Synthesis of novel hollow microflowers (NHMF) of Nb3O7F,their optical and hydrogen storage properties

A two step, facile surfactant free hydrothermal route was adopted to synthesize Nb₃O₇F novel hollow microflowers (NHMF). Time dependent experiments were performed which suggested Nb₃O₇F-NHMF were formed due to Ostwald-ripening process. Raman spectroscopy was conducted to understand different vibrational modes of Nb₃O₇F-NHMF. Its characteristic band at 692 cm⁻¹ was observed which is associated to NbO₆ octahedron sharing. The bandgap of 3.2 eV was calculated by using UV-VIS-NIR absorption spectrum. Considering importance of layered structures in energy storage applications, hydrogen storage ability of Nb₃O₇F-NHMF were measured for the first time. The maximum values of hydrogen absorption for Nb₃O₇F-NHMF at 373 K and 473 K were 0.789 wt.% and 1.08 wt.%, respectively. The hydrogen storage measurements revealed the potential of Nb₃O₇F-NHMF as prospective material for energy storage applications.     

Microstructural evolution and hydrogen storage properties of Mg1-xNbx(x=0.17~0.76) alloy films via Co-Sputtering

A series of Mg_1-xNb_x (x = 0.17–0.76) alloy films were prepared by means of magnetron co-sputtering in this work, on the purpose of obtaining better hydrogen storage materials with controllable component and structure. Mg(Nb) solid solution (Mg_0.83Nb_0.17 and Mg_0.76Nb_0.24 film), BCC-(Mg_1-xNb_x) structure (Mg_0.70Nb_0.30 and Mg_0.60Nb_0.40 film), and Nb(Mg) solid solution respectively (Mg_0.38Nb_0.62 and Mg_0.24Nb_0.76 film) formed in the Mg_xNb_1-x alloy films with the increases of Nb contents. It only took 3 min for BCC-Mg_0.60Nb_0.40 to absorb 2.3 wt% hydrogen at 473 K and took only 30 min to desorb 1.2 wt% hydrogen at 523 K. Moreover, the BCC structure maintained after hydrogenation or dehydrogenation, which promised good cyclic stability. The hydrogen storage capacities of Mg_1-xNb_x alloy films were decreased with the increases of Nb contents. Mg_0.83Nb_0.17 can absorb most hydrogen of 3.8 wt% and Mg_0.24Nb_0.76 absorbs least hydrogen of 1.0 wt%. The Nb not only played a role of catalyst but also cooperated with Mg to build the BCC-(Mg,Nb) structure. The former provided intergranular path for the hydrogen atoms to diffuse faster; the latter provided more and larger lattice interstices for hydrogen atoms to diffuse in grain more easily.     

Highly active FexCo1-xP cocatalysts modified CdS for photocatalytic hydrogen production

In this paper, we report a ternary Fe_xCo_1−xP co-catalyst, which can greatly improve the photocatalytic performance of CdS photocatalyst for hydrogen production under visible light irradiation. The high efficiency of ternary Fe_xCo_1-xP loaded CdS is mainly due to the high electrochemical activity and efficient charge transfer between Fe_xCo_1-xP cocatalyst and CdS. Experimental results have shown that the substitution of Fe ions for some Co ions in CoP can change the electrochemical properties of Fe_xCo_1-xP. The electrocatalytic performance of Fe_xCo_1-xP and the photocatalytic activity of Fe_xCo_1-xP/CdS are both dependent on the molar concentration x of Fe. When x = 0.4 the hydrogen generation rate (18.27 mmol h⁻¹ g⁻¹) and the quantum efficiency (50.6% at 420 nm) for 0.5 wt% Fe_0.4Co_0.6P/CdS photocatalyst is 5.85 times higher than that of pure CdS and 1.35 times higher than that of 0.5 wt% CoP/CdS. This new noble-metal-free Fe_xCo_1-xP cocatalyst is beneficial for the solar hydrogen economy.     

Improving hydrogen permeability and sustainability of Nb30Ti35Co35 eutectic alloy membrane by substituting Co using Fe

The microstructure and hydrogen permeation performance of Nb₃₀Ti₃₅Co_35-xFe_x (x = 0, 5, 10, 15, 20) alloys have been investigated. With Fe less than 15 at%, the as-cast Nb₃₀Ti₃₅Co_35-xFe_x ingots exhibit fully eutectic structure. When the Fe content is higher than 15 at%, primary bcc-(Nb, Ti) phase appears in combination with eutectic structure. Substituting Co using Fe leads to slightly increased hydrogen solubility but highly enhanced hydrogen permeability, which comes mainly from the increased hydrogen concentration-independent diffusion coefficient D1. With Fe content up to 10 at%, Nb₃₀Ti₃₅Co_35-xFe_x membranes exhibit stable and higher hydrogen permeation flux than Nb₃₀Ti₃₅Co₃₅ at 673 K during hydrogen permeation test up to 72 h. Nb₃₀Ti₃₅Co_35-xFe_x alloys of fully eutectic structures exhibit no hydrogen-induced failure when cooled down to room temperature under hydrogen atmosphere, indicating the potential application of the membrane at lower temperature range. An optimal combination of hydrogen permeability and hydrogen embrittlement resistance is achieved at 10 at% Fe, since further increase of Fe leads to comparable D1 as that of Nb₃₀Ti₃₅Co₂₅Fe₁₀ but higher hydrogen solubility.     

Vanadium based zinc spinel oxides: Potential materials as photoanode for water oxidation and optoelectronic devices

In the recent past, layered zinc-based vanadium spinel oxides (ZnVOs) have shown an intriguing way to accomplish the challenges of energy conversion, storage, and utilization issues. Here, through first-principles calculations, a comprehensive study has been carried out to investigate the AV₂M (where A = Zn, Zn₂, Zn₃, Zn_4, and M = O₄, O₆, O₇, O₈, O₉ respectively) electronic, photocatalytic, and optical properties. Formation energies with a negative sign express that the final compounds from the pure elements are possible and cohesive energies revealed that compounds are energetically stable. Spin-polarized calculations are also taken into account for better approximation of the electronic properties (band structure and density of states). All layered structures show indirect bandgap for spin-up calculations in range 0.3 eV–2.4 eV, while spin-down calculations show mix trends in range 2.3 eV–3.50 eV. An appropriate band edge with large enough kinetic over-potentials of the oxygen evolution reaction (ΔE_V ≥ 1.244 eV) makes them potential candidates as photoanode for water splitting. ZnV₂O₄ is more suitable for OER as it has small kinetic overpotential as compared to the oxidation potential of water. Interestingly, all ZnVOs display a dramatically large coefficient (~10⁵ cm⁻¹) for optical absorption. Photogenerated electrons and holes on the layered zinc-based vanadium spinel oxide surfaces could make these spinel oxides promising materials for photocatalytic water splitting and solar energy conversion.     

Photocatalytic production of hydrogen and methane from glycerol reforming over Pt/TiO2–Nb2O5

In this study, platinized mixed oxides (TiO₂–Nb₂O₅) were tested on photocatalytic hydrogen production from a glycerol solution under UV light. Different samples with different Ti:Nb ratios were prepared by using a simple method that simultaneously combined a physical mixture and a platinum photochemical reduction. This method led to improved physicochemical properties such as low band gap, better Pt nanoparticle distribution on the surface, and the formation of different Pt species. Niobia content was also found to be an important factor in determining the overall efficiency of the Pt–TiO₂–Nb₂O₅ photocatalyst in the glycerol reforming reaction. The photocatalytic results showed that Pt on TiO₂–Nb₂O₅ enhanced hydrogen production from the aqueous glycerol solution at a 5 wt% initial glycerol concentration. The influence of different operating conditions such as the catalyst dosage and initial glycerol concentration was also evaluated. The results indicated that the best hydrogen and methane production was equal to 6657 μmol/L and 194 μmol/L, respectively after 4 h of UV radiation using Pt/Ti:Nb (1:2) sample and with 3 g/L of catalyst dosage. Moreover, the role of water in photocatalytic hydrogen production was studied through photocatalytic activity tests in the presence of D₂O. The obtained results confirmed the role of water molecules on the photocatalytic production of hydrogen in an aqueous glycerol solution.     

CeO2 modified Fe2O3 for the chemical hydrogen storage and production via cyclic water splitting

The chemical hydrogen storage (hydrogen reduction) and production (water splitting) behaviour of Ce-modified Fe₂O₃ mixed oxides were investigated. Fe_1−xCe_xO_2−δ (x = 0, 0.05, 0.1, 0.2, 0.3, 0.4 and 1) oxides prepared by chemical precipitation were characterized by XRD (X-ray diffraction), H₂-TPR (hydrogen temperature-programmed reduction) and H₂O-TPO (steam temperature-programmed oxidation) tests. XRD results showed that two kinds of Fe–Ce–O solid solutions (Ce-based and Fe-based) coexisted in Fe–Ce mixed oxides. H₂-TPR experiment suggested that Ce addition could reduce hydrogen reduction temperature while H₂O-TPO experiments over reduced oxides showed that Fe–Ce mixed oxides could split water to produce hydrogen at a lower temperature and complete in a shorter time. Both redox reactions (hydrogen reduction and water splitting) were sensitive to the temperature and active at a high temperature. The successive redox cycles were carried out over the Fe_0.7Ce_0.3O_2−δ mixed oxide at 750 °C. It kept a stable production of hydrogen in the successive redox process at the condition of serious agglomeration of the materials. The highest hydrogen storage amount was up to 1.51 wt% for the Fe–Ce sample with a 30% substitution of Ce for Fe.     

NiMo-calcium-doped ceria catalysts for inert-substrate-supported tubular solid oxide fuel cells running on isooctane

A calcium-doped ceria (Ce_1-xCa_xO_2−δ, 0 ≤ x ≤ 0.3) has been applied as a ceramic support in NiMo-based catalysts for an internal reforming tubular solid oxide fuel cell running on isooctane. Introducing calcium into the CeO₂-based ceramic was found to improve conductivity of Ce_1-xCa_xO_2−δ. The Ce_0.9Ca_0.1O_2−δ (x = 0.10) sample exhibited an optimum conductivity of 0.045 S cm⁻¹ at 750 °C. The transport of oxygen ions in Ce_1-xCa_xO_2−δ promoted the catalytic partial oxidation of isooctane in the NiMo–Ce_1-xCa_xO_2−δ catalyst, which increased the fuel conversion as well as H₂ and CO yields. As a result, the NiMo–Ce_0.9Ca_0.1O_2−δ (x = 0.10) catalyst exhibited a high isooctane conversion of 98%, and the H₂ and CO yields achieved 74% and 83%, respectively, for reforming of isooctane and air at the O/C ratio of 1.0 at 750 °C. Furthermore, the NiMo–Ce_0.9Ca_0.1O_2−δ catalyst has been applied as an internal reforming layer for an inert-substrate-supported tubular solid oxide fuel cell running on isooctane/air. Due to its high reforming activity, the single cell presented an initial maximum power density of 355 mW cm⁻² in isooctane/air at 750 °C and displayed stable electrochemical performance during ~30 h operation. These results demonstrated the application feasibility of the NiMo–Ce_0.9Ca_0.1O_2−δ catalyst for direct internal reforming solid oxide fuel cells running on isooctane/air.     

Hydrogen evolution under visible light illumination on the solid solution CdxZn1-xS prepared by ultrasound-assisted route

The complete solid solution Cd_xZn_1-xS (0 ≤ x ≤ 1) prepared by ultrasound-assisted route is used for the H₂ formation upon visible light illumination. The correlation of chemical and physical characterizations permits to assess the feasibility of the system for the photocatalytic hydrogen evolution. The compounds crystallize in a cubic structure (x < 0.5) and convert to hexagonal variety above 0.5 with a crystallite size (8–17 nm). All materials exhibit n-type conduction with an activation energy (0.22–0.05 eV). The optical transitions are directly allowed (3.10–2.30 eV) and appropriately matched to the sun spectrum while the conduction band, deriving from (Zn, Cd) ns orbital (∼-1 V_SCE), is positioned above the H₂O/H₂ potential (∼-0.68 V_SCE), allowing H₂-liberation under visible illumination. The photocatalyst dose, pH and SO₃²⁻ concentration are optimized. Under the favorable conditions, the H₂ liberation rate reaches 12 × 10⁻⁴ mL mg⁻¹ min⁻¹ with a quantum yield η(H₂) of 1.40%.     

Fabrication of hierarchically one-dimensional ZnxCd1-xS/NiTiO3 nanostructures and their enhanced photocatalytic water splitting activity

Hierarchically one-dimensional nanomaterials represent a kind of promising catalyst for photocatalytic of hydrogen generation, where the photoinduced charge carriers can effectively separate and be engaged in the target reaction. Herein, we report the synthesis of hierarchically one-dimensional Zn_xCd_1-xS/NiTiO₃ nanofibers and the investigations of their photocatalytic performance. These well-designed nanofibers demonstrate a typically one-dimensional heterostructure with an excellent continuity, and the element mapping, X-ray diffraction, and X-ray photoelectron spectroscopy collectively confirm the Zn_xCd_1-xS nanoparticles being decorated on the surface of NiTiO₃ nanofibers successfully. The Zn_xCd_1-xS/NiTiO₃ nanofibers exhibit enhanced efficiency in photocatalytic hydrogen production under visible light, compared with the Zn_xCd_1-xS/TiO₂ nanofibers. The electrochemical impedance spectra measurements reveal that Zn_xCd_1-xS/NiTiO₃ nanofibers facilitated the transport and separation of the photoexcited charge carriers. The superior photocatalytic performance is synthetically attributed to the visible-light-responsive NiTiO₃ substrate, pure phase, large region of interface and relatively small grain size.     

MgH2–Nb2O5 investigated by in situ synchrotron X-ray diffraction

In situ real time synchrotron radiation powder X-ray diffraction (SR-PXD) experiments are utilized to study changes in the crystalline compounds under dynamic hydrogenation and dehydrogenation reactions of MgH₂ ball milled with 8 mol% Nb₂O₅. The ball milling conditions were systematically varied to prepare three samples with different reactivity. Up to eight full cycles of hydrogen release and uptake were investigated for each sample, which reveal that Nb₂O₅ reacts with Mg forming a ternary oxide, Mg_xNb_1−xO. The PXD data for the ternary oxide is similar to that observed for the isostructural compounds MgO and NbO although shifted to lower Bragg diffraction angles revealing an expansion of the unit cell. Rietveld refinements suggest that Mg_xNb_1−xO has a limiting composition of x ∼ 0.6 after eight cycles of hydrogen release and uptake. At elevated temperatures Nb(II) is reduced to metallic Nb(0) and extracted from the ternary oxide and forms in a reaction with Mg. This work suggests that a ternary solid solution Mg_xNb_1−xO is the active material responsible for the prolific kinetic properties for the additive Nb₂O₅. Mg_0.6Nb_0.4O has a ∼4.6% larger unit cell volume as compared to the binary oxides, MgO and NbO, which may lead to formation of cracks and hydrogen diffusion pathways in dense magnesium oxide surface layers.     

Fabrication of one-dimensional MnxCd1-xS@D-MoSeyS2-y heterostructure with enhanced visible-light photocatalytic hydrogen evolution

Developing a visible light photocatalysts for hydrogen (H₂) production to replacing fossil fuels is a huge challenge. Herein, one-dimensional Mn_xCd_1-xS@D-MoSe_yS_2-y heterostructure was prepared for improving the hydrogen generation. The molar ratio of Mn to Cd in Mn_xCd_1-xS solid solution was adjusted, which effectively enhances the photocatalytic H₂ evolution efficiency. MoSe_yS_2-y with defects (D-MoSe_yS_2-y) was synthesized by solvothermal method during the photocatalytic process as cocatalyst, which wrapping on the Mn_xCd_1-xS solid solution. Mn_xCd_1-xS@D-MoSe_yS_2-y shows improved photocatalytic H₂ evolution activity, which was endowed by suitable energy band structure, exposure of active sites, high carrier concentration and fast electrons transfer. The highest photocatalytic H₂ evolution rate of sample among prepared Mn_xCd_1-xS@D-MoSe_yS_2-y is 12.46 mmol/g/h, which is equivalent to 37 times that of CdS. This present study offers a insight to the preparation of CdS-based photocatalysts.     

Effect of scandium on the phase composition,microstructure and electrical conductivity of strontium hafnate

Effect of Sc-doping on crystal structure, morphology and conductivity of SrHfO₃ was studied for the first time. SrHf_1-xSc_xO_3-δ (x = 0–0.15) was synthesized by solid state reaction and examined using Rietveld refinement of X-ray diffraction patterns, scanning electron microscopy and four-probe DC technique. It was shown that scandium incorporates into the crystal lattice of SrHfO₃ and SrHf_1-xSc_xO_3-δ crystallizes in the orthorhombic Pbnm space group. Sc-doping enhances the grain growth and sinterability, which results in increased density of ceramics. The conductivity of SrHf_1-xSc_xO_3-δ increases with increasing Sc-content, which is consistent with the common model of oxygen vacancies formation. Increase in conductivity with increasing water vapor partial pressure indicates a significant contribution of protons to charge transport. High ionic conductivity is combined with high ion transference numbers, which makes SrHf_1-xSc_xO_3-δ promising electrolytes for use in electrolysis cells producing clean hydrogen from steam and fuel cells converting chemical energy into electricity.     

A wide visible light active photocatalyst Mg5Ta4O15-xNy for water oxidation and reduction

More than 1.6 eV band gap reductions have been realized on Mg₅Ta₄O₁₅ by nitrogen doping with its pseudobrookite structure maintained. The nitrogen doped Mg₅Ta₄O₁₅, i.e. Mg₅Ta₄O_15-xN_y, shows broad absorption in the visible light region and promising photocatalytic activity for both water reduction and oxidation reactions under visible light illumination (λ ≥ 400 nm). Apparent quantum efficiency as high as ~0.90% has been achieved at 420 ± 20 nm on Mg₅Ta₄O_15-xN_y which is comparable to a number of active metal oxynitrides photocatalysts. Apart from visible light absorption, Nitrogen doping on Mg₅Ta₄O₁₅ is also accompanied by improved surface hydrophilicity and a negative shift of flat band potential. This simple strategy for band gap engineering can be extended to other metal oxides which may open new playgrounds in the design and development of efficient visible light active photocatalysts.     

Visible-light-driven photocatalytic H2 evolution from water splitting with band structure tunable solid solution (AgNbO3)1−x(SrTiO3)x

(AgNbO₃)_1−x(SrTiO₃)_x samples were successfully employed as photocatalysts for photocatalytic hydrogen evolution under visible light. The samples were characterized by a series of techniques, including X-ray diffractometry, scanning electron microscopy, UV–Vis spectrophotometry, and electrochemistry technology. The band gaps of (AgNbO₃)_1−x(SrTiO₃)_x solid solutions can be tuned continuously from 3.21 to 2.65 eV and the flat-band potentials (V_fb) can be shifted positively from −0.79 to −0.31 V vs. SHE when x decreased from 1 to 0. Band positions of (AgNbO₃)_1−x(SrTiO₃)_x samples were further testified by density functional theory, suggesting that the band gap narrowing of the solid solutions derived from the hybridization of (Ti 3d and Nb 4d) and (O 2p and Ag 4d) orbital. The photocatalytic activities of samples for H₂ evolution with Pt cocatalyst were evaluated in aqueous methanol solution under visible light irradiation. The highest photocatalytic activity was obtained at (AgNbO₃)_0.25(SrTiO₃)_0.75. Photocatalytic activity in hydrogen evolution of these solid solutions proved to be closely dependent on band structures.     

Molybdenum doped bilayer photoanode nanotubes for enhanced photoelectrochemical water splitting

Conversion of solar energy into hydrogen energy via photoelectrochemical (PEC) water splitting is one of the most promising approaches for generation of clean and sustainable hydrogen energy in order to address the alarming global energy crisis and environmental problems. To achieve superior PEC performance and solar to hydrogen efficiency (STH), identification, synthesis, and development of efficient photoelectrocatalysts with suitable band gap and optoelectronic properties along with high PEC activity and durability is highly imperative. With the aim of improving the performance of our previously reported bilayer photoanode of WO₃ and Nb and N co-doped SnO₂ nanotubes i.e. WO₃-(Sn_0.95Nb_0.05)O₂:N NTs, herein, we report a simple and efficient strategy of molybdenum (Mo) doping into the WO₃ lattice to tailor the optoelectronic properties such as band gap, charge transfer resistance, and carrier density, etc. The Mo doped bilayer i.e. (W_0.98Mo_0.02)O_3-(Sn_0.95Nb_0.05)O₂:N revealed a higher light absorption ability with reduced band gap (1.88 eV) in comparison to that of the undoped bilayer (1.94 eV). In addition, Mo incorporation offered improvements in charge carrier density, photocurrent density, with reduction in charge transfer resistance, contributing to a STH (～3.12%), an applied bias photon-to-current efficiency (ABPE ～ 8% at 0.4 V), including a carrier density (N_d ～ 7.26 × 10²² cm^?3) superior to that of the undoped bilayer photoanode (STH ～2%, ABPE ～ 5.76%, and N_d ～5.11 × 10²² cm^?3, respectively). The substitution of Mo⁶⁺ for W⁶⁺ in the monoclinic lattice, forming the W–O–Mo bonds altered the band structure, realizing further enchantments in the PEC reaction and charge transfer kinetics. Additionally, doped bilayer photoanode revealed excellent long term PEC stability under illumination, suggesting its robustness for PEC water splitting. The present work herein provides a simple and effective Mo doping approach for generation of high performance photoanodes for PEC water splitting.     

Photoelectrochemical characterisation of indium nitride and tin nitride in aqueous solution

Indium nitride (InN) and tin nitride (SnN_x) films were produced with reactive d.c. magnetron sputtering technique. The thin film semiconductors were optically and photoelectrochemically characterised and the energetic positions of the two semiconductors’ band edges were determined with respect to the normal hydrogen electrode. The sputtered InN thin film showed an indirect bandgap of 1.4 eV and a direct bandgap of 1.8 eV. The optical spectra of SnN_x indicated a bandgap energy of approximately 1.4 eV. All nitride films showed n-type photoresponse in KI (aq) electrolyte at an irradiation intensity of 1000 W/m². The photoelectrochemical characterisation indicated that InN and SnN_x with a bias of about 400 mV or less can be used for photo-oxidation of water.     

Visible light driven photocatalytic hydrogen evolution and photophysical properties of Bi doped NaTaO3

Visible light active Bismuth doped NaTaO₃ powders were synthesized by the conventional solid state route for different Bi concentrations (2.5%, 5.0%, and 7.5% by moles). The optical properties of the doped samples were tuned by changing the molar ratio of Na and Ta in the initial reactants. The doped samples prepared with Na/Ta ratio close to unity (1.01–1.03) resulted in the highest band gap narrowing compared to the other synthesis conditions. It was shown that the photocatalytic hydrogen evolution occurred from these samples under the visible light irradiation (λ > 390 nm) after loading of appropriate amount of platinum co-catalyst. The other synthesis conditions (Na/Ta = 1/1−x; x = 0.025, 0.05, 0.075 and Ta/Na = 1/1−x; x = 0.025, 0.05, 0.075; x is bismuth content) were not useful for the photocatalytic hydrogen evolution. The structural characterization suggested that the samples prepared with Na/Ta ratio close to unity, contain Bi ions located at both Na and Ta sites in the lattice. The Mott–Schottky plots revealed that the flat band potential of the pristine NaTaO₃ is highly negative to the H₂/H₂O reduction potential (−1.19 eV vs. SCE, pH = 7) and for all Bi doped NaTaO₃ samples, the flat band potential was sufficient for the hydrogen generation.     

Photo-catalytic hydrogen production over Fe2O3 based catalysts

The hydrogen photo-evolution was successfully achieved in aqueous (Fe_1−xCr_x)₂O₃ suspensions (0 ≤ x ≤ 1). The solid solution has been prepared by incipient wetness impregnation and characterized by X-ray diffraction, BET, transport properties and photo-electrochemistry. The oxides crystallize in the corundum structure, they exhibit n-type conductivity with activation energy of ∼0.1 eV and the conduction occurs via adiabatic polaron hops. The characterization of the band edges has been studied by the Mott Schottky plots. The onset potential of the photo-current is ∼0.2 V cathodic with respect to the flat band potential, implying a small existence of surface states within the gap region. The absorption of visible light promotes electrons into (Fe_1−xCr_x)₂O₃-CB with a potential (∼−0.5 V_SCE) sufficient to reduce water into hydrogen. As expected, the quantum yield increases with decreasing the electro affinity through the substitution of iron by the more electropositive chromium which increases the band bending at the interface and favours the charge separation. The generated photo-voltage was sufficient to promote simultaneously H₂O reduction and SO₃²⁻ oxidation in the energetically downhill reaction (H₂O + SO₃²⁻ → H₂ + SO₄²⁻, ΔG = −17.68 kJ mol⁻¹). The best activity occurs over Fe_1.2Cr_0.8O₃ in SO₃²⁻ (0.1 M) solution with H₂ liberation rate of 21.7 μmol g⁻¹ min⁻¹ and a quantum yield 0.06% under polychromatic light. Over time, a pronounced deceleration occurs, due to the competitive reduction of the end product S₂O₆²⁻.     

Enhanced photocatalytic hydrogen evolution from reduced graphene oxide-defect rich TiO2-x nanocomposites

Solar-driven photocatalytic hydrogen generation by splitting water molecules requires an efficient visible light active photocatalyst. This work reports an improved hydrogen evolution activity of visible light active TiO_2-x photocatalyst by introducing reduced graphene oxide via an eco-friendly and cost-effective hydrothermal method. This process facilitates graphene oxide reduction and incorporates intrinsic defects in TiO₂ lattice at a one-pot reaction process. The characteristic studies reveal that RGO/TiO_2-x nanocomposites were sufficiently durable and efficient for photocatalytic hydrogen generation under the visible light spectrum. The altered band gap of TiO_2-x rationally promotes the visible light absorption, and the RGO sheets present in the composites suppresses the electron-hole recombination, which accelerates the charge transfer. Hence, the noble metal-free RGO/TiO_2-x photocatalyst exhibited hydrogen production with a rate of 13.6 mmol h^?1g^?1_cat. under solar illumination. The appreciable photocatalytic hydrogen generation activity of 947.2 μmol h^?1g^?1_cat with 117 μAcm^?2 photocurrent density was observed under visible light (>450 nm).