Hierarchical NiMo Phosphide Nanosheets Strongly Anchored on

Subscriber access provided by Kaohsiung Medical University

Energy, Environmental, and Catalysis Applications

Hierarchical NiMo Phosphide Nanosheets Strongly Anchored on Carbon Nanotubes as Robust Electrocatalysts for Overall Water Splitting Hui Xu, Jingjing Wei, Ke Zhang, Yukihide Shiraishi, and Yukou Du ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b10314 • Publication Date (Web): 06 Aug 2018 Downloaded from http://pubs.acs.org on August 6, 2018

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

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

Page 1 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Hierarchical NiMo Phosphide Nanosheets Strongly Anchored on Carbon Nanotubes as Robust Electrocatalysts for Overall Water Splitting Hui Xu†§, Jingjing Wei†§, Ke Zhang‡,Yukihide Shiraishi∆, and Yukou Du*†∆ †

College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, P.R. China

‡

The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan

∆

Tokyo University of Science Yamaguchi, Sanyo-Onoda-shi, Yamaguchi 756-0884, Japan * Corresponding author: Tel: 86-512-65880089, Fax: 86-512-65880089; E-mail: [email protected] (Y. Du)

ABSTRACT Although a great achievement has been made in the fields of electrochemistry, the exploration of high-efficiency catalysts for the generation of hydrogen and oxygen via overall water splitting is still a grand challenge. We herein report the successful construction of a new class of hierarchical catalysts with defect-enriched nickel-molybdenum phosphide nanosheets anchored on the surface of carbon nanotubes for efficient water splitting. Via the construction of hierarchical nanostructure, more efficient electron mobility and mass transfer occurrence was achieved, which ends up in a substantial enhancement of electrocatalytic 1 ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

performances. Interestingly, the overpotentials of only 255 and 135 mV are required for the optimized Ni1Mo1P NSs@MCNTs to afford a current of 10 mA cm−2 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. More significantly, the introduction of molybdenum and phosphorus is also significant for exposing surface active sites and modifying the bonding energy between hydrogen and metals, all of these advantages have endowed Ni1Mo1P NSs@MCNTs // Ni1Mo1P NSs@MCNTs couple to display highly efficient water electrocatalysis property with a relatively low overall potential of 1.601 V at 10 mA cm−2, shedding bright light for large-scale overall water electrocatalysis. KEYWORDS: Nickel-molybdenum phosphide; Nanosheets; Overall water splitting; Electrocatalysis; High performance 1. INTRODUCTION Regarding the continued energy consumption and associated environmental issues, the development and exploration of renewable and clean energy sources have spurred immense research enthusiasms.1-3 As a promising energy carrier, hydrogen has been generally considered as a desirable alternative fuel due to its high efficiency, renewability, and cleanliness.4-7 For sustainable hydrogen generation, electrochemcial water splitting has been extensively known as a highly efficient and continuable route for producing green hydrogen energy. 8-10 Currently, Pt-based nanomaterials and Ir/Ru-based oxides are generally considered as the most popular catalysts for HER and OER, respectively.11-12 Unfortunately, the skyrocketing high cost, rare storage, and unsatisfactory 2 ACS Paragon Plus Environment

Page 2 of 33

Page 3 of 33 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


performance have badly impeded their practical applications.

13

In addition, it is also

of vital challenge to fabricate bifunctional HER and OER catalysts in an integrated water-splitting cell because of their limited activity and durability.14-16 For addressing these issues, the design and development of high-performance and cost-efficient electrocatalysts are urgently sought. Accordingly, intensive endeavors have been devoted to fulfilling great improvement of electrocatalytic efficiencies in the field of overall water splitting. At present, some cost-effective first-row (3d) transition-metal electrocatalysts, such as cobalt (Co) and nickel (Ni)-based materials have been particularly

studied

because

of

their

high

activity, earth-abundance,

environmental-benign, which thus show great promising for water electrolysis.

and 17-19

Regardless of these favorable terms, achieving cost-efficient electrocatalysts for overall water splitting is far from our expectations. In general, the water electrolysis performances can be promoted via many approaches.20 On one hand, in-situ growing the two-dimensional (2D) active nanomaterials on conductive materials (such as multilayer carbon nanotubes (MCNTs)) is a suitable choice for enhancing conductivity, providing more surface active sites, as well as promoting the generation of gas bubbles.21-23 On the other hand, phosphorization is another effective route for achieving satisfied electrocatalytic activity because of the phosphorization of metal can well modify the metal-hydrogen bonding energy, affording the optimal Gibbs free energy for hydrogen evolving.24-26 Furthermore, generating bimetallic oxides or oxyphosphides catalysts is also a vital avenue to enhance their electrochemical properties because of the modified adsorption 3 ACS Paragon Plus Environment


energy of reactants.

27-29

In this regard, it would be of great significance for the

construction of cost-efficient and durable electrocatalysts for overall water splitting by integrating above methods.30-31 Motivated by above considerations, we herein created a facile one-pot hydrothermal approach to grow the 2D nickel-molybdenum phosphide nanosheets (NiMoP NSs) onto conductive MCNTs uniformly and form the hierarchical nanostructure. Remarkably, it was discovered that the doping of Mo could significantly modify their hierarchical surface to greatly increase their electrochemical surface active areas for exposing more accessible active sites for water electrolysis. As a result, the developed Ni1Mo1P NSs@MCNTs can exhibit superior OER and HER activity with extremely low overpotentials. Moreover, such NiMoP NSs@MCNTs can also display outstanding durability with limited activity variation for a long-term electrochemical test. More interestingly, the optimized Ni1Mo1P NSs@MCNTs // Ni1Mo1P NSs@MCNTs couple also show great promise toward overall water splitting, which displays the potential of only 1.601 V at 10 mA cm-2 in alkaline media, even outperforms to benchmark Ir/C // Pt/C couple, holding great potential for behaving as bifunctional electrode for large-scale overall water splitting. 2. EXPERIMETAL SECTION 2.1 Preparation of hierarchical NiMoP NSs@MCNTs The hierarchical NiMoP NSs@MCNTs is synthesized by a facile one-pot method. In a standard synthesis, 23.7 mg NiCl2·6H2O, 24.1 mg Na2MoO4·2H2O, 0.154 g 2-methylimidazole, 3 mg CNTs, and 6.4 mg NaH2PO2 were added into 5 mL 4 ACS Paragon Plus Environment

Page 4 of 33

Page 5 of 33 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


methanol under ultrasound. After sonicated for 30 min, the product was separated via centrifugation at 10000 rpm, washed with methanol, and then dispersed into the solution containing 9 mL ethylene glycol and 1 mL deionized water under ultrasound for 30 min. The mixture was then transferred to a reactor and heated from room temperature to 180 °C and maintained at 180 °C for 10 h. The products were then collected via centrifugation and washed several times with ethanol and acetone. For comparison, the other two types of Ni1Mo1.2P NSs@MCNTs and Ni1Mo0.5P NSs@MCNTs were also synthesized via the same method just tuning the amount of Na2MoO4·2H2O to 36.1 and 12.05 mg. And the NiP NPs@MCNTs were also achieved through the same method just without the addition of Na2MoO4·2H2O. 2.2 Characterizations The morphologies and compositions were characterized by a HITACHI HT7700 transmission electron microscopy (TEM) and XL30 ESEM FEG scanning electron microscope with energy dispersive X-ray (EDS) tests. The Brunauer–Emmett–Teller (BET) surface areas of the products were determined using a nitrogen adsorption analyzer (Quadrasorb-S1, Quantachrome, USA) and the pore-size distribution was estimated by the Barrett-Joyner-Halenda method. Power X-ray diffraction (PXRD) patterns were collected using an X`Pert-Pro X-ray powder diffractometer equipped with a Cu radiation source (λ = 0.15406 nm). X-ray photoelectron spectroscopy spectra (XPS) were conducted on a JEOL JPS-9010 MC spectrometer. 2.3 Electrochemical measurements All

the

electrochemical

measurements

were

conducted

5 ACS Paragon Plus Environment

in

a

CHI

760e


electrochemistry workstation. The working electrode was a glassy-carbon electrode (GCE) (diameter: 3 mm, area: 0.07 cm2 ) from the Pine Instrument. A Ag/AgCl electrode and graphite rod were used as reference and counter electrode, respectively. The GCE needs to be polished everytime before electrochemical measurements. The polarization curves with a iR compensation of at 95% were obtained using linear sweep voltammetry (LSV) for HER and OER in 1.0 M KOH solution at the scanning rate of 5 mV s-1. The Tafel plots were derived from the OER and HER polarization curves (1 mV s−1) and constructed by the Tafel equation. The chronopotentiometric (CP) measurements and LSV after continuous 3000 cycle cyclic voltammetry (CV) were also conducted to evaluate their durability. The electrocatalytic performances for overall water splitting was measured by employing Ni1Mo1P NSs@MCNTs as working electrodes for both OER and HER. The state-of-the-art Ir/C and Pt/C catalysts were also employed as the baseline catalysts for all the electrochemical measurements.

3. RESULTS AND DISCUSSION Experimentally, the hierarchical NiMoP NSs@MCNTs were created via a simple one-step method followed by hydrothermal process under 180 °C. As schematically shown in Scheme 1, the 2-methylimidazole modified CNTs are capable of attracting Ni2+, MoO42-, and H2PO2- ions. Then, these anchored cations were then reacted with urea and subsequently self-assembled into typical hierarchical nanosheets on the surface of CNTs.


Page 6 of 33

Page 7 of 33 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


Scheme 1. Illustration for the preparation of NiMoP NSs@MCNTs. The morphological features were studied via TEM. The unique hierarchical nanosheet morphology can be clearly observed in the TEM images (Figure 1a-d and Figure S1) with well-defined micropores, which can efficiently provide ion-diffusion routes that enable mass transfer and electron mobility.32-33 After a detailed observation of high-magnification TEM images (Figure S1d), we can clearly find that the lattice fringes in Ni1Mo1P NSs is around 0.225 nm, which is ascribed to the (103) crystalline plane of the NiMoP2, indicating the highly crystalline structure of Ni1Mo1P NSs.34 The chemical compositions of Ni1Mo1P NSs@MCNTs are examined by EDS (Figure 1e), where the molar ratio of Ni to Mo was ~ 1:1, being consistent with the feed amount. The presence of carbon signal in Figure S2 is associated with the CNTs. And the amount of P atom is 24.8%, which is also close to the feed amount of NaH2PO2 in the reaction. Moreover, the structure and composition of the as-obtained nanomaterials were also examined by XRD and XPS. As displayed in Figure 1f, the typical XRD peaks at around 25° and 40° were corresponding to the C (002) peak of



Page 8 of 33

CNTs and MoO3 peak, respectively, and the other three strong peaks were indexed to peaks of NiO (JCPDF#04-0835).35 More interestingly, the XRD diffraction peaks, particularly the one at 45°, display a slightly positive shift, indicating the successful doping of Mo into NiO, which is also another evidence for the successful synthesis of NiMoP NSs@MCNTs. In consideration of the hierarchical nanostructure of Ni1Mo1P NSs@MCNTs, we herein conducted the Brunauer–Emmett–Teller (BET) technique to deeply investigate the how the porous structure is. Figure S3 shows the N2 adsorption–desorption

isotherms

of

the

hierarchical

Ni1Mo1P

NSs@MCNTs nanostructures. As seen, the BET surface area of hierarchical Ni1Mo1P NSs@MCNTs is 266.7 m2 g-1, and the average pore size is about 9.1 nm, in accordance with the TEM observation.36


Page 9 of 33 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


Figure 1. (a-d) TEM images of hierarchical Ni1Mo1P NSs@MCNTs. (e) EDS spectrum and (f) XRD pattern of hierarchical Ni1Mo1P NSs@MCNTs. With the aim of thoroughly studying the surface chemical states on Ni1Mo1P



NSs@MCNTs, the XPS measurement was also carried out.

Page 10 of 33

37-39

Figure 2a shows the

survey scan spectrum of Ni1Mo1P NSs@MCNTs, as seen, the presence of P 2p, Mo 3d, C 1s, and Ni 2p peaks are corresponding to P, C, Mo, and Ni elements of as-prepared Ni1Mo1P [email protected] Figure 2b shows the representative spectrum of Ni 2p, as seen, the spectrum can be well fitted to two well-defined peaks arising from 2p1/2 and 2p3/2, as well as two shakeup satellites.41 With regard to Mo 3d, the two obvious peaks at around 232.4 and 235.3 eV are assigned to Mo 3d5/2 and 3d3/2, respectively, being in accordance with the chemical valence of Mo in the Ni1Mo1P NSs@MCNTs (Figure 2c). As seen in Figure 2d, the XPS spectrum of P 2p can be well deconvoluted into three peaks at around 131.8, 132.9 and 133.8 eV. The sharp peak at 131.8 eV can be assigned to partially negatively charged P (Pδ-), which is favorable for trapping the positively charged protons during the electrolysis.

42

And

the other two peaks at 132.9 and 133.8 eV are corresponding to PO43-.23, 36 The C 1s spectrum can be decomposed into two obvious peaks (Figure 2e), where the high-intensity peak at 284.6 eV is ascribed to the C-C bond with with sp2/sp3 hybrid carbon, while the other peak at 288.7 eV is assigned to O-C=O carbon groups.43 All of these characterizations have confirmed the successful construction of Ni1Mo1P NSs@MCNTs.


Page 11 of 33 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


Figure 2. XPS spectra of (a) survey scan and high-resolution XPS spectra of (b) Ni 2p, (c) Mo 3d, (d) P 2p, and (e) C 1s of Ni1Mo1P NSs@MCNTs. In order to investigate the influence of precursors concentrations on the final morphologies of NiMoP NSs@MCNTs, the other two types of nanomaterials were also prepared under the same conditions just tuning the amount of Na2MoO4·2H2O. 11 ACS Paragon Plus Environment


As seen in Figure 3a-d, both Ni1Mo0.5P NSs@MCNTs and Ni1Mo1.2P NSs@MCNTs also displayed the typical hierarchical nanostructure like that of Ni1Mo1P NSs@MCNTs, where ultrathin NiMoP NSs were uniformly anchored on the surface of CNTs, suggesting the successful construction of NiMoP NSs@MCNTs nanostructures regardless of the variations of precursor concentrations. Besides, the compositions of these two nanomaterials were also investigated thoroughly. As seen in Figure 3e and f, the atomic ratios of Ni/Mo/P were characterized to be 47.4: 24.8: 27.5 and 31.2: 36.3: 32.5, be consistent with Ni1Mo0.5P NSs@MCNTs and Ni1Mo1.2P NSs@MCNTs, respectively. All of these analyses have further confirmed the successful constructions of desirable NiMoP NSs@MCNTs nanostructure. Moreover, the NiP nanoparticles/MCNTs (NiP NPs/MCNTs) nanomaterials were also synthesized and characterized by TEM. As shown in Figure S4, the as-prepared NiP NPs were also anchored on the surface of CNTs, indicating the addition of Na2MoO4·2H2O in this reaction system was a key parameter for the successful generation of hierarchical NiMoP NSs@MCNTs nanostructure.


Page 12 of 33

Page 13 of 33 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


Figure 3. TEM images of (a and c) Ni1Mo0.5P NSs@MCNTs and (b and d) Ni1Mo1.2P NSs@MCNTs. EDS spectra of (e) Ni1Mo0.5P NSs@MCNTs and (f) Ni1Mo1.2P NSs@MCNTs.



Page 14 of 33

In consideration of the amazing hierarchical nanostructure, the newly-generated NiMoP NSs@MCNTs is thus highly expected to show outstanding electrocatalytic performances. In this regard, we first examine their electrocatalytic OER activity along with NiP NPs@MCNTs and Ir/C catalysts in 1.0 M KOH solution for comparison. Figure 4a shows the iR-compensated LSV curves of these five electrocatalysts. As observed, the Ni1Mo1P NSs@MCNTs catalyst exhibits the highest OER activity among these electrocatalysts investigated. Impressively, from Figure 4b, we can find that the optimal Ni1Mo1P NSs@MCNTs electrode requires an overpotential of 255 mV at 10 mA cm-2, while the overpotentials to afford the current density of 10 mA cm-2 are 283, 289, 319, and 325, for Ni1Mo1.2P NSs@MCNTs, Ni1Mo0.5P NSs@MCNTs, benchmarked Ir/C, and NiP NPs@MCNTs, respectively. What’s more, the OER activity of Ni1Mo1P NSs@MCNTs catalyst is also comparable to some of recently reported electrocatalysts (Table S1). Furthermore, to afford the current of 50 mA cm-2, the optimized Ni1Mo1P NSs@MCNTs electrode requires only 327 mV, which is also 60 mV lower than that of Ir/C catalyst, indicating the excellent OER activity of Ni1Mo1P NSs@MCNTs. Meanwhile, the Tafel slopes of these electrocatalysts were also measured to evaluate their catalytic OER kinetics. As seen in Figure 4c and S6, the smaller Tafel slope of Ni1Mo1P NSs@MCNTs (45.1 mV dec−1) in comparison with Ni1Mo1.2P NSs@MCNTs (75.5 mV dec−1), Ni1Mo0.5P NSs@MCNTs (77.6 mV dec−1), benchmarked Ir/C (67.8 mV dec−1), as well as NiP NPs@MCNTs (107.3 mV dec−1) indicates a more beneficial OER kinetics.

44-46

The

proposed OER on Ni1Mo1P NSs@MCNTs catalysts in an alkaline electrolyte involves 14 ACS Paragon Plus Environment

Page 15 of 33 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


the following consecutive steps: 47

Ni + OH− → MOH NiOH + OH− → NiO + H2O(l) 2NiO → 2Ni + O2(g) NiO + OH− →NiOOH + e− NiOOH + OH− →Ni + O2(g) + H2O(l) Besides the OER activity, it is also extensively acknowledged that stability is also significant for assessing the electrochemical properties of catalysts. Accordingly, the LSV polarization curves after long-term CV cycles and prolonged CP responses were also obtained. As shown in Figure 4d, after the continuous 3000 cycles CV, the LSV curve of Ni1Mo1P NSs@MCNTs was almost coincided with the initial one. Moreover, its prolonged CP curves at 10 mA cm-2 also showed limited potential variation after continous electrolysis for at least 36 h (Figure 4e). These results have revealed the outstanding electrocatalytic OER durability, which is meaningful for the commercial applications. To thoroughly understand the reasons for the improvement of OER performances of Ni1Mo1P NSs@MCNTs, we thus assumed the electrochemically surface area (ECSA) of these catalysts since the ECSA could significantly affect the catalytic performances of electrocatalysts. From Figure S5 and 4f, the ECSA of Ni1Mo1P NSs@MCNTs is 170 cm-2, which is 1.28, 2.06, and 3.40 times larger than those of Ni1Mo1.2P NSs@MCNTs, Ni1Mo0.5P NSs@MCNTs, and NiP NPs@MCNTs, repsectively. It was clearly found that the greatly enhanced electrocatalysis OER 15 ACS Paragon Plus Environment


activity of Ni1Mo1P NSs@MCNTs can mainly be associated with the high ECSA. 47

Figure 4. (a) LSV polarization curves, (b) histogram for the overpotentials 10 and 50 mA cm-2, and (c) Tafel slopes of Ni1Mo1P NSs@MCNTs, Ni1Mo1.2P NSs@MCNTs, Ni1Mo0.5P NSs@MCNTs, Ir/C, and NiP NPs@MCNTs. (d) OER stability test of Ni1Mo1P NSs@MCNTs for 3000 potential cycles of CV. (e) CP curves of Ni1Mo1P NSs@MCNTs for 36 h. (f) The capacitive current as a function of scan rates for 16 ACS Paragon Plus Environment

Page 16 of 33

Page 17 of 33 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


diﬀerent catalysts. With regard to HER activity, we herein performed the HER measurement in 1.0 M KOH solution at the scan rate of 5 mV s-1. From Figure 5a and b, we can see that the Ni1Mo1P NSs@MCNTs also display outstanding HER activity, which requires only 135 mV to reach to 10 mA cm-2, much lower than those of Ni1Mo1.2P NSs@MCNTs (182 mV), Ni1Mo0.5P NSs@MCNTs (228 mV), and NiP NPs@MCNTs (292 mV). For ease of comparison, the HER activity of MoNi NSs@MCNTs was also measured. Remarkably, the as-prepared MoNi NSs@MCNTs acquire the overpotential of 304 mV (Figure S7) to reach to 10 mA cm-2, which is 169 mV larger than Ni1Mo1P NSs@MCNTs, suggesting the doping of P into MoNi NSs@MCNTs is favorable for promotion of electrocatalytic performances. And the HER activity of the Ni1Mo1P NSs@MCNTs electrocatalyst is much better than those of some previously reported materials (Table S2). Moreover, the as-obtained Ni1Mo1P NSs@MCNTs also displayed the relatively lower Tafel slop of 137.5 mV dec-1 (Figure 5c), which was also much lower than those of Ni1Mo1.2P NSs@MCNTs (154.1 mV dec-1), Ni1Mo0.5P NSs@MCNTs (175.2 mV dec-1), and NiP NPs@MCNTs (189.3 mV dec-1). More importantly, the Ni1Mo1P NSs@MCNTs also exhibited outstanding HER durability with limited catalytic activity degradation for long-term electrochemical tests (Figure 5d and e), further confirming their superior durability. 48



Figure 5. (a) LSV curves, (b) histograms for overpotentials at 10 mA cm-2, and (c) Tafel slopes of Ni1Mo1P NSs@MCNTs, Ni1Mo1.2P NSs@MCNTs, Ni1Mo0.5P NSs@MCNTs, Ir/C, and NiP NPs@MCNTs. (d) HER stability test of Ni1Mo1P NSs@MCNTs for 3000 potential cycles of CV. (e) CP curves of Ni1Mo1P NSs@MCNTs for at least 36 h.


Page 18 of 33

Page 19 of 33 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


For the purpose of approaching practical applications, the as-obtained Ni1Mo1P NSs@MCNTs was selected as bifunctional electrocatalysts for overall water splitting. For comparison, the Ir/C (+) // Pt/C (-) was also constructed and measured in a two-electrode configuration. Figure 6a shows the scheme of overall water splitting using Ni1Mo1P NSs@MCNTs catalysts as both anode and cathode electrodes. From Figure 6b, we can find that the Ni1Mo1P NSs@MCNTs (+) // Ni1Mo1P NSs@MCNTs (-) couple needs the cell voltage of merely 1.601 V to drive the current of 10 mA cm-2, the electrochemical water splitting activity is much superior of Ir/C (+) // Pt/C (-) couple and outperforming some of reported electrocatalysts (Table S3). Significantly, Ni1Mo1P NSs@MCNTs (+) // Ni1Mo1P NSs@MCNTs (-) couple can also deliver higher current density of 62.5 and 99.8 mA cm-2, much superior to Ir/C (+) // Pt/C (-) (Figure 6c). All of these data have further demonstrated their excellent electrocatalytic overall water splitting activity.



Figure 6. (a) Illustration of overall water electrolysis. (b) Polarization curves Ni1Mo1P NSs@MCNTs (+) // Ni1Mo1P NSs@MCNTs (-) couple and Ir/C (+) // Pt/C (-) couple. (c) Current densities of Ni1Mo1P NSs@MCNTs (+) // Ni1Mo1P NSs@MCNTs (-) couple and Ir/C (+) // Pt/C (-) couple at different voltages. (d) Prolonged CP curves of Ni1Mo1P NSs@MCNTs for 36 h. Apart from the high water splitting activity, the Ni1Mo1P NSs@MCNTs (+) // Ni1Mo1P NSs@MCNTs (-) couple also showed excellent long-term stability, where the cell voltage displayed limited potential variations at 10 and 60 mA cm-2 for a long term (Figure 6d and Figure S8). Moreover, the Faradaic efficiency of the Ni1Mo1P NSs@MCNTs catalyst for OER was also measured and calculated to be 97.6% (Figure S9), indicating the detected oxidation current catalyzed by Ni1Mo1P


Page 20 of 33

Page 21 of 33 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


NSs@CNTs catalysts can be ascribed to the OER process, (detailed information seen in Supporting Information).48-49 Furthermore, for further confirming their durability, the morphology and composition of the electrodes for cell voltage have been also thoroughly studied. As seen in Figure 7, the morphology and composition of Ni1Mo1P NSs@MCNTs

nanocatalysts

display

unobvious

change

after

long-term

electrochemical tests.50 We have also conducted the XPS tests of the Ni1Mo1P/CNTs catalysts after long-term CP testing. And the XPS spectra of Ni 2p, Mo 3d, and P 2p have also been added in the Supporting Information as Figure S10. As seen, the Ni1Mo1P/CNTs after long term CP testing possessed the mixed metal valences (Ni2+, Ni3+, Mo4+) similar to the XPS spectra before CP tests. However, from the Figure S10a, we can see that the Ni 2p peak display an obvious increase at binding energy around 856.6 eV, being corresponding to oxidized Ni species.51 Moreover, the higher intensity of the oxidized phosphate species can also be observed, confirming the oxidation of surface Ni and P.52-54 All of these results have confirmed that the Ni1Mo1P NSs@MCNTs (+) // Ni1Mo1P NSs@MCNTs (-) couple can maintain high activity for long-term overall water electrolysis. 55-57



Figure 7. (a-c) TEM images of Ni1Mo1P NSs@MCNTs with different magnifications and (d) its EDS spectrum. 4. CONCLUSIONS In conclusion, an advanced class of hierarchical NiMoP NSs@MCNTs nanostructures have been successfully designed as robust electrocatalysts for both OER and HER for the first time. Owing to merits of hierarchical structure the active surface areas were greatly enlarged, electron mobility and mass transfer were drastically accelerated, the generated NiMoP NSs@MCNTs catalysts display substantial enhancement in OER performance. And the optimized Ni1Mo1P 22 ACS Paragon Plus Environment

Page 22 of 33

Page 23 of 33 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


NSs@MCNTs needed the overpotentials of only 255 and 135 mV to drive the current of 10 mA cm−2 for OER and HER, respectively. Notably, the successful doping of Mo and P is also favorable for facilitating the P-metal bonding energy, affording the optimized Gibbs free energy for the water electrolysis, and the Ni1Mo1P NSs@MCNTs (+) // Ni1Mo1P NSs@MCNTs (-) couple showed outstanding water electrolysis performances relative to Ir/C (+) // Pt/C (-). More importantly, such Ni1Mo1P NSs@MCNTs nanostructure also possess superior activity and structure stability for 36 h CP test, showing a promising earth-abundant electrocatalysts for practical water splitting. Our present work may provide a significant platform for further developing functional electrocatalysts for overall water splitting. ASSOCIATED CONTENT

The Supporting Information is available free of charge on the ACS Publications website. Calculation of ECSA and Faradic efficiency. Additional TEM images and EDS pattern of Ni1Mo1P NSs@MCNTs. TEM images of NiP NPs@MCNTs. LSVs, CVs, CPs, and scan cycling experiments of different catalysts modified electrode for OER, HER and water splitting. XPS spectra of Ni 2p, Mo 3d, and P 2p of Ni1Mo1P NSs@CNTs after CP test. Tables of the comparisons of OER, HER, and water splitting activity for various electrocatalysts in alkaline condition

AUTHOR INFORMATION Corresponding Author E-mail: [email protected] (Y.D.). Tel: +86-512-65880089, Fax: +86-512-65880089; 23 ACS Paragon Plus Environment


Page 24 of 33

Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

§

Hui Xu and Jingjing Wei

contributed equally to this work ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China (Grant No. 51373111), the Suzhou Industry (SYG201636), the project of scientific and technologic infrastructure of Suzhou (SZS201708), the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).

References 1.

Kowal, A.; Li, M.; Shao, M.; Sasaki, K.; Vukmirovic, M. B.; Zhang, J.; Marinkovic, N.

S.; Liu, P.; Frenkel, A. I.; Adzic, R. R., Ternary Pt/Rh/SnO2 Electrocatalysts For Oxidizing Ethanol to CO2. Nat. Mater. 2009, 8, 325-330. 2.

Pedireddy, S.; Lee, H. K.; Tjiu, W. W.; Phang, I. Y.; Tan, H. R.; Chua, S. Q.; Troadec, C.;

Ling, X. Y., One-Step Synthesis of Zero-Dimensional Hollow Nanoporous Gold Nanoparticles with Enhanced Methanol Electrooxidation Performance. Nat. Commun. 2014, 5, 4947. 3.

Liu, M.; Johnston, M. B.; Snaith, H. J., Efficient Planar Heterojunction Perovskite Solar

Cells by Vapour Deposition. Nature 2013, 501, 395-398. 4. Shi, R.; Cao, Y.; Bao, Y.; Zhao, Y.; Waterhouse, G. I. N.; Fang, Z.; Wu, L. Z.; Tung, C. H.; Yin, Y.; Zhang, T., Self-Assembled Au/CdSe Nanocrystal Clusters for Plasmon-Mediated Photocatalytic Hydrogen Evolution. Adv. Mater. 2017, 29, DOI: adma.201700803.


Page 25 of 33 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


5.

Wang, P.; Jiang, K.; Wang, G.; Yao, J.; Huang, X., Phase and Interface Engineering of

Platinum-Nickel Nanowires for Efficient Electrochemical Hydrogen Evolution. Angew. Chem. 2016, 55, 12859-12963. 6.

Chen, Y. Y.; Zhang, Y.; Zhang, X.; Tang, T.; Luo, H.; Niu, S.; Dai, Z. H.; Wan, L. J.; Hu,

J. S., Self-Templated Fabrication of MoNi4/MoO3-x Nanorod Arrays with Dual Active Components for Highly Efficient Hydrogen Evolution.. Adv. Mater. 2017, 29, DOI: adma.201703311.. 7.

Subbaraman, R.; Tripkovic, D.; Chang, K. C.; Strmcnik, D.; Paulikas, A. P.; Hirunsit, P.;

Chan, M.; Greeley, J.; Stamenkovic, V.; Markovic, N. M., Trends in Activity for the Water Electrolyser Reactions on 3d M(Ni,Co,Fe,Mn) Hydr(oxy)oxide Catalysts. Nat. Mater. 2012, 11, 550-557. 8.

Hu, C.; Zhang, L.; Zhao, Z. J.; Li, A.; Chang, X.; Gong, J., Synergism of Geometric

Construction and Electronic Regulation: 3D Se-(NiCo)Sx/(OH)x Nanosheets for Highly Efficient Overall Water Splitting. Adv. Mater. 2018, 30, e1705538. 9.

Garcia-Esparza, A. T.; Shinagawa, T.; Ould-Chikh, S.; Qureshi, M.; Peng, X.; Wei, N.;

Anjum, D. H.; Clo, A.; Weng, T. C.; Nordlund, D.; Sokaras, D.; Kubota, J.; Domen, K.; Takanabe, K., An Oxygen-Insensitive Hydrogen Evolution Catalyst Coated by a Molybdenum-Based Layer for Overall Water Splitting. Angew. Chem. 2017, 56, 5780-5784. 10. Yin, Z.; Sun, Y.; Zhu, C.; Li, C.; Zhang, X.; Chen, Y., Bimetallic Ni–Mo Nitride Nanotubes as Highly Active and Stable Bifunctional Electrocatalysts for Full Water Splitting. J. Mater. Chem. A 2017, 5, 13648-13658. 11. Zhang, B.; Lui, Y. H.; Gaur, A. P. S.; Chen, B.; Tang, X.; Qi, Z.; Hu, S., Hierarchical



FeNiP@Ultrathin Carbon Nanoflakes as Alkaline Oxygen Evolution and Acidic Hydrogen Evolution Catalyst for Efficient Water Electrolysis and Organic Decomposition. ACS Appl. Mater. Interfaces 2018, 10, 8739-8748. 12. Chung, D. Y.; Jun, S. W.; Yoon, G.; Kim, H.; Yoo, J. M.; Lee, K. S.; Kim, T.; Shin, H.; Sinha, A. K.; Kwon, S. G.; Kang, K.; Hyeon, T.; Sung, Y. E., Large-Scale Synthesis of Carbon-Shell-Coated FeP Nanoparticles for Robust Hydrogen Evolution Reaction Electrocatalyst. J. Am. Chem. Soc. 2017, 139, 6669-6674. 13. Li, R.; Zhou, D.; Luo, J.; Xu, W.; Li, J.; Li, S.; Cheng, P.; Yuan, D., The Urchin-Like Sphere Arrays Co3O4 as a Bifunctional Catalyst for Hydrogen Evolution Reaction and Oxygen evolution reaction. J. Power Sources 2017, 341, 250-256. 14. Zhang, Y.; Shao, Q.; Long, S.; Huang, X., Cobalt-Molybdenum Nanosheet Arrays as Highly Efficient and Stable Earth-Abundant Electrocatalysts for Overall Water Splitting. Nano Energy 2018, 45, 448-455. 15. Zhang, G.; Feng, Y.-S.; Lu, W.-T.; He, D.; Wang, C.-Y.; Li, Y.-K.; Wang, X.-Y.; Cao, F.-F., Enhanced Catalysis of Electrochemical Overall Water Splitting in Alkaline Media by Fe Doping in Ni3S2 Nanosheet Arrays. ACS Catal. 2018, 5431-5441. 16. Yan, K.-L.; Qin, J.-F.; Liu, Z.-Z.; Dong, B.; Chi, J.-Q.; Gao, W.-K.; Lin, J.-H.; Chai, Y.-M.; Liu, C.-G., Organic-Inorganic Hybrids-Directed Ternary NiFeMoS Anemone-Like Nanorods with Scaly Surface Supported on Nickel Foam for Efficient Overall Water Splitting. Chem. Eng. J. 2018, 334, 922-931. 17. Zhou, L.; Shao, M.; Zhang, C.; Zhao, J.; He, S.; Rao, D.; Wei, M.; Evans, D. G.; Duan, X., Hierarchical CoNi-Sulfide Nanosheet Arrays Derived from Layered Double Hydroxides


Page 26 of 33

Page 27 of 33 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


toward Efficient Hydrazine Electrooxidation. Adv. Mater. 2017, 29 DOI: adma.201604080. 18. Chi, J.; Yu, H.; Qin, B.; Fu, L.; Jia, J.; Yi, B.; Shao, Z., Vertically Aligned FeOOH/NiFe Layered Double Hydroxides Electrode for Highly Efficient Oxygen Evolution Reaction. ACS Appl. Mater. Interfaces 2017, 9, 464-471. 19. Zhang, G.; Wang, G.; Liu, H.; Qu, J.; Li, J., Rapidly Catalysis of Oxygen Evolution Through Sequential Engineering of Vertically Layered FeNi Structure. Nano Energy 2018, 43, 359-367. 20. Xu, H.; Wang, J.; Yan, B.; Zhang, K.; Li, S.; Wang, C.; Shiraishi, Y.; Du, Y.; Yang, P., Hollow AuxAg/Au Core/Shell Nanospheres as Efficient Catalysts for Electrooxidation of Liquid Fuels. Nanoscale 2017, 9, 12996-13003. 21. Shen, J.; Wang, M.; Zhao, L.; Jiang, J.; Liu, H.; Liu, J., Self-Supported Stainless Steel Nanocone Array Coated with a Layer of Ni-Fe Oxides/(Oxy)hydroxides as a Highly Active and Robust Electrode for Water Oxidation. ACS Appl. Mater. Interfaces 2018, 10, 8786-8796. 22. Du, J.; Zou, Z.; Liu, C.; Xu, C., Hierarchical Fe-Doped Ni3Se4 Ultrathin Nanosheets as an Efficient Electrocatalyst for Oxygen Evolution Reaction. Nanoscale 2018, 10, 5163-5170. 23. Xu, Q.; Jiang, H.; Zhang, H.; Jiang, H.; Li, C., Phosphorus-Driven Mesoporous Co3O4 Nanosheets with Tunable Oxygen Vacancies for the Enhanced Oxygen Evolution Reaction. Electrochim. Acta 2018, 259, 962-967. 24. Zhang, T.; Du, J.; Xi, P.; Xu, C., Hybrids of Cobalt/Iron Phosphides Derived from Bimetal-Organic Frameworks as Highly Efficient Electrocatalysts for Oxygen Evolution Reaction. ACS Appl. Mater. Interfaces 2017, 9, 362-370. 25. Ma, X.-X.; Dai, X.-H.; He, X.-Q., Co9S8--Modified N, S, and P Ternary-Doped 3D



Page 28 of 33

Graphene Aerogels as a High-Performance Electrocatalyst for Both the Oxygen Reduction Reaction and Oxygen Evolution Reaction. ACS Sustain. Chem. Eng. 2017, 5, 9848-9857. 26. Liu, K.; Wang, F.; Shifa, T. A.; Wang, Z.; Xu, K.; Zhang, Y.; Cheng, Z.; Zhan, X.; He, J., An Efficient ternary CoP2xSe2(1-x) Nanowire Array for Overall Water Splitting. Nanoscale 2017, 9, 3995-4001. 27. Liu, R.; Wang, Y.; Liu, D.; Zou, Y.; Wang, S., Water-Plasma-Enabled Exfoliation of Ultrathin Layered Double Hydroxide Nanosheets with Multivacancies for Water Oxidation. Adv. Mater. 2017 DOI: 10.1002/adma.201701546.. 28. Nadeema,

A.;

Dhavale,

V.

M.;

Kurungot,

S.,

NiZn

Double

Hydroxide

Nanosheet-Anchored Nitrogen-Doped Graphene Enriched with the Gamma-NiOOH Phase as an Activity Modulated Water Oxidation Electrocatalyst. Nanoscale 2017, 9, 12590-12600. 29. Diaz-Morales, O.; Ledezma-Yanez, I.; Koper, M. T. M.; Calle-Vallejo, F., Guidelines for the Rational Design of Ni-Based Double Hydroxide Electrocatalysts for the Oxygen Evolution Reaction. ACS Catal. 2015, 5, 5380-5387. 30. Schäfer, H.; Chatenet, M. Stainless Steel: The Resurrection of a Forgotten Water-Splitting Catalyst. ACS Energy Lett., 2018, 3, 574–591. 31. Liu, M.; Li, J., Cobalt Phosphide Hollow Polyhedron as Efficient Bifunctional Electrocatalysts for the Evolution Reaction of Hydrogen and Oxygen. ACS Appl. Mater. Interfaces 2016, 8, 2158-2165. 32. Huang, C.; Ouyang, T.; Zou, Y.; Li, N.; Liu, Z.-Q., Ultrathin NiCo2Px Nanosheets Strongly Coupled with CNTs as Efficient and Robust Electrocatalysts for Overall Water Splitting. J. Mater. Chem. A 2018, 6, 7420-7427.


Page 29 of 33 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


33. Wang, H.; Zhou, T.; Li, P.; Cao, Z.; Xi, W.; Zhao, Y.; Ding, Y., Self-Supported Hierarchical Nanostructured NiFe-LDH and Cu3P Weaving Mesh Electrodes for Efficient Water Splitting. ACS Sustain. Chem. Eng. 2017, 6, 380-388. 34. Wang, X.-D.; Chen, H.-Y.; Xu, Y.-F.; Liao, J.-F.; Chen, B.-X.; Rao, H.-S.; Kuang, D.-B.; Su, C.-Y., Self-Supported NiMoP2 Nanowires on Carbon Cloth as an Efficient and Durable Electrocatalyst for Overall Water Splitting. J. Mater. Chem. A 2017, 5, 7191-7199. 35. Ding, J.; Shao, Q.; Feng, Y.; Huang, X., Ruthenium-Nickel Sandwiched Nanoplates for Efficient Water Splitting Electrocatalysis. Nano Energy 2018, 47, 1-7. 36. Jin, Y.; Yue, X.; Shu, C.; Huang, S.; Shen, P. K., Three-Dimensional Porous MoNi4 Networks Constructed by Nanosheets as Bifunctional Electrocatalysts for Overall Water Splitting. J. Mater. Chem. A 2017, 5, 2508-2513. 37. Xu, H.; Zhang, K.; Yan, B.; Wang, J.; Wang, C.; Li, S.; Gu, Z.; Du, Y.; Yang, P., Ultra-Uniform PdBi Nanodots with High activity towards Formic Acid Oxidation. J. Power Sources 2017, 356, 27-35. 38. Xu, H.; Yan, B.; Wang, J.; Zhang, K.; Li, S.; Xiong, Z.; Wang, C.; Shiraishi, Y.; Du, Y.; Yang, P., Self-Supported Porous 2D AuCu Triangular Nanoprisms as Model Electrocatalysts for Ethylene Glycol and Glycerol Oxidation. J. Mater. Chem. A 2017, 5, 15932-15939. 40. Xu, H.; Song, P.; Fernandez, C.; Wang, J.; Zhu, M.; Shiraishi, Y.; Du, Y., Sophisticated Construction of Binary PdPb Alloy Nanocubes as Robust Electrocatalysts toward Ethylene Glycol and Glycerol Oxidation. ACS Appl. Mater. Interfaces 2018, 10, 12659-12665. 41. Yu, X.; Zhang, M.; Yuan, W.; Shi, G., A High-Performance Three-Dimensional Ni–Fe Layered Double Hydroxide/Graphene Electrode for Water Oxidation. J. Mater. Chem. A 2015,



3, 6921-6928. 42. Sun, M.; Liu, H.; Qu, J.; Li, J., Earth-Rich Transition Metal Phosphide for Energy Conversion and Storage. Adv. Energy Mater. 2016, 6, 1600087. 43. Schäfer, H.; Sadaf, S.; Walder, L.; Kuepper, K.; Dinklage, S.; Wollschläger, J.; Schneider, L.; Steinhart, M.; Hardege, J.; Daum, D., Stainless Steel Made to Rust: A Robust Water-Splitting Catalyst with Benchmark Characteristics. Energy Environ. Sci. 2015, 8, 2685-2697. 44. Xu, H.; Yan, B.; Zhang, K.; Wang, C.; Zhong, J.; Li, S.; Yang, P.; Du, Y., Facile Synthesis of Pd-Ru-P Ternary Nanoparticle Networks with Enhanced Electrocatalytic Performance for Methanol Oxidation. Int. J. Hydrogen Energy 2017, 42, 11229-11238. 45. Schäfer, H.; Chevrier, D. M.; Kuepper, K.; Zhang, P.; Wollschlaeger, J.; Daum, D.; Steinhart, M.; Heß, C.; Krupp, U.; Müller-Buschbaum, K.; Stangl, J.; Schmidt, M., X20CoCrWMo10-9//Co3O4: A Metal–Ceramic Composite with Unique Efficiency Values for Water-Splitting in the Neutral Regime. Energy Environ. Sci. 2016, 9, 2609-2622. 46. Zhang, G.; Wang, G.; Liu, Y.; Liu, H.; Qu, J.; Li, J., Highly Active and Stable Catalysts of Phytic Acid-Derivative Transition Metal Phosphides for Full Water Splitting. J. Am. Chem. Soc. 2016, 138, 14686-14693. 47. Suen, N. T.; Hung, S. F.; Quan, Q.; Zhang, N.; Xu, Y. J.; Chen, H. M., Electrocatalysis for the Oxygen Evolution Reaction: Recent Development and Future Perspectives. Chem. Soc. Rev. 2017, 46, 337-365. 48. Chen, P.; Xu, K.; Zhou, T.; Tong, Y.; Wu, J.; Cheng, H.; Lu, X.; Ding, H.; Wu, C.; Xie, Y., Strong-Coupled Cobalt Borate Nanosheets/graphene Hybrid as Electrocatalyst for Water


Page 30 of 33

Page 31 of 33 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


Oxidation Under Both Alkaline and Neutral Conditions. Angew. Chem. 2016, 55, 2488-2492. 49. Yu, X.; Zhang, M.; Yuan, W.; Shi, G., A high-performance three-dimensional Ni–Fe layered double hydroxide/graphene electrode for water oxidation. J. Mater. Chem. A 2015, 3, 6921-6928. 50. Xu, H.; Yan, B.; Li, S.; Wang, J.; Wang, C.; Guo, J.; Du, Y., N-doped Graphene Supported

PtAu/Pt

Intermetallic

Core/Dendritic

Shell

Nanocrystals

for

Efficient

Electrocatalytic Oxidation of Formic Acid. Chem. Eng. J. 2018, 334, 2638-2646. 51. Yu, X.-Y.; Feng, Y.; Guan, B.; Lou, X. W.; Paik, U., Carbon Coated Porous Nickel Phosphides Nanoplates for Highly Efficient Oxygen Evolution Reaction. Energy Environ. Sci. 2016, 9, 1246-1250. 52. Xu, H.; Wei, J.; Liu, C.; Zhang, Y.; Tian, L.; Wang, C.; Du, Y., Phosphorus-Doped Cobalt-Iron Oxyhydroxide with Untrafine Nanosheet Structure Enable Efficient Oxygen Evolution Electrocatalysis. J. Colloid Interface Sci. 2018, 530, 146-153. 53. Li, S.; Zhang, G.; Tu, X.; Li, J., Polycrystalline CoP/CoP2 Structures for Efficient Full Water Splitting. ChemElectroChem 2018, 5, 701-707 54. Xu, H.; Song, P.; Liu, C.; Zhang, Y.; Du, Y., Facile Construction of Ultrafine Nickel-Zinc Oxyphosphide Nanosheets as High-Performance Electrocatalysts for Oxygen Evolution Reaction. J. Colloid Interface Sci. 2018, 530, 58-66. 55. Xu, B.; Yang, H.; Yuan, L.; Sun, Y.; Chen, Z.; Li, C., Direct Selenylation of Mixed Ni/Fe Metal-Organic Frameworks to NiFe-Se/C Nanorods for Overall Water Splitting. J.Power Sources 2017, 366, 193-199. 56. Yuan, C.-Z.; Zhong, S.-L.; Jiang, Y.-F.; Yang, Z. K.; Zhao, Z.-W.; Zhao, S.-J.; Jiang, N.;



Xu, A.-W., Direct Growth of Cobalt-Rich Cobalt Phosphide Catalysts on Cobalt Foil: an Efficient and Self-Supported Bifunctional Electrode for Overall Water Splitting in Alkaline Media. J. Mater. Chem. A 2017, 5, 10561-10566. 57. Yang, Y.; Zhang, K.; Lin, H.; Li, X.; Chan, H. C.; Yang, L.; Gao, Q., MoS2–Ni3S2 Heteronanorods as Efficient and Stable Bifunctional Electrocatalysts for Overall Water Splitting. ACS Catal. 2017, 7, 2357-2366.


Page 32 of 33

Page 33 of 33 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


Table of Content


Hierarchical NiMo Phosphide Nanosheets Strongly Anchored on

Recommend Documents