Sites For Hydrogen Evolution Research Articles

Ar2+ Beam Irradiation-Induced Multivancancies in MoSe2 Nanosheet for Enhanced Electrochemical Hydrogen Evolution

Poor electronic conductivity and an inert basal plane restrict the further enhancement of hydrogen evolution reaction (HER) in 2H-phase MoSe2. Herein, we synthesized MoSe2 nanosheet arrays on carbon cloth and induced multivacancies in their basal plane via high-energy Ar2+ beam irradiation, which are confirmed by Raman, electron spin resonance, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy analyses. Electrical measurement results indicate that these vacancies in the MoSe2 basal plane can effectively improve their electrocatalytic performance, where the lowest overpotential of −171 mV at the current density of −100 mA/cm2 and Tafel slope of 35 mV/dec were achieved in Ar2+-irradiated (dose of 5 × 1015 ions/cm2) MoSe2 nanosheets. First-principles calculation results reveal that different cases of native vacancies in the MoSe2 basal plane could effectively enhance the conductivity of MoSe2 and produce more catalytic active sites for hydrogen evolution, giving rise to ...

Highly dispersed PtO nanodots as efficient co-catalyst for photocatalytic hydrogen evolution

PtO nanodots (∼2.5 nm) with high crystallinity are homogeneously deposited on the surface of g-C3N4 by a two-step refluxing-calcination method. XPS analysis indicates that a strong interaction is formed between PtO and g-C3N4, which is beneficial for the transportation of charge carriers from g-C3N4 to the co-catalyst and therefore results in a prolonged carrier life time in the composite. A series of electrochemical tests, including EIS, LSV and OCVD prove that PtO can significantly enhance the conductivity and light response of g-C3N4 compared with Pt. PtO and Serving as hydrogen evolution sites, the highly dispersed PtO nanodots can shorten the diffusion path lengths for photogenerated electrons in the host photocatalyst as well as suppress the undesired hydrogen oxidation reaction. Remarkably, PtO coupled g-C3N4 (0.19 wt% Pt) exhibits excellent hydrogen production activity, giving a turnover frequency of 552.7 h−1, which is 51 times that of Pt nanoparticles confined g-C3N4. The PtO nanodots also display high photostability and would not agglomerate into clusters or be reduced by the photogenerated electrons even after 40 h of irradiation. The present work also provides a new method for synthesis of high performance co-catalysts with low Pt content used in other photocatalytic reactions and energy applications.

Facile Modification of Titania with Nickel Sulfide and Sulfate Species for the Photoreformation of Cellulose into Hydrogen.

Photocatalytic cellulose reformation is regarded as a potential and affordable route for sustainable H2 evolution. However, direct photoreformation still suffers from challenges such as the limited solubility of cellulose and the dependence on the catalytic activity of noble metals. Herein, we report a new photoreformation of cellulose into H2 over TiO2 that is modified with nickel sulfide (Nix Sy ) and chemisorbed sulfate species (SO42- ) by a one-pot approach. A significant elevation in the photocatalytic hydrogen evolution rate is achieved with a maximal value of 3.02 mmol g-1 h-1 during the first 3 h, which is almost 76-fold higher than that of P25 and comparable to that of Pt-P25. Aided by systematic investigation, it is proposed that nickel sulfide and sulfate modification contribute synergistically to the remarkably increased efficiency of biomass transformation. Specifically, Nix Sy acts as a cocatalyst for photocatalytic H2 production, and we infer that SO42- ions promote cellulose hydrolysis and the consequent accessibility of the biomass to catalysts. Further, the accumulated formate intermediates have a poisoning effect on the catalysts, the desorption of which can be controlled by tuning the aqueous alkalinity. Overall, our strategy for the modification of TiO2 with SO42- and Nix Sy provides a new perspective for the concurrent acceleration of cellulose hydrolysis and increase of the number of hydrogen evolution sites for the efficient photocatalytic reformation of cellulose into H2 .

Enhanced visible light activated hydrogen evolution activity over cadmium sulfide nanorods by the synergetic effect of a thin carbon layer and noble metal-free nickel phosphide cocatalyst

Photocatalytic water splitting is considered to be a promising strategy for addressing the global energy crisis through the expanded use of solar energy. Herein, cadmium sulfide (CdS) nanorods modified with a thin conductive carbon layer and a nickel phosphide co-catalyst, referred to as cadmium sulfide coated with a carbon layer and nickel phosphide (CdS@C/Ni2P, where @ indicates a core–shell structure), were synthesized and applied as a novel composite photocatalyst for water splitting. The optimized CdS@C/Ni2P composite showed a high photocatalytic hydrogen generation rate of 32030 μmol h−1 g−1, which was approximately 19 times as high as that of pure CdS. We believed that the thin carbon layer acted as an electron acceptor to promote charge transfer and protect the CdS nanorods from photocorrosion. In addition, the surface loading of the nickel phosphide (Ni2P) cocatalyst was able to further draw photogenerated electrons from the cadmium sulfide coated with a carbon layer (CdS@C) heterojunction and provide active sites for hydrogen evolution. Thus, greatly enhanced hydrogen generation was achieved through a combination of carbon coating and surface cocatalyst loading. This development provides a new way to design composite photocatalysts with multiple junctions for efficient water splitting performance.

1D metallic MoO2-C as co-catalyst on 2D g-C3N4 semiconductor to promote photocatlaytic hydrogen production

The surface carrier density and hydrogen activation ability are crucial in photocatalytic hydrogen evolution reaction (HER), which can be improved by introducing noble-metal co-catalyst such as Pt into the system. However, the noble-metals suffer from high cost in terms of upscaling, thereby the exploration of low-cost HER co-catalysts is highly demanded. In this work, we report that one-dimensional (1D) metallic MoO2-C nanowire clusters can serve as a co-catalyst in assisting the photocatalytic hydrogen production over 2D g-C3N4. The multiple merits of MoO2-C are demonstrated: (i) noble-metal-free; (ii) highly effective transfer ability of the photogenerated electrons; (iii) high-density adsorption and active sites for hydrogen evolution. As demonstrated in photocatalytic hydrogen production, MoO2-C/2D g-C3N4 exhibits significant enhancement in comparison with pure 2D g-C3N4 semiconductor. The optimal hydrogen evolution rate achieving 1071.0 μmol g−1 h−1, almost 157.5 times higher than that of pure 2D g-C3N4.

The synergetic effect of graphene and MoS2 on AgInZnS for visible-light driven photocatalytic H2 evolution

A ternary complex of AgInZnS/MoS2-GO was successfully synthesized via a two-step hydrothermal method. Layered structured MoS2-GO plays a key role in enhancing the photocatalytic performance for hydrogen evolution. The synthesized product was further characterized by transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman et al. The nanocomposite with 1 wt % MoS2-GO in the heterojunction photocatalyst exhibits the highest rate of hydrogen evolution rate of 1302 μmol h−1. A detailed mechanism has been developed to explain the significantly enhanced catalytic activities. The nanohybrid showed enhanced photocatalytic activity towards water splitting, arising from synergetic effect of Graphene and MoS2 since MoS2 can provide active sites for hydrogen evolution while graphene can facilitate the charge transfer in the constructed system. This work may contribute to the design and construction of highly efficient visible-light responsive photocatalyst for sustainable energy harvesting and conversion.

Self-assembled MoS2-GO Framework as an Efficient Cocatalyst of CuInZnS for Visible-Light Driven Hydrogen Evolution

A ternary heterostructured CuInZnS/MoS2-GO (graphene oxide) photocatalyst was constructed by a simple two-step hydrothermal method. The three-dimensional hierarchical architecture of MoS2-GO hydrogel was first synthesized through a facile hydrothermal method. The obtained MoS2-GO hydrogel with ultralow density and high surface area was redispersed into water and composite with CuInZnS. The resulting catalysts were analyzed by systematic characterizations including X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), Raman, and UV–vis diffuse reflectance spectra (DRS), et al. The noble metal-free composite exhibited dramatically enhanced photocatalytic performance toward hydrogen evolution. The enhanced solar water splitting performance could be ascribed to the synergetic effect of GO and MoS2. GO served as an electron acceptor and transporter while MoS2 provided abundant active sites for hydrogen evolution. We hope this work may give some pe...

Enhanced photoelectrochemical performance of defect-rich ReS2 nanosheets in visible-light assisted hydrogen generation

Defect introduction is one of the most important motivations to produce highly efficient electrocatalyst in the field of water splitting. Here we report the visible-light enhanced photoelectrochemical performance derived from defect-rich ReS2 nanosheets with high activity towards hydrogen generation from water. After continuous pre-electrolysis under visible-light irradiation for about 2 h, the activated ReS2 nanosheets electrocatalyst performs highly enhanced catalytic activity, with an onset potential decreasing from 170 to 88 mV and a long stability over 10 h. It is worth noting that only a small overpotential of 116 mV is required to afford the current density of 10 mA cm−2, which is the highest activity to date for ReS2 electrocatalysts and much better than most transition-metal dichalcogenide materials electrocatalysts. Ex-situ transmission electron microscopy (TEM) and inductively coupled plasma emission spectrometer (ICP) examinations demonstrate that the performance improvement is attributed to the defect introduction during the visible-light assisted pre-electrolysis process involving the rhenium atoms vacancies on the basal planes and the lattice fringes of ReS2. Theoretical calculations further confirm that the abundant Re atoms vacancies with lower Gibbs free energy for H adsorption activate the inert basal plane as highly active sites for hydrogen evolution.

MXene nanoribbons as electrocatalysts for the hydrogen evolution reaction with fast kinetics.

MXenes, a new class of two-dimensional materials, arouse great interest due to their diverse chemistries, superior electrical conductivity and stability. Recently, the nanostructures of MXenes such as nanoribbons and nanodots have been synthesized in experiments, which show peculiar properties and expand the application spectrum of MXenes. Here we exploited MXene nanoribbons as potential electrocatalysts for the hydrogen evolution reaction (HER) by considering 12 kinds of MXene systems. Our first-principles calculations showed that the edges of the MXene nanoribbons can adsorb hydrogen species and serve as the reaction sites for hydrogen evolution. The binding strength of the ribbon edge is correlated with the d band center of metal atoms in MXenes. In particular, the nanoribbons of Ti3C2 and solid solution (Ti,Nb)C exhibit high activity for the HER with the adsorption free energy approaching zero and Tafel barrier below 0.42 and 0.17 eV, respectively. The low barrier is owing to the prominent charge transfer from the edge metal atoms to the H* reactants in the transition state. These theoretical results illuminate the principle for designing MXene nanostructures for electrocatalysts with fast kinetics, and shed light on the utilization of MXenes with more than one metal element for a broad range of electrochemical reactions.

Noble metal-free NiS/P-S codoped g-C3N4 photocatalysts with strong visible light absorbance and enhanced H2 evolution activity

Noble metal-free NiS/P-S codoped g-C3N4 (PSCN) nanocomposites were fabricated by combination of thermal copolymerization using ammonium O, O- diethyl dithiophosphate as P-S precursor and ion-exchange precipitation. The optimal H2-generation rate of NiS/PSCN is 30.5μmolh−1, which is 1.9 times higher than that of NiS/pristine g-C3N4. The codoping of P and S into g-C3N4 not only enhances the light harvesting, but also promotes the charge separation. Noble metal-free NiS loaded onto PSCN serves as electron trapping centers and active sites for hydrogen evolution which further enhances the photocatalytic H2 evolution activity of PSCN.

CoMoS2/rGO/C3N4 ternary heterojunctions catalysts with high photocatalytic activity and stability for hydrogen evolution under visible light irradiation

Noble metal free MoS2/g-C3N4 catalyst has attracted intense attentions for visible light photocatalytic hydrogen evolution as a result of its earth abundance, low cost and unique heterojunctions stacked with two dimensional sheets. However, the low charge separation efficiency resulted from the poor conductivity of g-C3N4 and MoS2, and lack of abundant active sites from coordinative unsaturated atoms in MoS2, restricts the photocatalytic hydrogen evolution activity and stability enhancement of MoS2/C3N4 composite catalysts. Herein, CoMoS2/rGO/g-C3N4 catalysts with ternary heterojunctions are prepared by facile solvothermal method, which exhibit high visible light photocatalytic activity and stability for hydrogen evolution. The optimal hydrogen evolution rate of CoMoS2/rGO/g-C3N4 catalysts is 684 μmol g−1 h−1 when the content of CoMoS2 is 2% and the content of rGO is 0.5%. The stability of CoMoS2/rGO/C3N4 catalysts just decrease about 3% after 4 cycling runs for 16 h. The good catalytic performances of catalysts are attributed to the synergistic effect among the g-C3N4 nanosheets, rGO nanosheets and CoMoS2 nanosheets. The high conductivity of rGO nanosheets enhances the electron-hole separation and charge transfer, and Co doping increases the active sites for hydrogen evolution due to the increase of unsaturated atoms in CoMoS2 nanosheets.

Semiconductive Copper(I)-Organic Frameworks for Efficient Light-Driven Hydrogen Generation Without Additional Photosensitizers and Cocatalysts.

As the first example of a photocatalytic system for splitting water without additional cocatalysts and photosensitizers, the comparatively cost-effective Cu2 I2 -based MOF, Cu-I-bpy (bpy=4,4'-bipyridine) exhibited highly efficient photocatalytic hydrogen production (7.09 mmol g-1 h-1 ). Density functional theory (DFT) calculations established the electronic structures of Cu-I-bpy with a narrow band gap of 2.05 eV, indicating its semiconductive behavior, which is consistent with the experimental value of 2.00 eV. The proposed mechanism demonstrates that Cu2 I2 clusters of Cu-I-bpy serve as photoelectron generators to accelerate the copper(I) hydride interaction, providing redox reaction sites for hydrogen evolution. The highly stable cocatalyst-free and self-sensitized Cu-I-bpy provides new insights into the future design of cost-effective d10 -based MOFs for highly efficient and long-term solar fuels production.

Semiconductive Copper(I)–Organic Frameworks for Efficient Light‐Driven Hydrogen Generation Without Additional Photosensitizers and Cocatalysts

AbstractAs the first example of a photocatalytic system for splitting water without additional cocatalysts and photosensitizers, the comparatively cost‐effective Cu2I2‐based MOF, Cu‐I‐bpy (bpy=4,4′‐bipyridine) exhibited highly efficient photocatalytic hydrogen production (7.09 mmol g−1 h−1). Density functional theory (DFT) calculations established the electronic structures of Cu‐I‐bpy with a narrow band gap of 2.05 eV, indicating its semiconductive behavior, which is consistent with the experimental value of 2.00 eV. The proposed mechanism demonstrates that Cu2I2 clusters of Cu‐I‐bpy serve as photoelectron generators to accelerate the copper(I) hydride interaction, providing redox reaction sites for hydrogen evolution. The highly stable cocatalyst‐free and self‐sensitized Cu‐I‐bpy provides new insights into the future design of cost‐effective d10‐based MOFs for highly efficient and long‐term solar fuels production.

Photochemical hydrogen evolution on metal ion surface-grafted TiO2-particles prepared by sol/gel method without calcination

We report here a new class of co-catalysts for hydrogen evolution on TiO2 particles upon photo-irradiation. TiO2 particles prepared by sol/gel method was allowed to graft metal ion by a simple treatment with metal salts (Pt (IV), Rh (III), Cu (II), Fe(III), Al (III) ions) in water. The metal ion surface-grafted particles of TiO2(sol/gel) exhibit excellent photochemical hydrogen evolution compared to Pt (0) cluster loaded particles of TiO2(sol/gel) under the UV light irradiation of λ>290nm. XPS analysis shows that the valence states of the metal ions grafted on the TiO2 particles are the same with the parent metal ion salts and no metal (0) clusters were detected. DFT calculation of the simple model of metal ion/TiO2 indicated that an injected electron mostly localized on the metal ion sites, but not on Ti sites, which rationalizes the metal ion serve as the hydrogen evolution sites. Earth abundant metal ions, Cu (II), Fe (III), and Al (III) thus can provide new class of hydrogen evolution sites for artificial photosynthetic systems. To explore the possibility of utilizing semiconductor as an electron relay in the future system of molecular-catalyst-sensitized water splitting into hydrogen and hydrogen peroxide, the stability of hydrogen peroxide on various TiO2 surfaces was examined. Hydrogen peroxide was found to be pretty stable on Rh (III), Fe (III), and Al (III) ions surface-grafted TiO2, while Pt (IV) and Cu (II) ion grafted one similarly caused decomposition of hydrogen peroxide as Pt (0) cluster loaded TiO2 (Pt(0)/TiO2).

Ultrathin Nitrogen-Doped Carbon Coated with CoP for Efficient Hydrogen Evolution

Searching for non-noble-metal-based electrocatalysts with high efficiency and durability toward the hydrogen evolution reaction (HER) is vitally necessary for the upcoming clean and renewable energy systems. Here we report the synthesis of CoP nanoparticles encapsulated in ultrathin nitrogen-doped porous carbon (CoP@NC) through a metal–organic framework (MOF) route. This hybrid exhibits remarkable electrocatalytic activity toward the HER in both acidic and alkaline media, with good stability. Experiments and theoretical calculations reveal that the carbon atoms adjacent to N dopants on the shells of CoP@NC are active sites for hydrogen evolution and that CoP and N dopants synergistically optimize the binding free energy of H* on the active sites, which results in a higher electrocatalytic activity in comparison to its counterparts without nitrogen doping and/or CoP encapsulation.

High-Sulfur-Vacancy Amorphous Molybdenum Sulfide as a High Current Electrocatalyst in Hydrogen Evolution.

The remote hydrogen plasma is able to create abundant S-vacancies on amorphous molybdenum sulfide (a-MoSx ) as active sites for hydrogen evolution. The results demonstrate that the plasma-treated a-MoSx exhibits superior performance and higher stability than Pt in a proton exchange membrane based electrolyzers measurement as a proof-of-concept of industrial application.

Ni-W Alloys for Hydrogen Evolution

Ni-W alloys were prepared by electrodeposition at diverse processing conditions. The Ni-W alloys were studied by SEM, EDX and XRD analysis to determine composition and morphology of the surface in dependence on electrodeposition conditions. Focus was put on surface with electroactive sites for hydrogen evolution. Stability of the alloys in chloride medium was determined applying chronopotentiometry and potentiodynamic polarization. Electrochemical behavior of the alloys was tested in alkaline solution by cyclic voltammetry. It was found that processing conditions directly influence quality of the Ni-W alloys concerning phase, morphology and composition. Prevailing amorphous phase of Ni-W alloys supports corrosion rate growth.

Polymer supported graphene–CdS composite catalyst with enhanced photocatalytic hydrogen production from water splitting under visible light

A polymer supported graphene structure was synthesized using organic microspheres as the support of the graphene oxide. Graphene oxide was reduced to graphene and CdS was decorated on the surface of the graphene through a solvothermal process. The photocatalytic hydrogen production reaction was carried out using the composite catalyst under visible light irradiation (λ>400nm). A series of composite catalysts were synthesized with different reaction time. The maximal hydrogen production rate of 175μmolh−1 was obtained from the 3h prepared sample (PSGM/rGO/CdS-3), which is 19.3 times higher than the mechanical mixing sample with the same composition. The quantum efficiency of the PSGM/rGO/CdS-3 sample was 3.99% at 420nm. Graphene served as electron acceptor and hydrogen evolution sites to promote the separation of the photo-induced charge carriers. Quantum size effect was observed from ultraviolet–visible diffuse reflectance spectroscopy and PL measurements. The presence of quantum size effect widened the bandgap of the catalyst and enhanced the photocatalytic hydrogen production rate. The stability of the composite catalyst was tested and demonstrated that this graphene-based composite catalyst was a stable and potential catalyst for photocatalytic hydrogen production.

Novel Au/TiO2 photocatalysts for hydrogen production in alcohol–water mixtures based on hydrogen titanate nanotube precursors

In this study, a series of titania nanorods with different phase compositions and surface areas were prepared by calcination of hydrogen titanate (H2Ti3O7) nanotubes at temperatures up to 1000°C. Gold nanoparticles were subsequently deposited on the obtained TiNTx (x=calcination temperature) nanorod supports at loadings between 0.5 and 2.0wt.%, and also onto a commercially available mixed-phase titania support (Degussa P25). TEM, XRF, UV–Vis, XPS and photoluminescence measurements confirmed the presence of gold nanoparticles of mean size 4–7nm on the surface of the Au/TiNTx (x=350–800) and Au/P25 photocatalysts, which suppressed electron–hole pair recombination in TiO2 under UV and created cathodic sites for hydrogen evolution. Hydrogen production tests were conducted on the Au/TiNTx and Au/P25 photocatalysts in various alcohol–water mixtures under UV excitation (6.5mWcm−2) with no external bias applied. The impact of the gold loading and the calcination temperatures on the structural, physico-chemical and photocatalytic properties of the TiNTx nanorods was investigated, and a comparison to P25 was made. A 0.5wt.% Au/TiNT600 photocatalyst demonstrated excellent H2 production activity in all the alcohol–water systems, performing similarly to a 1.5wt.% Au/P25 reference photocatalyst. For both the 0.5wt.% Au/TiNT600 and 1.5wt.% Au/P25 photocatalysts, H2 production rates decreased in the order triol (glycerol)>diol (1,2-ethanediol≈1,2-propanediol)>ethanol>1-propanol. Good correlations were found between the H2 production rates and alcohol properties such as the number of hydroxyl groups, polarity or standard oxidation potential.

Hydrogenated Defects in Graphitic Carbon Nitride Nanosheets for Improved Photocatalytic Hydrogen Evolution

Delaminated carbon nitride nanosheets were prepared by high-temperature H2 treatment of bulk carbon nitride with defects being introduced during this treatment. Although the defects can act as traps for charge carriers, reducing photoluminescence lifetime, they also form highly active photocatalytic sites for hydrogen evolution. The nanostructured materials exhibit substantially enhanced photocatalytic activity due to a synergistic effect between delamination, the presence of defects, and associated band gap changes.