Cobalt Phosphide Nanoparticles Research Articles

A 3D Nanostructure Based on Transition-Metal Phosphide Decorated Heteroatom-Doped Mesoporous Nanospheres Interconnected with Graphene: Synthesis and Applications.

A novel three-dimensional nanostructure based on cobalt phosphide nanoparticles (Co2P NPs) and heteroatom-doped mesoporous carbon spheres interconnected with graphene (3D PZM@Co2P@RGO) was facilely synthesized for the first time, and it was used for enhancing the flame retardancy and toxicity suppression of epoxy resins (EP) via a synergistic effect. Herein, the cross-linked polyphosphazene hollow spheres (PZM) were used as templates for the fabrication of 3D architecture. The 3D architecture based on Co2P-decorated heteroatom-doped carbon sphere and reduced graphene oxide was prepared via a carbonization procedure followed by a hydrothermal self-assembly strategy. The as-prepared material exhibits excellent catalytic activity with regard to the combustion process. Notably, inclusion of incorporating PZM@Co2P@RGO resulted in a dramatic reduction of the fire hazards of EP, such as a 47.9% maximum decrease in peak heat release rate and a 29.2% maximum decrease in total heat release, lower toxic CO yield, and formation of high-graphitized protective char layer. In addition, the mechanism for flame retardancy and toxicity suppression was proposed. It is reasonable to know that the improved flame-retardant performance for EP nanocomposites is attributed to tripartite cooperative effect from respective components (Co2P NPs and RGO) plus the heteroatom-doped carbon spheres.

Low Overpotential Water Splitting Using Cobalt–Cobalt Phosphide Nanoparticles Supported on Nickel Foam

We report a simple, facile, and safe route for preparation of cobalt–cobalt phosphide (Co/Co2P) nanoparticles and demonstrate their application as efficient low-cost catalysts for electrochemical water splitting. The catalyst achieves good performance in catalyzing both the cathode and anode half-cell water-splitting reactions in 1.0 M KOH and the hydrogen evolution reaction in an acidic electrolyte, 0.5 M H2SO4. For the oxygen evolution reaction in 1.0 M KOH, a current of 10 mA cm–2 was attained at 0.39 V overpotential on a glassy carbon electrode, while an overpotential of 0.19 V was attained at 50 mA cm–2 when the catalyst was supported on nickel foam.

A Hydrogen Evolution Reaction Catalyst Using Nickel Phosphides with Mixed Crystalline Structure

Introduction Proton Exchange Membrane (PEM) water electrolysis provides a sustainable solution for the production of hydrogen, and is well suited to couple with the intermittent nature of energy sources such as wind and solar. To spur large-scale commercial application of PEM water electrolysis, more efficient and less expensive non-noble metal electrocatalysts towards the hydrogen evolution reaction (HER) are required. Recently, transition metal phosphides (TMPs) have become the typical representatives of the burgeoning non-noble metal HER electrocatalysts due to that their intrinsic structures meet the criteria of outstanding electrocatalysts. It should be noted that the currently studied TMPs are mainly focusing on improving their HER performance by a series of structural engineering methods [1-3]. To the best of our knowledge, there are very few reports on promoting the intrinsic activity of the TMPs in water electrolysis. In this communication, we reported the scalable synthesis of nickel phosphides with a mixed crystalline structure (referred to as Ni2P&Ni3P) toward HER by a solution-phase reaction. To elucidate the superior catalytic activity of Ni2P&Ni3P, we also explored the preparation of the nickel phosphides in a single crystalline state (referred to as Ni2P) and that in a single amorphous state (referred to as Ni-P) for comparison. Result and DiscussionX-ray diffraction patterns of Ni2P&Ni3P、Ni2P and Ni-P are shown in Fig 1a. The analysis of the diffraction data reveals that both tiny Ni2P nanocrystallines and Ni3P nanocrystallines are observed for Ni2P&Ni3P. As for Ni2P, the Ni3P tiny nanocrystallines are vanished and only the intensive diffraction peaks corresponding to Ni2P are observed. In comparison with the crystalline state nickel phosphides, the Ni-P shows poor crystalline order with a very broad peak. The crystalline structures could take effects on the intermediate reaction of HER. In order to compare the hydrogen desorption ability of the three electrocatalysts, the hydrogen oxidation reaction (HOR) was investigated by LSV (Linear scan voltammetry) at 20 mA cm-2 for 5 min immediately after the hydrogen evolution reaction (HER). As it is shown in Fig 1b, the characteristic mixed crystalline structure is expected to promote the hydrogen desorption ability. Thus, the largest peak current density is obtained with Ni2P&Ni3P. Furthermore, steady state polarization curves of different electrocatalysts were shown in Fig 1c. As expected, the Ni2P&Ni3P shows the best HER activity, and the overpotentials required for Ni2P&Ni3P、Ni2P and Ni-P to produce cathodic current densities of 20 mA cm-2 are 154 mV, 221 mV, 262 mV, respectively. Fig 1 (a) XRD patterns of Ni2P&Ni3P, Ni2P and Ni-P; (b) LSV and (c) Steady-state polarization curves of the three types of prepared catalysts at a scan rate of 1 mV s-1. All the electrochemical characterizations are tested in the mixture of 0.1 M H2SO4 and 0.5 M Na2SO4 at 25 ◦C and atmosphere pressure. Reference[1] Liu P., Rodriguez J. A. Catalysts for Hydrogen Evolution from the [NiFe] Hydrogenase to the Ni2P (001) Surface: The Importance of Ensemble Effect [J]. Journal of the American Chemical Society, 2005,127(42):14871-14878. [2] Popczun E. J., Read C. G., Roske C. W., Lewis S., Schaak R. E. Highly Active Electrocatalysis of the Hydrogen Evolution Reaction by Cobalt Phosphide Nanoparticles [J]. Angewandte Chemie International Edition, 2014,53(21):5427-5430. [3] Liu Q., Pu Z. H., Asiri A. M., Sun X. P. Nitrogen-doped carbon nanotube supported iron phosphide nanocomposites for highly active electrocatalysis of the hydrogen evolution reaction [J]. Electrochim Acta, 2014,149(10):324-329. Figure 1

3D Graphene Aerogels Decorated with Cobalt Phosphide Nanoparticles as Electrocatalysts for the Hydrogen Evolution Reaction.

The development of non-precious-metal hydrogen evolution reaction (HER) electrocatalysts with high activity and excellent durability in acidic media is of significant importance for renewable energy research. We report a novel electrocatalyst based on a three-dimensional (3D) graphene aerogel decorated with cobalt phosphide nanoparticles (CoP/GA). The material has a unique hierarchical porous structure with CoP nanoparticles encapsulated uniformly within the graphene sheets. The optimized catalyst shows superior activity, with an overpotential of only 121 mV at 10 mA cm-2 , a Tafel slope of 50 mV dec-1 , and an exchange current density of 0.105 mA cm-2 , and it maintains its catalytic activity for at least 13 h. More importantly, this work provides a versatile way for the rational design and fabrication of 3D graphene-based multifunctional composite materials.

Cover Picture: Strongly Coupled Architectures of Cobalt Phosphide Nanoparticles Assembled on Graphene as Bifunctional Electrocatalysts for Water Splitting (ChemElectroChem 5/2016)

Cover Picture: Strongly Coupled Architectures of Cobalt Phosphide Nanoparticles Assembled on Graphene as Bifunctional Electrocatalysts for Water Splitting (ChemElectroChem 5/2016)

Strongly Coupled Architectures of Cobalt Phosphide Nanoparticles Assembled on Graphene as Bifunctional Electrocatalysts for Water Splitting

AbstractThe front cover artwork is provided by Jieshan Qiu, Chang Yu, and co‐workers, Dalian University of Technology (China). The work reports a novel approach to fabricate bifunctional electrocatalysts for full water splitting by anchoring the cobalt phosphide nanoparticles with enriched active sites onto conductive graphene matrix. Read the full text of the Article at 10.1002/celc.201600001.

Strongly Coupled Architectures of Cobalt Phosphide Nanoparticles Assembled on Graphene as Bifunctional Electrocatalysts for Water Splitting

AbstractEfficient bifunctional electrocatalysts for both the cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) are crucial for water splitting in a sustainable energy system. A strategy for fabricating strongly coupled cobalt phosphide (CoP)/graphene (G) architectures composed of CoP nanoparticles and G is described. Benefiting from synergetic effects of a dual support system of CoP for electroactive sites and G to enhance charge transfer, low overpotentials of 120 mV for the HER (0.5 m H2SO4) and 292 mV for the OER (1 m KOH) are required to achieve current densities of 10 mA cm−2. The as‐prepared CoP/G composites, which serve as bifunctional catalysts for both HER and OER in complete water splitting, can generate a current density of 10 mA cm−2 at 1.626 V. The present strategy provides a novel and efficient method for configuring high‐efficiency electrocatalysts for energy‐related storage and conversion devices.

One-pot, large-scale, simple synthesis of CoxP nanocatalysts for electrochemical hydrogen evolution

We report a one-pot, large-scale (tens of grams), facile synthesis of cobalt phosphide (CoxP) nanoparticles with impressive HER activities.

Shape-controlled cobalt phosphide nanoparticles as volatile organic solvent sensor

Shape-controlled cobalt phosphide nanostructures have been synthesized using a one-pot reaction strategy for sensing volatile organic solvent molecules.

In Situ Transformation of Hydrogen-Evolving CoP Nanoparticles: Toward Efficient Oxygen Evolution Catalysts Bearing Dispersed Morphologies with Co-oxo/hydroxo Molecular Units

Reported herein is elucidation of a novel Co-based oxygen evolution catalyst generated in situ from cobalt phosphide (CoP) nanoparticles. The present CoP nanoparticles, efficient alkaline hydrogen-evolving materials at the cathode, are revealed to experience unique metamorphosis upon anodic potential cycling in an alkaline electrolyte, engendering efficient and robust catalytic environments toward the oxygen evolution reaction (OER). Our extensive ex situ characterization shows that the transformed catalyst bears porous and nanoweb-like dispersed morphologies along with unique microscopic environments mainly consisting of discrete cobalt-oxo/hydroxo molecular units within a phosphate-enriched amorphous network. Outstanding OER efficiency is achievable with the activated catalyst, which is favorably comparable to even a precious iridium catalyst. A more remarkable feature is its outstanding long-term stability, superior to iridium and conventional cobalt oxide-based materials. Twelve-hour bulk electrolysis...

Cobalt phosphide nanoparticles film growth on carbon cloth: A high-performance cathode for electrochemical hydrogen evolution

In this communication, cobalt phosphide nanoparticles film was developed on carbon cloth (CoP NPs/CC) through low-temperature phosphidation of its corresponding Co NPs/CC precursor. When directly used as a cathode for electrochemical hydrogen evolution in strongly acidic solutions, the CoP NPs/CC electrode exhibits high performance with a low onset overpotential of 33 mV, a Tafel slope of 70 mV dec−1 and a Faradaic efficiency of nearly 100%. This catalyst maintain its catalytic activity for at least 30 h and only needs overpotentials of 48 and 190 mV to attain current densities of 10 and 100 mA cm−2, respectively.

Highly active electrocatalysis of the hydrogen evolution reaction by cobalt phosphide nanoparticles.

Nanoparticles of cobalt phosphide, CoP, have been prepared and evaluated as electrocatalysts for the hydrogen evolution reaction (HER) under strongly acidic conditions (0.50 M H2SO4, pH 0.3). Uniform, multi-faceted CoP nanoparticles were synthesized by reacting Co nanoparticles with trioctylphosphine. Electrodes comprised of CoP nanoparticles on a Ti support (2 mg cm(-2) mass loading) produced a cathodic current density of 20 mA cm(-2) at an overpotential of -85 mV. The CoP/Ti electrodes were stable over 24 h of sustained hydrogen production in 0.50 M H2SO4. The activity was essentially unchanged after 400 cyclic voltammetric sweeps, suggesting long-term viability under operating conditions. CoP is therefore amongst the most active, acid-stable, earth-abundant HER electrocatalysts reported to date.

Highly Active Electrocatalysis of the Hydrogen Evolution Reaction by Cobalt Phosphide Nanoparticles

AbstractNanoparticles of cobalt phosphide, CoP, have been prepared and evaluated as electrocatalysts for the hydrogen evolution reaction (HER) under strongly acidic conditions (0.50 M H2SO4, pH 0.3). Uniform, multi‐faceted CoP nanoparticles were synthesized by reacting Co nanoparticles with trioctylphosphine. Electrodes comprised of CoP nanoparticles on a Ti support (2 mg cm−2 mass loading) produced a cathodic current density of 20 mA cm−2 at an overpotential of −85 mV. The CoP/Ti electrodes were stable over 24 h of sustained hydrogen production in 0.50 M H2SO4. The activity was essentially unchanged after 400 cyclic voltammetric sweeps, suggesting long‐term viability under operating conditions. CoP is therefore amongst the most active, acid‐stable, earth‐abundant HER electrocatalysts reported to date.

Characterization of cobalt phosphide nanoparticles derived from molecular clusters in mesoporous silica

The synthesis of well dispersed cobalt phosphide nanoparticles (NPs) in SBA-15 mesoporous silica by wet impregnation of the molecular cluster (Co4(CO)10(l-dppa)) (1) (dppa = HN(PPh2)2 )i s described. The thermal activation of the silica impreg- nated precursor under a H2/N2 (5/95 %) stream at different temperatures to form NPs was studied and it was found that the size of the latter is limited in the 5.5-6.5 nm range by the size of the pores. The obtained materials were characterized by various analytical methods. The porosity and the structure of the mesoporous silica supports were analyzed by N2 adsorption/desorption and small-angle X-ray diffrac- tion. The nanoparticles were characterized by wide- angle X-ray diffraction, transmission electron micros- copy in conventional and scanning modes, electron tomography, energy-dispersive X-ray spectroscopy, and magnetic measurements. Cobalt phosphide NPs of few nanometers were observed in the pores of SBA-15.

Hydrothermal synthesis of cobalt phosphide nanoparticles

Cobalt phosphide (Co 2P) nanoparticles were prepared under mild hydrothermal conditions. The influence of the molar ratio of Co/P, temperature and duration were studied. The product was characterized by X-ray powder diffraction, transmission electron microscopy and energy dispersive spectroscopy tests, which indicated that the obtained products were pure and well crystallized Co 2P with an average particle size of about 30 nm.

The structural evolution and diffusion during the chemical transformation from cobalt to cobalt phosphide nanoparticles

We report the structural evolution and the diffusion processes which occur during the phase transformation of nanoparticles (NPs), e-Co to Co2P to CoP, from a reaction with tri-n-octylphosphine (TOP). Extended X-ray absorption fine structure (EXAFS) investigations were used to elucidate the changes in the local structure of cobalt atoms which occur as the chemical transformation progresses. The lack of long-range order, spread in interatomic distances, and overall increase in mean-square disorder compared with bulk structure reveal the decrease in the NP’s structural order compared with bulk structure, which contributes to their deviation from bulk-like behavior. Results from EXAFS show both the Co2P and CoP phases contain excess Co. Results from EXAFS, transmission electron microscopy, X-ray diffraction, and density functional theory calculations reveal that the inward diffusion of phosphorus is more favorable at the beginning of the transformation from e-Co to Co2P by forming an amorphous Co-P shell, while retaining a crystalline cobalt core. When the major phase of the sample turns to Co2P, the diffusion processes reverse and cobalt atom out-diffusion is favored, leaving a hollow void, characteristic of the nanoscale Kirkendall effect. For the transformation from Co2P to CoP theory predicts an outward diffusion of cobalt while the anion lattice remains intact. In real samples, however, the Co-rich nanoparticles continue Kirkendall hollowing. Knowledge about the transformation method and structural properties provides a means to tailor the synthesis and composition of the NPs to facilitate their use in applications.

The preparation of cobalt phosphide and cobalt chalcogenide (CoX, X = S, Se) nanoparticles from single source precursors

Dialkyldiselenophosphinatocobalt(II), [Co(Se2PR2)2] (R = iPr, Ph and tBu), complexes were used to grow cobalt selenide and cobalt phosphide nanoparticles by decomposition in trioctylphosphine oxide (TOPO) or hexadecylamine (HDA) at 300 °C. Orthorhombic CoSe2 nanoparticles are readily formed in HDA or TOPO, whereas, in TOP/TOPO or TOP/HDA only orthorhombic CoP or Co2P nanoparticles were formed. This observation suggests that TOP provides the phosphorus for nanoparticles. The composition of cobalt phosphide can be controlled by the reaction time. Co2P was obtained after 60 min of thermolysis at 300 °C whereas CoP was grown over 150 min. In order to confirm the effect of TOP on the thermolysis of the precursor, the related sulfur containing precursor, [Co(S2PtBu2)2], was decomposed in TOP/TOPO, TOP/HDA, TOPO or HDA. The thermolysis reaction in TOPO or HDA gave cubic Co9S8 nanoparticles whereas in TOP/TOPO or TOP/HDA only CoP nanoparticles were formed as expected due to the presence of TOP. Characterization of these nanoparticles by transmission electron microscopy, X-ray diffraction, and electron diffraction shows highly crystalline spherical CoP and Co2P nanoparticles with a size of 5 nm diameter, and CoSe2 nanoparticles are close to cubes of ca. 10 nm size. Co9S8 nanoparticles are aggregates composed of numerous small cuboid Co9S8 nanoparticles with average diameters of 10–20 nm. The optical spectra show that Co2P and CoP nanoparticles have a band gaps (Eg) = 3.14 and 1.71 eV, respectively, whilst CoSe2 nanoparticles a band gap of 1.45 eV.