Multilevel N-doped carbon nanotube/graphene supported cobalt phosphide nanoparticles for electrocatalytic hydrogen evolution reaction

Electrochemical water splitting plays an important role in alternative energy studies, since it is highly efficient and environment-friendly. Accordingly, it is an ideal way of providing alternative to meet the urgent need of finding sustainable and clean energy. This study presents the fabrication of CoP attached on multilevel N-doped CNT/graphene (CoP–CNT/NG) hybrids. The multilevel carbon structure can enhance electrical conductivity efficiently and increase the reaction active area immensely. The obtained electrocatalyst exhibits great electronic conductivity (17.8 s cm⁻¹) and HER activity with low overpotential (155 mV at 10 mA cm⁻²), low Tafel slope (69.1 mV dec⁻¹) in 0.5 M H₂SO₄. In addition, the CoP–CNT/NG displays prominent electrochemical durability after 18 h.     

Electrocatalytic performance of carbon dots/palladium nanoparticles composite towards hydrogen evolution reaction in acid medium

In this work, nitrogen doped carbon dots (NDCDs) and nitrogen doped carbon dots supported palladium nanoparticles composite (n-Pd@NDCDs) were synthesized through hydrothermal carbonization and thermolytic reduction using Morinda citrifolia (M. citrifolia) fruit and palladium chloride as carbon and Pd precursors, respectively. The synthesized materials viz., n-Pd@NDCDs and NDCDs were duly characterized by high resolution transmission electron microscopy (HR-TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The optical properties of NDCDs were studied by ultraviolet visible (UV–Vis), and fluorescence spectroscopy techniques. Further, the electrocatalytic hydrogen evolution reaction (HER) performance of n-Pd@NDCDs was evaluated by linear sweep voltammetry (LSV), Tafel, and electrochemical impedance spectroscopy (EIS) measurements in 0.5 M aqueous H₂SO₄. The onset potential of n-Pd@NDCDs was about −0.195 V_RHE, which was lower than NDCDS (−0.392 V_RHE) and bare glassy carbon (−0.603 V_RHE). The calculated Tafel slope values of n-Pd@NDCDs were 135 and 141.8 mV/dec, from the voltammetric and EIS methods, respectively. Moreover, the n-Pd@NDCDs exhibited small overpotential of 0.291 V to attain a current density of 10 mA/cm². The EIS studies revealed that the HER charge transfer resistance was dropped from 84.3 to 18.3 Ω/cm² while increasing of potential, which revealed good conductivity and electrocatalytic activity of n-Pd@NDCDs. Thus the present work vouched for the candidature of n-Pd@NDCDs as an effective electrocatalyst for the HER in acidic medium.     

Coupling molybdenum carbide nanoparticles with N-doped carbon nanosheets as a high-efficiency electrocatalyst for hydrogen evolution reaction

Searching for earth-abundant and high-efficiency electrocatalysts for the hydrogen evolution reaction (HER) is of critical importance for future energy conversion devices. To facilitate the HER on a nonprecious metal-based catalyst, integration of catalytically active nanoparticles with highly conductive carbon supports represents a promising strategy since the formed nanohybrid can offer available active sites and improved electron transfer capability. Herein, we demonstrate a feasible and scalable approach to fabricate well-dispersed Mo₂C nanoparticles firmly anchored on 2D ultrathin N-doped carbon nanosheets (denoted as Mo₂C@NC nanosheets) using inexpensive NaCl as recyclable templates. The adoption of NaCl template provides a 2D space for the one-step concurrent growth of Mo₂C nanoparticles and N-doped carbon nanosheets. Benefiting from the synergy between fine Mo₂C nanoparticles with high dispersity and N-doped C nanosheets, the resultant Mo₂C@NC nanosheets exhibit an outstanding HER performance with a low overpotential, a small Tafel slope and excellent stability under acidic medium, making them a promising noble-metal-free HER catalyst.     

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.     

Enhancement of electrocatalytic activity towards hydrogen evolution reaction by boron-modified nickel nanoparticles

Nanosized nickel particles have been synthesized by three different routes: polyol, microemulsion and precipitation/reduction methods. Nickel nanoparticles have been evaluated as electrocatalysts for the hydrogen evolution reaction (HER). The electrocatalysts have been characterized by using X-ray diffraction (XRD), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). Their electrocatalytic performance in the hydrogen evolution reaction has been evaluated by means of the Tafel curves recorded in alkaline medium. The activity for the hydrogen evolution reaction increases with the increasing amount of reduced Ni in the electrocatalysts. Remarkably, the formation of a nickel-boride alloyed phase (Ni₃B) is responsible for the higher activity of the sample prepared by the precipitation/reduction method for the HER. The crystalline phase Ni₃B appears to be responsible for the very high activity in hydrogen production.     

Electrocatalytic hydrogen evolution reaction on sulfur-deficient MoS2 nanostructures

Molybdenum disulfide (MoS₂) is a 2D layered structured material with a Mo:S of 1:2 and is a great attention seeker for hydrogen production through water-splitting. In the present work, we prepared nanostructured MoS_x with different sulfur molar concentrations (x = 2, 1, 0.5) through a one-step hydrothermal method. The decrease in sulfur concentration resulted in a new phase that is MoO₃ with a Mo:S of 1:0.5. The structural, morphological, and optical properties of all the samples were studied through X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared spectroscopy (FTIR), and Ultraviolet–Visible (UV–Vis) spectroscopy, respectively. Moreover, the electrochemical behavior was studied using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), and Tafel slope. Optimum properties were observed for Mo:S (1:1) with an onset potential of 96 mV, an overpotential of 130 mV for hydrogen evolution reaction (HER) coupled with a specific capacitance of 889 F/g and low charge transfer resistance of 43 Ω. Further, it was noted that the electrocatalytic activity of MoS₁ was better than that of the composite and bare MoO₃. It is proposed that the excellent electrochemical activity arises from sulfur vacancies which provide active sites for HER and a free path for ions to flow through the material.     

Electrocatalytic hydrogen evolution of manganese corrole

A series of manganese corroles bearing different substituents had been prepared and characterized by UV–vis, ¹H NMR, ¹⁹F NMR, HRMS and XPS. These manganese corrole complexes were applied to electrocatalytic hydrogen evolution reaction (HER) for the first time. The results showed that manganese corroles are effective catalysts for HER in DMF solvent by using acetic acid (AcOH), trifluoroacetic Acid (TFA) and p-toluenesulfonic acid (TsOH) proton sources, and strong acid leads to higher electrocatalytic activity. When using TsOH as proton source, protonation of corroles ligand may be involved in HER. The electrocatalytic HER activity can be improved by increasing the electron-withdrawing substituent of the corrole macrocycle in both organic and aqueous media.     

Ultrafine and highly-dispersed bimetal Ni2P/Co2P encapsulated by hollow N-doped carbon nanospheres for efficient hydrogen evolution

Ultrafine Ni₂P/Co₂P nanoparticles encapsulated in hollow porous N-doped carbon nanospheres are synthesized through a facile two-step access. Firstly, metallic Ni and Co coated by hollow N-doped spheres as precursors are obtained through a high temperature calcination route of organic polymer and inorganic Ni and Co salts. Then bimetal Ni₂P/Co₂P supported on N-doped carbon nanospheres are acquired by a facile phosphorization process. It is worth to note that aniline-pyrrole polymer can prevent fast growth and severe aggregation of Ni₂P/Co₂P, which implies more exposed active sites. Moreover, the calcination of hollow polymer spheres lead to the formation of ultrathin NC shell on the surface of Ni₂P/Co₂P hybrids, which can tune electronic structures, improve the conductivity and protect active sites from corrosion in harsh conditions. When used as HER catalyst, it displays remarkable catalytic activity in both acidic and alkaline solutions, which needs an onset potential of only 164 mV and 168 mV, respectively. Therefore, this work may propose a new strategy to design unique inorganic-organic heterostructures to combine ultrafine metal phosphides with porous carbon for efficient HER.     

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.     

Ru nanoclusters coupling with hierarchical phosphorus and oxygen dual-doped carbon nanotube architectures for effective hydrogen evolution reaction

The construction of an effective catalyst for hydrogen evolution reaction (HER) is a top priority. Herein, we demonstrate ruthenium (Ru) nanoclusters coupled with phosphorus and oxygen dual-doped carbon nanotube (CNT) architecture (Ru-POCA). The increased hydrophilicity and negatively charged surface of CNTs can strongly trap Ru ions. The hierarchical structure is favorable of providing abundant pathways and exposing more active sites for HER. Due to the synergistic effect of the hierarchical structure and modified surface chemistry, Ru-POCA exhibits excellent catalytic HER activity. The overpotential is 22 and 40 mV with a Tafel slope of 28.0 and 27.1 mV dec⁻¹ in 1 M KOH and 0.5 M H₂SO₄ at 10 mA cm⁻². Moreover, Ru-POCA processes good catalytic stability in both acidic and alkaline electrolytes, while the boosted catalytic HER activity is fundamentally studied by density functional theory calculation. This work provides a rational approach to constructing hierarchically structured Ru-CNTs-based catalysts for hydrogen evolution reaction.     

Cobalt nanoparticles encapsulated in nitrogen-rich carbonitride nanotubes for efficient and stable hydrogen evolution reaction at all pH values

Developing non-precious and high-efficiency Pt free electrocatalysts for the hydrogen evolution reaction (HER) in both acid and base remained as a significant challenge. Herein, a novel Co nanoparticles encapsulated in nitrogen-rich carbonitride (Co@Co–N–C) electrocatalyst was fabricated via a facile approach of melamine polymerization and Co²⁺ in situ deposition and reduction. The optimized Co@Co–N–C catalyst demonstrates outstanding catalytic activity for HER in a wide range pH values. In particular, it shows ultralow onset potentials of 62 mV and 46 mV and overpotentials of 178 mV and 157 mV to achieve current density of 10 mA cm^?2 in acidic and alkaline media, respectively. Moreover, it presents outstanding electrochemical durability without degradation at all pH values. Such highly efficient electrocatalytic performance is mainly attributed to the maximum of synergistic effects between uniform dispersed Co nanoparticles and N-rich carbonitride nanotubes.     

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.     

Cobalt phosphide nanoparticles film growth on carbon cloth: A high-performance cathode for electrochemical hydrogen evolution

In this communication, cobalt phosphide nanoparticles film was developed on carbon cloth (CoP NPs/CC) through low-temperature phosphidation of its corresponding Co NPs/CC precursor. When directly used as a cathode for electrochemical hydrogen evolution in strongly acidic solutions, the CoP NPs/CC electrode exhibits high performance with a low onset overpotential of 33 mV, a Tafel slope of 70 mV dec⁻¹ and a Faradaic efficiency of nearly 100%. This catalyst maintain its catalytic activity for at least 30 h and only needs overpotentials of 48 and 190 mV to attain current densities of 10 and 100 mA cm⁻², respectively.     

Low loading of P modified Rh nanoparticles encapsulated in N,P-doped carbon for boosted and pH-universal hydrogen evolution reaction

Searching for highly efficient and Pt-free electrocatalysts with comparable hydrogen evolution reaction (HER) activities to the benchmark Pt/C catalyst is highly demanded for developing renewable water electrolysis system but still remains challenging. In the current work, low loading of P modified ultrafine Rh nanoparticles encapsulated in N, P dual-doped carbon layers (Rh–P@NPC) have been prepared through a facile polymerization-impregnation followed by high-temperature pyrolysis process. Benefiting from the unique core-shell structural advantages and synergistic effect of Rh–P and NPC components, the resulting Rh–P@NPC catalyst not only exhibits remarkable electrocatalytic activity for HER in the whole pH range with a low overpotential of 31 mV, 65 mV, and 130 mV to drive a current density of 10 mA cm^?2 in 0.5 M H₂SO₄, 1.0 M KOH, and 1.0 M PBS, respectively, but also demonstrates high durability. It is worth to note that all these HER performances are on a par with commercial Pt/C catalysts for HER. This synthetic strategy provides possibility for the fabrication of carbon-based heterostructures with high catalytic activity and durability in harsh environments.     

Embedding Co2P nanoparticles into N&P co-doped carbon fibers for hydrogen evolution reaction and supercapacitor

The demands for highly efficient and low-cost electrochemically active materials are still urgent needs for the fields of electro-catalysis and supercapacitor. Herein, a facile strategy for preparing high-efficient bi-functional electrode material was reported. The electrode material was prepared through embedding Co₂P nanoparticles in the binary co-doped carbon nanofibers (Co₂P@N&P-CNFs). This unique structure can effectively prevent the Co₂P from detaching and provide abundant active sites. Materials prepared in this work showed the superior hydrogen evolution reaction (HER) performance with overpotential of 192 mV at a current density of 10 mA cm^?2 and remarkable stability for 20 h. Moreover, the asymmetric supercapacitor (ASC) was fabricated using the Co₂P@N&P-CNFs as the positive electrode material and carbon nanofibers (CNFs) as the negative electrode material, which shows an outstanding cycle stability (91.5% of the initial capacitance is retained throughout 10,000 charge-discharge tests) and a high E of 22.31 Wh kg^?1 at the P of 225.02 W kg^?1 at 0.3 A g^?1. This work offers an effective route in designing bi-functional active materials for HER and supercapacitor.     

Facile one-step in-situ encapsulation of non-noble metal Co2P nanoparticles embedded into B,N, P tri-doped carbon nanotubes for efficient hydrogen evolution reaction

Developing high performance, good stability and noble-metal-free electrocatalysts for renewable hydrogen evolution reaction (HER) remain a substantial challenge. Herein, we introduce a novel facile one-step in-situ strategy through pyrolysis for the synthesis of Co₂P nanoparticles encapsulated Boron, Nitrogen, and Phosphorous tri-doped carbon nanotubes (Co₂P/BNP-CNTs). The synergetic effect between Co₂P nanoparticles and heteroatom doped CNTs contributes to the remarkable HER performance. The Co₂P/BNP-CNT-900 electrocatalyst shows a low overpotential of 133 mV at a current density of 10 mA cm⁻² and a small Tafel slope of 90 mV dec⁻¹ in 0.1 M KOH media. More importantly, the Co₂P/BNP-CNT-900 electrocatalyst exhibits superior long-term stability in alkaline solution at −0.25 V versus Reversible Hydrogen Electrode (RHE) for 15 h and up to 1000 cycles with negligible performance loss. Overall, our works suggest a one-pot facile synthesis strategy for rational designing high-performance electrocatalysts with enhanced HER performance.     

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.     

Ultra-fine Ru nanoparticles decorated V2O3 as a pH-universal electrocatalyst for efficient hydrogen evolution reaction

Developing high-efficiency electrocatalysts viable for pH-universal hydrogen evolution reaction (HER) has attracted great interest because hydrogen is a promising renewable energy carrier for replacing fossil fuels. Herein, we present a facile strategy for fabricating ultra-fine Ru nanoparticles (NPs) decorated V₂O₃ on the carbon cloth substrates as efficient and stable pH-universal catalysts for HER. Benefiting from the metallic property and electronic conductivity of V₂O₃ matrix, the optimized hybrid (Ru/V₂O₃-CC) exhibits excellent HER activities in a wide pH range, achieving lower overpotentials of 184, 219, and 221 mV at 100 mA cm⁻² in 0.5 M H₂SO₄, 1.0 M KOH and 1.0 M phosphate-buffered saline, respectively. Moreover, the electrode remains superior stability with negligible degradation after 5000 cyclic voltammetry scanning whether in acidic, alkaline or neutral media. Experimental results, combined with theoretical calculations, demonstrate that the interaction between Ru NPs and the support V₂O₃ induces the local electronic density diversity, allowing optimization of the adsorption energy of Ru towards hydrogen intermediate H1, thus favoring the HER process.     

Phase transformation of iron phosphide nanoparticles for hydrogen evolution reaction electrocatalysis

Transition metal phosphides have emerged as alternative electrocatalysts for hydrogen evolution reaction (HER) due to their high activity and low cost compared to the conventional HER electrocatalysts such as Pt. However, the dependency of HER activity on different crystal phases is not well-understood. Here, we synthesized iron phosphide nanoparticles with two distinct phases via chemical transformation from iron metal to iron phosphides. During the development of iron phosphide phases by varying the synthesis conditions such as reaction temperature and time, the HER activities of the nanoparticle were examined. The HER activities of the iron phosphide nanoparticles were found to be phase-dependent.     

Facile electrodeposition fabrication of molybdenum-tungsten sulfide on carbon cloth for electrocatalytic hydrogen evolution

In this work, we have described a facile fabrication of molybdenum-tungsten sulfide on carbon cloth (Mo-W-S/CC) by one-step electrodeposition process. The morphology, composition and catalytic property of as-prepared samples have been characterized through scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photo-electron spectroscopy (XPS) and electrochemical methods. The electrodeposition conditions have been optimized systematically. Mo-W-S/CC has achieved excellent performance and durability as an electrocatalyst for hydrogen evolution reaction (HER) in acidic electrolytes.