Nickel Cobalt Phosphide Research Articles

3D nickel-cobalt phosphide heterostructure for high-performance solid-state hybrid supercapacitors

Transition-metal phosphides are emerging candidates for supercapacitors owing to their high conductivity and electrochemical activity. It still remains a great challenge to develop phosphide-based supercapacitors with advanced phosphide architectures and optimized device components, which are crucial for realizing their high-energy storage. Herein, hierarchical Ni–Co–P heterostructure assembled by porous nanoplates is achieved. It displays the metalloid property, multi-component synergy, high reaction activity, and rapid electron transfer/ion diffusion behavior. Benefitted from these merits, Ni–Co–P offers respectable gravimetric capacity and high-rate capability (653 and 470 C g−1 at 1 and 30 A g−1) over Ni–P (520 and 39 C g−1) and Co–P (169 and 122.4 C g−1). Moreover, the areal capacity of 5.8 C cm−2 at 1 A g−1 is delivered under high mass loading of 15 mg cm−2. When integrating Ni–Co–P as positive electrode material and active carbon as negative electrode material, the developed hybrid supercapacitor with PVA/KOH gel electrolyte presents prominent energy/power density of 30.2 Wh kg−1/12620 W kg−1 with superior cycling stability of 10,000 times. It can also light the LED indicator, and work well in a temperature range of -10–60 °C. This research enriches the energy-related material system and boost the development of existing energy devices.

Iron-Doped Nickel Cobalt Phosphide Nanoarrays with Urchin-like Structures as High-Performance Electrocatalysts for Oxygen Evolution Reaction

It is challenging to explore non-noble metal-based electrocatalysts with high-performance and long-term stability for oxygen evolution reaction (OER). Herein, urchin-like iron-doped nickel cobalt p...

NiCoO2/NiCoP@Ni nanowire arrays: tunable composition and unique structure design for high-performance winding asymmetric hybrid supercapacitors

Transition metal phosphides (TMPs) are recognized as such promising supercapacitor materials for the practical application, due to their superior electrical conductivity and excellent redox activity. Here, self-supported three-dimensional NiCoP nanoparticles embedded in NiCoO2 nanowires (NiCoO2/NiCoP) electrode consisting of nickel cobalt phosphides (NiCoP) with high activity and nickel cobalt oxides (NiCoO2) with good stability were fabricated by a hydrothermal and phosphorization method. The electrode integrates the advantages of nanowire arrays for fast ion transport and foam Ni for effective charge transport and flexibility. Benefitting the proper composition control of the nanohybrid and unique structure design, the optimized NiCoO2/NiCoP-20 exhibits a high specific capacitance of 3204 F·g−1 at 1 A·g−1 in 3 mol·L−1 KOH aqueous electrolyte in a three-electrode system. Moreover, the asymmetric supercapacitor assembled with the prepared NiCoO2/NiCoP-20 and activated carbon achieves a specific capacitance of 116 F·g−1 with a high energy density of 40.32 Wh·kg−1 at the power density of 800.18 W·kg−1. The practical application is further demonstrated with all-solid-state winding supercapacitor devices, with decent flexibility, in series to light the Central South University (CSU) logo consisting of 21 red LED indicators. The NiCoO2/NiCoP-20 combines the superior electrical conductivity and preeminent redox activity of NiCoP and excellent electrochemical stability of NiCoO2 together, which performed the best electrochemical performance.

Facile route of nitrogen doping in nickel cobalt phosphide for highly efficient hydrogen evolution in both acid and alkaline electrolytes

Ternary nickel cobalt phosphide (NiCoP) is believed to be a promising water-splitting electrocatalyst owing to the synergistic effect between different transition metals. Herein, nitrogen doping NiCoP (N-NiCoP) nanowire arrays on carbon fiber paper skeleton (CFP) are synthesized by a facile hydrothermal reaction and subsequent phosphorization-nigtrogenization method. Structural characterizations and density functional theory (DFT) calculations demonstrate that N dopant prefer to replace O defects rather than P atoms in NiCoP lattice. It is illustrated that the Gibbs free energy of H (ΔGH*) in Ni-Co bridge sites is lowered from −0.35 eV of NiCoP to −0.26 eV of N-NiCoP by 25.7%, moreover, the increased d-orbital electronic density of Co and Ni promotes the charge transfer of hydrogen evolution reaction (HER). Consequently, the HER performance of N-NiCoP is substantially enhanced as compared to NiCoP. For N-NiCoP, the overpotentials to reach a current density of 100 mA·cm−2 are 149 and 162.5 mV in 0.5 M H2SO4 and 1 M KOH, respectively, and their Tafel slopes are 40.1 and 59.8 mV·dec−1, respectively. N doping offers an effective and promising route for improved HER performance of NiCoP catalyst in acid and alkaline electrolytes.

Thermal decomposition assisted one-step synthesis of high surface area NiCoP nanospheres for simultaneous sensing of Lead, Mercury and Cadmium ions in groundwater samples

Here we report a one-pot thermal decomposition assisted synthesis of nickel cobalt phosphide (NiCoP) hollow-nanospheres for simultaneous sensing of the Lead (Pb2+), Mercury (Hg2+) and Cadmium (Cd2+) ions in the groundwater samples. The as-fabricated sensor exhibits distinct peak potentials for Pb2+, Hg2+ and Cd2+ using anodic differential pulse stripping voltammetry technique. The peak separation ΔEP between PbHg and PbCd is 770 mV and 300 mV, respectively. The sensor exhibits an excellent selectivity, sensitivity and the limit of detection (LOD) of 1.59 nM, 2.52 nM and 1.70 nM for Pb2+, Hg2+ and Cd2+ ions, respectively which are below the prescribed maximum contaminant level goal (MCLG) values. The sensing ability of the sensor is attributed towards the high surface area of the as-synthesised NiCoP hollow nanospheres with the presence of orthorhombic plane Co2P as electrocatalytic active sites and the excellent conductivity. The sensor is successfully employed in the determination of heavy metal ions (HMIs) in groundwater samples with an excellent recovery percentage. This is the first report, on the successful demonstration of NiCoP as an active material for simultaneous detection of HMIs which can be effectively used for various environmental analysis.

In situ formation of NiCoP@phosphate nanocages as an efficient bifunctional electrocatalyst for overall water splitting

The construction of bifunctional highly active and durable electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is attractive and challenging for overall water splitting. Herein, we reported a Ni–Co phosphide @phosphate nanocages (NCPP NCs) catalyst prepared by phosphorization of Ni–Co layered double hydroxide (Ni–Co LDH) with in-situ formation of phosphate. The NCPP NCs exhibited an improved wettability with a contact angle of approximately 0° compared with those of Ni–Co LDH (52°) and nickel-cobalt phosphides (NiCoP) (99°). NCPP NCs have been used for enhancing the water-splitting efficiency, and it only required the overpotentials of 291 mV and 140 mV for OER and HER in 0.1 M KOH to achieve the current densities of 10 mA cm−2, respectively. Impressively, the overpotential of NCPP NCs decreased by 42 mV and 64 mV at 10 mA cm−2 for OER in comparison with those of RuO2 and NiCoP (without phosphate phase). Consequently, NCPP NCs, as the bifunctional catalysts, displayed an outstanding performance for the whole water-splitting process with a small potential of 1.60 V at 10 mA cm−2 and long-term stability. These performances enabled this material to be a promising catalyst for overall water electrolysis.

Optimizing the rate capability of nickel cobalt phosphide nanowires on graphene oxide by the outer/inter-component synergistic effects

Bimetallic phosphides have been identified as promising alternative electrode materials owing to their admirable conductivity and electrochemical activity.

Plasma-assisted synthesis of hierarchical NiCoxPy nanosheets as robust and stable electrocatalyst for hydrogen evolution reaction in both acidic and alkaline media

Transition metal phosphides are emerging non-noble metal electrocatalysts for hydrogen evolution reaction (HER) in water splitting. Herein, porous nickel cobalt phosphide nanosheet arrays with hierarchical structure were synthesized on carbon cloth (NiCoxPy-P/CC) as a robust and stable HER electrocatalyst by a facile approach involving electrodeposition and an effective PH3 plasma-assisted phosphorization. Owing to the unique structure with porous nanosheets composed of defect-abundant fine nanocrystals, the as-synthesized NiCoxPy/CC electrocatalyst demonstrates superior catalytic activity for HER to its thermally-phosphorized counterpart. Only at the overpotential as low as 70 (in 0.5 M H2SO4) and 42 mV (in 1 M KOH), the current density of 10 mA/cm2 is achieved for the NiCoxPy/CC, which is among the best reported values for metal phosphide electrocatalysts. Moreover, the catalyst shows satisfying long-term durability up to 24 h in both the acidic and alkaline media. The outstanding HER performance and efficient synthesis strategy for the NiCoxP-P/CC makes it a promising electrocatalyst for hydrogen production.

Hydrodeoxygenation of Palmitic and Stearic Acids on Phosphide Catalysts Obtained In Situ in Reaction Medium

Unsupported phosphide catalysts of composition Ni2P and CoP are prepared in situ in the reaction medium from oil-soluble precursors in the course of hydrodeoxygenation of palmitic and stearic acids. The obtained catalysts are characterized by X-ray powder diffraction and X-ray photoelectron spectroscopy; they show high activity in the hydrodeoxygenation of model substrates. After 6 h of the hydrodeoxygenation reactions, the conversion of palmitic acid reaches 93 and 92% and the conversion of stearic acid is as high as 94 and 91% in the presence of nickel phosphide and cobalt phosphide, respectively. It is shown that the catalyst formed in situ can be isolated and recycled.

Template synthesis of structure-controlled 3D hollow nickel-cobalt phosphides microcubes for high-performance supercapacitors

Given that combined merits of both compositions and novel structures play important roles in energy storage of electrode materials, we herein use [CH3NH3][NixCo1-x(HCOO)3] as self-sacrificed precursors to synthesize structure-controlled hollow nickel cobalt phosphides microcubes. The as-obtained hollow NiCoP-2 displays the highest specific capacity of 629 C g−1 at 1 A g−1 and superior cycling stability with 81.3% capacitance retention at 6 A g−1 after 8000 cycles. Moreover, the asymmetric supercapacitor composed of NiCoP-2 and commercial active carbon (YP-80F) presents the remarkable battery storage performance in terms of outstanding specific capacitance (121.5 F g−1 at 1 A g−1), excellent cycling durability (90.1% capacitance retention after 10,000 cycles) and high energy density of 43.2 Wh kg−1 at a power density of 801.6 W kg−1. The attractive performance can be ascribed to superiority of the transition metal phosphides, hollow structures, as well as synergism between Ni and Co.

Facile self-template fabrication of hierarchical nickel-cobalt phosphide hollow nanoflowers with enhanced hydrogen generation performance

Developing facile methods to construct hierarchical-structured transition metal phosphides is beneficial for achieving high-efficiency hydrogen evolution catalysts. Herein, a self-template strategy of hydrothermal treatment of solid Ni-Co glycerate nanospheres followed by phosphorization is delivered to synthesize hierarchical NiCoP hollow nanoflowers with ultrathin nanosheet assembly. The microstructure of NiCoP can be availably tailored by adjusting the hydrothermal treatment temperature through affecting the hydrolysis process of Ni-Co glycerate nanospheres and the occurred Kirkendall effect. Benefitting from the promoted exposure of active sites and affluent mass diffusion routes, the HER performance of the NiCoP hollow nanoflowers has been obviously enhanced in contrast with the solid NiCoP nanospheres. The fabricated NiCoP hollow nanoflowers yield the current density of 10 mA cm−2 at small overpotentials of 95 and 127 mV in 0.5 mol L−1 H2SO4 and 1.0 mol L−1 KOH solution, respectively. Moreover, the two-electrode alkaline cell assembled with the NiCoP and Ir/C catalysts exhibits sustainable stability for overall water splitting. The work provides a simple but efficient method to regulate the microstructure of transition metal phosphides, which is helpful for achieving high-performance hydrogen evolution catalysts based on solid-state metal alkoxides.

Facile one-pot synthesis of hollow NiCoP nanospheres via thermal decomposition technique and its free-standing carbon composite for supercapacitor application

Development of electrode materials with faster charge kinetics and high electrical conductivity are a major challenge to achieve high-performance supercapacitor. In this work, a novel bimetallic nickel cobalt phosphide hollow nanospheres of different Ni/Co molar ratios were synthesized via one-pot thermal decomposition method. Uniform presence of both Ni and Co species was confirmed by energy dispersive spectroscopy (EDS). In particular, a sample with the Ni: Co molar ratio of 1:9 exhibits the most optimized performance, i.e., high specific capacitance of 160 Fg−1 at 0.8 Ag−1, which might be attributed to the strong synergistic effect between Ni and Co species and rich surface electroactive sites in the sample. Besides, the sample also showed low charge transfer resistance (Rct), which in turn gives high electrical conductivity in comparison with other nickel cobalt phosphide (NiCoP) samples. The hollow nanospheres were incorporated into carbon nanofibers to form a free-standing carbon composite that exhibits excellent capacitance retention of 88.5% even after 5000 charge/discharge cycles. The strategy outlined here presents a facile synthesis technique of nickel-cobalt phosphide hollow nanostructures, a promising electrode material which can be explored for a wide variety of electrochemical energy storage applications.

Versatile Functional Porous Cobalt-Nickel Phosphide-Carbon Cocatalyst Derived from a Metal-Organic Framework for Boosting the Photocatalytic Activity of Graphitic Carbon Nitride.

Metal-organic framework-templated g-C3N4-NiCoP2-porous carbon (PC) ternary hybrid nanomaterials were designed by taking full advantage of the metal-organic framework (MOF) derivative in the photocatalytic reaction for the first time. The MOF-templated porous structure could prevent the stacking of the carbon nitride nanosheet, and the carefully designed NiCoP2, possessing low electrocatalytic hydrogen evolution reaction (HER) overpotential and flat-band potential, could improve the separation as well as the utilization efficiency of photogenerated electron-hole pairs. Moreover, the ligand-templated porous carbon, acting as an interface mediator between g-C3N4 and the NiCoP2 cocatalyst, could boost the charge carrier transport. Consequently, the optimal ternary g-C3N4-NiCoP2-PC heterostructure exhibited enhanced photocatalytic HER performance and considerable H2 evolution performance of 5.8 μmol/h/g under UV-visible light with stoichiometric H2O2 production even in pure water. This work took full advantage of the MOF derivative for improving the photocatalytic reaction activity and provided a method that can hopefully help in designing a novel high-performance catalyst for solar conversion.

Microwave absorption enhancement of nickel cobalt phosphides by decorating on reduced graphene oxide

Herein, NiCoP nanoparticles decorated on reduced graphene oxide (rGO) were synthesized through a two-step hydrothermal-phosphorization route as enhanced microwave absorbers. Microstructure investigations indicate that NiCoP nanoparticles are uniformly anchored on the surface of rGO. Compared with the bare NiCoP, NiCoP/rGO nanocomposites reveal clearly improved microwave absorbing performance. The strongest reflection loss (RL) values of NiCoP/rGO hybrid absorber can reach −20.61 dB at 6.43 GHz with a matching thickness of 4.4 mm, and a broad effective absorption bandwidth (RL < −10 dB) of 4.13 GHz (13.87–18 GHz) can be obtained at only 2.0 mm, while the RL values of the pure NiCoP cannot reach −10 dB in the entire measurement frequency range. This improvement of microwave absorption is ascribed to the polarization, interface interaction and synergistic effect between NiCoP and rGO nanosheets. NiCoP/rGO nanocomposites are expected to be novel microwave absorption materials with high microwave absorption properties.

A Self‐Assembled Flower‐Like Structure of Nickel‐Cobalt Phosphide Nanosheets Supported on Nickel Foam for Electrochemical Hydrogen Evolution Reaction

AbstractIn this study, flower‐like nickel‐cobalt phosphide (NiCoP) on Ni foam (flower‐like NiCoP/NF) was fabricated via a two‐step process, including hydrothermal and phosphorization. Hydrogen evolution reaction (HER) measurements show that such flower‐like NiCoP/NF is a highly efficient and stable electrocatalyst, which can keep high activity for more than 20 h at ambient temperature. Scanning electron microscope (SEM) images show that flower‐like NiCoP/NF uniformly covered the Ni foam surface. In the hydrothermal step, X‐ray photoelectron spectroscopy (XPS) results show that partial Co2+ ions from Co(NO3)2⋅6H2O were oxidized to Co3+ ions in the ethanol‐water solution. Meanwhile, NO3− ions from Ni(NO3)2⋅6H2O and Co(NO3)2⋅6H2O triggered the ethanol‐water solution to release OH− ions, which subsequently reacted with Ni2+, Co2+ and Co3+ ions to generate NiCo‐OH precipitation. Subsequently, in the phosphorization step NiCo‐OH was converted to NiCoP nanosheets by NaH2PO2 at a low temperature of 350 °C. The two‐step method employed in the present work avoids an addition of alkali sources or precipitators to the hydrothermal reaction solution, which is favorable for environmental protection strategies and sustainable development principles.

Bimetallic Ni‒Co phosphide nanosheets self-supported on nickel foam as high-performance electrocatalyst for hydrogen evolution reaction

In this work, bimetallic nickel-cobalt phosphide (Ni-Co-P/NF) self-supported on nickel foam (NF) is synthesized for hydrogen evolution reaction (HER). A two-step method of electrodeposition with subsequently low-temperature phosphatizing is adopted. The physicochemical characterizations of the as-prepared Ni-Co-P/NF show that the surface is covered by metallic phosphide compounds (NiCoP, NiP and Co2P) with unique morphology, consisted of nanosheets randomly dispersed on villiform 3D integrated framework. The electrochemical characterizations demonstrate that Ni-Co-P/NF exhibits the highest performance for HER, in 1.0 M KOH aqueous solution, compared to other as-prepared electrocatalysts. Specifically, it requires very low overpotential values of 85, 210 and 350 mV for delivering large current densities of −10, −500 and −1,500 mA cm−2, respectively, revealing a low Tafel slope of 46 mV dec−1. Besides, Ni-Co-P/NF also displays long-term durability lasting 24 h without obvious deactivation. This work highlights that the NiCoP, NiP and Co2P active phases play a crucial role for the good HER activity. In addition, the unique morphology with self-supported structure provides large electrochemical surface area, allowing the exposure of higher amount of active sites for HER. These self-supported electrocatalysts, without binder, could also improve the electrode's HER activity and stability. This work, therefore, provides a controllable and feasible strategy to synthesize bimetallic phosphides of unique morphology with high HER activity.

Bi-metallic cobalt-nickel phosphide nanowires for electrocatalysis of the oxygen and hydrogen evolution reactions

Transition metal phosphides (TMPs) have emerged as a new class of electrocatalysts capable of catalyzing the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) with high efficiency and good stability. Here, we report a facile fabrication of a series of cobalt-nickel phosphide nanowires (CoNiP NWs) containing different compositions of Co and Ni, which is accomplished by hydrothermal growth of cobalt-nickel-carbonate-hydroxide NWs and a subsequent post-phosphorization treatment. We investigate and compare the electrocatalytic performance of the CoNiP NWs for the OER and HER in alkaline solution. The results show that CoNiP NWs with equimol Co and Ni, i.e. CoNiP-1:1, show the best apparent and intrinsic activities for both OER and HER, compared to CoNiP NWs with other Co/Ni ratios as well as the mono-metallic CoP and Ni5P4 controls. The CoNiP-1:1 can deliver the benchmark apparent current density of 10 mA cm−2 at an overpotential of 301 and 252 mV for the OER and the HER, respectively, and show good stability over 24 h without obvious degradation, holding substantial promise for use as an effective and inexpensive alternative in alkaline water electrolysis.

Hierarchically porous nickel–cobalt phosphide nanoneedle arrays loaded micro-carbon spheres as an advanced electrocatalyst for overall water splitting application

Due to the easy recyclability and pollution-free nature of hydrogen fuel, its highly purified production through electrochemical water splitting process has been attracting increasing attention. In this work, a hybrid of hierarchical porous nickel–cobalt phosphide nanoneedle arrays supported micro-carbon spheres was successfully synthesized and employed as robust bifunctional electrocatalyst for overall water splitting. The optimized Ni1Co3–P@CSs displayed catalytic activity with a low overpotential (η) of 57 mV at 10 mA cm−2 for hydrogen evolution and a η of 330 mV at 20 mA cm−2 for oxygen evolution, along with good stability after testing for 30 h. The water splitting cell of the Ni1Co3–P@CSs delivered smaller cell voltage at a current density of 50 mA cm−2 and much better durability than a similar device based on RuO2/C and Pt/C. The enhanced performance was assumed to the unique hierarchical three-dimensional urchin nanostructure of bimetallic phosphide nanoneedles, which resulted in the synergetic effects to modulate electronic properties and electroactive surface area. These improved the reactant's intermediates adsorption energy, number of exposed active sites, and various shortened channels for charge transfer and reactant/electrolyte diffusion. Our finding offers an attractive electrocatalyst with low cost and high catalytic activity for efficient water electrolysis.

Hierarchical nickel-cobalt phosphide hollow spheres embedded in P-doped reduced graphene oxide towards superior electrochemistry activity

Hierarchical bimetallic Ni-Co phosphides hollow spheres were encapsulated in P-doped reduced graphene oxide (PrGO) to provide superior electrochemistry performances. The hollow spheres with controlling Co/Ni ratios were obtained via a hydrothermal process and following phosphorization reaction using Ni-Co based glycerate microsphere as a self-sacrificing template. The hollow shell with vertical branches was formed via a morphology evolution of solid, yolk-shell to hollow. The hollow spheres were encapsulated in PrGO networks by a hydrothermal synthesis and phosphorization process to fabricate PrGO/Ni-Co phosphide composite (PrGO/NiCoP). Because of unique morphology and composition, the composite with a Ni/Co molar ratio of 1:1 exhibits enhanced supercapacitor and electrocatalysis properties. As a supercapacitor electrode, PrGO/NiCoP provides high discharge specific capacity, excellent rate performance and cycle stability. An asymmetric supercapacitor assembled with PrGO/NiCoP and activated carbon possesses an energy density of 49.7 Wh/Kg with power density of 0.366 kW/kg, which can successfully illuminate red-light light emitting diode. As an electrocatalyst, PrGO/NiCoP exhibits high hydrogen and oxygen evolution reaction activities in 1 M KOH electrolyte. PrGO/NiCoP electrolyzer shows excellent overall water splitting performance and durability, which required a cell voltage of 1.56 V to achieve a current density of 10 mA cm−2.

Fully Solar‐Powered Uninterrupted Overall Water‐Splitting Systems

AbstractExtensive research efforts have been recently devoted to the development of self‐driven electrocatalytic water‐splitting systems to generate clean hydrogen chemical fuels. Currently, self‐driven electrocatalytic water‐splitting devices are powered by solar cells, which operate intermittently, or by aqueous batteries, which deliver stored electric power, leading to high operating costs and environmental pollution. Thus, a fully solar‐powered uninterrupted overall water‐splitting system is greatly desirable. Here, the solar cells, stable output voltage of 1.75 V Ni–Zn batteries, and high efficiency zinc–nickel–cobalt phosphide electrocatalysts are successfully assembled together to create a 24 h overall water‐splitting system. Specifically, the silicon‐based solar cells enable the charging of aqueous Ni–Zn batteries for energy storage as well as providing sufficient energy for electrocatalysis throughout the day; in addition, the high‐capacity Ni–Zn batteries offer a steady output voltage for overall water‐splitting at night. Such an uninterrupted solar‐to‐hydrogen system opens up exciting opportunities for the development and applications of renewable energy.