Ni(OH)2 Derived Porous

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Core-Shell FeCo Prussian Blue Analogue/Ni(OH)2 Derived Porous Ternary Transition Metal Phosphides Connected by Graphene for Effectively Electrocatalytic Water Splitting Yuanxin Du, Jing Chen, Lin Li, Hongyu Shi, Kangjian Shao, and Manzhou Zhu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/acssuschemeng.9b03166 • Publication Date (Web): 17 Jul 2019 Downloaded from pubs.acs.org on July 21, 2019

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ACS Sustainable Chemistry & Engineering

Core-Shell FeCo Prussian Blue Analogue/Ni(OH)2 Derived Porous Ternary Transition Metal Phosphides Connected by Graphene for Effectively Electrocatalytic Water Splitting Yuanxin Du,* Jing Chen, Lin Li, Hongyu Shi, Kangjian Shao, Manzhou Zhu* Department of Chemistry and Centre for Atomic Engineering of Advanced Materials, Anhui Province Key Laboratory of Chemistry for Inorganic/Organic Hybrid Functionalized Materials, Anhui University, 111 Jiu Long Rd, Hefei, Anhui Province 230601, China. E-mail: [email protected]; [email protected]

Abstract As a promising new-star electrocatalyst, transition metal phosphide (TMP) has been widely applied in electrocatalytic hydrogen and oxygen evolution reaction (HER and OER). However, the current catalytic activity and stability is unsatisfactory. Herein, we started from optimizing the geometric and electronic structure of the catalyst, chosen FeCo Prussian blue analogues (PBAs) with rich pores as precursors, epitaxially grown Ni(OH)2, and connected each other though graphene oxide (GO) by electrostatic interaction, then finally transformed to ternary TMPs and graphene composites (Fe2P/CoP/Ni5P4/RGO). Due to the porous structure of phosphides and the large surface area and excellent conductivity of RGO, the Fe2P/CoP/Ni5P4/RGO exposed more active sites, promoted electrolyte diffusion and gas release, and accelerated the charge transport. The synergistic effect among ternary TMPs and between

them

and

RGO

made

Fe2P/CoP/Ni5P4/RGO

as

highly-efficient

electrocatalyst for water splitting with only 57 mV, 232 mV overpotential, and 1.56 V cell voltage for obtaining 10 mA/cm2 current density in HER, OER, and overall water splitting. Benefiting from the protection of RGO, the Fe2P/CoP/Ni5P4/RGO remained the original structure and showed good stability during long-term test. This work proposed a design thought to improve the activity and stability of metal phosphides which may be extended to other metal organic framework-derived compounds and

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carbon-based materials composites. Keywords: transition metal phosphide, electrochemical water splitting, graphene composite, metal organic framework Introduction As a promising renewable and clean energy supply technology, electrolysis water can easily and efficiently produce high purity hydrogen and oxygen, reduce environmental pollution and consumption of fossil fuels, which is widely used in industrial production and related special industries.1-3 For now, the electrochemical water splitting efficiency is relatively low, which still requires a large overpotential to drive the reaction due to the slow kinetics of two half reactions, hydrogen evolution and oxygen evolution reaction (HER and OER).4-6 Although some precious metal based catalysts, such as Pt, Ir, Ru-based materials, are state-of-art catalysts that can effectively enhance the activity of HER and OER, their high prices and scarce resources limit the widespread. Therefore, seeking cheap and abundant materials with good catalytic activity and stability to replace them is still urgent task. Recently, transition metal compounds, including oxides,7-8 sulfides,9-10 selenides,11-12 nitrides,13-14 hydroxides,15-16 and phosphides,17-21 et ac. have gained intensive attention because of their high efficiency in electrocatalytic HER and OER. Among them, transition metal phosphide (TMP) is particularly special due to its hydrogenase-like properties with high activity and stability.22-27 However, the present catalytic efficiency is not satisfied mainly because of poor electrical conductivity and too few active sites. Currently, there are three mainstream methods to improve the activity of TMP: 1) bring in new composition to synthesize multi-metallic phosphides, and utilize synergistic effect to tune electronic structure; 2) build porous structure and increase surface area to create more active sites; 3) introduce conductive material to promote charge transport capability. Based on the above strategies, to achieve high activity, previous researches have prepared a series of metal-organic framework (MOF) derivatives/carbon composites,28-33 in which metal center ions and organic


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ligand transformed to metal phosphides and amorphous carbon, respectively. But, the MOF

precursors

are

mainly

mono

or

bimetallic

cannot

obtain

multielement-compounds. Besides, the transformed carbon is low-degree graphitized and it is only act as the thin-shell on the outside of the active derivatives cannot effectively connect the isolated active particles, thus the conductivity is not good enough. To obtain higher activity, maximizing the synergies between the components, fully exposing active sites, and constructing interlinked charge transfer network should be carried out simultaneously. Here, we used bimetallic MOF - FeCo Prussian blue analogues (PBAs) as precursors and epitaxially grown Ni(OH)2 for introducing three kinds of synergistic elements. By the attraction of opposite charges, graphene oxide (GO) wrapped the particle and interconnected each other. Followed by phosphidation

treatment,

ternary

TMPs

and

graphene

composites

(Fe2P/CoP/Ni5P4/RGO) with original cubic profile were prepared owing to the protection of RGO. The Fe2P/CoP/Ni5P4/RGO exhibited abundant active sites and excellent conductivity which is benefic for mass transfer and charge transport in electrolysis water process. At the same time, the synergies among ternary TMPs and between them and RGO also promoted the catalytic activity and stability. Therefore, only 57 mV and 232 mV overpotential, and 1.56 V cell voltage were required for generating 10 mA/cm2 current density for HER, OER, and overall water splitting, respectively. Furthermore, the potential and current were rarely changed during the 24 h test. Results and Discussions The preparation process of the ternary TMPs and graphene mixture (Fe2P/CoP/Ni5P4/RGO) is illustrated in Scheme 1. FeCo PBA is firstly prepared by a simple chemical precipitation method. Ni(II) salt are then introduced to deposited Ni(OH)2 nanosheet on the surface of FeCo PBA in ammonia atmosphere. Subsequently, FeCo PBA/Ni(OH)2 is functionalized with positively charged poly diallyl dimethyl ammonium chloride (PDDA). By electrostatic interaction, GO is



tightly wrapped around the FeCo PBA/Ni(OH)2, thus making the isolated FeCo PBA/Ni(OH)2 connect to each other to improve the charge transport. Finally, the Fe2P/CoP/Ni5P4/RGO is obtained via low-temperature phosphidation.

Scheme 1. Illustration for the preparation of Fe2P/CoP/Ni5P4/RGO.

The morphology and structure evolution of products from FeCo PBA to Fe2P/CoP/Ni5P4/RGO was recorded by electronic microscopy images and X-ray diffraction (XRD) pattern. FeCo PBAs are uniform cubic nanoparticles with average size of ~ 200 nm (Figure 1A and Figure S1A). The XRD peaks are all match well with Co3[Fe(CN)6]2·10H2O (JCPDS No. 46-0907), as shown in Figure S2A. After reacting with Ni(II) in alkaline atmosphere, thin Ni(OH)2 nanosheet are deposited on the FeCo PBA surface, making the original smooth surface become rough (Figure 1B and Figure S1B). The corresponding XRD pattern is displayed in Figure S2B, except the fingerprint peaks of FeCo PBA, in which a characteristic peak belonged to β-Ni(OH)2 (JCPDS No. 14-0117) appears obviously. The FeCo PBA/Ni(OH)2 is then filled with positive charge through surface charge modification, and tightly wrapped in GO gauze by the electrostatic interaction (Figure 1C and Figure S1C). In XRD pattern of FeCo PBA/Ni(OH)2/GO, there is an extra peak at around 10.6 °, which is consistent with C (001) diffraction peak of thin GO layer (Figure S2B).


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Figure 1. TEM images of (A) FeCo PBA, (B) FeCo PBA/Ni(OH)2, (C) FeCo PBA/Ni(OH)2/GO, and corresponding phosphidation products (D) Fe2P/CoP, (E) Fe2P/CoP /Ni5P4, (F) Fe2P/CoP /Ni5P4/RGO; (G) HRTEM image, (H) SAED pattern, and (I) elemental mapping images of the Fe2P/CoP /Ni5P4/RGO.

After low-temperature phosphidation, a series of corresponding metal phosphides are obtained. FeCo bimetallic phosphide is derived from FeCo PBA, it still remains cubic profile, but with loose structure (Figure 1D). The XRD pattern reveals that it is composed of Fe2P (JCPDS No. 27-1171) and CoP (JCPDS No. 29-0497) (Figure 2). FeCoNi ternary TMP is transformed from FeCo PBA/Ni(OH)2, Ni phosphide as a shell encapsulates the Fe2P and CoP particles, which is demonstrated by a distinct boundary in Figure 1E. FeCo PBA/Ni(OH)2/GO converts to Fe2P/CoP/Ni5P4/RGO, their morphologies are similar, just abundant pores are in Fe2P/CoP/Ni5P4/RGO (Figure 1F). In XRD characterizations, a lot of new peaks appear in comparison to Fe2P/CoP, which can be assigned to Ni5P4 (JCPDS No.



18-0883) (Figure 2). In addition, a broad bulge located at 20 ~ 35 ° maybe come from the layer distance of graphite carbon, corresponding to the C (002) plane. In Figure 1G, the high-resolution transmission electron microscopy (HRTEM) image of Fe2P/CoP/Ni5P4/RGO shows three sets of lattice fringe are 0.247 nm, 0.207 nm, and 0.272 nm, which are corresponded to the CoP (111) plane, Ni5P4 (212) plane and (004) plane, respectively. The diffraction concentric rings in selected-area electron diffraction (SAED) pattern are assigned to the (004) and (006) planes of Ni5P4 and the (111) and (301) planes of CoP (Figure 1H). The elemental mapping images indicate the uniform distribution and correspondence of Fe, Co, Ni, P, C elements in Fe2P/CoP/Ni5P4/RGO. Specially, Ni element mainly locate on the outside of the cube, which is consistent well of the Ni(OH)2 deposited on the surface of FeCo PBA (Figure 1I).

Figure 2. XRD patterns of Fe2P/CoP, Fe2P/CoP/Ni5P4/RGO, standard Fe2P (JCPDS No. 27-1171), CoP (JCPDS No. 29-0497), and Ni5P4 (JCPDS No. 18-0883).

The Raman spectra of FeCo PBA/Ni(OH)2/GO precursor and derived Fe2P/CoP/Ni5P4/RGO both show a significant D band and G band of carbon (Figure S3). Usually, the ratio of ID and IG band intensity is used to indicate the disorder or defect degree of carbon material.34-36 The ID/IG of Fe2P/CoP/Ni5P4/RGO is 0.86, smaller than that of FeCo PBA/Ni(OH)2/GO (1.02), suggesting that the success transformation from GO to RGO and the Fe2P/CoP/Ni5P4/RGO has a lower defect degree and higher conductivity. In addition, compared to the G band of FeCo PBA/Ni(OH)2/GO located at 1588.9 cm-1, the G band of Fe2P/CoP/Ni5P4/RGO shifts


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to 1591.5 cm-1, suggesting the charge transfer from RGO to metal phosphides.37-38 Weak and broad G and D bands are observed in Fe2P/CoP/Ni5P4. That is because the PBA precursor has CN- group maybe transform to carbon during the phosphidation.31, 39

After combining with RGO, the BET surface area of Fe2P/CoP/Ni5P4 becomes

obviously increased from 31.67 to 69.20 m2/g (Figure S4), confirming that the Fe2P/CoP/Ni5P4/RGO has a larger surface area and better ability of mass transfer. The surface compositions of Fe2P/CoP/Ni5P4 and Fe2P/CoP/Ni5P4/RGO were analyzed by X-ray photoelectron spectroscopy (XPS). In the Co 2p region, the Fe2P/CoP/Ni5P4/RGO exhibits two peaks at 778.7 eV and 793.6 eV belonged to Co 2p3/2 and Co 2p1/2 signals of Co species from CoP. The other two peaks at 781.9 eV and 797.4 eV are assigned to Co 2p3/2 and Co 2p1/2 signals of cationic Co species from the superficial oxidation of CoP. Another two satellite peaks at 785.5 eV and 803.1 eV are also observed (Figure 3A).28, 38 In the Ni 2p region of Fe2P/CoP/Ni5P4/RGO, two peaks at 853.3 eV and 870.6 eV are corresponded to Ni 2p3/2 and Ni 2p1/2 signals of Ni species from Ni5P4, the other two peaks at 856.3 eV and 874.4 eV are related to the surface-oxidized Ni species, two weak satellite peaks are accompanied appeared (Figure 3B).18, 40 In the Fe 2p region of Fe2P/CoP/Ni5P4/RGO, two peaks at 707.5 eV and 720.4 eV are assigned to Fe 2p3/2 and Fe 2p1/2 signals of Fe species from Fe2P. The other two peaks at 711.7 eV and 724.3 eV suggest the occurrence of the superficial oxidation of Fe2P, which are also accompanied with two satellite peaks (Figure 3C).17,

22

In the P 2p region, the Fe2P/CoP/Ni5P4/RGO show two peaks at

129.2 and 130.1 eV attributed to P 2p3/2 and P 2p1/2 signals from metal phosphides. Another one peak at 133.6 eV is from oxidized phosphate species due to the exposure to air (Figure 3D).41 It is worth noting that the binding energies of Co 2p3/2 (778.7 eV), Ni 2p3/2 (853.3 eV), and Fe 2p3/2 (707.5 eV) are positively shifted compared to the metallic Co (778.2 eV), Ni (852.6 eV), and Fe (706.8 eV), while the binding energy of P 2p3/2 (129.2 eV) is negatively shifted in comparison with the elemental P (130.2 eV).39,

42-43

These information indicate the Co, Ni and Fe are partially

positively charged and the P has a partial negative charge in Fe2P/CoP/Ni5P4/RGO, they can act as hydride-acceptor and proton-acceptor centers, respectively, which is



favorable for HER.39, 43 Additionally, the metal species with high valence state can promote OH- adsorption in OER process, which is beneficial to OER activity.44-45 Besides, the Co 2p3/2 (778.7 eV), Ni 2p3/2 (853.3 eV), Fe 2p3/2 (707.5 eV), and P 2p3/2 (129.2 eV) binding energies of Fe2P/CoP/Ni5P4/RGO are negatively shifted 0.2 eV, 0.3 eV, 0.2 eV, and 0.2 eV, respectively, in comparison to those of Fe2P/CoP/Ni5P4. This implies the existence of interaction between RGO and metal phosphide and the charge transfer from RGO to metal phosphide.38 In addition, the ratio of metal-P species to oxidized metal species in Fe2P/CoP/Ni5P4/RGO are all larger than that in Fe2P/CoP/Ni5P4, indicating the RGO can protect metal phosphides from oxidation.

Figure 3. (A) Co 2p, (B) Ni 2p, (C) Fe 2p, and (D) P 2p XPS spectra of Fe2P/CoP/Ni5P4/RGO and Fe2P/CoP/Ni5P4.

The electrocatalytic HER and OER activities of different electrocatalysts were evaluated by linear sweep voltammetry (LSV) in 1M KOH solution. The commercial Pt/C shows the best performance for HER with an onset potential almost close to zero and η10 (the overpotential at 10 mA/cm2) of 0.031 V. Fe2P/CoP/Ni5P4 shows better HER performance than that of Fe2P/CoP, Fe2P, CoP, and Fe2P-CoP mixture (Figure


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4A, S5A). To obtain the optimal catalytic activity, three kinds of Fe2P/CoP/Ni5P4 with different composition ratios were synthesized and tested. Among the three catalyst, the Fe2P/CoP/Ni5P4 with the Fe: Co: Ni ratio of 13.86 : 21.90 : 19.52 has the best catalytic activity (Figure S6A, Table S1). Compared to the Fe2P/CoP/Ni5P4, the Fe2P/CoP/Ni5P4/RGO exhibits the higher current density at the same potential and the lower overpotential at the same current density in HER test (Figure 4A). The η10 and η100 of Fe2P/CoP/Ni5P4/RGO are 0.057 V and 0.135 V smaller than those of Fe2P/CoP/Ni5P4 (η10: 0.083 V, η100: 0.170 V) and Fe2P/CoP (η10: 0.109 V, η100: 0.221 V). The HER kinetics were assessed by Tafel plots. The commercial Pt/C has the smallest Tafel slope (27 mV/dec). The Tafel slopes of other catalysts follow the order: Fe2P/CoP (64 mV/dec) ＞ Fe2P/CoP/Ni5P4 (55 mV/dec) ＞ Fe2P/CoP/Ni5P4/RGO (47 mV/dec), suggesting ternary metal phosphides and combined RGO can improve the HER kinetics and the Fe2P/CoP/Ni5P4/RGO produces H2 through the Volmer − Heyrovsky mechanism (Figure 4B).42 The HER performance of each catalyst under acidic condition were also tested, and the Fe2P/CoP/Ni5P4/RGO exhibits the better performance than that of Fe2P/CoP and Fe2P/CoP/Ni5P4 (Figure S7). For OER activity, Fe2P/CoP/Ni5P4 shows better performance than that of Fe2P/CoP/Ni5P4-I, Fe2P/CoP/Ni5P4-II, Fe2P/CoP, Fe2P, CoP, and Fe2P-CoP mixture (Figure 4B, S5B, S6B), and Fe2P/CoP/Ni5P4/RGO still displays the best performance. The onset potential (defined the potential at 1 mA/cm2) of Fe2P/CoP/Ni5P4/RGO is 1.406 V (corresponded to 176 mV overpotential), lower than those of Fe2P/CoP/Ni5P4 (1.412 V, corresponded to 182 mV overpotential), Fe2P/CoP (1.435 V, corresponded to 205 mV overpotential), and commercial RuO2 (1.461 V, corresponded to 231 mV overpotential). At the same current density, the Fe2P/CoP/Ni5P4/RGO always shows the smallest overpotential, indicating the best activity. For instance, the η10 and η100 of it are 232 mV and 361 mV, while the η10 and η100 are 267 mV and 404 mV for Fe2P/CoP/Ni5P4, 289 mV and 430 mV for Fe2P/CoP, and 318 mV and 486 mV for RuO2 (Figure 4C). The Fe2P/CoP/Ni5P4/RGO has the fastest OER kinetics with the smallest Tafel slope (47 mV/dec) among these catalysts, while the tafel slopes of Fe2P/CoP/Ni5P4, Fe2P/CoP, and RuO2 are 71 mV/dec, 80 mV/dec, and 83 mV/dec,



respectively (Figure 4D).

Figure 4. (A) Polarization curves for HER and (B) corresponding Tafel plots of different samples; (C) polarization curves for OER and (D) corresponding Tafel plots of different samples.

The electrochemical active surface areas (ECSAs) of these samples were compared by measuring the double-layer capacitances (Cdl) in nonfaradic reaction potential range. The Fe2P/CoP/Ni5P4/RGO has the largest Cdl (25.4 mF/cm2), which is the 1.67 and 2.06 times as much as Fe2P/CoP/Ni5P4 (15.2 mF/cm2) and Fe2P/CoP (12.3 mF/cm2) (Figure 5A). It is suggested that Fe2P/CoP/Ni5P4/RGO exhibits more active sites for electrocatalytic HER and OER. In order to compare the catalytic activity of materials under the same standard, the electrocatalytic HER and OER LSV curves normalized by ECSA and BET surface area are also performed (Figure S8, S9), in which the Fe2P/CoP/Ni5P4/RGO shows the best intrinsic catalytic activity. Additionally, the Fe2P/CoP/Ni5P4/RGO displays fastest charge transfer ability and is favorable for electrocatalytic kinetics process, which is reflected by the smallest charge transfer resistance (Rct) in electrochemical impedance spectroscopy (EIS) (Figure 5B). The synergistic effect among ternary TMPs and the introduction of


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graphene not only increase the specific surface area and active sites of the composite benefiting the mass transfer and gas release, but also accelerate the charge transport process and improve the electrocatalytic activity. To evaluate the stability of the catalyst, a long term HER and OER tests were conducted at 10 mA/cm2 and η10, respectively (Figure 5C-F), it can be seen that Fe2P/CoP/Ni5P4/RGO exhibits nearly unchanged current density and potential during 24 h test. Considering the outstanding HER and OER performance of Fe2P/CoP/Ni5P4/RGO (Table S2, S3), the Fe2P/CoP/Ni5P4/RGO was loaded on the carbon paper to work as both anode and cathode for overall water splitting. It can produce 10 mA/cm2 current density at a cell voltage of 1.56 V, which is superior to other phosphides catalysts (Figure 6, Table S4).

Figure 5. (A) Scan rate dependence of the current density at 0.7 V and (B) Nyquist plots for different samples, the inset is the equivalent circuit diagram; (C-D) Chronoamperometric analysis at -0.057 V and 1.462 V and (E-F) chronopotentiometric analysis at -10 mA/cm2 and 10 mA/cm2 for HER and OER stability tests of Fe2P/CoP/Ni5P4/RGO.

Besides, the morphology and structure of Fe2P/CoP/Ni5P4/RGO after HER and



OER test were also investigated. The Fe2P/CoP/Ni5P4/RGO still remains the original cubic morphology except a little aggregation (Figure S10). In XRD pattern, the positions of the main peaks are unchanged, only the intensities of them are decreased (Figure S11). The surface structure and composition were analyzed by XPS. After OER, the XPS peaks assigned to M-P species in Ni 2p, Co 2p, and Fe 2p spectrum are all disappeared, only left the M&+ species signals. In P 2p spectrum, only one peak exists which is ascribed to the P-O species (Figure S12). That indicates the corresponding metal oxides/oxyhydroxides are generated during the OER process and beneficial to electrocatalytic activity, which is consistent with previous reports.42, 44 After HER, the peaks ascribed from M-P species are still existed but with significant decrease, while the peaks derived from M&+ species are increased. That suggests metal phosphides are also oxidized in HER process, but the oxidation degree is slight due to the protection of RGO.28, 38

Figure 6. Polarization curve of Fe2P/CoP/Ni5P4/RGO in two-electrode system, the inset is the photo of the Fe2P/CoP/Ni5P4/RGO two-electrode system for water splitting.

Generally, the above results elucidate the excellent catalytic performance of Fe2P/CoP/Ni5P4/RGO is mainly attributed to the three following aspects: 1) The porous property of metal phosphide. It is come from the instinct uniform and abundant pore structure of PBA precursor and the decomposition of organic ligand during phosphidation process. The porous characteristic exposes more active sites and facilitates electrolyte diffusion and gas release. Of course, RGO introducing also enhances this aspect due to its large surface area.46 2) The good conductivity and stability of RGO.47 It connects the isolated TMP together, accelerates the charge


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transfer process and protects the inner metal phosphides from collapsing during phosphidation and electrocatalytic process. 3) The synergistic effect among ternary metal phosphides and between them and RGO. It effectively controls the electronic structure of them and promotes the catalytic activity that can be seen from the XPS and Raman analyses. Conclusion In summary, we designed and synthesized ternary metal phosphides encapsulated in RGO for effectively electrocatalytic HER and OER. Thanks to the outstanding mass transfer ability and charge transport property, the Fe2P/CoP/Ni5P4/RGO showed good activity and stability in electrocatalytic water splitting with η10: 57 mV, 232 mV, and η100: 135 mV, 361 mV for HER and OER, respectively, and 1.56 V cell voltage for generating 10 mA/cm2 current density. This work provides a synthetic strategy for preparing ternary metal phosphides and RGO composites that maybe generalized to other MOF-derived compounds and carbon-based material composites and in other advanced energy conversion fields. Experimental Section Materials Cobalt(II) chloride hexahydrate (CoCl2·6H2O), trisodium citrate dehydrate (Na3C6H5O7·2H2O), tetrahydrate

potassium

ferricyanide

(Ni(CH3COO)2·4H2O),

tris

(K3[Fe(CN)6]),

(C4H11NO3),

nickel(II)

sodium

acetate

hypophosphite

(NaH2PO2) were purchased from Aladdin. Polyvinyl pyrrolidone (PVP, Mw=40000), poly diallyl dimethyl ammonium chloride (PDDA, 35 wt %) were purchased from Sigma-Aldrich. Graphene oxide (GO) was buy from Nanjing xianfeng nanomaterials technology co., LTD. Synthesis of FeCo PBA, FeCo PBA/Ni(OH)2, FeCo PBA/Ni(OH)2/GO, Fe2P/CoP, Fe2P/CoP/Ni5P4, and Fe2P/CoP/Ni5P4/RGO FeCo PBA: 0.143 g CoCl2·6H2O and 0.387 g Na3C6H5O7·2H2O were dissolved in 20 ml deionized water and formed solution A. 0.132 g K3[Fe(CN)6] was dissolved



in 20 ml deionized water and formed solution B. Mixed the solution A and B together and aged for 24 h. Then, collected the precipitate, washed it with ethanol and deionized water for at least three times, and dried it at 50℃ for 12 h. FeCo PBA/Ni(OH)2: 1.2 g PVP was dissolved in the mixed solution of 40 ml ethanol and 40 ml deionized water. Added 0.086 g Ni(CH3COO)2·4H2O and 0.1g FeCo PBA in to the mixed solution, then carried out the ultrasonic dispersion. The mixture was heated at 80 ℃ in the atmosphere of ammonia for 12 h. The obtained precipitate was centrifuged and washed three times. FeCo PBA/Ni(OH)2/GO: 0.1 g FeCo PBA/Ni(OH)2 was dispersed in 30 ml deionized water and formed solution A. 1.07 g PDDA, 0.18 g tris and 0.09 g NaCl were dissolved in 30 ml deionized water and formed solution B. Mixed solution A and B together, collected the precipitate and washed it thoroughly to remove the excessive

PDDA. Then, the positively charged FeCo PBA/Ni(OH)2 was dispersed

in 20 ml deionized water, and mixed with GO solution (20 ml, 0.5 mg/ml). The product was collected by centrifugation and freeze drying. Fe2P/CoP, Fe2P/CoP/Ni5P4, and Fe2P/CoP/Ni5P4/RGO: Put the precursor (FeCo PBA, FeCo PBA/Ni(OH)2, FeCo PBA/Ni(OH)2/GO) and NaH2PO2 at both ends of tube furnace. Note: NaH2PO2 was placed upstream of the airstream. Heated the tube furnace to 300℃ by the rate of 3℃/min, then kept it at 300℃ for 2 h in Argon. After cooling down to the room temperature, the Fe2P/CoP, Fe2P/CoP/Ni5P4, and Fe2P/CoP/Ni5P4/RGO were obtained. Electrochemical Measurements A three-electrode system on CHI760D electrochemical workstation (Shanghai, Chenhua Co., China) was used. Glassy carbon electrode (GCE, diameter = 5 mm), saturated Ag/AgCl and graphite rod were used as the working, reference and counter electrodes, respectively. 2 mg catalyst was dispersed in 1 ml ethanol with 10 ul Nafion solution (5 wt%, Du pont) and ultrasonicated to obtain homogeneous ink. Then, 20 ul of the ink was dropped onto the surface of GCE and dried in air. The electrochemical tests were conducted in a N2-saturated 1.0 M KOH electrolyte. After several potential sweeps until stable the data were recorded and without iR


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compensation. The polarization curves were swept by the rate of 5 mV/s. The chronoptentiometry and chronoamperometry method was conducted for 24 h to investigate the stability. The EIS measurements were performed with frequency range of 0.01 to 105 Hz, at open circuit potential. The electrochemical surface area (ECSA) was estimated using the capacitance (Cdl), as: ECSA = Cdl/Cs, Cs is 40 µF/cm2 per cm2.38, 48-50 For overall water splitting, the electrocatalysts on the carbon paper were used as cathode and anode in a two-electrode system. The final potentials were all converted to the reversible hydrogen electrode (RHE) according to ERHE =EAg/AgCl + 0.058pH + 0.1988.51-52 Author Information Corresponding Author *E-mail: [email protected]; [email protected] Notes There are no conflicts to declare. Associated Content Electronic Supplementary Material The Supporting Information is available free of charge on the ACS Publications website. SEM

images,

XRD

patterns,

XPS

spectra,

Raman

spectra,

nitrogen

adsorption/desorption isotherms, tables of electrocatalytic performance comparison. Acknowledgements The work is supported by National Natural Science Foundation of China (61601001， 21871001, 21631001), the Anhui province key research and development program project (201904d07020001), and the Anhui Provincial Natural Science Foundation (1708085QB37). References (1) Qiu, Z.; Tai, C.-W.; Niklasson, G. A.; Edvinsson, T. Direct observation of active catalyst



surface phases and the effect of dynamic self-optimization in NiFe-layered double hydroxides for alkaline water splitting. Energy Environ. Sci. 2019, 12, 572-581. (2) Chen, P. Z.; Tong, Y.; Wu, C. Z.; Xie, Y. Surface/Interfacial Engineering of Inorganic Low-Dimensional Electrode Materials for Electrocatalysis. Acc. Chem. Res. 2018, 51, 2857-2866. (3) Xiong, B. Y.; Chen, L. S.; Shi, J. L. Anion-Containing Noble-Metal-Free Bifunctional Electrocatalysts for Overall Water Splitting. ACS Catal. 2018, 8, 3688-3707. (4) He, L. H.; Liu, J. M.; Liu, Y. K.; Cui, B. B.; Hu, B.; Wang, M. H.; Tian, K.; Song, Y. P.; Wu, S. D.; Zhang, Z. H.; Peng, Z. K.; Du, M. Titanium dioxide encapsulated carbon-nitride nanosheets derived from MXene and melamine-cyanuric acid composite as a multifunctional electrocatalyst for hydrogen and oxygen evolution reaction and oxygen reduction reaction. Appl. Catal., B 2019, 248, 366-379. (5) Huang, S. C.; Meng, Y. Y.; Cao, Y. F.; He, S. M.; Li, X. H.; Tong, S. F.; Wu, M. M. N-, O- and P-doped hollow carbons: Metal-free bifunctional electrocatalysts for hydrogen evolution and oxygen reduction reactions. Appl. Catal., B 2019, 248, 239-248. (6) Pu, Z. H.; Amiinu, I. S.; Kou, Z. K.; Li, W. Q.; Mu, S. C. RuP2-Based Catalysts with Platinum-like Activity and Higher Durability for the Hydrogen Evolution Reaction at All pH Values. Angew. Chem. Int. Ed. 2017, 56, 11559-11564. (7) Ling, T.; Zhang, T.; Ge, B.; Han, L.; Zheng, L.; Lin, F.; Xu, Z.; Hu, W.-B.; Du, X.-W.; Davey, K.; Qiao, S.-Z. Well-Dispersed Nickel- and Zinc-Tailored Electronic Structure of a Transition Metal Oxide for Highly Active Alkaline Hydrogen Evolution Reaction. Adv. Mater. 2019, 31 (16), 1807771. (8) Han, L.; Yu, X.-Y.; Lou, X. W. Formation of Prussian-Blue-Analog Nanocages via a Direct Etching Method and their Conversion into Ni–Co-Mixed Oxide for Enhanced Oxygen Evolution. Adv. Mater. 2016, 28, 4601-4605. (9) Joo, J.; Kim, T.; Lee, J.; Choi, S.-I.; Lee, K. Morphology-Controlled Metal Sulfides and Phosphides for Electrochemical Water Splitting. Adv. Mater. 2019, 31 (14), 1806682. (10)

Yu, X. Y.; Lou, X. W. Mixed Metal Sulfides for Electrochemical Energy Storage

and Conversion. Adv. Energy Mater. 2018, 8 (3), 1701592. (11)

Fang, Z.; Peng, L.; Lv, H.; Zhu, Y.; Yan, C.; Wang, S.; Kalyani, P.; Wu, X.; Yu, G.


Page 16 of 21

Page 17 of 21 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


Metallic Transition Metal Selenide Holey Nanosheets for Efficient Oxygen Evolution Electrocatalysis. ACS Nano 2017, 11, 9550-9557. (12)

Ao, K.; Dong, J.; Fan, C.; Wang, D.; Cai, Y.; Li, D.; Huang, F.; Wei, Q. Formation

of Yolk–Shelled Nickel–Cobalt Selenide Dodecahedral Nanocages from Metal–Organic Frameworks for Efficient Hydrogen and Oxygen Evolution. ACS Sustainable Chem. Eng. 2018, 6, 10952-10959. (13)

Dutta, S.; Indra, A.; Feng, Y.; Han, H.; Song, T. Promoting electrocatalytic overall

water splitting with nanohybrid of transition metal nitride-oxynitride. Appl. Catal., B 2019, 241, 521-527. (14)

Zhang, Y.; Ouyang, B.; Xu, J.; Chen, S.; Rawat, R. S.; Fan, H. J. 3D Porous

Hierarchical Nickel–Molybdenum Nitrides Synthesized by RF Plasma as Highly Active and Stable Hydrogen-Evolution-Reaction Electrocatalysts. Adv. Energy Mater. 2016, 6 (11), 1600221. (15)

Jung, E.; Park, H.-Y.; Cho, A.; Jang, J. H.; Park, H. S.; Yu, T. Aqueous-phase

synthesis of metal hydroxide nanoplates and platinum/nickel hydroxide hybrid nanostructures and their enhanced electrocatalytic properties. Appl. Catal., B 2018, 225, 238-242. (16)

Ma, Y.; Chu, J.; Li, Z.; Rakov, D.; Han, X.; Du, Y.; Song, B.; Xu, P. Homogeneous

Metal Nitrate Hydroxide Nanoarrays Grown on Nickel Foam for Efficient Electrocatalytic Oxygen Evolution. Small 2018, 14 (52), 1803783. (17)

Xi, W.; Yan, G.; Lang, Z.; Ma, Y.; Tan, H.; Zhu, H.; Wang, Y.; Li, Y.

Oxygen-Doped Nickel Iron Phosphide Nanocube Arrays Grown on Ni Foam for Oxygen Evolution Electrocatalysis. Small 2018, 14 (42), 1802204. (18)

Chu, S.; Chen, W.; Chen, G.; Huang, J.; Zhang, R.; Song, C.; Wang, X.; Li, C.;

Ostrikov, K. Holey Ni-Cu phosphide nanosheets as a highly efficient and stable electrocatalyst for hydrogen evolution. Appl. Catal., B 2019, 243, 537-545. (19)

Sun, M.; Liu, H. J.; Qu, J. H.; Li, J. H. Earth-Rich Transition Metal Phosphide for

Energy Conversion and Storage. Adv. Energy Mater. 2016, 6 (13), 1600087. (20)

Zhang, G.; Wang, G. C.; Liu, Y.; Liu, H. J.; Qu, J. H.; Li, J. H. Highly Active and

Stable Catalysts of Phytic Acid-Derivative Transition Metal Phosphides for Full Water Splitting. J. Am. Chem. Soc. 2016, 138, 14686-14693.



(21)

Wang, P. Y.; Pu, Z. H.; Li, Y. H.; Wu, L.; Tu, Z. K.; Jiang, M.; Kou, Z. K.; Arniinu,

I. S.; Mu, S. C. Iron-Doped Nickel Phosphide Nanosheet Arrays: An Efficient Bifunctional Electrocatalyst for Water Splitting. ACS Appl. Mater. Interfaces 2017, 9, 26001-26007. (22)

Cao, L.-M.; Hu, Y.-W.; Tang, S.-F.; Iljin, A.; Wang, J.-W.; Zhang, Z.-M.; Lu, T.-B.

Fe-CoP Electrocatalyst Derived from a Bimetallic Prussian Blue Analogue for Large-Current-Density Oxygen Evolution and Overall Water Splitting. Adv. Sci. 2018, 5 (10), 1800949. (23)

Xu, J.; Liu, T.; Li, J.; Li, B.; Liu, Y.; Zhang, B.; Xiong, D.; Amorim, I.; Li, W.; Liu,

L. Boosting the hydrogen evolution performance of ruthenium clusters through synergistic coupling with cobalt phosphide. Energy Environ. Sci. 2018, 11, 1819-1827. (24)

Du, H. T.; Kong, R. M.; Guo, X. X.; Qu, F. L.; Li, J. H. Recent progress in

transition metal phosphides with enhanced electrocatalysis for hydrogen evolution. Nanoscale 2018, 10, 21617-21624. (25)

Li, S. P.; Zhang, G.; Tu, X. M.; Li, J. H. Polycrystalline CoP/CoP2 Structures for

Efficient Full Water Splitting. Chemelectrochem 2018, 5, 701-707. (26)

Zhang, C. T.; Pu, Z. H.; Amiinu, I. S.; Zhao, Y. F.; Zhu, J. W.; Tang, Y. F.; Mu, S.

C. Co2P quantum dot embedded N, P dual-doped carbon self-supported electrodes with flexible and binder-free properties for efficient hydrogen evolution reactions. Nanoscale 2018, 10, 2902-2907. (27)

Pu, Z. H.; Zhao, J. H.; Amiinu, I. S.; Li, W. Q.; Wang, M.; He, D. P.; Mu, S. C. A

universal synthesis strategy for P-rich noble metal diphosphide-based electrocatalysts for the hydrogen evolution reaction. Energy Environ. Sci. 2019, 12, 952-957. (28)

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. (29)

He, P.; Yu, X.-Y.; Lou, X. W. Carbon-Incorporated Nickel–Cobalt Mixed Metal

Phosphide Nanoboxes with Enhanced Electrocatalytic Activity for Oxygen Evolution. Angew. Chem. Int. Ed. 2017, 56, 3897-3900. (30)

Xia, W.; Mahmood, A.; Zou, R.; Xu, Q. Metal–organic frameworks and their


Page 18 of 21

Page 19 of 21 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


derived nanostructures for electrochemical energy storage and conversion. Energy Environ. Sci. 2015, 8, 1837-1866. (31)

Han, L.; Yu, T.; Lei, W.; Liu, W.; Feng, K.; Ding, Y.; Jiang, G.; Xu, P.; Chen, Z.

Nitrogen-doped carbon nanocones encapsulating with nickel–cobalt mixed phosphides for enhanced hydrogen evolution reaction. J. Mater. Chem. A 2017, 5, 16568-16572. (32)

Weng, B.; Grice, C. R.; Meng, W.; Guan, L.; Xu, F.; Yu, Y.; Wang, C.; Zhao, D.;

Yan, Y. Metal–Organic Framework-Derived CoWP@C Composite Nanowire Electrocatalyst for Efficient Water Splitting. ACS Energy Lett. 2018, 3, 1434-1442. (33)

Wang, R.; Dong, X.-Y.; Du, J.; Zhao, J.-Y.; Zang, S.-Q. MOF-Derived Bifunctional

Cu3P Nanoparticles Coated by a N, P-Codoped Carbon Shell for Hydrogen Evolution and Oxygen Reduction. Adv. Mater. 2018, 30 (6), 1703711. (34)

Patel, K. D.; Singh, R. K.; Kim, H. W. Carbon-based nanomaterials as an emerging

platform for theranostics. Mater. Horiz. 2019, 6, 434-469. (35)

Ramakrishnan, S.; Karuppannan, M.; Vinothkannan, M.; Ramachandran, K.; Kwon,

O. J.; Yoo, D. J. Ultrafine Pt Nanoparticles Stabilized by MoS2/N-Doped Reduced Graphene Oxide as a Durable Electrocatalyst for Alcohol Oxidation and Oxygen Reduction Reactions. ACS Appl. Mater. Interfaces 2019, 11, 12504-12515. (36)

Xie, J.; Li, B. Q.; Peng, H. J.; Song, Y. W.; Li, J. X.; Zhang, Z. W.; Zhang, Q. From

Supramolecular Species to Self-Templated Porous Carbon and Metal-Doped Carbon for Oxygen Reduction Reaction Catalysts. Angew. Chem. Int. Ed. 2019, 58, 4963-4967. (37)

Du, Y.; Tao, Z.; Guan, J.; Sun, Z.; Zeng, W.; Wen, P.; Ni, K.; Ye, J.; Yang, S.; Du,

P.; Zhu, Y. Microwave-assisted synthesis of hematite/activated graphene composites with superior performance for photocatalytic reduction of Cr(vi). RSC Adv. 2015, 5, 81438-81444. (38)

Tian, J.; Chen, J.; Liu, J.; Tian, Q.; Chen, P. Graphene quantum dot engineered

nickel-cobalt phosphide as highly efficient bifunctional catalyst for overall water splitting. Nano Energy 2018, 48, 284-291. (39)

Zhu, X.; Liu, M.; Liu, Y.; Chen, R.; Nie, Z.; Li, J.; Yao, S. Carbon-coated hollow

mesoporous FeP microcubes: an efficient and stable electrocatalyst for hydrogen evolution. J. Mater. Chem. A 2016, 4, 8974-8977. (40)

Zhang, L.; Chang, C.; Hsu, C.-W.; Chang, C.-W.; Lu, S.-Y. Hollow nanocubes



composed of well-dispersed mixed metal-rich phosphides in N-doped carbon as highly efficient and durable electrocatalysts for the oxygen evolution reaction at high current densities. J. Mater. Chem. A 2017, 5, 19656-19663. (41)

Xuan, C.; Wang, J.; Xia, W.; Peng, Z.; Wu, Z.; Lei, W.; Xia, K.; Xin, H. L.; Wang,

D. Porous Structured Ni–Fe–P Nanocubes Derived from a Prussian Blue Analogue as an Electrocatalyst for Efficient Overall Water Splitting. ACS Appl. Mater. Interfaces 2017, 9, 26134-26142. (42)

Ray, C.; Lee, S. C.; Jin, B.; Kundu, A.; Park, J. H.; Jun, S. C. Stacked Porous

Iron-Doped Nickel Cobalt Phosphide Nanoparticle: An Efficient and Stable Water Splitting Electrocatalyst. ACS Sustainable Chem. Eng. 2018, 6, 6146-6156. (43)

Jia, H.; Jiang, R.; Lu, W.; Ruan, Q.; Wang, J.; Yu, J. C. Aerosol-spray metal

phosphide microspheres with bifunctional electrocatalytic properties for water splitting. J. Mater. Chem. A 2018, 6, 4783-4792. (44)

Zhao, Y.; Fan, G.; Yang, L.; Lin, Y.; Li, F. Assembling Ni–Co phosphides/carbon

hollow nanocages and nanosheets with carbon nanotubes into a hierarchical necklace-like nanohybrid for electrocatalytic oxygen evolution reaction. Nanoscale 2018, 10, 13555-13564. (45)

Xiao, X.; He, C.-T.; Zhao, S.; Li, J.; Lin, W.; Yuan, Z.; Zhang, Q.; Wang, S.; Dai,

L.; Yu, D. A general approach to cobalt-based homobimetallic phosphide ultrathin nanosheets for highly efficient oxygen evolution in alkaline media. Energy Environ. Sci. 2017, 10, 893-899. (46)

He, D. P.; Tang, H. L.; Kou, Z. K.; Pan, M.; Sun, X. L.; Zhang, J. J.; Mu, S. C.

Engineered Graphene Materials: Synthesis and Applications for Polymer Electrolyte Membrane Fuel Cells. Adv. Mater. 2017, 29 (20), 1601741. (47)

Kou, Z. K.; Meng, T.; Guo, B. B.; Amiinu, I. S.; Li, W. Q.; Zhang, J.; Mu, S. C. A

Generic Conversion Strategy: From 2D Metal Carbides (MxCy) to M-Self-Doped Graphene toward High-Efficiency Energy Applications. Adv. Funct. Mater. 2017, 27 (8), 1604904. (48)

Wang, X.; Zhou, H.; Zhang, D.; Pi, M.; Feng, J.; Chen, S. Mn-doped NiP2

nanosheets as an efficient electrocatalyst for enhanced hydrogen evolution reaction at all pH values. J. Power Sources 2018, 387, 1-8. (49)

Sumboja, A.; An, T.; Goh, H. Y.; Lübke, M.; Howard, D. P.; Xu, Y.; Handoko, A.


Page 20 of 21

Page 21 of 21 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


D.; Zong, Y.; Liu, Z. One-Step Facile Synthesis of Cobalt Phosphides for Hydrogen Evolution Reaction Catalysts in Acidic and Alkaline Medium. ACS Appl. Mater. Interfaces 2018, 10, 15673-15680. (50)

Chen, Y.-Y.; Zhang, Y.; Jiang, W.-J.; Zhang, X.; Dai, Z.; Wan, L.-J.; Hu, J.-S.

Pomegranate-like N,P-Doped Mo2C@C Nanospheres as Highly Active Electrocatalysts for Alkaline Hydrogen Evolution. ACS Nano 2016, 10, 8851-8860. (51)

Zhou, X.; Liu, Y.; Ju, H.; Pan, B.; Zhu, J.; Ding, T.; Wang, C.; Yang, Q. Design and

Epitaxial Growth of MoSe2–NiSe Vertical Heteronanostructures with Electronic Modulation for Enhanced Hydrogen Evolution Reaction. Chem. Mater. 2016, 28, 1838-1846. (52)

Du, Y. X.; Ni, K.; Zhai, Q. X.; Yun, Y. P.; Xu, Y. J.; Sheng, H. T.; Zhu, Y. W.; Zhu,

M. Z. Facile air oxidative induced dealloying of hierarchical branched PtCu nanodendrites with enhanced activity for hydrogen evolution. Appl. Catal., A 2018, 557, 72-78.

Table of Content

Due to fast mass transfer and charge transport, the Fe2P/CoP/Ni5P4/RGO shows excellent activity in electrocatalytic water splitting.


Ni(OH)2 Derived Porous

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