Nanoporous carbon coated bimetallic phosphides for efficient

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Nanoporous carbon coated bimetallic phosphides for efficient electrochemical water splitting Yu Liu, Qishun Wang, Lanlan Wu, Yan Long, Jian Li, Shuyan Song, and Hongjie Zhang Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.8b00117 • Publication Date (Web): 19 Apr 2018 Downloaded from http://pubs.acs.org on April 19, 2018

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Crystal Growth & Design

Nanoporous carbon coated bimetallic phosphides for efficient electrochemical water splitting Yu Liu,†,‡ Qishun Wang,†,§ Lanlan Wu,†,‡ Yan Long,†,‡ Jian Li,†,§ Shuyan Song,*,† Hongjie Zhang*,†

†State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin Street, Changchun 130022, China ‡University of Chinese Academy of Sciences, Beijing 100049, China §University of Science and Technology of China, Hefei 230026, China

AUTHOR INFORMATION * Corresponding authors. Tel.:+86 431 85262127; fax: +86 431 85698041. E-mail addresses: [email protected] (S. Song), [email protected] (H. Zhang).

ABSTRACT: Developing highly efficient and low-cost electrocatalyst for water splitting to produce H2 and O2 as sustainable energy fuel to replace noble metal catalyst is vital and urgent for the large-scale deployment of key energy technologies. Here, in combination of composition, structure and catalytic mechanism analysis, the porous Co0.7Fe0.3P@C catalyst was synthesized

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by a facile phosphidation process of the Co0.7Fe0.3@C which derived from the corresponding CoFe

coordination

polymer

precursors.

The

Co0.7Fe0.3P@C

catalyst

shows

enhanced

electrochemical activity towards oxygen evolution reaction (OER) and water splitting due to the incorporation of Fe element and the porous structure, comparable to the commercial noble metal catalyst. Furthermore, the coated carbon can not only promote electronic transmission but also protect the active Co0.7Fe0.3P nanoparticles, resulting in good activity and stability. These fascinating findings in this work would promote the designation and preparation of promising bimetallic OER electrocatalyst utilizing coordination polymer as precursors for various energy systems in future. INTRODUCTION Owing to the rapid consumption of fossil fuels and the rising global warming problems, alternative environmental friendly and renewable energy has attracted much attention.1-7 Electrochemical water splitting, providing a feasible method to produce high purity hydrogen and oxygen, has been recognized as one of the promising ways for the production of hydrogen as sustainable fuel. Noble metal and noble metal oxide are always considered as desirable hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysts.8 However, the scarcity, high cost and poor stability greatly impede their scale-up development. Therefore, earthabundant metals, often inexpensive, have been developed as potential HER/OER catalysts which show superior activity and stability.9-12 It is well known that composition is essential for catalyst activity, moreover, in some times nanostructure and the specific surface area could also have an important impact on the inherent activity of some inorganic materials.13 Thus, inorganic materials with particular compositions


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have attracted much more attention to enhance the activity of electrocatalyst.14-16 For example, to meet the cost effective and high efficient requirement for promising water splitting application, several transition metal compounds including carbides, chalcogendies, and nitrides have been synthesized.17-20 Among these materials, transition metal phosphides have emerged as a new water splitting catalyst family because of their superior activity.21 In spite of the great progress achieved in recent years, like Co-P22,23 and Ni-P24-26, their performance does not reach the limit. Many previous reports have proved that binary material with a secondary metal incorporated to the crystal lattice can lead to enhancement in the electrocatalytic activity.27-30 The possible reason is proposed that with the incorporation of an addition metal, the electronic structure of these transition metal can be tuned to favor the catalytic process, which in turn promote their catalytic performance.23,27,28 So, bimetallic phosphides would perform better than monometallic phosphides in electrochemistry. Simultaneously, it has been proved that a tight connection at atomic level between metallic catalyst and the nanocarbon could further improve its activity.17 The nanocarbon with high electrical conductivity plays an important role in promoting the charge transfer from electrode to active sites and maintaining the stability of catalytic structure.31-33 What’s more, porous structure of some carbon layer could provide a high specific surface area to expose a large number of active sites enhancing the contact between electrolyte and electrode.34,35 As shown above, not only the composition but also the morphology and structure could affect the electrochemical activity. Therefore, it is highly desirable to fabricate a carbon coated bimetallic phosphides with porous structure, which will promote their electrochemical activity for energy applications. Herein, we demonstrate a facile strategy to synthesize the homogenous Fe doped CoP nanocrystal coated by carbon shell with porous structure, as shown in Scheme 1. The porous carbon coated


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CoxFe1-xP is developed via a phosphidation treatment of CoxFe1-x@C that derived from binary Co-Fe coordination polymers. Among the CoxFe1-xP@C, the as synthesized Co0.7Fe0.3P@C shows remarkable electrochemical activities towards OER and HER in alkaline solution, and the OER activity achieved a low overpotential of 300 mV at a current density of 10 mA/cm2, suppressing the benchmark RuO2 catalyst. When the Co0.7Fe0.3P@C was integrated with Ni foam as bifunctional electrodes towards water splitting cells, it could achieve a current density of 10 mA/cm2 at an operating voltage of 1.6 V, and that is comparable to the noble metal catalysts.

Scheme 1. Illustration of the approach to synthesize CoxFe1-xP@C nanorods. EXPERIMENTAL SECTION Materials. Analytical grade CoCl2·6H2O, FeSO4·7H2O, FeCl3, nitrilotriacetic acid (NTA), NaH2PO2, NH4HCO3 and isopropanol were purchased from Beijing Chemical Reagent. All of these chemicals were analytical grade and used as received without further purification. Deionized water was used throughout the experiments.


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Synthesis of CoFe-NTA nanowires. In a typical synthesis, 0.7 mmol of CoCl2·6H2O, 0.3 mmol of FeSO4·7H2O and 2 mmol of nitrilotriacetic acid (NTA) are dissolved in a mixture of 3 mL water and 9 mL isopropanol. The solution is then transferred to a stainless steel autocave and kept at 180 °C for 6 h. After cooling to room temperature, the obtained CoFe-NTA nanowires are separated by centrifugation and dried at 80 °C for 12 h. Synthesis of Co0.7Fe0.3@C nanowires. The Co0.7Fe0.3@C was obtained through a thermal treatment in N2 atmosphere at the temperature of 450 °C for 2 h. Synthesis of Co0.7Fe0.3P@C. Co0.7Fe0.3P@C is prepared via a low temperature phosphidation process. The NaH2PO2 is used to phosphidate the as prepared Co0.7Fe0.3@C. 50 mg of Co0.7Fe0.3@C nanowires and 500 mg of NaH2PO2 are put in two separate ceramic boats with NaH2PO2 at the upstream. Then the samples are annealed at 350 °C for 3 h under N2 atmosphere. The samples with different Fe doped are prepared with the same procedures but with different amount of CoCl2·6H2O and FeSO4·7H2O added at the first step. Synthesis of Co0.7Fe0.3P nanoparticles. The Co0.7Fe0.3OOH is first prepared by adding NH4HCO3 into the solution containing CoCl2·6H2O and FeCl3 with appropriate molar ratio. The precipitation process is kept for 5 h. Then the precipitate is collected by centrifuging and dried at 80 °C for 12 h. After the phosphidation process mentioned above, the Co0.7Fe0.3P nanoparticles are obtained. Characterization. X-ray diﬀraction (XRD) was performed on a Bruker D8 X-ray diﬀractometer with Cu-Kα radiation (λ = 1.5418 Å). The field-emission scanning electron microscopy (FESEM) images were obtained using Hitachi S-4800. Transmission electron microscopic (TEM) images were obtained with a TECNAI G2 high-resolution transmission


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electron microscope, operating at 200 kV. XPS measurement was performed on an ESCALABMKII 250 photoelectron spectrometer (VG Co.) with Al Kα X-ray radiation as the X-ray source for excitation. Inductively coupled plasma (ICP) analyses were performed with a Varian Liberty 200 spectrophotometer to determine the contents. TGA data was collected on Netzsch STA 449F3. Raman spectra was tested on T64000 Triple Raman Spectrometer. Fourier transform infrared spectroscopy (FT-IR) was recorded on a PerkinElmer 580B IR spectrophotometer. Electrochemical measurements. The electrochemical measurements were carried out using the CHI 760E equipment on glassy carbon electrodes with 3 mm in diameter. The catalyst inks were prepared by dispersing 5 mg of catalyst materials to the mixture of isopropanol, water and nafion. Then, the ink solutions were ultrasound sonicated for at least 1 h to give a uniform suspension. Next 5 µL of the above suspension was dropped onto a glassy carbon electrode. After the catalyst had dried at room temperature, the linear sweep voltammetry was recorded in 1.0 M KOH solution at a scan rate of 5 mV/s. Eis measurement was carried on the frequency from 0.1 Hz to 10000 Hz with the amplitude of 10 mV at the potential of 1.53 V vs. RHE. The catalytic water splitting electrodes were prepared by covering an area of 0.5 cm2 of Ni foam to reach the amount of 3 mg/cm2, and then naturally dried at room temperature. The stability tests for water-splitting were performed by chronoamperometry at the overpotential that giving the current density of 10 mA/cm2. RESULTS AND DISCUSSION The Co0.7Fe0.3@C nanowires were prepared by the direct pyrolysis of Co-Fe coordination polymer precursors36. The Co-Fe coordination polymer nanowires were synthesized in a hydrothermal reaction of Co2+ and Fe2+ with the organic linker nitrilotriacetic acid (NTA) as


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ligand. The morphology of the precursor was determined by field-emission scanning electron microscope (FESEM) that shown in Figure 1a. The precursor features a well nanowire like morphology with diameter of around 0.5 µm. The XRD pattern in Figure S1a shows the good crystallinity of this coordination polymer, and the peak at around 12° demonstrate the coordination character.37 The FT-IR spectra in Figure S1b shows the coordination structure of NTA and the CoFe-NTA. The spectra of NTA exhibits a strong peak at 1716 cm-1 which can be assigned to the carboxylic acid group. The peaks at 1679 cm-1 and 1577 cm-1 in CoFe-NTA is attributed to the coordination of Co or Fe to the carboxylate group. Then the thermal stability of CoFe-NTA nanowires was investigated by thermogravimetric analysis (TGA) at a temperature ranging from 25 °C to 700 °C with a heating rate of 10 °C/min in N2 atmosphere. The TGA curves show two major weight loss steps as illustrated in Figure 1b. The initial weight loss of the sample at around 50 °C could arise from desorption of the absorbed water. And with the temperature increasing, the great weight loss from 350 °C to 450 °C attributes to the pyrolysis of the coordination polymer precursor CoFe-NTA. The final weight left after the thermal process is about 30%. According to the TGA results, the CoFe-NTA precursors can be easily transformed into Co0.7Fe0.3@C after annealing at 450 °C for 2 hours in N2. XRD patterns of the thermal pyrolysis products demonstrated in Figure S2 correspond well to the Co0.7Fe0.3 phase (PDF#481818). The typical SEM image in Figure 1c shows that the Co0.7Fe0.3@C displays wire like structure with a diameter of around 300 nm. It is important to point out that the diameter of Co0.7Fe0.3@C is smaller than CoFe-NTA, such a decrease may be caused by the shrink of samples during annealing process.38 It is also demonstrated in Figure 1d that the nanowires composite with a number of small nanoparticles with 20 nm diameter. The energy-dispersive X-


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ray spectroscopy (EDX) shows the presence of Co, Fe, C, and O in the products (Figure S3). The appearance of oxygen element may emerge from the left oxygen in the carbon layer.39

Figure 1. (a) SEM image of the CoFe-NTA; (b) TGA curve of the CoFe-NTA; (c) and (d) SEM images of the Co0.7Fe0.3@C. The phosphidation calcination of Co0.7Fe0.3@C was carried out in N2 atmosphere at 350 °C with NaH2PO2. The Co/Fe molar ratio in Co0.7Fe0.3P@C sample is 2.3, determined by the inductively coupled plasma atomic emission spectroscopy (ICP-AES). This result corresponds well with the Co0.7Fe0.3@C samples. The obtained samples were first characterized by powder XRD (Figure 2a). It shows that the diffraction peaks can be fully indexed to the CoP phase (PDF#29-0497). The absence of Co0.7Fe0.3 diffraction peaks shows the completely conversion to phosphides after a low-temperature phosphidation reaction. The incorporated Fe in the Co0.7Fe0.3P@C samples does not result in the peaks of FeP phase, these results reveal that the secondary Fe element is homogeneously intercalated into the crystal lattice of CoP.30 Moreover,


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the EDX spectrum results confirm the presence of Co, Fe, P, C and O elements (Figure S4). The signal of O could be originated from surface phosphate species (POx or P–O species) on metal phosphides formed by oxidation in air6 and the oxygen element in carbon layer. What’s more, the EDX results of Co0.7Fe0.3P nanoparticles in Figure S5 confirm the Co, Fe, P, O chemical compositions. The EDX mapping data in Figure S6 shows the uniform distribution of Co, Fe and P elements. The sample was further characterized by the electron microscopy to reveal its unique morphology. Figure 2b shows that the Co0.7Fe0.3P@C inherits the porous morphology but with a small length which would be caused by the fracture during thermal phosphidation reaction. The TEM images in Figure 2c and 2d indicate that the Fe doped CoP nanocrystal possesses a diameter of about 20 nm. As shown in Figure 2e, a well resolved crystal lattice fringe spacing of 0.284 nm is observed, corresponding to the (011) crystal plane of CoP. X-ray photoelectron spectroscopy (XPS) was used to characterize the surface composition and chemical nature of the Co0.7Fe0.3P@C hybrids (Figure S7). The XPS spectra further confirms the existence of Co, Fe, P, C, and O elements in the product. As shown in the high-resolution XPS spectra, the peak around 778.8 eV in the Co 2p3/2 spectrum is assigned to Co in CoP. The spectrum in the Fe 2p region of 707.4 eV is assigned to the binding energy for Fe in Co0.7Fe0.3P@C. The P species with binding energy of 129.6 eV can be attributed to the CoP phosphide, and the peak centered at 134.7 eV is supposed causing by the oxidation of P species due to the contact with air.40. The BET surface area of the porous Co0.7Fe0.3P@C was tested to be 119.0 m2/g, and the pore-size distribution shows a peak ranging from 5 nm to 15 nm (Figure S8a). And the surface area of Co0.7Fe0.3P nanoparticles was also tested to be 69.06 m2/g as shown in Figure S8b. These results reveal that the Co0.7Fe0.3P@C has a mesoporous structure with large surface area that could provide more active sites for electrochemical process.


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Figure 2. (a) XRD pattern of Co0.7Fe0.3P@C; (b) FESEM image of Co0.7Fe0.3P@C; (c), (d) TEM images of Co0.7Fe0.3P@C; (e) HRTEM image of Co0.7Fe0.3P@C. The Raman spectra of Co0.7Fe0.3@C and Co0.7Fe0.3P@C in Figure S9a exhibit two Raman bands corresponding to the D and G bands of carbon. In order to further confirm the existence of carbon in Co0.7Fe0.3@C and Co0.7Fe0.3P@C, the thermogravimetric (TG) analysis was carried out from 20 to 850 °C in the atmosphere of air, as shown in Figure S9b. The TGA data of Co0.7Fe0.3@C shows that it is almost stable below 250 °C, and the data above 250 °C reveals the results of oxidation of Co0.7Fe0.3 nanoparticles and coated carbon layer. And the oxidation of carbon mainly contributes to the following weight loss starting at 400 °C. As the carbon components can be fully consumed in air, the TGA data slightly changes over 550 °C, and the


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final weight loss is about 20%. The result of Co0.7Fe0.3P@C shows great weight loss below 520 °C because of the oxidation of carbon. The following weight increase is owing to the oxidation of Co0.7Fe0.3P nanoparticles. From the Raman spectra and TGA data above, we can confirm the existence of carbon in Co0.7Fe0.3@C and [email protected] The unique composition and structure of Co0.7Fe0.3P@C is expected to show superior electrocatalytic performance. Firstly, the activity of Co0.7Fe0.3P@C sample towards OER was assessed by linear scan voltammetry (LSV) using a typical three-electrode cell in 1.0 M KOH solution. The corresponding polarization curves were obtained at a scan rate of 5 mV/s after a constant potential activation process. The catalytic performance of samples with different amount of Fe doped was tested. As shown in Figure S10a Co0.7Fe0.3P@C achieved the best activity among the CoxFe1-xP@C samples. And, the polarization curves in Figure 3a clearly reveal that the Co0.7Fe0.3P@C also possesses enhanced OER activity compared with Co0.7Fe0.3@C and CoFe-NTA, with the overpotential at 10 mA/cm2 decreasing from 320 mV for Co0.7Fe0.3@C and 330 mV for CoFe-NTA to 300 mV. Simultaneously, the catalytic performance of Co0.7Fe0.3P nanoparticles was also tested for comparison. It is obvious that the Co0.7Fe0.3P nanoparticles are less active than the Co0.7Fe0.3P@C sample. Moreover, such a lower overpotential is comparable to the performance of the state of the art catalyst RuO2 (320 mV) and many other nonprecious metal OER catalysts17-21 (Table S1). To gain a further insight into the OER kinetics, tafel slopes of the prepared samples derived from LSV polarization curves were investigated. As shows in Figure 3b, while the Co0.7Fe0.3@C and CoFe-NTA show a tafel slope of 60 and 62 mV/dec, the Co0.7Fe0.3P@C has a little smaller tafel slope of around 52 mV/dec, which is also better than the Co0.7Fe0.3P nanoparticles and other Fe-incorporated CoP (Figure S10b), indicating its favorable OER kinetics.19-21 We then evaluated the HER


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performance of Co0.7Fe0.3P@C in a 1 M KOH solution. As can be seen from the polarization curves in Figure 3c, the Pt/C exhibits the best HER activity with an overpotential of about 10 mV to reach the current density of 10 mA/cm2. Simultaneously, the Co0.7Fe0.3P@C achieves a low overpotential of 160 mV at the current density of 10 mA/cm2, which is better than the Co0.7Fe0.3P nanoparticles, the precursor CoFe-NTA, the Co0.7Fe0.3@C and many other reported metal phosphide electrocatalysts (Table S2).22-25 Tafel slopes were then valued by fitting the linear regions of tafel plots to the tafel equation to elucidate the catalytic kinetics for HER. As presented in Figure 3d, the tafel slope of Co0.7Fe0.3P@C is 72 mV/dec which suggests that the rate-limiting step of HER process is the first electron transfer process26, and that result is better than the other samples. Besides the activity, the stability performance is also a crucial parameter for catalyst. Here the stability of Co0.7Fe0.3P@C catalyst was evaluated by accelerated degradation test. The methodology was performed by a continuous CV scanning at the scan rate of 100 mV/s. From the results in Figure S11 the typical Co0.7Fe0.3P@C catalyst shows well OER catalytic stability with slight negative shift in LSV curves after 3000 CVs compared to the initial one. The long term durability of the Co0.7Fe0.3P@C has also been tested with the sweeps potential between -0.3 - 0.1 V for HER. And the polarization curve of the Co0.7Fe0.3P@C after 3000 CVs shows little activity loss (Figure S12). Both results demonstrate a well durability of this catalyst.


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Figure 3. (a) Polarization curves of Co0.7Fe0.3P nanoparticles and Co0.7Fe0.3P@C in 1 M KOH solution at 5 mV/s for OER; (b) Tafel plots of Co0.7Fe0.3P nanoparticles and Co0.7Fe0.3P@C for OER; (c) Polarization curves of Co0.7Fe0.3P nanoparticles, Co0.7Fe0.3P@C and Pt/C in 1 M KOH solution at 5 mV/s for HER; (d) Tafel plots of Co0.7Fe0.3P nanoparticles, Co0.7Fe0.3P@C and Pt/C for HER; To get a deep understand of the superior electrochemical performance of the Co0.7Fe0.3P@C catalyst, the values of Cdl used to estimate the electrochemical active surface area were calculated by CV measurement of different scan rates in the potential region without faradaic processes (Figure S13).42 As revealed in Figure S14 the Co0.7Fe0.3P@C has a much larger Cdl


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(130 mF/cm2) than the CoFe-NTA, Co0.7Fe0.3@C and Co0.7Fe0.3P nanoparticles. This indicates that the porous structure provides more active sites and larger accessible surface area for Co0.7Fe0.3P@C that leads to the superior electrocatalytic activity. The electrochemical impedance spectroscopy (EIS) analysis is employed to study the electron transfer kinetics of electrochemical process. As shown in the Figure S15, the EIS spectra shows the Co0.7Fe0.3P@C possess a little Rct than the Co0.7Fe0.3P nanoparticles, suggesting the Co0.7Fe0.3P@C has a fast electron transport ability. It is believed that the conductive carbon and the close connection between the Co0.7Fe0.3P and carbon played a crucial role for the electron transfer and mass transport during the electrocatalysis reactions, resulting in remarkable electrochemical activities. What’s more, the atomic core/shell interfacial between the inner Co0.7Fe0.3P nanoparticles and the carbon provides a fast transfer channel for electron to transfer from electrode to carbon and then to the active Co0.7Fe0.3P nanoparticles, making the interfacial C atoms to have a synergistic effects between the Co0.7Fe0.3P nanoparticles, thus resulting in facilitated electrical activity.43 In addition, it has been identified that, as for OER in alkaline solution, the Co-Fe (oxy)hydroxides derived from the Co-Fe phosphides are the real active sites. It is also suggested that the FeOOH has a higher intrinsic OER activity but suffer from the low electrical conductivity and chemically instability. When the CoOOH in CoxFe1-x(OOH) with high conductivity, well stability and porous surface serves as the host for high active Fe, it shows enhanced OER activity. However, when the amount of doped Fe surpasses the optimum, for example the Co0.6Fe0.4P@C, the insulated FeOOH occupy more place at the active sites leading to the decrease of the OER activity.38 So, as for Co0.7Fe0.3P@C, the doped Fe into the crystal of CoP results in both high conductivity and good activity. Also, compared with CoP@C, the Co in Co0.7Fe0.3P@C may have lower chemical bonding energy values caused by the incorporation of Fe species. The lower bonding energy of


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Co was supposed to have a strong electron-donating ability, which could facilitate the electrochemical reaction. Thus, the doped Fe in Co0.7Fe0.3P@C was supposed to have a synergism with Co which could explain its high catalytic activity.44 Meanwhile, the porous structure could expose more active sites which are also protected by the carbon layer leading to the high active and stable electrocatalytic performance.

Figure 4. (a) Cyclic voltammogram curves of Co0.7Fe0.3P@C/Ni foam in a two-electrode system in 1 M KOH solution; (b) Chronoamperometry curves of a water-splitting cell at 1.60 V. Considering the outstanding electrocatalytic performance of the Co0.7Fe0.3P@C, we then use Co0.7Fe0.3P@C/NF as bifunctional catalytic electrodes to study its performance towards overall water splitting in a two-electrode cell. And the Pt/C-RuO2 on Ni foam were also tested as reference. It can be seen in Figure S16a that the pure Ni foam electrodes show negligible water splitting activity compared to the benchmark Pt/C-RuO2 catalysts which need an operating voltage of 1.61 V to reach the current density of 10 mA/cm2. The Co0.7Fe0.3P@C/NF electrodes show a similar overall water splitting activity and the current density of 10 mA/cm2 was reached at approximately 1.60 V, which is comparable to some other reported electrocatalysts (Table


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S3).45,46 Furthermore, the electrocatalysts show a negligible performance degradation for a 12 h chronoamperometric test at a constant voltage of 1.60 V, and that shows better stability than Pt/C-RuO2 catalysts (Figure S16b). CONCLUSION In conclusion, porous Co-Fe phosphides have been synthesized as efficient water splitting catalyst. The Co0.7Fe0.3@C nanowires were prepared by the thermal pyrolysis of CoFe-NTA coordination polymer nanowires. After the phosphidation process, the Co0.7Fe0.3@C can in situ changing into Co0.7Fe0.3P@C. The resulting Co0.7Fe0.3P@C shows excellent catalytic activities towards OER and HER process. The enhanced activity was attributed to the complex composition of bimetallic phosphides and coated carbon with porous structure which exposed much active sites together with high charge transfer rate. Moreover, the as-fabricated water splitting cell with Co0.7Fe0.3P@C modified Ni Foam as bifunctional electrodes demonstrated the promising application in overall water splitting because of the low potential and remarkable stability. This study provides a new road for the use of coordination polymers to synthesize porous metal phosphides coated with porous carbon serving as bifunctional electrochemical catalysis for practical applications.

ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge via the Internet at http://pubs.acs.org.


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Figure S1-S16. Table S1-S3. The XRD, FT-IR, EDX, XPS spectra; The elemental mapping images; N2 adsorption-desorption isotherms; The Raman spectra and TGA data; The polarization curves and Tafel slopes of CoP with different amount Fe doped; The polarization curves of stability performance; Cyclic voltammograms curves and Cdl plots; The EIS spectra; The polarization curves of Pt/C-RuO2 catalysts and Ni foam. AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected] *E-mail: [email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS The authors are grateful for the financial aid from the National Natural Science Foundation of China (21590794, 21210001, 21771173, and 21521092), Ministry of Science and Technology of China (No. 2016YFB0100103), Youth Innovation Promotion Association of Chinese Academy of Sciences (2011176), and Chinese Academy of Sciences-Commonwealth Scientific and Industrial Research Organization (CAS-CSIRO) project (GJHZ1730). REFERENCES


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For Table of Contents Use Only Nanoporous carbon coated bimetallic phosphides for efficient electrochemical water splitting Yu Liu,†,‡ Qishun Wang,†,§ Lanlan Wu,†,‡ Yan Long,†,‡ Jian Li,†,§ Shuyan Song,*,† Hongjie Zhang*,†

We prepared Fe doped CoP nanocrystal enclosed in porous carbon derived from coordination polymers. The bimetallic phosphides show enhanced electrochemical activity. The effect of Fe doped towards catalytic activity and the function of carbon have been discussed.


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Nanoporous carbon coated bimetallic phosphides for efficient

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