One-step synthesis of Ni3S2 nanowires at low temperature as efficient electrocatalyst for hydrogen evolution reaction

Ni₃S₂ is an emerging cost-effective catalyst for hydrogen generation. However, a large amount of reported Ni₃S₂ was synthesized via multi-step approaches and few were fabricated based on the one-step strategies. Herein, we report a facile one-step low-temperature synthesis of Ni₃S₂ nanowires (NWs). In this strategy, a resin containing sulfur element is recommended as a sulfur resource to form Ni₃S₂ NWs. It presents a plausible explanation on the vapor–solid–solid (VSS) growth mechanism according to the results of this experiment and reported in literature that has been published. The Ni₃S₂ NW exhibits a potential ∼199 mV at 10 mA cm⁻² and the long-term durability over 30 h at 20 mA cm⁻² HER operation, better than other reported Ni₃S₂. More importantly, according to replace transition metal foam as the initial metal, other transition metal sulfide can be readily synthesized via this original approach.     

Quaternary-metal phosphide as electrocatalyst for efficient hydrogen evolution reaction in alkaline solution

Hydrogen evolution reaction (HER) is a critical process in electrocatalytic water splitting for hydrogen production. However, the development of low-cost electrocatalysts for highly efficient HER is still a huge challenge. Hence, we fabricate a multi-metal phosphide on Ni foam, FeCoNiNb_xP, through a facile hydrothermal reaction followed by phosphorization. We find that Nb promotes the formation of metal phosphides, and the main phases of the catalysts with Nb are multiphase phosphides. Importantly, the Nb incorporation significantly improves the HER activity of FeCoNiP. We show that FeCoNiNb_0.3P has the best HER activity, which only requires an overpotential of 78 mV to achieve a current density of 10 mA cm^?2 in 1 M KOH, and demonstrates excellent stability under both constant potential and varied current densities. Our findings show that the multiple-metal compounds are beneficial to the improvement of catalytic activity and provide guidance on the design of novel catalysts for applications.     

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.     

Copper induced phosphide for enhanced electrochemical hydrogen evolution reaction

Research on highly efficient catalysts for electrochemical hydrogen evolution reaction (HER) remains a challenge. In this work, we successfully wrap copper (Cu) inside of copper phosphide (Cu₃P) nanoparticle to form a copper/copper phosphide (Cu/Cu₃P) core/shell structure attached on carbon nanotubes (CNTs) for enhanced HER activity in acid. The average size of the core/shell particles is around 25 nm, with about 5 nm of Cu₃P as the outer layer. The catalytic activity of the core/shell structure is significantly promoted compared to the metallic Cu and Cu₃P pure phases nanoparticles on CNTs, requiring overpotentials of 84 and 161 mV to achieve 10 and 100 mA cm⁻² of current density, respectively. The core/shell structure also presents high HER durability and stability, with the polarization curve overlapped after 5000 cycles of CVs and steady current density at 25 mA cm⁻² for as long as 10 h. To account for the promoted HER performance, the Cu/Cu₃P structure is fully investigated by physical and electrochemical characterizations and density functional theory (DFT) calculations. The DFT results depict that the neutralized the adsorption Gibbs free energy of hydrogen atoms (ΔG_H1) is induced by the electronic interactions between metallic Cu and phosphide phase.     

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.     

Palladium-coated polyaniline nanofiber electrode as an efficient electrocatalyst for hydrogen evolution reaction

In this study, polyaniline (PANI) with abundant protonated regions was used for the first time as a palladium (Pd) support for enhanced performance in hydrogen evolution reaction (HER). For this purpose, the hierarchical Pd@PANI nanofiber electrode was easily synthesized by electrochemical polymerization of aniline on Au followed by potential-controlled electrochemical deposition of Pd nanoclusters on the PANI. The reported catalyst was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy. Linear sweep voltammetry analysis was performed to evaluate the HER performance. Ion transfer behavior was investigated using electrochemical impedance spectroscopy analysis. The electrochemical tests show that the Pd@PANI/Au electrode has a low overpotential of ～60 mV at 10 mA cm^?2 and a small Tafel slope of 35 mV dec^?1 for HER in acidic media, with high catalytic activity and stability. These features will make the Pd@PANI/Au a promising candidate as a high-performance electrocatalyst for HER applications.     

WSe2/rGO hybrid structure: A stable and efficient catalyst for hydrogen evolution reaction

The number of exposed active sites in a catalyst plays a key role in determining its catalytic performance. However, the aggregation effect in nanostructured catalysts causes much less reactive sites exposed. In this paper, we report a novel structure of WSe₂/rGO with highly exposed WSe₂ active edge sites by uniformly imbedding the rGO between each WSe₂ nanosheets. With the introduction of rGO, the electron transport property of the WSe₂/rGO hybrid structure has also been enhanced. The structure and composition of the samples were investigated by the X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. Our electrochemical characterizations confirm that the WSe₂/rGO hybrid structure exhibits enhanced electrochemical catalytic performance with a Tafel slop of 85 mV/dec for HER, much smaller than that of the pure WSe₂.     

Ion exchange synthesis of Fe-doped clustered CoP nanowires as superior electrocatalyst for hydrogen evolution reaction

Green hydrogen production from electrochemical water splitting currently suffers from the key issues of high energy consumption and cost. Herein, we demonstrated the synthesis of highly efficient and stable clustered CoP nanowires electrocatalysts on nickel foam. Moreover, an ion exchange strategy was proposed to precisely control the doping content of iron to further modify the intrinsic electrochemical activity of CoP nanowires. The introduction of iron effectively alters the surface atomic configuration and electronic structure of CoP and increases the active sites, thus accelerating the overall reaction rate and enhancing the catalytic performance. It has been demonstrated that the CoFeP-30-30/NF electrode exhibits platinum-like catalytic activity with only an overpotential of 29.8 mV at 10 mA·cm⁻² and outstanding stability toward hydrogen evolution reaction. The synthetic strategy of CoFeP/NF electrode proposed in this work will significantly promote the development of highly efficient transition metal phosphides electrocatalysts with lower overpotential and better stability.     

MOF-derived cobalt manganese phosphide as highly efficient electrocatalysts for hydrogen evolution reaction

Hydrogen is considered as a viable alternative to traditional fossil fuels. Hydrogen evolution reaction (HER) by electrochemical water splitting is the most reliable and effective way for the sustainable production of pure hydrogen. The design and synthesis of highly active and stable non-noble-metal-based electrocatalysts is the core of the large-scale application of this technology. Herein, peony petal-like CoMnP/NF nanomaterials growing on nickel foam (NF) are prepared via facile hydrothermal and phosphorization methods. The results showed that CoMnP/NF had excellent HER activity in acidic and alkaline media. In 0.5 M H₂SO₄, CoMnP/NF only needed 66.6 mV overpotential to drive the current density of 10 mA cm^?2, with a Tafel slope of 38.8 mV dec^?1. In addition, a particularly low overpotential of 53.9 mV and Tafel slope of 63 mV dec^?1 are required to achieve the same current density in the 1 M KOH electrolyte. Meanwhile, the electrocatalyst showed good stability after 1000 cyclic voltammetry tests and 12 h I-T tests. In the 1 M KOH electrolyte, the current density of 10 mA cm^?2 achieved with only 1.70 V battery voltage, and the electrocatalyst showed excellent stability. The performance of CoMnP/NF can be attributed to the synergistic effect between Co and Mn atoms and the high electrochemical surface area (ECSA). This study provides a valuable strategy for the synthesis of non-precious metals and high-performance catalytic materials.     

Engineering multiphase for activating electroactive sites for highly efficient hydrogen evolution: Experimental and theoretical investigation

An ideal electrocatalyst for the hydrogen evolution reaction of water splitting requires substantial active sites with high catalytic activity, fast electron and mass transfer, low gas adsorption energy, and high stability. However, a single component catalyst usually has only one of the many properties of an ideal electrocatalyst. Herein, for the first time, we synthesize Co_xSe/MoSe₂ micro-prisms on foam via a hydrothermal and selenization strategy. After selenization, a crystallized CoMoO₄ smooth prismatic structure can be converted into a Co_xSe/MoSe₂ prismatic structure with lamellar morphology. Such synergistic effects lead to Co_xSe/MoSe₂ superior electrochemical catalytic activity with a 109 mV over-potential at 10 mA cm⁻² and 204 mV over-potential at 100 mA cm⁻², an appropriate Tafel slope of 90 mV dec⁻¹, and remarkable long-term stability during 20 h of testing for the hydrogen evolution reaction in an alkaline medium. Density-functional calculations reveal the absorption energy of water and Gibbs free-energy of intermediate adsorb hydrogen of Co_xSe/MoSe₂ is more favorable for hydrogen evolution reaction than single component catalyst. Both experimental and theoretical calculation results reveal that synergistic effect can efficiently reduce energy barrier of both the initial water adsorption step and subsequent H₂ generation on binary catalysts, and improve catalytic activity.     

Edge-halogenated graphene nanosheets as an efficient metal-free electrocatalyst for hydrogen evolution reaction

Application of carbonic materials as catalysts has recently been considered due to some advantages like tunable molecular structures, easy synthesis methods, abundance, and high tolerance in acidic and alkaline media. Here, a new metal-free electrocatalyst of halogenated reduced graphene oxide was prepared using cyclic voltammetry X (F, Br, and I)-RGO electrodeposition method. The prepared electrocatalysts were studied as a novel metal-free electrocatalyst for the hydrogen evolution reaction, and the presence of several halogen and oxygen functional groups on the surface of nanosheets was verified by the furrier transform infra-red, FT-IR, spectroscopy, and the presence of doped halogens on the RGO surface was confirmed by energy-dispersive X-ray, EDX, spectroscopy. The structural features and surface morphology of electrocatalysts were investigated by scanning electron microscopy (SEM) analysis. The electrochemical treatment of the X (F, Br, I)-RGO electrode was studied by some techniques like electrochemical impedance spectroscopy, EIS, chronoamperometry, CA, and linear sweep voltammetry, LSV. The X (F, Br, I)-RGO catalyst showed a lower onset potential (?0.81 V. vs. SHE), higher exchange current density (3.1 × ×10^?1 mA cm^?2), and lower charge transfer resistance (1.09 Ω cm²) related to the RGO catalyst due to the high active sites by heteroatoms and graphene nanosheets.     

Nitrogen-doped cobalt sulfide as an efficient electrocatalyst for hydrogen evolution reaction in alkaline and acidic media

The enhancement in intrinsic catalytic activity and material conductivity of an electrocatalyst can leads to promoting HER activity. Herein, a successful nitrogenation of CoS₂ (N–CoS₂) catalyst has been investigated through the facile hydrothermal process followed by N₂ annealing treatment. An optimized N–CoS₂ catalyst reveals an outstanding hydrogen evolution reaction (HER) performance in alkaline as well as acidic electrolyte media, exhibiting an infinitesimal overpotential of ?0.137 and ?0.097 V at a current density of ?10 mA/cm² (?0.309 and ?0.275 V at ?300 mA/cm²), corresponding respectively, with a modest Tafel slope of 117 and 101 mV/dec. Moreover, a static voltage response was observed at low and high current rates (?10 to ?100 mA/cm²) along with an excellent endurance up to 50 h even at ?100 mA/cm². The excellent catalytic HER performance is ascribed to improved electronic conductivity and enhanced electrochemically active sites, which is aroused from the synergy and mutual interaction between heteroatoms that might have varied the surface chemistry of an active catalyst.     

Facile synthesis of self-supported intertwined columnar NiCoP as a high efficient electrocatalyst for hydrogen evolution reaction

A new self-supported nickel-cobalt phosphide (NiCoP) on Ni foam (NiCoP/NF) is fabricated by simple immersion in Co(NO₃)₂ solution followed by subsequent phosphorization. NiCoP/NF displays intertwined and porous columnar morphology derived from topological transformation of corresponding columnar amorphous hydroxides precursor. NiCoP/NF manifests the most prominent hydrogen evolution reaction (HER) performance in both 0.5 M H₂SO₄ and 1 M KOH with the overpotentials of 49 and 57 mV to achieve 10 mA cm^?2, respectively. Also, NiCoP/NF showed excellent oxygen evolution reaction (OER) performance, requiring 256 mV to achieve 10 mA cm^?2, even superior to that of RuO₂ and IrO₂. Such impressive HER performance of NiCoP/NF is mainly attributed to the collective effects of enlarged surface area and enriched exposed active sites, affording faster charge transfer kinetic in HER process. This simple immersion method offers a new insight to design cost-effective and efficient electrocatalysts for large scale application.     

Amorphous CoFeB on nickel foam as a high efficient electrocatalyst for hydrogen evolution reaction

The development of high-performance, low cost and earth abundant catalysts for hydrogen evolution reaction (HER) is desired. This work presents amorphous CoFeB supported on nickel foam (NF), prepared by a facial chemical reduction method, as an active catalyst for HER in alkaline solution. Structure characterization indicated that with the incorporation of Fe atom, CoFeB catalysts exhibit similar petal-like granular morphology as CoB. The optimal CoFeB/NF-0.15 catalyst exhibits Brunauer-Emmett-Teller (BET) surface area of 27.4 m² g^?1, nearly two times larger than 13.2 m² g^?1 for CoB, suggesting higher specific surface area. CoFeB/NF-0.15 catalyst shows excellent HER performance and reaches ?10 mA cm^?2 at overpotential of 35 mV in alkaline solution, and Tafel slope of 84.7 mV dec^?1, indicative of Volmer-Heyrovsky reaction mechanism. The synergistic effect among Fe, Co and B atoms and the more exposed active sites as well as faster electron transfer kinetics collectively contributed to the improved intrinsic activity of CoFeB for HER. Moreover, CoFeB/NF-0.15 exhibits good stability for over 16 h.     

Multi-walled carbon nanotubes reinforced nickel phosphide composite: As an efficient electrocatalyst for hydrogen evolution reaction by one-step powder sintering

Transition metal phosphides (TMPs) have been proven to be a high-performance non-noble metal electrocatalyst with high activity and nearly ~100% Faraday efficiency. However, their applications remain faces great challenging due to its unsatisfactory exposure to catalytic active sites and electronic conductivity. Here, powder sintering was used to prepare Ni–P-Multi-walled carbon nanotubes (Ni–P-MWCNTs) composite electrodes with a hierarchical flower-like structure with a large surface area, the composite electrodes were synthesized by phosphating mixed powder (porous nickel powder, red phosphorus and MWCNTs). Due to the flower-like nanoplate hierarchical structure, the fast vectorial electron transfer along the building block nanoplates was effectively induced and active sites were highly exposed. The resulting Ni_xP-43 wt%MWCNTs shows high activity and durability towards the Hydrogen evolution reaction (HER) under acidic conditions. It demands extremely low onset-potential of 29 mV, 96 mV to achieve a current density of 10 mA cm⁻². This work suggests an effective method to facilitate grain preferred orientation growth and exposure high activity active, experimental results demonstrate that the electrocatalytic performance of as-prepared Ni–P-MWCNTs were successfully optimized through the addition of MWCNTs, and might promote further study of the TMPs catalysts for HER.     

Hierarchical NiMo alloy microtubes on nickel foam as an efficient electrocatalyst for hydrogen evolution reaction

Developing efficient, non-noble electrocatalysts for hydrogen evolution reaction (HER) is of high significance for future energy supplement, but challenging. NiMo alloy is a non-noble-metal-based efficient catalyst for HER due to its appropriate hydrogen binding energy and excellent alkali corrosion resistance. Herein, for the first time, we report the preparation of radially aligned NiMo alloy microtubes on Ni foam (NiMo MT/NF). The synthesized NiMo alloy catalyst was composed of the Ni₁₀Mo phase; notably, this hierarchically structured material possessed abundant active sites and a high surface area, and exhibited efficient electronic transport properties. The NiMo MT/NF electrode exhibited a low overpotential of 119 mV at 10 mA/cm² in a base solution, which was 50 mV less than that of NiMo alloy nanoparticles on NF (169 mV).     

Ruthenium quantum dots supported on carbon nanofibers as an efficient electrocatalyst for hydrogen evolution reaction

The hydrogen evolution reaction (HER) is a key step for producing hydrogen by water electrolysis, and an economical, facile and environment friendly method of fabricating catalysts for HER is urgent and essential. In this work, we design a high efficient and stable HER catalyst though a simple adsorption and pyrolysis method. The fabricated catalyst presents ruthenium (Ru) quantum dots (QDs) uniformly distributes on the carbon nanofibers (CNF) with a three dimensional (3D) networks structure (Ru@CNF). By means of quantum size effect of Ru QDs and the 3D networks structure of the carbon nanofibers, the former is beneficial to provide more catalytic active sites and the latter is in favour of electron transport. The sample Ru@CNF exhibits a low overpotential of 20 mV at a current density of 10 mA cm⁻² and Tafel slope of 31 mV dec⁻¹ in 1 M KOH, which is better than that of Pt/C (28 mV and 36 mV dec⁻¹), and most of reported Ru-based and transition metal catalysts. Furthermore, it exhibits robust stability when testing at an overpotential of 75 mV for 24 h. Therefore, this work provides a low-cost, simple and feasible method for fabricating HER catalyst, which possesses commercial application prospect in the field of producing hydrogen by water electrolysis.     

Nickel selenide nanostructures as an electrocatalyst for hydrogen evolution reaction

Electrochemical water splitting has gained momentum for the development of alternative energy sources. Herein, we report the synthesis of two different nickel selenide nanostructures of different morphology and composition employing hydrothermal method. NiSe₂ nanosheets were obtained by the anion-exchange reaction of Ni(OH)₂ with Se ions for 15 h. On the other hand, NiSe nanoflakes were synthesized by the direct selenization of nickel surface with the reaction time of 2 h. Tested as an electrocatalyst for hydrogen evolution reaction, NiSe₂ nanosheets and NiSe nanoflakes can afford a geometric current density of 10 mA cm^?2 at an overpotential of 198 mV and 217 mV respectively. The measured Tafel slope values of NiSe nanoflakes are 28.6 mV dec^?1, which is three times lower as compared with NiSe₂ nanosheets (72.1 mV dec^?1). These results indicates the HER kinetics of NiSe nanoflakes are at par with the state-of-the-art Pt/C catalyst and also complimented with the short synthesis time of 2 h. Further, both nickel selenides exhibit ultra-long term stability for 30 h as evident from constant current chronopotentiometry and electrochemical impedance spectroscopy results.     

Novel one-step synthesis of nickel encapsulated carbon nanotubes as efficient electrocatalyst for hydrogen evolution reaction

In this work, we report the synthesis of Ni nanoparticles encapsulated in carbon nanotubes (CNTs) by a facile and novel one-step pyrolysis method which are obtained from fumaric acid and nickel acetate as carbon and nickel sources respectively. The synthesized Ni encapsulated CNTs were characterized by various methods and were confirmed to possess large surface areas and numerous mesopores, they were applied as non-precious metal electrocatalyst for HER in 1 M KOH solution. The results show that the Ni encapsulated carbon nanotubes synthesized at 650 °C exhibited the best catalytic activity and stability with the smallest Tafel slope of 102 mV dec⁻¹, an onset potential of 110 mV and overpotential of 266 mV to achieve a current density of −10 mA cm⁻².     

Facile synthesis of MoS2/N-doped macro-mesoporous carbon hybrid as efficient electrocatalyst for hydrogen evolution reaction

A novel three-dimensional (3D) hybrid consisting of molybdenum disulfide nanosheets (MoS₂) uniformly bound at N-doped macro-mesoporous carbon (N-MMC) surface was fabricated by the solvothermal method. The resulting MoS₂/N-MMC hybrid possesses few-layer MoS₂ nanosheets structure with abundant edges of MoS₂ exposed as active sites for hydrogen evolution reaction (HER), in sharp contrast to large aggregated MoS₂ nanoflowers without N-MMC. The high electric conductivity of N-MMC and an abundance of exposed edges on the MoS₂ nanosheets make the hybrid excellent electrocatalytic performance with a low onset potential of 98 mV, a small Tafel slope of 52 mV/decade, and a current density of 10 mA cm^?2 at the overpotential of 150 mV. Moreover, the MoS₂/N-MMC hybrid exhibits outstanding electrochemical stability and structural integrity owing to the strong bonding between MoS₂ nanosheets and N-MMC.