In-situ synthesis of porous Ni2P nanosheets for efficient and stable hydrogen evolution reaction

The design and development of highly efficient and stable non-noble metal electrocatalysts for hydrogen evolution reaction (HER) have attracted increasing attention. However, some key issues related to large overpotential, high cost and poor stability at high current density still remains challenging. In this work, we report a facile in-situ integration strategy of porous Ni₂P nanosheet catalysts on 3D Ni foam framework (PNi₂P/NF) for efficient and stable HER in alkaline medium. The two-step method can creates high density of ultra-thin porous Ni₂P nanosheets firmly rooted into Ni foam substrate which can guarantee excellent electrical contacts, strong substrate adherence and large amount of active sites. Such a binder-free flexible HER cathode exhibits superior electrocatalytic performance with an overpotential of 134 mV at current density of 10 mA cm⁻². It also shows superior stability at higher current densities of 100 and 500 mA cm⁻² for at least 48 h and negligible performance degradation is observed.     

MOF-derived NiSe2 nanoparticles grown on carbon fiber as a binder-free and efficient catalyst for hydrogen evolution reaction

It is challenging to grow inexpensive cathode material with superior catalytic properties for hydrogen evolution reaction (HER). Metal-organic frameworks (MOFs) have emerged as powerful platforms to synthesize efficient and ultrastable catalysts for hydrogen production. In this research, NiSe₂ nanoparticles were derived from Ni-based MOF, which grown in situ on carbon fiber (NiSe₂/C/CF) through pyrolysis and selenization processes. NiSe₂/C/CF displays a higher HER performance than that of Ni/C/CF and Ni-MOF-74/CF. Notably, the NiSe₂/C/CF electrode gives a low overpotential of 209 mV, a Tafel slope of 74.1 mV/dec, and outstanding stability with slight decay after operating for 12 h. The high HER catalytic activity of NiSe₂/C/CF is mainly ascribed to the emerging effects of NiSe₂ nanoparticles and three-dimensional conductive substrate CF, facilitating active moieties exposure and electron transfer during the electrocatalytic process. Therefore, this work illustrates a novel approach for the preparation of transition metal chalcogenides as low-cost and stable catalysts for HER.     

NiCoP–CoP heterostructural nanowires grown on hierarchical Ni foam as a novel electrocatalyst for efficient hydrogen evolution reaction

The design and manufacture of effective non-noble metal catalysts for the H₂ evolution reaction (HER) are urgent for realizing a cost-effective hydrogen production. We report herein on flower-like structures consisting of NiCoP–CoP heterostructural nanowires grown directly on the hierarchically porous nickel framework (NiCoP–CoP/Ni/NF) to achieve a highly efficient HER in alkaline solution (1.0 M KOH). The NiCoP–CoP/Ni/NF is synthesized by electrodeposition of porous Ni layers on Ni foam, followed by simple hydrothermal reaction and phosphorization. For HER, the binder-free NiCoP–CoP/Ni/NF electrode can reach 10 mA cm^?2 current density at a quite low overpotential of 49 mV, because of the combination of porous Ni layers and highly active NiCoP–CoP nanowires. In addition, the NiCoP/CoP heterostructures exhibited remarkable stability under the long-term durability test. This work provides a new strategy that combines electrodeposition and hydrothermal reaction to synthesize effective HER catalysts.     

Facile synthesis of Ni5P4 nanosheets/nanoparticles for highly active and durable hydrogen evolution

It is essential to search highly active, steady and cheap non-noble electrocatalyst for hydrogen evolution reaction (HER). At present, nickel phosphides are extensively used in electrochemical hydrogen evolution due to its excellent stability and activity. Hence, we report a facile, effective and feasible strategy to synthesis of Ni₅P₄ nanosheets/nanoparticles structure on carbon cloth, which was fabricated by electroless nickel plating on carbon cloth followed via straightforward thermal phosphidation treatment with NaH₂PO₂ as phosphorus source. The as-prepared CC@Ni–P electrocatalyst exhibits HER activity with low overpotentials (93 mV vs. RHE) to attain current density 10 mA/cm² as well as small Tafel slope (58.2 mV/dec), which outperforms most nickel phosphides electrocatalysts. The excellent HER performance can be ascribed to the large electrochemically active surface area, and phosphorus-rich Ni₅P₄ phase can supply further bridges sites of Ni and P. Significantly, as-prepared CC@Ni–P catalyst electrode exhibits no apparent HER activity decay after continuous stability test. Beyond that, the approach can be readily used to fabricate large size (5 × 5 cm) nickel phosphide electrocatalyst with excellent HER performance, which may be conducive to the proton exchange membrane (PEM) water electrolyser applications in future. This work opens an effective way to construct excellent performance transition-metal phosphides for HER.     

Synthesis of Ni2P/Ni5P4 on porous N decorated rGO foam for efficiently electrocatalytic hydrogen evolution reaction

As a new generation of non-precious metal catalysts, nickel phosphide is regarded as an ideal substitute for precious metal platinum in electrochemical hydrogen evolution. Here, a hydrogen evolution reaction (HER) electrocatalyst is developed by in situ growth of Ni₂P/Ni₅P₄ heterostructures on porous N decorated rGO foam (named Ni₂P/Ni₅P₄/N-rGO). The porous rGO foam structure provides a larger surface area and abundant active sites. The Ni₂P/Ni₅P₄ nanoparticles with heterostructures are uniformly distributed on the rGO sheet, which enhance the charge transfer ability. The decorating of N element also correspondingly improves the HER performance. The as-prepared Ni₂P/Ni₅P₄/N-rGO exhibits excellent HER performance in alkaline medium. When the current density is 10 mA cm^?2, the overpotential is only 22 mV. No obvious loss of HER activity after 2000 cyclic voltammetry indicates that the composite has excellent stability. This work presents a valuable route for fabricating inexpensive and high-performance catalysts for electrocatalysis.     

Fe-Cu coated nickel mesh usage as cathode catalyst for hydrogen evolution reaction

Nickel mesh electrodes were used as the working electrode. Iron and copper were electrochemically deposited on the nickel mesh in different amounts. When electrochemical coatings had been carried out, different currents were passed from the circuit at different times and coatings were accumulated at constant load. The prepared electrodes called as FexCux, FexCu3x and FexCu9x and these electrodes have been used for hydrogen evolution reaction (HER). The surface morphologies were investigated by scanning electron microscopy. The HER activity is assessed by recording cathodic current–potential curves, cyclic voltammetry, electrochemical impedance spectroscopy. The results show that FexCu9x catalysts have a compact and porous structure as well as good electrocatalytic activity for the HER in alkaline media.     

Novel peapod-like Ni2P@N-doped carbon nanorods array on carbon fiber for efficient electrocatalytic urea oxidation and hydrogen evolution reaction

Designing and optimizing structure is an effective method to enhance electrocatalytic performance of transition metal-based catalysts. In this work, an innovative nanostructured electrode, consisted of peapod-like Ni₂P@N-doped carbon nanorods array coating on carbon fiber (CF@p-Ni₂P@NC), is devised and synthesized. The N-doped carbon layer is crucial for maintaining the peapod-like nanostructure, which allows for multi-channel electrolyte transport and gas product release. And the carbon layer coating Ni₂P nanoparticles also enhance electrical conductivity and stability, thus ensuring fast electron transport from/to active sites and the long-term stability of catalyst during urea oxidation reaction (UOR)/hydrogen evolution reaction (HER). Benefit from the reasonable structure, CF@p-Ni₂P@NC present perfect performance with getting 100 mA cm^?2 at potential/overpotential of 1.417/0.194 V for UOR/HER in 1.0 M KOH containing 0.5 M urea. In addition, the overall urea-electrolysis system using CF@p-Ni₂P@NC bifunctional electrode only requires 1.590 V to obtain 100 mA cm^?2.     

3D self-standing grass-like cobalt phosphide vesicles-decorated nanocones grown on Ni-foam as an efficient electrocatalyst for hydrogen evolution reaction

The growing hydrogen consumption has greatly promoted the development of efficient, stable and low-cost electrocatalysts for the hydrogen evolution reaction (HER). Constructing functional nanostructures is an efficacious strategy to optimize catalytic performance. Herein, we present a feasible route to fabricate distinctive 3D grass-like cobalt phosphide nanocones clad with mini-vesicles on the hierarchically porous Ni foam, which can directly serve as a binder-free electrocatalyst with superior catalytic activity and durability in HER. Thanks to its distinctive 3D microstructure featured with favourable pore-size distribution, abundant active sites provided by mini-vesicles and rapid electron transfer with the assistance of Ni foam, the as-grown grass-like CoP/NF electrocatalyst has shown a favourable overpotential in an acidic solution with an onset overpotential of ∼35 mV, an overpotential of 71 mV at a current density of 10 mA cm⁻², reduced by 60 mV in comparison with that realized by urchin-like CoP/NF nanoprickles. Moreover, it has exhibited an excellent HER activity in the alkaline medium, with an overpotential of 117 mV at 10 mA cm⁻², a Tafel slope of 63.0 mV dec⁻¹ and a long-term electrochemical durability.     

N-doped MoP nanoparticles for improved hydrogen evolution

It is still strongly required to explore non-noble catalysts with excellent performances for hydrogen generation. MoP-based catalysts are demonstrated as good candidates and further improvements are highly encouraged. Herein, a novel strategy of N-doping has been proposed to increase the HER performance over the MoP-based catalysts, in which nitrilotriacetic acid (N(CH₂COOH)₃, NTA) is selected to provide the doping element of N. With the addition of NTA, the N-doped MoP catalysts with good distribution have been successfully prepared, showing smaller particle size, reduced electrical resistance, increased amount and better quality of active sites, resulting in much better performances compared to pure MoP. This strategy can also be extended to other counterparts for the further improvement of HER activity by N-doping.     

Copper-N-SiO2 nanoparticles catalyst for hydrogen evolution reaction

Herein, we report the Cu(0)-based nanoparticles film generated by in situ electrochemical reductions of Cu(II) ions modified silica exhibits a high activity and durable HER catalyst in acid solution. Copper ions were attached to silica surface using chemical modification with propyl ethylene diamine (PEDA) linker followed by treating with copper sulfate solution to form Cu(II)-PEDA/silica complex. Copper nanoparticles then were obtained by electrochemical reduction of the silica immobilized Cu(II) ions in sulfuric acid solution. The physicochemical properties of the resulted from copper nanoparticles incorporated silica were investigated and analyzed by Energy Dispersive x-ray Spectroscopy (EDS), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction XRD, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM). The electrochemical characterizations confirm that the Cu(0) nanoparticles supported on silica substrate combining both high activity and stability for hydrogen evolution reaction with overpotential(η), of 200 mV and Tafel slope of 67 mV/dec could serve as Cu-based electrocatalysts in practical applications for hydrogen production in 0.5 M of H₂SO₄ solution.The catalyst exhibited respectable stability and steadily produced hydrogen at several potentials. The catalyst has the perspective to expressively lower the cost of manufacturing hydrogen fuel, thus helping to spread the use of hydrogen fuel which does not harm the environment.     

P doped CoMoO4/RGO as an efficient hybrid catalyst for hydrogen evolution

Transition metal oxides, as newly earth-abundant and low-cost catalysts, have been regarded as promising materials for electrocatalytic oxygen evolution. However, they are rarely used as an electrocatalyst in hydrogen evolution reaction (HER) due to the poor HER activity. Herein, we present a facile two-step method to synthesize P doped CoMoO₄/RGO (P-CoMoO₄/RGO) with different atomic ratios of Co²⁺/Co³⁺ through a simple phosphorization strategy by changing the mass of NaH₂PO₂. The effective P-doping into CoMoO₄/RGO can modify the electronic properties and modulate the atomic ratio of Co²⁺/Co³⁺, which promotes the electron transfer and creates more activity sites. Therefore, the optimized P-CoMoO₄/RGO with a relatively larger atomic ratio of Co²⁺/Co³⁺ shows superior HER performances in alkaline media, which affords a current density of 10 mA cm⁻² at a small overpotential of 90 mV and a low Tafel slope of 62 mV dec⁻¹ along with having satisfactory long-term stability. This work provides a valuable route to enhance the HER activity of transition metal oxides.     

Carbon supported nickel phosphide as efficient electrocatalyst for hydrogen and oxygen evolution reactions

Hydrogen production through water splitting is an efficient and green technology for fulfilling future energy demands. Carbon nanotubes (CNT) supported Ni₂P has been synthesized through a simpler hydrothermal method. Ni₂P/CNT has been employed as efficient electrocatalysts for hydrogen and oxygen evolution reactions in acidic and alkaline media respectively. The electrocatalyst has exhibited low overpotential of 137 and 360 mV for hydrogen and oxygen evolution reactions respectively at 10 mA cm^?2. Lower Tafel slopes, improved electrochemical active surface area, enhanced stability have also been observed. Advantages of carbon support in terms of activity and stability have been described by comparing with unsupported electrocatalyst.     

Hollow bimetallic M-Fe-P (M=Mn,Co, Cu) nanoparticles as efficient electrocatalysts for hydrogen evolution reaction

Searching for low-cost electrocatalysts with high activity towards the hydrogen evolution reaction (HER) is of great significance to enable large-scale hydrogen production via water electrolysis. In this study, by using inverse spinel MFe₂O₄(M = Mn, Fe, Co, Cu) nanoparticles (NPs) as the precursors, monodisperse bimetallic phosphide M-Fe-P NPs/C with hollow structures were readily obtained by a gas-solid annealing method. These hollow phosphide NPs displayed excellent HER activity in an acidic medium with a low loading amount of 0.2 mg cm⁻². In particular, the Co–Fe–P NPs/C shows highest HER activity that only requiring an overpotential of 97 mV to retain a current density of 10 mA cm⁻². A volcano relation between activity and incorporated elements was revealed. Incorporation of cation with high electronegativity stabilized the FeP active centres, while phase segregation resulted in the loss of activity for Cu–Fe–P NPs/C.     

Synthesis of functional Ni2P/CC catalyst and the robust performances in hydrogen evolution reaction and nitrate reduction

The non-precious transition metal phosphides (TMPs) as robust and effective hydrogen evolution reaction (HER) catalysts have attracted enormous attention, due to the merits of earth-abundance, low price, desirable stability and high efficiency. However, the conventional preparation process of this kind of catalyst is inconvenient. Herein, we report a facile approach toward the fabrication of nickel phosphide (Ni₂P) assembled on carbon cloth (CC) via the coupling method of electroless plating and low temperature phosphorization. Then, the crystallinity, morphology and chemical component of fabricated self-supporting Ni₂P/CC catalyst employed for the HER process were characterized, and the HER property was successively evaluated in three types of electrolytes (i.e., acidic, neutral and alkaline solutions). The as-prepared Ni₂P/CC catalyst displays a remarkable HER performance, which can be corroborated by the small Tafel slope (b = 50 mV dec⁻¹), high exchange current density (j₀ = 6.6 × 10⁻² mA cm⁻²), acceptable overpotential (119 mV) to attain the current density of 10 mA cm⁻², as well as the superb stability (<5% decay after 24 h potentiostatic test) in 0.5 M H₂SO₄. In addition, it should be noted that the HER process of Ni₂P/CC catalyst can be competent for the reduction of nitrate from the solution, and an efficiency of 63.2% for this nutrient pollutant is achieved.     

Synthesis of ultrafine ruthenium phosphide nanoparticles and nitrogen/phosphorus dual-doped carbon hybrids as advanced electrocatalysts for all-pH hydrogen evolution reaction

Pt-group metal phosphides are widely utilized as efficient electrocatalysts for hydrogen evolution reaction (HER), whereas most of the synthetic strategies are complicated, dangerous, and toxic with the use of large amount of nitrogen (N) and/or phosphorus (P) sources. Here, we report the synthesis of ruthenium phosphide nanoparticles (NPs) confined into N/P dual-doped carbon by pyrolyzing self-prepared ruthenium-organophosphine complex using 1,3,5-triaza-7-phosphadamantane (PTA) as the ligand and N/P sources. The achieved S–RuP₂/NPC displayed excellent electrocatalytic activity (overpotentials of 19, 37, and 49 mV in alkaline, neutral, and acidic media, respectively, at 10 mA cm⁻²) toward HER at all pH ranges. The high performance of S–RuP₂/NPC must be ascribed to the homogeneously distributed and P-rich RuP₂ NPs with the diameter of 3.29 nm on the NPC surface, which can considerably improve the atom utilization for HER. The present synthetic strategy not only avoids the use of additional N/P sources but also the generation of flammable and toxic PH₃ gas. This synthetic strategy can be extended to prepare other traditional metal phosphides for electrocatalytic applications.     

Ultra-small RuPx nanoparticles on graphene supported schiff-based networks for all pH hydrogen evolution

As a promising candidate to replace Pt in hydrogen evolution reaction (HER), ruthenium phosphide catalysts have shown excellent performance and attract increasing attention. However, it is still a challenge to control the particle sizes of RuP_x were on the supports. In this study, the Schiff-based networks with 3D rigid organic networks are successfully grown on graphene, and the obtained composite was used as a new support for the RuP_x. This composite can not only provide more metal coordinating sites but also restrict the growth of RuP_x. Therefore, ultra-small RuP_x nanoparticles are uniformly dispersed via a subsequent phosphating and pyrolysis process. The final RuP_x/NPG catalyst exhibits low overpotentials at the current density of 10 mA cm⁻² (32 mV in 0.5 M H₂SO₄ solution, 13 mV in 1 M KOH solution, and 50 mV in 1 M PBS solution). This work provides a new strategy to solve the aggregation problem of the metal phosphides on the substrate by introducing Schiff-based networks into the graphene.     

Efficient and stable Ni–Co–Fe–P nanosheet arrays on Ni foam for alkaline and neutral hydrogen evolution

The development of highly efficient and superior durability electrocatalysts is vital to expedite hydrogen evolution reaction (HER). Herein, a mixed amorphous and nano-crystalline Ni–Co–Fe–P alloy on Ni foam after 75 s dealloying in 3 M HCl (Ni–Co–Fe–P/NF-3-75) is synthesized by the preparation strategy of two-step method consisting of electroless deposition and dealloying process. Ni–Co–Fe–P/NF-3-75 shows an excellent HER performance and high durability in both alkaline and neutral conditions by optimizing the composition of the catalysts, acid concentration, and the time of dealloying. Benefitting from the high conductivity of Ni foam carrier, coordination between polymetallic phases, and the large exposure of defects, the as-prepared Ni–Co–Fe–P/NF-3-75 requires only a low overpotential of 56 mV and 104 mV to reach the current density of 10 mA cm⁻² in 1.0 M KOH and 1.0 M phosphate buffer (PBS), respectively. Remarkably, the Ni–Co–Fe–P/NF-3-75 electrode exhibits superior cycling stability and long-term robust durability without obvious overpotential decline. The successful preparation of the Ni–Co–Fe–P/NF-3-75 catalyst indicates that this method provides an efficient way to synthesize polymetallic phosphides for hydrogen evolution reaction.     

Nickel nanocones as efficient and stable catalyst for electrochemical hydrogen evolution reaction

In this work, nickel nanocones (NNCs) were fabricated by single-step electrodeposition method. The NNCs were used as hydrogen evolution electrode and their electrocatalytic activity was compared with pure nickel film. Linear Sweep Voltammetry (LSV), Tafel polarization, Electrochemical Impedance Spectroscopy (EIS), Cyclic Voltammetry (CV) and chronopotentiometry in 1 M KOH were used for study of the electrocatalytic activity for hydrogen evolution reaction (HER). The active surface area was increased by formation of NNCs and hence, the electrocatalytic activity of nickel electrode was improved. Results indicate that the current density corresponding to the amount of evolved hydrogen of NNCs is five times more than pure nickel film formed in the Watts bath.     

Cobalt phosphide nanoparticles embedded in 3D N-doped porous carbon for efficient hydrogen and oxygen evolution reactions

An electrocatalyst based on a unique three-dimensional (3D) N-doped porous carbon sheet networks embedded with CoP₂ nanoparticles (CoP₂@3D-NPC) was synthesized by a facile pyrolysis process as well as an in-situ phosphatization method. The improved CoP₂@3D-NPC hybrid materials show excellent electrocatalytic activity toward HER and OER. This material provides a low overpotential of 126 mV at 10 mA cm⁻² in 0.5 M H₂SO₄ and 167 mV at 20 mA cm⁻² in 1.0 M KOH for HER with a small Tafel slope value of 59 mV dec⁻¹, respectively. Besides, it is also active for the OER under alkaline conditions. Such a prominent property of the CoP₂@3D-NPC electrocatalyst could be attributed to its excellent electrical conductivity of 3D carbon substrate, strong synergistic effect between CoP₂ nanoparticles and carbon nanosheet as well as extra active sites created by the N-doped structure.     

Phosphatizing engineering of heterostructured Rh2P/Rh nanoparticles on doped graphene for efficient hydrogen evolution in alkaline and acidic media

A wide diversity of phosphides of platinum-group metal including Rh, Ru and Ir exhibit intriguing electrocatalytic activity toward hydrogen evolution reaction (HER). The phosphidation degree, namely the P dosage in these phosphides shows pronounced influence on the catalytic performance but is hard to control. In this work we developed a reliable strategy to synthesize Rh₂P-based nanoparticles with controlled phosphidation degree, and investigated the influence of phosphidation degree on HER. It is found that the heterostructured Rh₂P/Rh nanoparticle, i.e., the P-deficient composite with mixed metallic and phosphide phases, outperforms either the metallic Rh or pure Rh₂P nanoparticles. As-synthesized Rh₂P/Rh nanoparticles supported on P/N co-doped graphene (denoted as Rh₂P/Rh-G) display remarkable HER activity with tiny overpotential of 17 and 19 mV at 10 mA cm^?2 current density in alkaline and acid, efficiently surpassing its Rh-based rivals and benchmark Pt/C catalyst. Meanwhile it illustrates a large mass-specific activity (3.23 and 6.26 A mg^?1 @50 mV overpotential in alkaline and acid, respectively) due to its high activity and low metal loading. Density functional theory (DFT) calculation indicates that the Rh₂P/Rh heterostructured interface possesses the optimal close-to-zero value of hydrogen adsorption energy and water dissociation process is accelerated, and thus boosts HER activity.