Nickel Cobalt Phosphide Research Articles

Advanced N-doping nickel-cobalt phosphides for boosting hydrogen evolution in acid and alkali media

In this article, the hydrogen evolution performance in 0.5 M H2SO4 and 1.0 M KOH is improved by introducing N atoms into Ni2P/Co2P through high-temperature doping (N–Ni2P/Co2P). N–Ni2P/Co2P has a lower overpotential than Ni2P/Co2P, which can achieve cathodic current densities of 10 mA cm−2, 100 mA cm−2 at overpotentials of 48 mV, 228 mV in 1.0 M KOH and 63 mV, 211 mV in 0.5 M H2SO4. Density functional theory (DFT) results found that the introduction of N atoms changed the electronic structure of the catalyst. Due to the forward shift of d-band center, the binding force between the catalyst and H∗ is enhanced, providing favorable conditions for hydrogen evolution. Furthermore, the results of scaled-up tests show that 5 cm × 5 cm N–Ni2P/Co2P electrodes still exhibit superior performance, revealing a prospect of industrialization.

Improved Nitrate-to-Ammonia Electrocatalysis through Hydrogen Poisoning Effects.

Electrochemical conversion from nitrate to ammonia is a key step in sustainable ammonia production. However, it suffers from low productive efficiency or high energy consumption due to a lack of desired electrocatalysts. Here we report nickel cobalt phosphide (NiCoP) catalysts for nitrate-to-ammonia electrocatalysis that display a record-high catalytic current density of -702±7 mA cm-2, ammonia production rate of 5415±26 mmol gcat-1 h-1 and Faraday efficiency of 99.7±0.2 % at -0.3 V vs. RHE, affording the estimated energy consumption as low as 22.7 kWh kgammonia-1. Theoretical and experimental results reveal that these catalysts benefit from hydrogen poisoning effects under low overpotentials, which leave behind catalytically inert adsorbed hydrogen species (HI*) at Co-hollow sites and thereupon enable ideally reactive HII* at secondary Co-P sites. The dimerization between HI* and HII* for H2 evolution is blocked due to the catalytic inertia of HI* thereby the HII* drives nitrate hydrogenation timely. With these catalysts, the continuous ammonia production is further shown in an electrolyser with a real energy consumption of 18.9 kWh kgammonia-1.

Construction of iron-doped nickel cobalt phosphide nanoparticles via solvothermal phosphidization and their application in alkaline oxygen evolution

Multi-metallic phosphides offer the possibility to combine the strategies of surface reconstruction, electronic interaction and mechanistic pathway tuning to achieve high electrocatalytic oxygen evolution activity. Here, iron-doped nickel cobalt phosphide nanoparticles (FexCoyNi2-x-yP) with the crystalline NiCoP phase are for the first time synthesized by the solvothermal phosphidization method via the reaction between metal–organic frameworks and white phosphorus. When used to electrochemically catalyze oxygen evolution reaction (OER), the Fe0.4Co0.8Ni0.8P supported by nickel foam requires only 248 mV overpotential to achieve 10 mA cm−2 current densities, and is robust towards the long-term OER in 1 M KOH. The higher number of electrochemically active sites can account for the good OER activity, along with the improved intrinsic activity which is caused by the electron interaction that optimizes the adsorption energy of hydroxyl intermediates, and that increases the acidity of high-valent metal centers. The OER mechanistic pathway involves both adsorbate and lattice oxygen. Surface conversion is observed after OER in alkaline solution, and metal phosphide layer transforms to metal oxides and (oxy)hydroxides.

Carbon-Monoxide Assisted Synthesis of Cobalt-Nickel Phosphides for Hydrogen Evolution Reaction

Alkaline water electrolysis is a method for production of hydrogen as an alternative source for renewable energy. This method can be completely free of greenhouse gas emissions if it is paired with another alternative energy source, such as solar energy or wind power, to provide the necessary electricity to drive the reaction. Water electrolysis requires catalysts to make that necessary amount of electricity low enough for competitive hydrogen production in the current market. Vast numbers of studies have been performed in an attempt to fill this need for cost-effective catalysts for water electrolysis. This work focuses on the development of synthesis methods for cobalt-nickel phosphide catalysts for the hydrogen evolution reaction (HER) for water electrolysis in alkaline media. The methods for preparation of the catalysts are explored for cobalt, nickel, and cobalt-nickel alloy phosphides in the presence of carbon monoxide as a shape-controlling capping agent. Depending on the condition of carbon monoxide addition, the reaction results in high vs. low-aspect ratio nanorods or nanospheres for mono- or bimetallic cobalt-nickel phosphide nanostructures. These phosphides are then subjected to evaluation for HER via cyclic voltammetry and linear sweep voltammetry to study the effects of morphology on their HER activity. Materials characterization such as XRD, TEM, and ICP-MS are performed before the HER electrochemical evaluation for better understanding of the structure-activity relationship. The catalytic activities of these phosphides are also compared to the noble metal benchmark HER catalyst Pt/C in the same environment at their equal mass loadings. The best-performing phosphide is further tested for HER at increased mass loadings to study the effects of catalyst loadings on the mass transport and thus the activity. Further TEM characterization is performed on the most active catalyst after HER to evaluate morphological stability. It is found that in order to achieve an overpotential at the current density of 100 mA/cm2 comparable to Pt/C for 50 μg/cm2, the necessary loading for the phosphide is 250 µg/cm2.

Bi-Interlayer Strategy for Modulating NiCoP-Based Heterostructure toward High-Performance Aqueous Energy Storage Devices.

Nickel-cobalt (NiCo) phosphides (NCPs) possess high electrochemical activity, which makes them promising candidates for electrode materials in aqueous energy storage devices, such as supercapacitors and zinc (Zn) batteries. However, the actual specific capacitance and rate capability of NCPs require further improvement, which can be achieved through reasonable heterostructural design and loading conditions of active materials on substrates. Herein, novel hierarchical Bi-NCP heterogeneous structures with built-in electric fields consisting of bismuth (Bi) interlayers (electrodeposited on carbon cloth (CC)) are designed and fabricated to ensure the formation of uniform high-load layered active materials for efficient charge and ion transport. The resulting CC/Bi-NCP electrodes show a uniform, continuous, and high mass loading (>3.5mg) with a superior capacitance reaching 1200 Fg-1 at 1 Ag-1 and 4129 mFcm-2 at 1 mAcm-2 combined with high-rate capability and durable cyclic stability. Moreover, assembled hybrid supercapacitors (HSCs), supercapatteries, and alkaline Zn-ion (AZBs) batteries constructed using these electrodes deliver high energy densities of 64.4, 81.8, and 319.1 Whkg-1, respectively. Overall, the constructed NCPs with excellent aqueous energy storage performance have the potential for the development of novel transition metal-based heterostructure electrodes for advanced energy devices.

Electrochemical synthesis of hybrid nanostructure of nickel cobalt phosphide/molybdenum disulfide on nickel foam as an effective electrode material in supercapacitor

In the present work, molybdenum disulfide (MoS2) was synthesized on nickel cobalt phosphide (NiCoP)-coated nickel foam (NF) using cyclic voltammetry (CV) as an effective electrode material in supercapacitor. The physical, chemical, and electrochemical properties of the electrodes were evaluated using different characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge (GCD). The electrochemical performance of this bilayer-structured electrode was investigated. The two-layered structure of NiCoP@MoS2 provided a high specific capacitance of 2352.407 F g−1 at 1 A g−1, energy density of 52 Wh Kg−1 at power density of 321 W kg−1. Consequently, the NiCoP@MoS2 electrode material is expected to be a promising option for supercapacitor applications and other energy devices.

Innovative Catalyst Design of Sea-Urchin-like NiCoP Nanoneedle Arrays Supported on N-Doped Carbon Nanospheres for Enhanced HER Performance.

Hydrogen (H2) stands as a clean energy alternative to fossil fuels, especially within the domain of the hydrogen evolution reaction (HER), offering prospective solutions to mitigate both environmental and energy-related challenges. In this work, we successfully synthesized a sea-urchin-like catalyst, specifically a nickel-cobalt phosphide nanoneedle array on N-doped carbon nanospheres (Ni0.5Co1.5P@NCSs), for efficient HER by a sequential hydrothermal and low-temperature phosphating process. The catalyst exhibits sea-urchin-like structures, offering a specific surface area of 298 m2 g-1 and consequently furnishing a greater abundance of active sites. Comparing with non-sea-urchin-like Ni0.5Co1.5P@CN catalysts, the Ni0.5Co1.5P@NCSs exhibit an overpotential of 163 mV at 10 mA cm-2, a Tafel slope of 60 mV dec-1, and a maintained current density of approximately 90% during 50 h of continuous electrolysis. Experiments demonstrate that the outstanding electrochemical properties of the Ni0.5Co1.5P@NCSs originate from nitrogen doping of carbon spheres, the distinctive morphology of sea-urchin-like nanoneedle arrays, and simultaneous enhancements in intermediate adsorption energy, charge transfer, and electrolyte diffusion channel shortening. This work emphasizes a preparation strategy for synthesizing an attractive electrocatalyst with a low cost and efficient HER performance.

Synergistic modulation of the localized electrons and lattice distortion of cobalt-nickel phosphide motivates intrinsic activity through heteroatoms for efficient electrocatalytic water oxidation

The development of non-precious metal-based catalysts for efficient renewable energy conversion remains a significant challenge. In this study, we synthesized petal-shaped spherical electrocatalysts based on cobalt–nickel phosphate (NiCoP) doped with Mo at different concentrations (Mo-NiCoP; 0.05 %, and 0.1 %) using a facile process. Mo doping provides abundant active sites for electrochemical water oxidation. The 0.1 %Mo-NiCoP electrocatalyst exhibited superior electrocatalytic activity for the oxygen evolution reaction (OER), with a low overpotential of 277 mV, compared to NiCoP (313 mV), 0.05 %Mo-NiCoP (292 mV), and noble-metal catalysts for OER. Additionally, the long-term stability of 0.1 %Mo-NiCoP under a fixed voltage for 20 h revealed only a minor decline in current density. The results of density functional theory calculations suggest that the exceptional electrocatalytic activity of Mo-NiCoP is due to the optimized adsorption energy barrier of intermediates in the OER process, the modulation of the electronic structure, and the introduction of rich lattice disorder defects in NiCoP by the Mo heteroatoms. This work presents a practical and economical approach to fabricating ternary transition-metal phosphates for water oxidation.

Three-dimensional heterostructured nickel phosphide @ nickel cobalt phosphide nanocomposites with highly porous surface for high-performance supercapacitor

Nickel phosphide @ nickel cobalt phosphide heterostructure nanocomposites (NP@NCP) are prepared by phosphidization of metal-organic framework (MOF) precursors. The NP@NCP have similar morphology as MOF, but are highly porous. When used as the electrode material, the NP@NCP31/carbon cloth exhibits a specific capacity of 868.1 C g−1 at 1 A g−1 and 82.05% capacity is maintained after 5000 cycles in 4 M KOH. An asymmetric supercapacitor constructed with NP@NCP31 and activated carbon exhibits an energy density of 61.9 Wh kg−1 at a power density of 800.1 W kg−1 and a capacity retention rate of 94.17% after 5000 cycles. The high charge-storage performance of the NP@NCP is owing to the formation of heterointerface that causes charge redistribution, increases the electrochemically active sites, and facilitates the ion diffusion. The highly porous morphology also contributes to the high specific surface area and the increased active sites. Developing heterostructure materials based on transition metal phosphides is a viable approach to enhance the electrochemical capabilities of supercapacitors.

MnOx-decorated MOF-derived nickel-cobalt bimetallic phosphide nanosheet arrays for overall water splitting.

Exploring non-noble metal dual-functional electrocatalysts with high activity and stability for water splitting is highly desirable. In this study, using zeolitic imidazolate framework-L (ZIF-L) nanoarrays as the precursor, manganese oxide-decorated porous nickel-cobalt phosphide nanosheet arrays have been prepared on nickel foam (denoted as MnOx/NiCoP/NF) through cation etching, phosphorization and electrodeposition, which are utilized as an efficient dual-functional electrocatalyst for overall water splitting. The hierarchical porous nanosheet arrays provide abundant active sites for the electrochemical process, while the MnOx modification induces strong interfacial interaction, benefiting charge transfer. Thus, the MnOx/NiCoP/NF exhibits excellent electrocatalytic activity toward the hydrogen evolution reaction (HER, overpotential of 93 mV at 10 mA cm-2), oxygen evolution reaction (OER, overpotential of 240 mV at 10 mA cm-2) and overall water splitting (cell voltage of 1.59 V at 10 mA cm-2). Furthermore, it shows superior stability during continuous overall water splitting for 200 h. This work provides a simple and effective approach for developing efficient non-noble metal dual-functional catalysts for overall water splitting.

Controlled synthesis of Co2P/Ni12P5@NF nanoarray as electrocatalyst for urea assisted hydrogen production in freshwater and seawater

The research and development of environmentally friendly, stable and low cost catalyst for water electrolysis is the general trend and imminent direction. In this paper, the cobalt-nickel phosphide with nanoflake (Ni12P5/Co2P@NF) was prepared by a simple hydrothermal reaction and low temperature phosphating process for the first time. As a catalyst for urea assisted water electrolysis, Ni12P5/Co2P@NF exhibits excellent hydrogen evolution reaction (HER) activity, providing a very small overpotential of 124 mV at a current density of 10 mA cm−2 in 1.0 M KOH solution containing 0.5 M urea. At the same time, it also present a very low Tafel slope (61.98 mA dec−1), which demonstrates that the faster the rate of charge transfer is, the better the reaction is. We also tested HER performance in seawater solution containing 0.5 M urea and 1.0 M KOH, and the overpotential was 146 mV at a current density of 10 mA cm−2. Moreover, the stability of the Ni12P5/Co2P@NF material for HER was also tested for a long time, and the result showed that the catalytic performance decreased first and then was relatively stable. Density functional theory (DFT) calculation demonstrates that the Ni12P5 monomer presents the optimal Gibbs free energy for hydrogen, the introduction of Co2P promotes the conductivity of the electrode, and the synergistic catalysis of the Ni12P5 and Co2P promotes the electrochemistry performance of the electrode. This work proposes a novel idea and strategy for designing reasonable metal phosphide as an environmentally friendly and stable electrode.

Enhanced Synergistic Effect by Facile Tuning of Nickel Doping on Cobalt Phosphide as Electrochemical Catalysts for Hydrogen Evolution Reaction in Alkaline Water Electrolysis

The development of efficient and cost-effective electrocatalyst for the hydrogen evolution reaction (HER) is essential for alkaline water electrolysis. Cobalt phosphide (Co2P) is a promising non-noble electrocatalyst material for HER due to its low cost and high stability in alkaline solutions. However, improving the HER performance of Co2P is still challenging due to its catalytic mechanism in which Volmer reaction is the dominated rate-determining step. In this study, we introduced nickel to cobalt phosphide in order to improve its performance as an electrocatalyst because nickel is known to be beneficial for water dissociation (Volmer reaction), while cobalt is beneficial for producing gaseous hydrogen (Heyrovsky or Tafel reaction). This synergistic effect between nickel and cobalt phosphide contributes to enhancing HER performance. Also, it is crucial to find the optimal ratio of nickel and cobalt for maximizing synergistic effect. To facilitate the optimization process, a co-sputtering system was used to fabricate the electrodes. The resulting Ni-doped Co2P showed significantly enhanced HER performance with low overpotential of ~91 mV at 10 mA/cm2 and Tafel slope of ~47 mV/dec compared to pristine Co2P in electrochemical analysis. This enhancement is attributed from the optimized ratio between the sites where water dissociation and adsorbed hydrogen recombination reactions occur. The findings of this study demonstrate that the nickel cobalt phosphide electrode is a promising electrocatalyst for HER in alkaline water electrolysis.

Manganese-Doped Bimetallic (Co,Ni)2P Integrated CoP in N,S Co-Doped Carbon: Unveiling a Compatible Hybrid Electrocatalyst for Overall Water Splitting.

Rational design of highly efficient noble-metal-unbound electrodes for hydrogen and oxygen production at increased current density is crucial for robust water-splitting. A facile hydrothermal and room-temperature aging method is presented, followed by chemical vapor deposition (CVD), to create a self-sacrificed hybrid heterostructure electrocatalyst. This hybrid material, (Mn-(Co,Ni)2P/CoP/(N,S)-C), comprises manganese-doped cobalt nickel phosphide (Mn-(Co,Ni)2P) nanofeathers and cobalt phosphide (CoP) nanocubes embedded in a nitrogen and sulfur co-doped carbon matrix (N,S)-C on nickel foam. The catalyst exhibits excellent performance in both the hydrogen evolution reaction (HER; η10 = 61mV) and oxygen evolution reaction (OER; η10 = 213mV) due to abundant active sites, high porosity, and enhanced hetero-interface interaction between Mn-(Co2P-Ni2P) CoP, and (N,S)-C supported by significant synergistic effects observed among different phases through density functional theory (DFT) calculations. Impressively, (Mn-(Co,Ni)2P/CoP/(N,S)-C (+,-) shows an extra low cell voltage of 1.49 V@10mA cm-2. Moreover, the catalyst exhibits remarkable stability at 100 and 300mA cm-2 when operating as a single stack cell electrolyzer. The superior electrochemical activity is attributed to the enhanced electrode-electrolyte interface among the multiple phases of the hybrid structure.

Nickel-cobalt phosphide nanowires as precatalysts for surface reconstruction to prepare durable and efficient OER catalysts

The investigation of transition metal phosphides (TMPs) as efficient electrocatalysts for water splitting has garnered significant attention in academic research. Nevertheless, limited research has been conducted on the alteration of the structural and morphological properties of TMPs resulting from the unavoidable surface reconstruction during the oxygen evolution reaction (OER). This study introduces a newly developed catalyst, namely nickel–cobalt phosphide nanowires (NiCoP), which facilitates the in-situ growth of nickel–cobalt oxide (NiCo2O4) through surface reconstruction during anodic potential cycling in alkaline electrolytes. The catalyst's extensive modification can be observed through ex-situ characterization techniques. The catalyst undergoes a significant transformation that ultimately yields a phosphide scaffold, leading to the formation of a spinel oxide surface. This transformation enhances the catalytic environment for the OER, making it highly efficient and potent. The transformed catalyst demonstrates comparable catalytic performance to the precious RuO2 catalyst across various current densities. Importantly, it exhibits remarkable long-term stability, as demonstrated by its ability to sustain continuous operation for 72 h at a current density of 50 mA while maintaining stable catalytic performance.

Non‐Carbon‐Dominated Catalyst Architecture Enables Double‐High‐Energy‐Density Lithium–Sulfur Batteries

AbstractThe commonly used “catalyst on carbon” architecture as a sulfur host is difficult to jointly achieve high gravimetric and volumetric energy densities for lithium–sulfur (Li–S) batteries due to the contradiction between low tap density/poor catalytic activity of carbon and the easy agglomeration of metal‐based compounds without carbon. Here, a non‐carbon‐dominated catalytic architecture using macroporous nickel/cobalt phosphide (NiCoP) is reported as the sulfur host for Li–S batteries. The macroporous framework, which accommodates a large amount of sulfur, can accelerate the electrochemical reaction kinetics by accelerated e− transport, Li+ diffusion, and superior adsorption and catalytic activity of inherent Ni2P/CoP heterostructures. The high tap density (0.45 g cm−3) and mechanically hard features contribute to the excellent structural and physicochemical stability of the NiCoP@S electrode after the pressing and rolling process. These features enable the Li–S coin cell to exhibit excellent electrochemical performance under conditions of high sulfur loading (10.2 mg cm−2) and lean electrolyte (electrolyte/sulfur of 2 µL mg−1). Inspiringly, the assembled pouch cell can simultaneously deliver a gravimetric energy density of 345.2 Wh kg−1 and an impressive volumetric energy density of 952.7 Wh L−1 based on the entire device configuration.

BiVO4 Photoanodes Enhanced with Metal Phosphide Co-Catalysts: Relevant Properties to Boost Photoanode Performance.

Achieving highly performant photoanodes for oxygen evolution is key to developing photoelectrochemical devices for solar water splitting. In this work, BiVO4 photoanodes are enhanced with a series of core-shell structured bimetallic nickel-cobalt phosphides (MPs), and key insights into the role of co-catalysts are provided. The best BiVO4 /Ni1.5 Co0.5 P and BiVO4 /Ni0.5 Co1.5 P photoanodes achieve a 3.5-fold increase in photocurrent compared with bare BiVO4 . It is discovered that this enhanced performance arises from a synergy between work function, catalytic activity, and capacitive ability of the MPs. Distribution of relaxation times analysis reveals that the contact between the MPs, BiVO4 , and the electrolyte gives rise to three routes for hole injection into the electrolyte, all of which are significantly improved by the presence of a second metal cation in the co-catalyst. Kinetic studies demonstrate that the significantly improved interfacial charge injection is due to a lower charge-transfer resistance, enhanced oxygen-evolution reaction kinetics, and larger surface hole concentrations, providing deeper insights into the carrier dynamics in these photoanode/co-catalyst systems for their rational design.

An efficient cerium dioxide incorporated nickel cobalt phosphide complex as electrocatalyst for All-pH hydrogen evolution reaction and overall water splitting

Transition metal phosphides (TMPs) have been considered as potential electrocatalysts with adjustable valence states, metal characteristics, and phase diversity. However, it is necessary but remains a major challenge to obtain efficient and durable TMPs catalysts, which can realize efficiently for not only all-pH hydrogen evolution reaction (HER), but also oxygen evolution reaction (OER). Hence, cerium dioxide incorporated nickel cobalt phosphide growth on nickel foam (CeO2/NiCoP) is fabricated by hydrothermal and phosphating reaction. CeO2/NiCoP shows excellent activity for all-pH HER (overpotentials of 48, 58 and 72 mV in alkaline, neutral and acidic solution at the current density of 10 mA cm−2), and has a small OER overpotential (231 mV @ 10 mA cm−2). Moreover, the voltage of overall water splitting in alkaline solution and simulated seawater electrolyte is only 1.46 and 1.41 V (10 mA cm−2), respectively, coupled with outstanding operational stability and corrosion resistance. Further mechanism research shows that CeO2/NiCoP possesses rich heterointerfaces, which serves more exposed active sites and possesses a promising superhydrophilic and superaerophobic surface. Density functional theory calculations manifest that CeO2/NiCoP has appropriate energy for intermediates of reactions. This work provides a deep insight into the CeO2/NiCoP catalyst for high-performance water/seawater electrolysis.

Enhanced electrocatalytic efficiencies for water electrolysis and para-nitrophenol hydrogenation by self-supported nickel cobalt phosphide-nickel iron layered double hydroxide p-n junction

Charge redistribution across heterointerfaces is an important tactic to enhance the catalytic activities and bifunctionality of hybrid catalysts, especially for green hydrogen production from water electrolysis and harmless electrocatalytic valorization of organics. Herein, a self-supported p-n junction catalytic electrode was constructed by tandem electrodeposition of nickel cobalt phosphide (NiCoP) and nickel iron layered double hydroxide (NiFe LDH) onto Ni foam (NF) substrate, denoted as NiCoP@NiFe LDH/NF, to enhance the electrocatalytic capabilities for water electrolysis and hydrogenation of an organic, para-nitrophenol (4-NP). Benefitting from the charge redistribution across the p-n junction, high electrocatalytic efficiencies for oxygen evolution reaction (OER, overpotential of 388 mV at 100 mA cm−2) and hydrogen evolution reaction (HER, overpotential of 132 mV at 10 mA cm−2) could be achieved concurrently by the NiCoP@NiFe LDH/NF electrode, and both overpotentials were located within the mainstream levels in this domain. The bifunctional catalytic features enabled a full water electrolysis response of 10 mA cm−2 at 1.61 V. In addition, the p-n junction electrode catalyzed the hydrogenation of 4-NP at a conversion of 100%, para-aminophenol (4-AP) selectivity of 90% and faradaic efficiency (FE) of 88% at −0.18 V. The current work offers a feasible strategy for fulfilling electrochemical H2 production and hydrogenation valorization of 4-NP pollutant by constructing a self-supported p-n junction catalytic electrode.

Nickel-cobalt phosphide interfacial heterostructures as supercapacitor electrode material for electrochemical energy storage application

Transition metal phosphides have become one of the excellent electrode material choices for improving the electrochemical performance of supercapacitors due to their high theoretical capacity and good redox ability. The introduction of secondary metals in single metal phosphides can enhance the properties and chemical stability of their redox sites. Combining multiple types of transition metal phosphides can comprehensively utilize the properties of each component and improve the charge efficiency at the interface, thus exhibiting good electrochemical performance. Therefore, in this work, nickel–cobalt phosphide heterojunction Co2P/NiCoP/Ni2P was prepared. At the current density of 1 A/g, the specific capacitance of the Co2P/NiCoP/Ni2P electrode material is 174.2 mAh/g. And its specific capacitance is higher than each of its components at any current density. An asymmetric supercapacitor was assembled with Co2P/NiCoP/Ni2P as the positive electrode and activated carbon as the negative electrode. When the power density is 800 W kg−1, the device can exhibit an energy density of 42.29 W h kg−1, which shows a high energy density while maintaining the power density. At the current density of 2 A/g, the assembled supercapacitor could still maintain 90% of the initial specific capacitance after 10,000 cycles, showing high cycle stability. This provides ideas for future research on this type of energy storage materials.

Highly active Mo-modified NiCoP/NiCoN flower-like sphere: Controlled phase engineering for efficient water splitting

Reasonable design and preparation of a versatile catalyst for the ultra-high efficiency energy conversion system has remarkable practical significance. Herein, a facile phase engineering strategy is employed to synthesize molybdenum modified nickel cobalt nitride and nickel cobalt phosphide flower-like sphere heterostructure (labeled as Mo-NiCoP/NiCoN FS) to improve the performance of Mo-NiCoN FS. The significant geometric structure advantages, the exposure to abundant active centers and the interfacial effect of heterostructure of the target product is evaluated in detail. When the as-obtained Mo-NiCoP/NiCoN FS is applied to the electrochemical bifunctional hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), it demonstrates remarkable electrocatalytic activity, high-conductivity and excellent corrosion resistance compared with Mo-NiCoN FS with a single phase. As a result, Mo-NiCoP/NiCoN FS indicates a low overpotential towards HER (204 mV at 10 mA/cm2) and OER (262 mV at 10 mA/cm2) compared with Mo-NiCoN (234 mV for HER and 357 mV for OER at 10 mA/cm2) in an alkaline medium and it exhibits excellent activity and stability during the dual-electrode full water-splitting. Therefore, the advanced nano-catalyst with superior activity developed through the controllable phase engineering method illustrates a potential application prospect in high efficiency energy equipment water-splitting and fuel-cells.