Facile synthesis of carbon encapsulated RuO2 nanorods for supercapacitor and electrocatalytic hydrogen evolution reaction

In this work, carbon encapsulated RuO₂ nanorods (RuO₂ NRs/C) has been synthesized by thermolysis of ruthenium chloride and Punica granatum (P. granatum) peel under N₂ atmosphere. The synthesized RuO₂ NRs/C was characterized using Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction method (XRD), field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) with energy dispersive spectroscopy (EDS) analyses. The FT-IR results suggested that the organic constituents of P. granatum have been carbonized and encapsulated over RuO₂ nanorods (RuO₂ NRs). The XRD pattern of RuO₂ NRs/C revealed its crystalline nature and carbon encapsulation. The synthesized RuO₂ NRs/C has been well dispersed with the average width of 20 nm, exposed from the FE-SEM and HR-TEM images. The EDS results of RuO₂ NRs/C showed the existence of three elements viz., Ru, O and C. Further, the supercapacitor and electrocatalytic hydrogen evolution reaction (HER) activities of RuO₂ NRs/C were studied using standard electrochemical methods. The synthesized RuO₂ NRs/C offered a maximum specific capacitance of 151.3 F g⁻¹ at a scan rate of 5 mV s⁻¹, obtained from the cyclic voltammetry results. The onset over potential and Tafel slope of synthesized RuO₂ NRs/C for HER were −0.099 V_RHE and −99.4 mV dec⁻¹, respectively. The present study revealed that RuO₂ NRs/C as a better candidate for supercapacitor and HER.     

Facile synthesis of MoS2/CuS nanoflakes as high performance electrocatalysts for hydrogen evolution reaction

The fabrication of metal sulfides heterostructure is a promising strategy for enhancing catalytic activity. Herein, the MoS₂/CuS heterostructure was successfully grown on carbon cloth (MoS₂/CuS/CC) through an efficient method. The SEM results confirmed that the fabricated MoS₂/CuS/CC composites have a flake morphology, which can not only improves the surface area but also offers ample surface catalytic active sites. Particularly, the optimized MoS₂/CuS/CC-2 electrocatalyst showed a small overpotential of 85 mV@10 mA cm^?2 and exceptional long-term cycling durability for hydrogen evolution in 1 M KOH. The outstanding catalytic activity is attributed to the fact that the combination of MoS₂ with CuS can greatly enhance the charge transport rate and improve the structural stability. These results suggest that the MoS₂/CuS/CC heterostructure is a potential electrocatalyst for hydrogen production.     

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.     

Ultrafine monodisperse NiS/NiS2 heteronanoparticles in situ grown on N-doped graphene nanosheets with enhanced electrocatalytic activity for hydrogen evolution reaction

The exploration of highly active and stable nonprecious electrocatalysts for the hydrogen evolution reaction (HER) is of great significance for the advancement of diverse sustainable energy storage and conversion systems. Herein, we demonstrate a facile one-pot hydrothermal synthesis of ultrafine and monodisperse NiS/NiS₂ heteronanoparticles (ca. 3.2 nm) uniformly in situ grown on N-doped reduced graphene oxide nanosheets (denoted as NiS/NiS₂@N-rGO hereafter). In such unique NiS/NiS₂@N-rGO sample, the tiny-sized NiS/NiS₂ heteronanoparticles with abundant intimate interfacial contacts allow the effective modification of the electronic structure and more exposure of catalytically active sites. Moreover, the conductive N-rGO support could serve as a “highway” of in-plane charge transfer and facilitate the mass diffusion during the electrocatalytic process. As a consequence, the resultant NiS/NiS₂@N-rGO catalyst exhibits a superior HER performance with an overpotential of 148 mV to deliver a current density of 10 mA cm⁻² in 1.0 M KOH solution. The NiS/NiS₂@N-rGO catalyst could also endure long-term operation for 12 h with negligible activity attenuation and morphological change. The present study provides a feasible approach to explore efficient and robust non-noble metal-based electrocatalysts for a variety of renewable electrochemical applications.     

Phase evolution and electrocatalytic performance for the hydrogen evolution reaction of MoxRe1-xS2 nanosheets

Transition metal doping is an effective method to induce a structural phase transition and improve the electrocatalytic performance of transition metal chalcogenides (TMDs). In this study, Mo_xRe_1-xS₂ nanosheets with Mo fraction x from 0 to 1 were grown on a carbon nanotube/carbon cloth (CNT@CC) substrate using a hydrothermal method by changing the molar ratio of Na₂MoO₄·2H₂O to NH₄ReO₄ in the precursor solution. The effect of the Mo fraction x on the phase structure and electrocatalytic performance for the hydrogen evolution reaction (HER) of Mo_xRe_1-xS₂ nanosheets was studied. The results indicated that Mo_xRe_1-xS₂ consists of the 1T′ phase (Re, Mo)S₂ and the 2H phase (Mo, Re)S₂, and the proportion of the 1T′ phase is in the range of 40–50%. Mo_0.5Re_0.5S₂/CNT@CC shows the best HER catalytic activity with an overpotential of 85 mV at a current density of 10 mAcm^?2, a Tafel slope of 38 mV dec^?1 and a charge transfer resistance of 1.04 Ω. This excellent HER catalytic activity is attributed to the phase transition, defects and S vacancies on the basal planes, as well as the synergistic effect between the Mo_xRe_1-xS₂ nanosheets and CNT.     

Reduced graphene oxide-supported ruthenium nanocatalysts for highly efficient electrocatalytic hydrogen evolution reaction

Hydrogen energy has received great attention because of its advantages such as large energy density and not producing carbon dioxide, and it is currently considered to be one of the most valuable green energy sources. Therefore, the development of efficiently hydrogen production is of great importance. Hydrogen production from water electrolysis has large application prospects due to its cleanliness and no pollution. However, how to prepare an efficient, stable and low-cost electrocatalyst for this process is still challenging. Here, we develop a reduced graphene oxide-supported ruthenium (Ru) nanoparticle electrocatalyst synthesized by a simple method. The ruthenium precursors are encapsulated and isolated with N,N-dimethylformamide (DMF) (Ru³⁺-DMF), which effectively inhibits the further agglomeration growth of ruthenium. After Ru³⁺-DMF being loaded on graphene oxide, Ru is supported on reduced graphene oxide (Ru/rGO) by the liquid phase chemical reduction method and the remaining organic solvent could be removed by calcination to form a well-dispersed Ru-based electrocatalyst. Ru/rGO shows excellent electrocatalytic activity and long-term stability for hydrogen evolution reaction (HER). In a solution of 1.0 M KOH, the overpotential of 3.0 wt%Ru/rGO for the HER at 100 mA cm^?2 is only 111.7 mV, and the Tafel slope is 31.5 mV dec^?1. It exhibits better HER performance compared to commercial Pt/C and other Ru/rGO catalysts with different Ru loadings. The work could give a new strategy for the synthesis of efficient electrocatalysts.     

Facile hydrothermal synthesis of combined MoSe2PS nanostructures on nickel foam with superior electrocatalytic properties for hydrogen evolution reaction

Producing an efficient and inexpensive electrocatalyst for use in the water electrolysis process is the most efficient and logical way to industrialize this method to produce hydrogen as a clean and alternative fuel for fossil fuels. In this study, combined and unique MoSe₂PS nanostructures are synthesized on nickel foam by three steps hydrothermal process. Microstructural observations reveal the unique morphology of the petals covered by the elongated nano-blades. A high electrocatalytic performance is attained with this nanostructure in hydrogen evolution reaction, so that the 90 mV overpotential is achieved at a current density of ?10 mA/cm². The near-platinum activity is due to the unique and combined nanostructure due to the synergistic properties of S and P on MoSe₂ as well as the high electrochemical active sites in the specimen. Additionally, excellent stability of the synthesized electrocatalyst is observed in the alkaline medium for 30 h, which confirms its potential application in relevant industries such as fuel cells and transportation.     

Facile synthesis of tubular CoP as a high efficient electrocatalyst for pH-universal hydrogen evolution

A facile three-step approach for tubular CoP preparation and its catalytic activity for HER and OER are reported. The CoP microtubes show superior HER performance in a wide pH range with low overpotentials of 91, 101 and 113 mV at 10 mA cm^?2 in 0.5 M H₂SO₄, 1 M KOH and 1 M PBS, respectively. Additionally, it also depicts superior OER performance with an overpotential of 300 mV at 10 mA cm^?2, which is lower than reported precious metal oxides. The improved electrocatalytic performance of tubular CoP is likely attributed to the porous tube-like structural features, which not only afford rich exposed active sites, but also accelerate the charge or mass transfer efficiency, and thus efficiently promote the HER performance. The synthesis of tubular CoP confirms the importance of morphology features and provides a new insight to rationally design and synthesize highly effective non-noble metal phosphide-based pH-universal electrocatalysts for HER.     

Tungsten-molybdenum oxide nanowires/reduced graphene oxide nanocomposite with enhanced and durable performance for electrocatalytic hydrogen evolution reaction

Hydrogen has attracted huge interest globally as a durable, environmentally safe and renewable fuel. Electrocatalytic hydrogen evolution reaction (HER) is one of the most promising methods for large scale hydrogen production, but the high cost of Pt-based materials which exhibit the highest activity for HER forced researchers to find alternative electro-catalyst. In this study, we report noble metal free a 3D hybrid composite of tungsten-molybdenum oxide and reduced graphene oxide (GO) prepared by a simple one step hydrothermal method for HER. Benefitting from the synergistic effect between tungsten-molybdenum oxide nanowires and reduced graphene oxide, the obtained W-Mo-O/rGO nanocomposite showed excellent electro-catalytic activity for HER with onset potential 50 mV, a Tafel slope of 46 mV decade^?1 and a large cathodic current, while the tungsten-molybdenum oxide nanowires itself is not as efficient HER catalyst. Additionally, W-Mo-O/rGO composite also demonstrated good durability up to 2000 cycles in acidic medium. The enhanced and durable hydrogen evolution reaction activity stemmed from the synergistic effect broadens noble metal free catalysts for HER and provides an insight into the design and synthesis of low-cost and environment friendly catalysts in electrochemical hydrogen production.     

Facile hydrothermal synthesis of rare earth phosphate for boosting hydrogen evolution reaction

The water electrolysis process has attracted great attention due to the production of high energy density pure hydrogen. However, the involved cell reactions in this process such as hydrogen and oxygen evolution reactions are kinetically sluggish and demands high input energy to accelerate the rate of these reactions. Therefore, the development and application of efficient electrocatalyst is essential for hydrogen evolution reaction (HER) as well as oxygen evolution reaction (OER). In the present work, we have successfully synthesized two rare earth phosphates through the hydrothermal route and used as a catalysts towards HER in an acidic medium. The rare earth phosphate PrPO₄ exhibits better catalytic activity than YPO₄ catalyst. The overpotential of PrPO₄, YPO₄ and standard Pt/C were found as 147, 484.3 and 58 mV vs. reversible hydrogen electrode, respectively, to reach current density 10 mA·cm^?2 and corresponding Tafel slopes were found as 107.58, 118.73 and 80.89 mV decade^?1, respectively in 0.5 M H₂SO₄. The catalytic activity of PrPO₄ (472.83 mA·cm^?2) overcome standard Pt/C (179.60 mA·cm^?2) at high overpotential 450 mV vs. reversible hydrogen electrode. The prepared PrPO₄ shows efficient electrocatalytic activity towards HER in acidic medium because it possess high BET surface area, large ECSA value and small charge transfer resistance than YPO₄.     

Co/Mo2C composites for efficient hydrogen and oxygen evolution reaction

Non-precious transition metal electrocatalysts with high catalytic performance and low cost enable the scalable and sustainable production of hydrogen energy through water splitting. In this work, based on the polymerization of CoMoO₄ nanorods and pyrrole monomer, a heterointerface of carbon-wrapped and Co/Mo₂C composites are obtained by thermal pyrolysis method. Co/Mo₂C composites show considerable performance for both hydrogen and oxygen evolution in alkaline media. In alkaline media, Co/Mo₂C composites show a small overpotential, low Tafel slope, and excellent stability for water splitting. Co/Mo₂C exhibits a small overpotential of 157 mV for hydrogen evolution reaction and 366 mV for oxygen evolution reaction at current density of 10 mA cm⁻², as well as a low Tafel slope of 109.2 mV dec⁻¹ and 59.1 mV dec⁻¹ for hydrogen evolution reaction and oxygen evolution reaction, respectively. Co/Mo₂C composites also exhibit an excellent stability, retaining 94% and 93% of initial current value for hydrogen evolution reaction and oxygen evolution reaction after 45,000 s, respectively. Overall water splitting via two-electrode water indicates Co/Mo₂C can hold 91% of its initial current after 40,000 s in 1 M KOH.     

Surfactant-assisted hydrothermal synthesis of nitrogen doped Mo2C@C composites as highly efficient electrocatalysts for hydrogen evolution reaction

We describe a facile surfactant-assisted hydrothermal route to synthesize nitrogen doped Mo₂C@C composites in the presence of cetyltrimethylammonium bromide (CTAB) as carbon source and structure guiding agent. The resulting Mo₂C@C composites consist of Mo₂C nanocrystals with sheet-like morphology and well-dispersed nitrogen element doping. Controllable experiments indicate that the additive amount of CTAB can efficiently tune porous structure and electrochemical activity of the as-prepared Mo₂C@C materials. This unique nitrogen doped Mo₂C@C composite provides several advantages for electrocatalytic applications: (1) nitrogen doped carbons can prevent the aggregation of Mo₂C nanocrystals and render it high conductivity; (2) the homogeneous dispersion of Mo₂C nanocrystals provides abundant active sites; (3) 2D morphology, the hierarchical porosity, and high surface areas allow large exposed field of active sites and facilitate mass transfer. As a result, the nitrogen doped Mo₂C@C composites deliver superior HER electrocatalytic activities with a low overpotential of only 100 mV and also a low Tafel slope of 53 mV/dec in alkaline condition. Such CTAB-assisted strategy may open up an opportunity towards synthesis of low cost and high performance Mo-based electrocatalysts for various applications, such as water splitting.     

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.     

Flower-like CoS2/MoS2 nanocomposite with enhanced electrocatalytic activity for hydrogen evolution reaction

Molybdenum sulfide (MoS₂) has received tremendous attracts for its promising performance in the aspects of hydrogen evolution reaction (HER). To improve the HER activity of MoS₂, we designed a flower-shaped CoS₂/MoS₂ nanocomposite with enhanced HER electroactivity compared with MoS₂ nanosheets by a simple one-step hydrothermal method. The facile approach brings about distinct transformation of the morphology from nanosheets to nanoflower structures. The introduction of Co element into MoS₂ results in the larger active surface area, more edge-terminated structures, and higher conductivity of the CoS₂/MoS₂ nanocomposite, which are good for improving the HER electroactivity. In brief, the optimized catalyst exhibits the low overpotential of 154 mV at 10 mA cm^?2, small Tafel slope of 61 mV dec^?1, and excellent stability in acidic solution.     

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.     

Ni foil supported FeNiP nanosheet coupled with NiS as highly efficient electrocatalysts for hydrogen evolution reaction

The investigation and development of bimetallic phosphosulphide electrocatalyst with low cost and abundant reserves is extremely significant for the improvement of the efficiency of hydrogen evolution reaction (HER), while it remains a challenge. Herein, we explored a feasible method to prepare three-dimensional (3D) self-supported FeNiP-S/NF-5 nanosheet arrays on Ni foil (NF) by hydrothermal method and in situ phosphorization and following sulfurization treatment. The as-obtained FeNiP-S/NF-5 only needs a potential of 183 mV vs. RHE to reach 20 mA cm⁻², which is smaller than that of FeNiP/NF (187 mV vs. RHE) and FeNiS/NF-5 (239 mV vs. RHE), presenting excellent electrocatalytic stability. Such outstanding performance of the FeNiP-S/NF-5 can be attributed to following several reasons: (i) bi-metallic phosphide and sulphide have the high intrinsic activity because of its synergistic effect; (ii) the 3D nanosheet arrays structure of FeNiP-S/NF-5 is conducive to expose plentiful active sites and facilitate the electrolyte penetration along with electron transportation; (iii) the sulfurization process followed phosphorization treatment could further optimize their electronic structure and inhibited the surface oxidation of catalyst in the catalytic process.     

Monometallic,bimetallic, and trimetallic chalcogenide-based electrodes for electrocatalytic hydrogen evolution reaction

Cu₂CoSnS₄, Cu₂SnS₃, Cu₂CoS₄, Co₂SnS₃, Cu₂S, CoS₂, and SnS₂ were synthesized using a one-step solvent-free solid-phase approach. The surface structure, morphology, and composition were characterized using an X-ray diffractometer (XRD), Fourier-Transform Infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), and X-ray Photoelectron Spectroscopy (XPS). The characterizations reveal pure phase formation and porous morphology. Further, the Hydrogen evolution reaction was performed using Cu₂CoSnS₄, Cu₂SnS₃, Cu₂CoS₄, Co₂SnS₃, Cu₂S, CoS₂, and SnS₂-based electrodes. Amid all electrocatalysts, Cu₂CoSnS₄ shows an excellent hydrogen evolution reaction with a low overpotential of ?192.1 mV at ?10 mA/cm² in 0.5 M H₂SO₄. And higher current density. Cu₂CoSnS₄ also shows a lower Tafel slope of 98.6 mV/dec and charge transfer resistance than mono and bimetallic chalcogenide-based electrodes. The Cu₂CoSnS₄ exhibit very good stability for ～22 h at ?10 mA/cm² current density in 0.5 M H₂SO₄.     

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.     

Plasmonic Au nanoparticle-decorated Bi2Se3 nanoflowers with outstanding electrocatalytic performance for hydrogen evolution

Hydrogen production from water splitting through electrocatalytic or photoelectrochemical route shows great potential for renewable energy conversion. Herein, the plasmon-enhanced photoelectrical nanocatalysts (NCs) have been successfully developed by Au nanoparticle-decorated Bi₂Se₃ nanoflowers (Au@Bi₂Se₃ NFs) as catalysts for hydrogen evolution reaction (HER), leading to a more than 3-fold increase of current under excitation of Au localized surface plasmon resonance (LSPR) and affording a markedly decreased overpotential of 375 mV at a current density of 10 mA cm⁻². The HER enhancement can be largely attributed to effective electron-charge separation and the increase of carrier density in Bi₂Se₃ induced by the injection of hot electrons of Au nanoparticles. Meanwhile, Bi₂Se₃ nanoflowers (NFs), a kind of topological insulators, possess gapless edges on boundary and show metallic character on surface, providing a path for the flow of electrons in the electrocatalytic system. This study opens up a new avenue towards the design of higher energy conversion catalytic water splitting systems with the assistance of light energy, which could increase of HER catalysis efficiency by plasmonic excitation.     

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.