Graphene confined MoS2 particles for accelerated electrocatalytic hydrogen evolution

MoS₂ is a promising noble-metal-free electrocatalyst for the hydrogen evolution reaction. Extensive trials have been carried out to increase its low electrical conductivity and insufficient active sites. Here, a remarkable electrocatalyst for hydrogen evolution is developed based on the in-situ preparation of MoS₂ confined in graphene nanosheets. Graphene effectively controls the growth of MoS₂ and immensely increases the conductivity and structural stability of the composite materials. Remarkably, because of the plentiful active sites, sufficient electrical contact and transport, MoS₂ particles confined in graphene nanosheets exhibit an onset overpotential as small as 32 mV, an overpotential approaching 132 mV at 10 mA cm⁻², and a low Tafel slope of 45 mV dec⁻¹. This work presents a reasonable architecture for practical applications in efficient electrocatalytic H₂ generation.     

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.     

Growth of iron diselenide nanorods on graphene oxide nanosheets as advanced electrocatalyst for hydrogen evolution reaction

Advanced electrocatalysts for the fabrication of sustainable hydrogen from water splitting are innermost to energy research. Herein, we report the growth of iron diselenide (FeSe₂) nanorods on graphene oxide (GO) sheets using two-step process viz., simple hydrothermal reduction and followed by wet chemical process. The orthorhombic phase of FeSe₂ incorporated GO nanosheet was developed as a low-cost and efficient electrocatalyst for hydrogen evolution reaction (HER) by water splitting. The phase purity, crystalline structure, surface morphology and elemental composition of the synthesized samples have been investigated by UV–visible absorption spectroscopy (UV–vis), fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDS). Voltammetry and Tafel polarization methods have been utilized to assess the performance of various weight ratio of GO nanosheet in FeSe₂ nanorods towards H₂ evolution. Detailed electrochemical investigations revealed that the 30% FeSe₂/GO composite showed a tremendous electrocatalytic HER activity in acidic medium with high cathodic current density of 9.68 mA/cm² at η = 250 mV overpotential and with a Tafel slope of 64 mV/dec. The 30% FeSe₂/GO composite offers a high synergistic effect towards HER activity, which is mainly due to high electrochemical active catalytic sites, low charge-transfer resistance and enhanced electrocatalytic performances of H₂ production. The present analysis revealed the possible application of FeSe₂/GO composite as a promising low-cost alternative to platinum based electrocatalysts for H₂ production.     

Ni-W nanostructure well-marked by Ni selective etching for enhanced hydrogen evolution reaction

Designing active, stable and affordable electrocatalysts is a promising pathway for fulfilling the mankind's dream of preserving unsustainable fuel sources. Herein, the facile utilization of Romanesco-like and arrow-like nanostructures of Ni-W samples is introduced. Exclusive emphasis is placed on achievement of the unique nanostructure through cost-effective, repeatable and readily accessible two-step techniques, i.e. Ni-W electrodeposition approach followed by etching treatment. Microscopic study was fully utilized for surface morphology and structural investigation. The electrochemical analysis was used to evaluate the electrocatalytic activity and stability. The surface roughness of the Ni-W film electrodeposited by D.C = 90% and etched via acidic solution was up to 93.85, considerably higher than that of the Ni-W electrodeposited by D.C = 20% and without etched Ni-W films (55.36 and 41.51 respectively). Therefore, HER activity was improved with η₁₀ and η₂₀ of 169 and 226 mV vs. RHE, respectively, due to higher effective active surface for H⁺ adsorption. The Tafel slope analysis suggests Volmer mechanism as the HER rate-determining step. The electrochemically active surface area was also enhanced from roughly 2 to 10 cm². In addition, wettability was investigated by a contact angle of less than 65°, which indicates high penetration of electrolyte to the nanostructure. Rapid separation of bubbles on the arrow-like nanostructure of Ni-W films exhibited unstable H₂ bubbles on surface of the electrode.     

Synergistic coupling of CoFe-layered double hydroxide nanosheet arrays with reduced graphene oxide modified Ni foam for highly efficient oxygen evolution reaction and hydrogen evolution reaction

Novel CoFe-LDH (layered double hydroxide) nanosheet arrays in situ grown on rGO (reduced graphene oxide) uniformly modified Ni foam were synthesized by a citric acid-assisted aqueous phase coprecipitation strategy. Systematic characterizations indicates that the series of Co_xFe₁-LDH/rGO/NF (x = 4, 3, 2) all show Co_xFe₁-LDH nanosheets (150–180 × 15 nm) grown vertically on the surface of rGO/NF. Especially, the Co₃Fe₁-LDH/rGO/NF exhibits the best performance with overpotentials of 250 and 110 mV at 10 mA cm^?2 in 1 M KOH for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. When it is used as cathode and anode simultaneously for overall water splitting, they require 1.65 and 1.84 V at 10 and 100 mA cm^?2, respectively. Excellent performance of Co₃Fe₁-LDH/rGO/NF is due to the nanosheet arrays structure with open channels, synergistic coupling between Co₃Fe₁-LDH and rGO enhancing electrical conductivity, and in-situ growth of Co₃Fe₁-LDH on rGO/NF enhancing stability.     

MoS2 confined on graphene by triethanolamine for enhancing electrocatalytic hydrogen evolution performance

The reduction of active sites due to reunion and slow electron transfer rates and low electronegativity greatly reduced the catalytic performance of many two-dimensional materials. In this paper, we synthesized composites for partially reducing graphene oxide and molybdenum disulfide (MoS₂@prGO) by one-step hydrothermal method. With the addition of triethanolamine, MoS₂ is highly dispersed on the prGO carrier and converted into the 1T phase MoS₂ (50.4%). Meanwhile, it helps to increase the electron transfer rate of the MoS₂@prGO composites. MoS₂@prGO composites presents a high electron cloud density due to the existence of N atoms and prGO, which promotes the occurrence of hydrogen ion conversion hydrogen reaction and decreases the electrocatalytic hydrogen evolution overpotential. MoS₂@prGO composites exhibits an overpotential of 263 mV at 10 mA/cm² and a small Tafel slope of 60 mV/dec. This work is devoted to offer a new prospect and direction for the improvement of electrochemical HER performance.     

Polysulfide functionalized reduced graphene oxide for electrocatalytic hydrogen evolution reaction and supercapacitor applications

Functionalized carbon based 2D materials are promising candidates for low cost and environment friendly electrocatalyst for hydrogen evolution reaction (HER) and supercapacitor applications. To overcome the limitations posed by the noble metals and transition metal based composites, we have successfully synthesized metal free polysulfide functionalized reduced graphene oxide (GPS) in a simple chemical route. Structure and morphology of the material are characterized via XRD, FTIR, Raman, TEM, XPS measurements. The material behaves as an efficient HER electrocatalyst in acidic medium as well as energy storage device. It shows an onset potential of 97 mV and overpotential of 254 mV to reach a high current density of 10 mA/cm². DFT calculations are carried out to understand the structural stability and identification of active sites of the material. Boosting catalytic activity via increasing the number of active sites is an elegant approach. In this material we have used the S atoms of polysulfide polymer to facilitate hydrogen adsorption and desorption, thus improving the hydrogen evolution ability. The supecapacitor attains the high specific capacitance 347 F/g at the current density of 1 A/g. The origin of such performances is due to synergistic effect of both the graphene network and the polysulfide functionalizations.     

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.     

MOF-directed templating synthesis of hollow nickel-cobalt sulfide with enhanced electrocatalytic activity for oxygen evolution

The development of efficient, universal and cheap electrocatalysts for the utilization in the oxygen evolution reaction (OER) by desired morphology and composition remains a great challenge. Herein, we report a facile and novel method to prepare the porous hollow nickel-cobalt sulfide (NiCoS) by using zeolitic imidazolate framework-67 (ZIF-67) as the template. The obtained NiCoS-3 polyhedron shows superior catalytic activity toward OER with a low overpotential of 320 mV at the current density of 10 mA cm^?2, a small Tafel slope of 58.8 mV dec^?1 and excellent stability. Benefiting from their structural and compositional merits, the as-synthesized NiCoS-3 polyhedron may be a good promising candidate electrocatalysts for water splitting. Present work provides a simple strategy to regulated composition, morphology and catalytic activity relationship, offer an effective way to design a low-cost and efficient electrocatalyst.     

A platinum modulated tungsten oxide on Ag nanowires network as an indicator for in-situ visualized evaluation of the hydrogen evolution performance

The development of the real-time evaluation for the catalytic hydrogen evolution performance under a simple and convinient condiction is urgently needed, but still a great challenge. Herein, a platinum modulated WO_x on Ag nanowires (Pt-WO_x@Ag NWs) is developed as an optical-electrochemical catalyst to realize an in-situ intuitive evaluation for the hydrogen evolution performance, in which the color of as-prepared Pt-WO_x@Ag NWs catalyst changes from the transparent to the deep blue with the increase of the applied potential. The real-time H₂ evolution with an H₂ turnover frequency (from 0 to 2.26 s^?1 per site), optical transmittance (from 80.3% to 48.7% at the wavelength of 630 nm) and energy consumption (from 0 to 0.74 W h in 1 h) is established. The charge transfer and mass transport are greatly promoted by the three demensional Ag NWs conductive network and abundant active sites, which are provided by the platinum modulated WO₃ on the Ag substrate. Density functional theory (DFT) calculations indicate that the modified WO_x shows the preferred adsorption affinity toward H₂O (ΔG_H2O, ?0.17 eV), which reach a high coloration efficiency and optical modulation range for the electrochromic reaction. The Pt sites on WO_x with a suitable H binding energy (ΔG_H1, 0.38 eV) efficiently promote the H1 conversion and H₂ release of water splitting. This work propose an intelligent hydrogen evolution indicator by real-time color change to boost the high-quality development of green hydrogen energy.     

Improved electrochemical performance of nickel-cobalt hydroxides by electrodeposition of interlayered reduced graphene oxide

Efficient, economical, and eco-friendly water splitting catalysts are in priority to replace the fossil fuels. In the presented work, reduced graphene oxide is formed through electrochemical reduction and applied as an effective interlayer between nickel foam substrate and nickel-cobalt hydroxide catalyst to augment its activity toward hydrogen evolution reaction. Through subsequent cyclic voltammetry deposition of nickel-cobalt hydroxide over the surface of supported interlayer, the prepared electrocatalyst exhibited remarkable performance by reaching a current density of 10 mA cm⁻² at a small overpotential of 60 mV in 1.0 M KOH electrolyte, much lower than that of the same electrocatalyst without interlayer (78 mV). The proposed strategy made the active metallic catalyst phase acquiring a small Tafel slope and superior durability for hydrogen production in alkaline medium. By utilizing the reduce graphene oxide interlayer, the electrical conductivity of the final nickel-cobalt hydroxide electrode was boosted. Furthermore, a clear transition from ordered reticulated arrays of nanosheets to roughened and disordered nanosheet-comprised nanospheres is demonstrated for surface morphology of nickel-cobalt electrocatalyst that indeed prompts the increase in its electrochemically active surface area.     

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.     

Atomically dispersed palladium supported on nitrogen-doped mesoporous carbon for drastic electrocatalytic hydrogen evolution

The electrocatalysis of water to hydrogen is expected to play an essential and significant role in the development of future electrochemical energy conversion and storage technologies, together with the exploration of green energy. However, the high cost of noble metal catalysts remains a key challenge and it still requires further investigations to fabricate high mass activity and stable electrocatalysts. Herein, we report a facile and economical approach to achieve atomically dispersed palladium on the nitrogen-doped mesoporous carbon matrix (Pd₁/NMC) as the electrocatalyst for hydrogen evolution, which exhibits an overpotential of 37 and 118 mV at the current density of 10 and 100 mA cm^?2, respectively, superior to the commercial platinum/carbon (Pt/C) and palladium/carbon (Pd/C) catalysts. Moreover, the mass activity of the Pd₁/NMC catalyst surpasses that of Pt/C and Pd/C at 100 mV versus RHE in HER. Systematic characterizations demonstrate that the Pd atoms are atomically dispersed on the surface of NMC and stabilized by active nitrogen sites, inducing the isolated Pd atoms to form a favorable bivalent oxidation state. This method provides an atomic-level insights into preparing superior single-atom catalysts for energy-related applications and devices.     

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.     

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.     

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.     

Nickel-based nanosheets array as a binder free and highly efficient catalyst for electrochemical hydrogen evolution reaction

Hydrogen technology through water electrolyzer systems has attracted a great attention to overcome the energy crisis. So, rationally designed non-noble metal based-electrocatalysts with high activity and durability can lead to high performance water electrolyzer systems and high purity hydrogen generation. Herein, a facile two-step method: hydrothermal and electrodeposition, respectively, are developed to decorate highly porous three-dimensional binder-free structure NiFeO/NiO nanosheets array on Ni foam (NiFeO/NiO/NF) with robust adhesion as a high-performance electrode for Hydrogen Evolution Reaction (HER).The electrodeposition process applied after the initial hydrothermal process provides a stable structure and, in addition, enhances the sluggish hydrogen evolution efficiency. In alkaline media, the developed electrode needs an overpotential of 48 and 188 mV to drive current densities (j) of 10 and 100 mA cm^?2, respectively. After continuous 110 h electrochemical stability test under j = 150 mA cm^?2 conditions, demonstrates an excellent stability with ignorable activity decrease. Such superior HER catalytic performance can be derived from the synergistic effect between Ni and Fe atoms, also exposure to a high number of active sites on the nanosheets, and good dynamic with effective electron transport along the nanosheets. The present work provides a promising route for the design and fabrication of cost-effective and highly efficient HER electrocatalysts.     

Porous CoS2 nanostructures based on ZIF-9 supported on reduced graphene oxide: Favourable electrocatalysis for hydrogen evolution reaction

The research and developments of porous, highly active non-noble metal cathode materials are the current hot spots. In our work, ZIF-9 (Zeolitic imidazolate framework-9) as a cobalt source provide porous structure, we have sulfurized the ZIF-9 into CoS₂ by a simple hydrothermal method. Ultimately, the porous CoS₂/RGO cathode material was obtained. Through a series of characterization analyses (powder X-ray diffraction, X-ray photoelectron spectroscopy), it is confirmed that the CoS₂/RGO composite was successfully formed. Furthermore, electrochemical tests demonstrated that the pursued catalyst exhibited remarkable hydrogen evolution reaction (HER) activities with a favorable overpotential (only 180 mV for 10 mA cm^?2 vs reversible hydrogen electrode), a low Tafel slopes (75 mV decade^?1) and high stability in acidic condition (more than 18 h).     

Defective-MoS2/rGO heterostructures with conductive 1T phase MoS2 for efficient hydrogen evolution reaction

As a two-dimensional material, molybdenum disulfide (MoS₂) exhibits great potential to replace metal platinum-based catalysts for hydrogen evolution reaction (HER). However, poor electrical conductivity and low intrinsic activity of MoS₂ limit its application in electrocatalysis. Herein, we prepare a defective-MoS₂/rGO heterostructures material containing 1T phase MoS₂ and evaluate its HER performance. The experimental results shown that defective-MoS₂/rGO heterostructures exhibits outstanding HER performance with a low overpotential at 154.77 mV affording the current density of 10 mA cm^?2 and small Tafel slope of 56.17 mV dec^?1. The unique HER performance of as-prepared catalyst can be attributed to the presence of 1T phase MoS₂, which has more active sites and higher intrinsic conductivity. While the defects of as-prepared catalyst fully expose the active sites and further improve catalytic activity. Furthermore, the interaction between MoS₂ and rGO heterostructures can accelerate electron transfer kinetics, and effectively ensure that the obtained catalyst displays excellent conductivity and structural stability, so the as-prepared catalyst also exhibits outstanding electrochemical cycling stability. This work provides a feasible and effective method for preparation of defective-MoS₂/rGO heterostructures, which also supplies a new strategy for designing of highly active and conductive catalysts for HER.