseudocapacitors. Nanoscale 2015, 8, 812-825. (39) Wang, X.-W.; Wu, K.-L.; Liu, K.; Wang, W.-Z.; Yue, Y.-X.; Zhao, M.-L.; Cheng, 25



Page 26 of 28

J.; Ming, J.; Wei, X.-W.; Liu, X.-W. Sacrificial template synthesis of (CoxNi1-x)0.85Se nanostructures with different morphologies for reduction of 4-nitrophenol. CrystEngComm 2015, 17, 734-739. (40) Chen, H.; Hu, L.; Chen, M.; Yan, Y.; Wu, L. Nickel-Cobalt Layered Double Hydroxide Nanosheets for High-performance Supercapacitor Electrode Materials. Adv. Funct. Mater. 2014, 24, 934-942. (41) Liu, Z.; Ma, R.; Osada, M.; Iyi, N.; Ebina, Y.; Takada, K.; Sasaki, T. Synthesis, Anion Exchange, and Delamination of Co−Al Layered Double Hydroxide: Assembly of the Exfoliated Nanosheet/Polyanion Composite Films and Magneto-Optical Studies. J. Am. Chem. Soc. 2006, 128, 4872-4880. (42) Li, S.; Peng, S.; Huang, L.; Cui, X.; Al-Enizo, A. M.; Zheng, G. Carbon-Coated Co3+-Rich Cobalt Selenide Derived from ZIF-67 for Efficient Electrochemical Water Oxidation. ACS Appl. Mater. Inter. 2016, 8, 20534-20539. (43) Yu, B.; Qi, F.; Wang, X.; Zheng, B.; Hou, W.; Hu, Y.; Lin, J.; Zhang, W.; Li, Y.; Chen,

Y.

Nanocrystalline

Co0.85Se

as

a highly

efficient non-noble-metal

electrocatalyst for hydrogen evolution reaction. Electrochim. Acta 2017, 247, 468-474. (44) Sheng, Z. H.; Shao, L.; Chen, J. J.; Bao, W. J.; Wang, F. B.; Xia, X. H. Catalyst-Free Synthesis of Nitrogen-Doped Graphene via Thermal Annealing Graphite Oxide with Melamine and Its Excellent Electrocatalysis. ACS Nano 2011, 5, 4350-4358. (45) Xia, C.; Jiang, Q.; Zhao, C.; Hedhili, M. N.; Alshareef, H. N. Selenide-Based Electrocatalysts and Scaffolds for Water Oxidation Applications. Adv. Mater. 2016, 28, 77-85. (46) Pan, Y.; Sun, K.; Liu, S.; Cao, X.; Wu, K.; Cheong, W.-C.; Chen, Z.; Wang, Y.; Li,

Y.;

Liu,

Y.;

Wang,

D.;

Peng,

Q.;

Chen,

C.;

Li,

Y.

Core-Shell

ZIF-8@ZIF-67-Derived CoP Nanoparticle-Embedded N-Doped Carbon Nanotube Hollow Polyhedron for Efficient Overall Water Splitting. J. Am. Chem. Soc. 2018, 140, 2610-2618. (47) Ming, F.; Liang, H.; Shi, H.; Mei, G.; Xu, X.; Wang, Z. Hierarchical 26


Page 27 of 28 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


(Ni,Co)Se2/Carbon Hollow Rhombic Dodecahedra Derived from Metal-Organic Frameworks for Efficient Water-Splitting Electrocatalysis. Electrochim. Acta 2017, 250, 167-173. (48) Mccrory, C. C. L.; Jung, S.; Peters, J. C.; Jaramillo, T. F. Benchmarking Heterogeneous Electrocatalysts for the Oxygen Evolution Reaction. J. Am. Chem. Soc. 2013, 135, 16977-16987. (49) Guan, C.; Liu, X.; Elshahawy, A. M.; Zhang, H.; Wu, H.; Pennycook, S. J.; Wang, J. Metal-organic framework derived hollow CoS2 nanotube arrays: an efficient bifunctional electrocatalyst for overall water splitting. Nanoscale Horiz. 2017, 2, 342-348. (50) Kwak, I. H.; Im, H. S.; Jang, D. M.; Kim, Y. W.; Park, K.; Lim, Y. R.; Cha, E. H.; Park, J. CoSe2 and NiSe2 Nanocrystals as Superior Bifunctional Catalysts for Electrochemical and Photoelectrochemical Water Splitting. ACS Appl. Mater. Inter. 2016, 8, 5327-5334. (51) Zhou, J.; Dou, Y.; Zhou, A.; Guo, R.-M.; Zhao, M.-J.; Li, J.-R. MOF Template-Directed Fabrication of Hierarchically Structured Electrocatalysts for Efficient Oxygen Evolution Reaction. Adv. Energ. Mater. 2017, 7, 1602643.

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TOC

Synopsis: Hydrogen and oxygen evolution reaction even water splitting belong to renewable technologies and thus emphasis the efficient utilization of earth resources.

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Formation of yolk-shelled nickel-cobalt selenide dodecahedral

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