One dimensional nickel phosphide polymorphic heterostructure as carbon-free functional support loading single-atom iridium for promoted electrocatalytic water oxidation

Although conducting materials such as carbon nanotube and carbon fiber paper(CFP)have been extensively employed as support of electrocatalytic active sites,most of them are of poor catalytic functionality by themselves and undesirable stability during strong acid/alkaline environments or oxidation process.Here we report a novel one-dimensional(1D)nickel phosphide polymorphic heterostructure(denoted as NPPH)to work as one effective carbon-free functional support for loading of single-atom Ir water oxidation electrocatalyst.Specifically,the NPPH composed of both Ni12P5and Ni2P phases is not only active for robust alkaline water oxidation but also is of good stability and hydrophilicity for favorable loading of single-atom dispersed iridium.The NPPH supported single-atom Ir electrocatalyst(Ir/NPPH)is found to exhibit remarkably superior water oxidation activity with respect to the NPPH itself or CFP supported single-atom Ir catalyst(Ir/CFP),demonstrating the synergetic promotion effect between NPPH and single-atom Ir catalyst.Furthermore,the NPPH supported single-atom Ir catalyst can bear alkaline water oxidation for over 120 h at current density of 50 mA cm^(-2).The NPPH developed here is expected as functional support to composite with other water oxidation catalysts,as may be an alternative strategy of developing highly efficient carbon-free electrocatalysts.

Effect of nickel phosphide nanoparticles crystallization on hydrogen evolution reaction catalytic performance

In order to investigate the effect of nickel phosphide nanoparticles’ （Ni-P NPs） crystallization on hydrogen evolution reaction （HER） catalytic performance, amorphous Ni-P NPs and crystalline Ni12P5 were synthesized by a simple and low-cost autocatalytic reduction method and heat treatment process. The result of electrochemical tests shows that crystalline Ni12P5 has much higher HER catalytic activity than the amorphous one. X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy revealed that Ni？P bond formed during crystallization, making Ni positively charged and P negatively charged. This charged nature of Ni12P5 is similar to [NiFe] hydrogenase and its analogous, which make the removal of H2 less energy-cost.

Stable overall water splitting in an asymmetric acid/ alkaline electrolyzer comprising a bipolar membrane sandwiched by bifunctional cobalt-nickel phosphide nanowire electrodes

Water splitting has been proposed to be a promising approach to producing clean hydrogen fuel.The two half-reactions of water splitting,that is,the hydrogen evolution reaction(HER)and oxygen evolution reaction(OER),take place kinetically fast in solutions with completely different pH values.Enabling HER and OER to simultaneously occur under kinetically favorable conditions while using exclusively low-cost,earth-abundant electrocatalysts is highly desirable but remains a challenge.Herein,we demonstrate that using a bipolar membrane(BPM)we can accomplish HER in a strongly acidic solution and OER in a strongly basic solution,with bifunctional self-supported cobaltnickel phosphide nanowire electrodes to catalyze both reactions.Such asymmetric acid/alkaline water electrolysis can be achieved at 1.567 V to deliver a current density of 10 mA/cm2 with ca.100%Faradaic efficiency.Moreover,using an“irregular”BPM with unintentional crossover the voltage needed to afford 10 mA/cm2 can be reduced to 0.847 V,due to the assistance of electrochemical neutralization between acid and alkaline.Furthermore,we show that BPM-based asymmetric water electrolysis can be accomplished in a circulated single-cell electrolyzer delivering 10 mA/cm2 at 1.550 V and splitting water very stably for at least 25 hours,and that water electrolysis is enabled by a solar panel operating at 0.908 V(@13 mA/cm2),using an“irregular”BPM.BPMbased asymmetric water electrolysis is a promising alternative to conventional proton and anion exchange membrane water electrolysis.

Study on the mechanism of hydrodesulfurization of tetrahydrothiophene catalyzed by nickel phosphide

Hydrodesulfurization(HDS)reaction can significantly reduce the viscosity and sulfur content of heavy oil,while the HDS reaction mechanism of tetrahydrothiophene as the main sulfide in heavy oil is still unclear.The HDS experiment of tetrahydrothiophene catalyzed by nickel phosphide(Ni_(2)P)is carried out at 200-300°C.The results indicate that the H_(2)S production under the catalysis of Ni_(2)P increases obviously within 200-250°C.The main gas products of HDS reaction are butane,butene and H_(2)S.Meanwhile,the mechanism of tetrahydrothiophene catalyzed by Ni_(2)P is analyzed based on Density Functional Theory(DFT).It is revealed that the adsorption model is most stable when tetrahydrothiophene is vertically adsorbed on the V-Ni-Hcp1 site of Ni_(2)P(001).The C-S bond is elongated and the C-C bond is shortened after adsorption.Hydrogenation(HYD)is the most possible reaction route of tetrahydrothiophene on Ni_(2)P(001)surface.There are two routes with the lowest activation energy,which are C_(4)H_(8)S→C_(4)H_(8)SH^(*)→C_(4)H_(9)SH^(*)→C_(4)H_(10)+H_(2)S and C_(4)H_(8)S→C_(4)H9S^(*)→C_(4)H_(9)^(*)+SH^(*)→C_(4)H_(10)+H_(2)S.Butane and H_(2)S are produced in the reaction,corresponding to the experimental results.This study provides a basis for understanding of the HDS mechanism of tetrahydrothiophene catalyzed by Ni_(2)P.

Urea electrooxidation-boosted hydrogen production on nitrogen-doped porous carbon nanorod-supported nickel phosphide nanoparticles

Urea electro-oxidation reaction(UEOR)-boosted water electrolysis can supplant the kinetics-restricted oxygen evolution reaction(OER)and provide an energy-saving method of hydrogen generation.However,low UEOR activity and the poisoning issue of the catalyst limit its practical application.Herein,a simple coordination reaction is used to synthesize the dimethylglyoxime-NiⅡcomplex(DMGNiⅡ),which efficiently serves as the initial precursor to synthesize nitrogen-doped carbon nanorodsupported nickel phosphide nanoparticle(Ni_(2)P/N-C)nanocomposites.The density functional theory calculations and electrochemical results reveal that nitrogen doping can weaken the adsorption of hydrogen and the generated CO_(2)resulting in an enhancement of hydrogen evolution reaction(HER)and UEOR activity.In addition,N-doping can also promote the generation of Ni,which can further promote the UEOR and HER performance.Concretely,the overpotential for the HER on Ni_(2)P/N-C-2h nanocomposites is only 201 m V at 10 mA cm,and the onset potential of the UEOR on NiP/NC-2h nanocomposites is only 1.34 V.Additionally,the Ni_(2)P/N-Cnanocomposites also show excellent long-term stability due to the introduction of nitrogen-doped carbon material.Consequently,the symmetric Ni_(2)P/N-C-2h||Ni_(2)P/N-C-2h urea electrolyzer requires 1.41 V of electrolysis voltage for urea electrolysis,which can be applied in energy-saving H_(2) production and environment purification.

Facile synthesis of a novel P-doped carbon coated nickel phosphides nanorods as sodium storage anode materials

Nickel-based phosphides as anode materials of sodium ion batteries have high capacity,but poor cycle stability and low electrical conductivity.Rational structural design for nickel-based phosphides with carbon provides a new way to address the above shortcomings.This paper presents a simple method to synthesize a novel carbon coated Ni_(x)P(x=2.4-3.0,denoted as Ni_(x)P@PC)nanorods using phosphoric acid resin as phosphorus and carbon sources.The Ni_(x)P nanocrystals are in-situ generated in the P-doped carbon without further phosphatization.The carbon layer can confine the volume changes during charging/discharging process.Additionally,the enriched P doping in the carbon layer greatly increases the electrical conductivity of the Ni_(x)P-based composite and provides more active sites for sodium storage.The as-obtained Ni_(x)P@PC nanorods reveal excellent reversible sodium storage performance(271.6 mA·h/g based on the mass of Ni_(x)P@PC at 0.1 A/g after 300 cycles)and outstanding cycling stability(0.005%capacity decay per cycle after 5000 cycles at 2 A/g).Meanwhile,the formation mechanism of Ni_(x)P@PC is evidenced by monitoring the evolution of morphology and structure during the preparing process.This paper may provide a feasible way for constructing high-performance transitional metal compounds for sodium-ion batteries.

Recent advances in transition metal phosphide materials:Synthesis and applications in supercapacitors

Supercapacitors(SCs)are considered promising energy storge systems because of their outstanding power density,fast charge and discharge rate and long-term cycling stability.The exploitation of cheap and efficient electrode materials is the key to improve the performance of supercapacitors.As the battery-type materials,transition metal phosphides(TMPs)possess high theoretical specific capacity,good electrical conductivity and superior structural stability,which have been extensively studied to be electrode materials for supercapacitors.In this review,we summarize the up-to-date progress on TMPs materials from diversified synthetic methods,diverse nanostructures and several prominent TMPs and their composites in application of supercapacitors.In the end,we also propose the remaining challenges toward the rational discovery and synthesis of high-performance TMP electrodes materials for energy storage.

Nickel phosphide for MRI-guided synergistic photo-immunotherapy

Developing a phototherapy modality to ablate tumor and then trigger immunogenic cell death(ICD)for simultaneously eliminating distal and metastatic tumors holds great promise in clinical applications.Herein,the polyethylene glycol functionalized Ni_(2)P(Ni_(2)P@PEG NPs)is developed with enhanced biocompatibility,high photoabsorption and photothermal efficiency,as well as reactive oxygen species generation ability.Of particular note,Ni_(2)P@PEG NPs mediated phototherapy could not only realize efficient ablation of primary tumors,but also inhibit distal tumors and metastatic tumors by triggering an antitumor immune response.The above conclusions were verified by B mode ultrasound,western blot assay,and immunohistochemistry analysis.Meanwhile,Ni_(2)P@PEG NPs showed excellent magnetic resonance imaging(MRI)properties.In summary,the MRI-guided multimodal cancer therapies of Ni_(2)P@PEG NPs represent significant potential for clinical applications.

Sponge-like nickel phosphide-carbon nanotube hybrid electrodes for efficient hydrogen evolution over a wide pH range

Cost-effective hydrogen production via electrolysis of water requires efficient and durable earth-abundant catalysts for the hydrogen evolution reaction （HER） over a wide pH range. Herein, we report sponge-like nickel phosphide- carbon nanotube （NixP/CNT） hybrid electrodes that were prepared by facile cyclic voltammetric deposition of amorphous NixP catalysts onto the three- dimensional （3D） porous CNT support. These compounds exhibit superior catalytic activity for sustained hydrogen evolution in acidic, neutral, and basic media. In particular, the NixP/CNT electrodes generate cathodic currents of 10 and 100 mA.cm-2 at overpotentials of 105 and 226 mV, respectively, in a 1 M phosphate buffer solution （pH = 6.5） with a Tafel slope of 100 mV.dec-1; the currents were stable for over 110 h without obvious decay. Our results suggest that the 3D porous CNT electrode supports could serve as a general platform for earth-abundant HER catalysts for the development of highly efficient electrodes for hydrogen production.

Metal phosphonate-derived cobalt/nickel phosphide@N-doped carbon hybrids as efficient bifunctional oxygen electrodes for Zn-air batteries

The exploration of efficient bifunctional electrocatalysts for oxygen reduction reaction and oxygen evolution reaction is pivotal for the development of rechargeable metal–air batteries.Transition metal phosphides are emerging as promising catalyst candidates because of their superb activity and low cost.Herein,a novel metal phosphonate-derived cobalt/nickel phosphide@N-doped carbon hybrid was developed by a carbothermal reduction of cobalt/nickel phosphonate hybrids with different Co/Ni molar ratios.The metal phosphonate derivation method achieved an intimately coupled interaction between metal phosphides and a heteroatom-doped carbon substrate.The resultant Co_(2)P/Ni_(3)P@NC-0.2 enables an impressive electrocatalytic oxygen reduction reaction activity,comparable with those of state-of-the-art Pt/C catalysts in terms of onset potential(0.88 V),4e‒selectivity,methanol tolerance,and long-term durability.Moreover,remarkable oxygen evolution reaction activity was also observed in alkaline conditions.The high activity is ascribed to the N-doping,abundant accessible catalytic active sites,and the synergistic effect among the components.This work not only describes a highefficiency electrocatalyst for both oxygen reduction reaction and oxygen evolution reaction,but also highlights the application of metal phosphonate hybrids in fabricating metal phosphides with tunable structures,which is of great significance in the energy conversion field.

Nickel Phosphide Nanorod Arrays Vertically Grown on Ni Foam as High-Efficiency Electrocatalyst for the Hydrogen Evolution Reaction

An electrocatalyst of nickel phosphide （Ni2P） nanorod arrays vertically grown on Ni foam composite （NNFC） was prepared successfully using NaHzPO2 as phosphorus source by means of a facile method of in situ phospho- rization of Ni foam. The as-prepared NNFC exhibits excellent HER performance with an onset overpotential of 100 mV, a small Tafel slope of only 55 mV/dec, and a low overpotential involving 200 mV at a current density of 10 mA·cm^-2. Furthermore, the electrocatalyst was also demonstrated to possess high stability with a neglectable de- crease in activity even after durability test for 25 h.

Integrated Ni2P nanosheet arrays on three-dimensional Ni foam for highly efficient water reduction and oxidation

The large-scale synthesis of efficient nonprecious bifunctional electrocatalysts for overall water splitting is a great challenge for future renewable energy conversion systems. Herein, Ni2P nanosheet arrays directly grown on three-dimensional(3 D) Ni foam(Ni P/NF) are fabricated by hydrothermal treatment of metallic Ni foam with H2O2solution and subsequent phosphidation with NaH2PO2. The Ni P/NF as electrocatalyst exhibits superior activities for both hydrogen evolution reaction(HER) and oxygen evolution reaction(OER). Most importantly, employing both as the cathode and anode for an alkaline water electrolyzer, Ni P/NF only requires a cell voltage of 1.63 V to reach a current density of 10 mV cm-2, together with stronger durability. Preliminary catalytic information suggests that the tailored 3 D superstructure and integrated electrode configurations afford improved active sties and enhanced electron/mass transfer,responding for the outstanding activity and stability.

Integrated Ni-P-S nanosheets array as superior electrocatalysts for hydrogen generation

Searching for efficient and robust non-noble electrocatalysts for hydrogen generation is extremely desirable for future green energy systems.Here, we present the synthesis of integrated Ni-P-S nanosheets array including Ni_2P and NiS on nickel foam by a simple simultaneous phosphorization and sulfurization strategy. The resultant sample with optimal composition exhibits superior electrocatalytic performance for hydrogen evolution reaction(HER) in a wide pH range. In alkaline media, it can generate current densities of 10, 20 and 100 mA cm^(-2) at low overpotentials of only-101.9,-142.0 and-207.8 mV with robust durability. It still exhibits high electrocatalytic activities even in acid or neutral media. Such superior electrocatalytic performances can be mainly attributed to the synergistic enhancement of the hybrid Ni-P-S nanosheets array with integration microstructure. The kind of catalyst gives a new insight on achieving efficient and robust hydrogen generation.

Cobalt‐regulation‐induced dual active sites in Ni_(2)P for hydrazine electrooxidation

Better understanding of electrochemical reaction behaviors of hydrazine electrooxidation at metal phosphides has long been desired and the optimization of reaction kinetics has been proved to be operable.Herein,the dehydrogenation kinetics of hydrazine electrooxidation at Ni_(2)P is adjusted by Co as the(Ni_(0.6)Co_(0.4))_(2)P catalyzes HzOR effectively with onset potential of–45 mV and only 113 mV is needed to drive the current density of 50 mA cm^(‒2),showing over 60 mV lower than Ni_(2)P and Co_(2)P.It also delivers the maximum power density of 263.0 mW cm^(-2) for direct hydrazine fuel cell.Detailed experimental results revealed that Co doping not only decreases the adsorption energy of N_(2)H_(4) on Ni sites,lowering the energy barrier for dehydrogenation,but also acts as the active sites in the optimal reaction coordination to boost the reaction kinetics.This work represents a breakthrough in improving the catalytic performance of non‐precious metal electrocatalysts for hydrazine electrooxidation and highlights an energy‐saving electrochemical hydrogen production method.

Interface engineering of NiSe_(2) nanowrinkles/Ni_(5)P_(4)nanorods for boosting urea oxidation reaction at large current densities

Deliberate modulation of the electronic structure via interface engineering is one of promising perspectives to build advanced catalysts for urea oxidation reaction(UOR)at high current densities.However,it still remains some challenges originating from the intrinsically sluggish UOR dynamics and the high energy barrier for urea adsorption.In response,we report the coupled NiSe_(2)nanowrinkles with Ni_(5)P_(4)nanorods heterogeneous structure onto Ni foam(denoted as NiSe_(2)@Ni_(5)P_(4)/NF)through successive phosphorization and selenization strategy,in which the produced closely contacted interface could provide high-flux electron transfer pathways.Theoretical findings decipher that the fast charge transfer takes place at the interfacial region from Ni_(5)P_(4)to NiSe_(2),which is conducive to optimizing adsorption energy of urea molecules.As expected,the well-designed NiSe_(2)@Ni_(5)P_(4)/NF only requires the low potential of 1.402 V at the current density of 500 mA·cm^(-2).More importantly,a small Tafel slope of 27.6 mV·dec^(-1),a high turnover frequency(TOF)value of 1.037 s^(-1)as well as the prolonged stability of 950 h at the current density of 100 mA·cm^(-2)are also achieved.This study enriches the understanding on the electronic structure modulation via interface engineering and offers bright prospect to design advanced UOR catalysts.

Ni2P Nanosheets:A High Catalytic Activity Platform for Electrochemical Detection of Acetaminophen

Main observation and conclusion Accurate determination of acetaminophen concentration is essential for studying the metabolic status of acetaminophen in clinical practice.In this study,nickel phosphide was used for electrochemical detection of acetaminophen for the first time.

A core-shell catalyst design boosts the performance of photothermal reverse water gas shift catalysis

Photothermal reverse water gas shift(RWGS)catalysis holds promise for efficient conversions of greenhouse gas CO_(2) and renewable H_(2),powered solely by sunlight,into CO,an important feedstock for the chemical industry.However,the performance of photothermal RWGS catalysis over existing supported catalysts is limited by the balance between the catalyst loading and dispersity,as well as stability against sintering.Herein,we report a core-shell strategy for the design of photothermal catalysts,by using Ni1_(2)P_(5) as an example,with simultaneously strong light absorption ability,high dispersity and stability.The core-shell structured Ni1_(2)P_(5)@SiO_(2) catalyst with a relatively small Ni1_(2)P_(5) particle size of 15 nm at a high Ni1_(2)P_(5) loading of 30 wt%exhibits improved activity,nearly 100%CO selectivity,and superior stability in photothermal RWGS catalysis,particularly under intense illuminations.Our study clearly reveals the effectiveness of the core-shell strategy in breaking the limitation of supported catalysts and boosting the performance of photothermal CO_(2) catalysis.

Metal-organic framework-derived Ni2P/nitrogendoped carbon porous spheres for enhanced lithium storage

Transition metal phosphides(TMPs)/carbonaceous matrices have gradually attracted attention in the field of energy storage.In this study,we presented nickel phosphide(Ni2P)nanoparticles anchored to nitrogen-doped carbon porous spheres(Ni2P/NC)by using metal-organic framework-Ni as the template.The comprehensive encapsulation architecture provides closer contact among the Ni2P nanoparticles and greatly improves the structural integrity as well as the electronic conductivity,resulting in excellent lithium storage performance.The reversible specific capacity of 286.4 mA hg^-1 has been obtained even at a high current density of 3.0 Ag^-1 and 450.4 mA hg^-1 is obtained after 800 cycles at 0.5 Ag^-1.Furthermore,full batteries based on LiNi1/3Co1/3Mn1/3O2||Ni2P/NC exhibit both good rate capability and cycling life.This study provides a powerful and indepth insight on new advanced electrodes in high-performance energy storage devices.