Enhanced hydrogen production with photo‐induced phase transformation and cocatalyst loading

In this study, reduced graphene oxide (RGO)‐Cd_{(1 ? x)}Zn_xS nanocomposites have been synthesized with the solvothermal method in one pot. Moreover Pt, Ru, and Rh nanoparticles have been loaded on the RGO‐Cd_{(1 ? x)}Zn_xS nanocomposites as cocatalysts with the aim of increasing the photocatalytic (PC) performance for hydrogen evolution reaction. The structure of Cd_{(1 ? x)}Zn_xS blend transforms from cubic to hexagonal structure during the PC hydrogen evolution reaction (PCHER) at the room temperature. This photo‐induced phase transformation (PIPT) enhances not only the hydrogen evolution rate, but also the stability of the photocatalysts. Interestingly, RGO triggers the PIPT process only during the PCHER under solar light illumination. On the other hand, the loading of Pt, Ru, and Rh cocatalysts do not affect the PIPT process. However, they enhance the PC and photoelectrochemical (PEC) hydrogen production activity of RGO‐Cd_{(1 ? x)}Zn_xS photocatalyst. PEC performance increases about 5.5 times when Pt (5%) and RGO are added to the Cd_0.60Zn_0.40S catalyst. RGO‐Cd_0.60Zn_0.40S including 1.5% Rh photocatalyst reaches a remarkable PC hydrogen production rate of 135 μmolh^?1 with QE of 23.3% at 460 nm. Therefore, Rh cocatalyst appears as a good alternative to Pt.     

Scope of doped mesoporous (<10 nm) surfactant‐modified alumina templated carbons for hydrogen storage applications

Metal (Ni/Pd) and nitrogen codoped mesoporous templated carbons were synthesized using low‐cost surfactant‐modified mesoporous alumina as a hard template via chemical vapor deposition for hydrogen storage application. Initially, high surface area (1508 m²/g) nitrogen‐doped templated carbon was successfully prepared. Pore volume was also significant (1.64 cm³/g). The codoping with metals (Ni or Pd) reduced both the area and pore volume. All the codoped carbons were mesoporous (2‐8 nm). Aggregated morphology was observed for nitrogen‐doped carbon; tubular or noodle shape appeared on codoping with metals. The dispersion of Pd metal within the carbon framework was highest. The 2 wt% Pd codoped carbon showed the highest hydrogen uptake of 5 wt% (?196°C; 25 bar). This may be attributed to its most number of active sites corresponding to the highest metal dispersion and amount of nitrogen present. The cyclic stability of the samples was also good with only 3% to 5% loss in storage capacity up to 10 cycles.     

Thermodynamic analysis of two‐step solar water splitting with mixed iron oxides

A two‐step thermochemical cycle for solar production of hydrogen from water has been developed and investigated. It is based on metal oxide redox pair systems, which can split water molecules by abstracting oxygen atoms and reversibly incorporating them into their lattice. After successful experimental demonstration of several cycles of alternating hydrogen and oxygen production, the present work describes a thermodynamic study aiming at the improvement of process conditions and at the evaluation of the theoretical potential of the process. In order to evaluate the maximum hydrogen production potential of a coating material, theoretical considerations based on thermodynamic laws and properties are useful and faster than actual tests. Through thermodynamic calculations it is possible to predict the theoretical maximum output of H₂ from a specific redox‐material under certain conditions. Calculations were focussed on the two mixed iron oxides nickel–iron‐oxide and zinc–iron‐oxide. In the simulation the amount of oxygen in the redox‐material is calculated before and after the water‐splitting step on the basis of laws of thermodynamics and available material properties for the chosen mixed iron oxides. For the simulation the commercial Software FactSage and available databases for the required material properties were used. The analysis showed that a maximum hydrogen yield is achieved if the reduction temperature is raised to the limits of the operation range, if the temperature for the water splitting is lowered below 800°C and if the partial pressure of oxygen during reduction is decreased to the lower limits of the operational range. The predicted effects of reduction temperature and partial pressure of oxygen could be confirmed in experimental studies. The increased hydrogen yield at lower splitting temperatures of about 800°C could not be confirmed in experimental results, where a higher splitting temperature led to a higher hydrogen yield. As a consequence it can be stated that kinetics must play an important role especially in the splitting step. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermo-catalytic conversion of greenhouse gases (CO2 and CH4) to CO-rich hydrogen by CeO2 modified calcium iron oxide supported nickel catalyst

In this study, the thermo-catalytic conversion of two principal greenhouse gases (methane and carbon dioxide) to carbon monoxide (CO)-rich hydrogen (H₂) is investigated over cerium oxide (CeO₂) promoted calcium ferrite supported nickel (Ni/CaFe₂O₄) catalyst. The CeO₂ promoted Ni/CaFe₂O₄ catalyst was prepared using wet-impregnation technique. To ascertain the physicochemical properties, the as-prepared catalyst was characterized using various instrument techniques. The characterization of the catalysts reveals that CeO₂-Ni/CaFe₂O₄ possesses suitable physicochemical properties for the conversion of methane (CH₄) and carbon dioxide (CO₂) to CO-rich H₂. The thermo-catalytic reaction revealed that the CeO₂ promoted Ni/CaFe₂O₄ catalyst displayed a higher CH₄ and CO₂ conversions of 90.04% and 91.2%, respectively, at a temperature of 1073 K compared to the unpromoted catalyst. The highest H₂ and CO yields of 78% and 76%, respectively, were obtained over the CeO₂-Ni/CaFe₂O₄ at 1073 K and CH₄/CO₂ ratio of 1. The CeO₂ promoted Ni/CaFe₂O₄ catalyst remained stable throughout the 30 hours time on stream (TOS) while that of the unpromoted Ni/CaFe₂O₄ catalyst sharply decreased after 22 hours TOS. The characterization of the used catalysts confirms the evidence of carbon depositions on the unpromoted Ni/CaFe₂O₄ which is solely responsible for its deactivation. Whereas, there was a slightly gasifiable carbon deposited on the CeO₂ promoted Ni/CaFe₂O₄ catalyst which could be ascribed to the interaction effect of the CeO₂ promoter on the Ni/CaFe₂O₄ catalyst.     

PdCu bimetallic nanoparticles decorated on ordered mesoporous silica (SBA-15) /MWCNTs as superior electrocatalyst for hydrogen evolution reaction

In the present study, a novel electrocatalyst with excellent catalytic performance based on PdCu bimetallic nanoparticles (NPs) supported on ordered mesoporous silica and multi-walled carbon nanotubes (PdCu NPs/SBA-15-MWCNT) was prepared for electrochemical hydrogen evolution reaction (HER). For this purpose, low-cost mesoporous SBA-15 was synthesized using silica extracted from Stem Sweep Ash (SSA) as an economically attractive silica source. Mesoporous SBA-15 with unparalleled porous structure is a stable support for PdCu bimetallic NPs which prevents the accumulation of PdCu bimetallic NPs and improves its efficiency in the catalytic process. The main advantage of this strategy is low loading of bimetallic catalyst with high catalytic activity. The presence of both mesoporous SBA-15 and MWCNTs materials in PdCu/SBA15-MWCNTs/carbon paste electrode (CPE) increases the metallic active sites and the electrical conductivity of electrode which provides great performance for HER. PdCu/SBA15-MWCNTs-CPE provided small Tafel slope (45 mV dec^?1), low onset potential (~-150 mV), high current density (?165.24 mA cm^?2at -360 mV) and exchange current density (2.51 mA cm^?2) with great durability for HER in H₂SO₄ solution. Analysis of kinetic data suggests that the electrocatalyst controls HER by the Volmer-Heyrovsky mechanism. In addition, studies showed that the presence of sodium dodecyl sulfate (SDS) in electrolyte can decrease the potential of HER and increase the current density.     

Kinetic investigations of the hydrogen production step of a thermochemical cycle using mixed iron oxides coated on ceramic substrates

A two‐step thermochemical cycle for solar hydrogen production using mixed iron oxides as the metal oxide redox system has been investigated. The ferrite is coated on a honeycomb structure, which serves as the absorber for solar irradiation and provides the surface for the chemical reaction. Coated honeycomb structures have already been tested in a solar receiver reactor in the solar furnace of DLR in Cologne with respect to their water splitting capability and their long‐term stability. The concept of this new reactor design has proven feasible and constant hydrogen production during repeated cycles has been shown. For a further optimization of the process and in order to gain reliable performance predictions more information about the process especially concerning the kinetics of the oxidation and the reduction step are essential. To examine the hydrogen production during the water splitting step a test rig has been built up on a laboratory scale. In this test rig small coated honeycombs are heated by an electric furnace. The honeycomb is placed inside a tube reactor and can be flushed with water vapour or with an inert gas. A homogeneous temperature within the sample is reached and testing conditions are reproducible. Through analysis of the product gas the hydrogen production is monitored and a reaction rate describing the hydrogen production rate per gram ferrite can be formulated. Using this test set‐up, SiC honeycombs coated with zinc ferrite have been tested. The influences of the temperature and the water concentration on the hydrogen production during the water splitting step have been investigated. An analysis of the ferrite conversion was performed using the Shrinking Core Model. A mathematical approach for the peak reaction rate at the beginning of the water splitting step was formulated and the activation energy was calculated from the experimental data. An activation energy of 110 kJ mol⁻¹ was found. Copyright © 2009 John Wiley & Sons, Ltd.     

Visible‐light response photocatalytic water splitting over CdS/TiO2 and CdS–TiO2/metalosilicate composites

In this work, we have synthesized two different phases of CdS nanoparticles, CdS/TiO₂ composites and their supported form on ZSM‐5 type metalosilicates (ferrisilicate and aluminosilicate) as CdS–TiO₂/metalosilicate composites. The photocatalytic performance of these samples was evaluated by monitoring the amount of hydrogen evolved from water under visible‐light irradiation. The supported composites of TiO₂–CdS/metalosilicate exhibited a higher photocatalytic activity in the photocatalytic water splitting than that of CdS/TiO₂ composites under visible‐light irradiation, suggesting an important role of support. Metalosilicate as a support, which can offer a very high surface area, provides effective and homogenous dispersion of the CdS/TiO₂ composite on the external surface or within the pores of metalosilicate and inhibits agglomeration of the formed composite. We observed that using the solvothermal method for the synthesis of CdS and the hydrothermal method for the synthesis of CdS/TiO₂ or CdS–TiO₂/metalosilicate results in the enhancement of the photocatalytic activity of these composite compared with other procedures, which has been reported previously. We have realized that the support of the CdS/TiO₂ composite on ferrisilicate enhances the photocatalytic activity; however, using aluminosilicate as a support results in the abatement of the photocatalytic activity in comparison with the unsupported composite. This can be attributed to the presence of partially occupied ‘d’ orbitals in the electronic configuration of Fe³⁺ in the structure of ferrisilicate which can interact with TiO₂ molecular orbitals. This interaction leads to the effective distribution of the composite on the support and the decreasing crystallite size of the composite and then enhancement of the photocatalytic activity. Copyright © 2014 John Wiley & Sons, Ltd.     

Enhancement effect of zero-valent iron nanoparticle and iron oxide nanoparticles on dark fermentative hydrogen production from molasses-based distillery wastewater

This study investigates the effect of two different iron compounds (zero-valent iron nanoparticle: nZVI and iron oxide nanoparticles: nIO) and pH on fermentative biohydrogen production from molasses-based distillery wastewater. The nZVI and nIO of optimum particle sizes of 50 nm and 55 nm respectively were synthesized and applied for fermentative hydrogen (H₂) production. The addition of nIO & nZVI at (0.7 g/L, pH: 6) resulted in the highest H₂ yield, H₂ production rate, H₂ content and COD reduction. Moreover, the kinetic parameters of H₂ production potential (P) and H₂ production rate (R_m) increased to 387 mL, and 22.2 mL/h, respectively for nZVI, these values were 363 mL and 21.8 mL/h for nIO. The results obtained indicated the positive effect of nZVI and nIO addition on enhanced fermentative H₂ production. The addition of nZVI & nIO resulted in 71% and 69.4% enhancement in biohydrogen production respectively.     

New low cost mesoporous silica (MSN) as a promising support of Ni-catalysts for high-hydrogen generation via dry reforming of methane (DRM)

In this study, a new nano-sized mesoporous silica (MSN) as support for Ni-based catalysts was produced from natural resources and tested in the dry reforming of methane between 823 and 1023 K. The fresh and spent catalysts Ni-x/MSN (x = 5, 10 and 20 wt.%) were characterized by various techniques. All catalysts are selective for hydrogen production and exhibited long-term stability with low coke formation predominantly as carbon nanotubes, for Ni loadings less than 10% at 973 K. The catalytic results were correlated with the in situ generation of Ni nanoparticles which are highly dispersed on the MSN surface due to strong metal-support interactions thus preventing the sintering process. No significant deactivation was recorded along 25 h on stream meaning that the textural properties of the catalysts have not been altered by the coke deposition or reaction temperature. The prepared MSN is a potential support to be utilized for hydrogen generation.     

Stack performance of phosphotungstic acid functionalized mesoporous silica (HPW-meso-silica) nanocomposite high temperature proton exchange membrane fuel cells

In this paper, a series of short stacks with 2-cell, 6-cell and 10-cell employing phosphotungstic acid functionalized mesoporous silica (HPW-meso-silica) nanocomposite proton exchange membranes (PEMs) have been successfully fabricated, assembled and tested from room temperature to 200 °C. The effective surface area of the membrane was 20 cm² and fabricated by a modified hot-pressing method. With the 2-cell stack, the open circuit voltage was 1.94 V and it was 5.01 V for the 6-cell stack, indicating a low gas permeability of the HPW-meso-silica membranes. With the 10-cell stack, a maximum power density of 74.4 W (equivalent to 372.1 mW cm⁻²) occurs at 150 °C in H₂/O₂, and the stack produces a near-constant power output of 31.6 W in H₂/air at 150 °C without external humidification for 50 h. The short stack also displays good performance and stability during startup and shutdown cycling testing for 8 days at 150 °C in H₂/air. Although the stack test period may be too short to extract definitive conclusions, the results are very promising, demonstrating the feasibility of the new inorganic HPW-meso-silica nanocomposites as PEMs for fuel cell stacks operating at elevated temperatures in the absence of external humidification.     

CNT/g‐C3N4 photocatalysts with enhanced hydrogen evolution ability for water splitting based on a noncovalent interaction

Graphite carbon nitride (g‐C₃N₄) as a novel photocatalyst has attracted growing attention, but its photocatalytic efficiency should be further improved. Based on the large work function and fast electron conductivity of carbon nanotubes (CNTs), here CNT/g‐C₃N₄ photocatalysts with improved H₂ evolution ability and stable water splitting ability were synthesized. The improvement was attributed to the synergistic effect between CNTs and g‐C₃N₄. As for the mechanisms, CNTs strongly attracted photoelectrons and, because of excellent conductibility, rapidly transferred photoelectrons from the catalyst interface. Thereby, the photoelectron migration rate and the photogenerated charge separation and the use efficiency of photoelectrons in g‐C₃N₄ were improved, which largely enhanced the hydrogen production ability. Moreover, the addition of CNTs improved the service life and stability of g‐C₃N₄‐based photocatalytic H₂ production. After 10 hours of visible light irradiation, the maximum H₂ yield from the 12‐mg/L CNT/g‐C₃N₄ (CG12) was 138.7 times larger than that of g‐C₃N₄ (6548.4 vs 47.2 μmol/g), and the H₂ evolution rate was 138.7 times that of g‐C₃N₄ (654.8 vs 4.72 μmol/g/h). After 50 hours, the apparent quantum efficiency of CG12 was up to 37.9%, indicating that the addition of CNTs improved the photocatalytic splitting and stability of g‐C₃N₄. The mechanism of photocatalytic hydrogen production and the roles of CNTs in improving water splitting were discussed through characterization and activity experiments. It was found that the addition of CNTs accelerated the migration, separation, and utilization of photoelectrons and thereby significantly enhanced the photocatalytic performance.     

Techno economic feasibility study on hydrogen production using concentrating solar thermal technology in India

The techno-economic analysis of hydrogen (H₂) production using concentrating solar thermal (CST) technologies is performed in this study. Two distinct hydrogen production methods, namely: a) thermochemical water splitting [model 1] and b) solid oxide electrolysers [model 2], are modeled by considering the total heat requirement and supplied from a central tower system located in Jaisalmer, India. The hourly simulated thermal energy obtained from the 10 MW_th central tower system is fed as an input to both these hydrogen production systems for estimating the hourly hydrogen production rate. The results revealed that these models yield hydrogen at a rate of 31.46 kg/h and 25.2 kg/h respectively for model 1 and model 2. Further, the Levelized cost of hydrogen (LCoH) for model 1 and model 2 is estimated as ranging from $ 8.23 and $ 14.25/kg of H₂ and $ 9.04 and $ 19.24/kg, respectively, for different scenarios. Overall, the present work displays a different outlook on real-time hydrogen production possibilities and necessary inclusions to be followed for future hydrogen plants in India. The details of the improvisation and possibilities to improve the LCoH are also discussed in this study.     

Multilayered large‐area WO3 films on sheet and mesh‐type stainless steel substrates for photoelectrochemical hydrogen generation

The objective of this study is to demonstrate the significant improvement in the photoelectrochemical (PEC) hydrogen generation by a photoanode owing to the increased surface area of the substrate. In this work, multilayered tungsten oxide (WO₃) films have been successfully synthesized onto the large‐area sheet (9 × 9cm²) and mesh (1 × 20cm²) ‐type stainless steel (SS) substrates using screen printing and brush painting methods, respectively. All the WO₃ films are porous and nanocrystalline (30–80 nm) in nature with a monoclinic crystal structure as revealed from X‐ray diffraction and scanning electron microscopy studies. The PEC water splitting study is performed under simulated 1 SUN illumination (AM1.5 G) in a typical two‐electrode cell configuration with WO₃ photoanode and Pt wire immersed in 0.5 M H₂SO₄ electrolyte. The photocurrent as well as hydrogen generation rate for WO₃ photoanodes coated on the plane SS sheet substrate is relatively low and showed minimal change with increasing film thickness. On the other hand, the photocurrent as well as the hydrogen generation is enhanced by a 3–4 fold degree for the WO₃ photoanodes coated on SS mesh. We attribute such efficient water splitting to the increment in the filling factor of the WO₃ material due to the large effective surface area of the SS mesh as compared to the SS sheet substrate. Copyright © 2011 John Wiley & Sons, Ltd.     

Fabrication of zinc‐loaded hollow glass microspheres (HGMs) for hydrogen storage

The greatest challenge for a feasible hydrogen economy lies on the production of pure hydrogen and the materials for its storage with controlled release at ambient conditions. Hydrogen with its great abundance, high energy density and clean exhaust is a promising candidate to meet the current global challenges of fossil fuel depletion and green house gases emissions. Extensive research on hollow glass microspheres (HGMs) for hydrogen storage is being carried out world‐wide, but the right material for hydrogen storage is yet underway. But many other characteristics, such as the poor thermal conductivity etc. of the HGMs, restrict the hydrogen storage capacity. In this work, we have attempted to increase the thermal conductivity of HGMs by ZnO doping. The HGMs with Zn weight percentage from 0 to 10 were prepared by flame spheroidization of amber‐colored glass powder impregnated with the required amount of zinc acetate. The prepared HGMs samples were characterized using field emission‐scanning electron microscope (FE‐SEM), environmental SEM (ESEM), high‐resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy and X‐ray diffraction (XRD) techniques. The deposition of ZnO on the microsphere walls was observed using FE‐SEM, ESEM and HRTEM which was further confirmed using the XRD and ultraviolet–visible absorption data. The hydrogen storage studies done on these samples at 200 °C and 10‐bar pressure for 5 h showed that the hydrogen storage increased when the Zn percentage in the sample increased from 0 to 2%. The percentage of zinc beyond 2, in the microspheres, showed a decline in the hydrogen storage capacity. The closure of the nanopores due to the ZnO nanocrystal deposition on the microsphere surface reduced the hydrogen storage capacity. The hydrogen storage capacity of HAZn2 was found 3.26 wt% for 10‐bar pressure at 200 °C. Copyright © 2015 John Wiley & Sons, Ltd.     

The role of Al2O3, MgO and CeO2 addition on steam iron process stability to produce pure and renewable hydrogen

Steam iron process represents a technology for H₂ production based on iron redox cycles. Fe_xO_y are reduced by syngas/carbon to iron, which is subsequently oxidized by steam to produce pure H₂. However, the system shows low stability.In this work, the effect of promoters (Al₂O₃, MgO and CeO₂) on Fe_xO_y stability is investigated (10 consecutive redox cycles). Bioethanol is used as a reducing agent. The particles are synthesized by coprecipitation method, analysed by BET, XRD, SEM and tested in a fixed bed reactor (675 °C, 1 bar). Pure H₂ is obtained controlling the Fe_xO_y reduction degree feeding different amounts of ethanol (4.56–1.14 mmol) until no CO is detected in oxidation. The results show that the promoters not only improve the thermal stability of Fe_xO_y but also affect its redox activity and react with iron forming spinel structures. MgO led to the highest activity and cyclability (H₂ = 0.15 NL; E = 35%).     

Highly-stable,bifunctional, binder-free & stand-alone photoelectrode (FexNi1-xO@a-CC) for natural waters splitting into hydrogen

Photoelectrochemical (PEC) water splitting is a promising approach to boost green hydrogen production. Herein, we prepared novel binder-free photoelectrode by direct growth of iron doped nickel oxide catalyst over activated carbon cloth (Fe_xNi_1-xO@a-CC) having band gap energy of 2.2 eV for overall water splitting. Fe_xNi_1-xO@a-CC photoelectrode had shown remarkable lower potential of only 1.36 V for oxygen evolution reaction (OER) to reach 10 mA cm^?2 current density using very low photonic intensity of 8.36 × 10^?4 E/L.s. For the first time, we also reported electrical efficiency required for PEC water splitting for 1 m³ of water that is equal to 0.09 kWh/m³. Fe_xNi_1-xO@a-CC photoelectrode also exhibits low potentials of 1.44 V (OER) and ?0.210 V (HER) at 10 mA cm^?2 to split sea water. Our results confirmed that designing Fe_xNi_1-xO@a-CC photoelectrode would be an innovative step to widen green energy conversion applications using natural waters (both sea and fresh water).     

Design for a BlackLight Power multi‐cell thermally coupled reactor based on hydrogen catalyst systems

The design and cost estimates compared with other systems of an energy‐producing reactor system are presented. Heat from hydrino reactions within individual cells provides both the reactor power and the heat for regeneration of the reactants. These processes occur continuously over a plurality of cells in different phases of the processes. The hydrino reactions are maintained and regenerated in a batch mode using thermally coupled multi‐cells arranged in bundles wherein cells in the power‐production phase of the cycle heat cells in the regeneration phase. In this intermittent cell power design, the thermal power is statistically constant as the cell number becomes large, or the cell cycle is controlled to achieve steady power. The conversion of thermal power to electrical power requires the use of a heat engine exploiting a cycle such as a Rankine, Brayton, Stirling, or steam‐engine cycle (Int. J. Energy Res. 1997; 21 :113–127; Int. J. Energy Res. 1998; 22 :237–248; Int. J. Energy Res. 1998; 22 :991–1000; Int. J. Energy Res. 2010; 34 :1071–1087; Int. J. Energy Res. 2009; 33 :1203–1232). Owing to the temperatures, economy goal, and efficiency, the Rankine cycle is the most practical and can produce electricity from a steam source at 30–40% efficiency with a component capital cost of about $300 per kW electric. Conservatively, assuming a conversion efficiency of 25%, the total cost with the addition of the boiler and chemical components is estimated at $1380 per kW electric. The system applications for distributed power (1–10 MW electric) and central generation retrofit and green‐field projects are projected to be very competitive relative to existing power sources and systems. Copyright © 2011 John Wiley & Sons, Ltd.     

Thermochemical hydrogen production by a redox system of ZrO2-supported Co(II)-ferrite

The thermochemical two-step water splitting was examined on ZrO₂-supported Co(II)-ferrites below 1400 °C, for purpose of converting solar high-temperature heat to clean hydrogen energy as storage and transport of solar energy. The ferrite on the ZrO₂-support was thermally decomposed to the reduced phase of wustite at 1400 °C under an inert atmosphere. The reduced phase was reoxidized with steam on the ZrO₂-support to generate hydrogen below 1000 °C in a separate step. The ZrO₂-supporting alleviated the high-temperature sintering of iron oxide. As the results, the ZrO₂-supported ferrite realized a greater reactivity and a better repeatability of the cyclic water splitting than the conventional unsupported ferrites. The Co_xFe_3−xO₄/ZrO₂ with the x value of around 0.4–0.7 was found to be the promising working material for the two-step water splitting when thermally reduced at 1400 °C under an inert atmosphere.     

Pt‐Rh/TiO2/activated carbon as highly active and stable HI decomposition catalyst for hydrogen production in sulfur‐iodine (SI) process

Pt‐TiO₂ loaded on activated carbon was studied as an active and stable catalyst to HI decomposition for H₂ formation in the sulfur‐iodine process. Although the activity of TiO₂‐loaded catalyst was slightly lower HI conversion than that of CeO₂ loaded one, the higher stability against HI decomposition reaction was achieved and almost equilibrium conversion was sustained over ~65 h examined. Moreover, effects of Rh or Ir addition on HI conversion were studied and it was found that Pt‐Rh bimetallic system was highly active and stable to HI decomposition. Scanning transmission electron micrograph observation suggested that the increased HI decomposition activity was assigned to the increased dispersion of Pt particles. High dispersion state of Pt was sustained after HI decomposition at 773 K by addition of Rh. Since the formation of PtI₄ was suggested by X‐ray photoelectron spectroscopy measurement during HI decomposition, increased stability by addition of Rh seems to be assigned to the high chemical stability of Rh against iodine. Almost the equilibrium HI conversion on Pt‐Rh‐TiO₂/M563 was sustained over 300 hours at 673 K.     

Enhanced photocatalytic hydrogen production under visible light over a material based on magnesium ferrite derived from layered double hydroxides (LDHs)

The magnesium ferrite derived from layered double hydroxides (molar ratio Mg/Fe = 2), synthesized by coprecipitation method is found to be an active photocatalyst for hydrogen production from water under visible light. The structural, morphological, and optical properties of the material are characterized by powder X‐ray diffraction, scanning electron microscopy, and Fourier transform infrared and UV‐Vis diffuse reflectance spectroscopy. The results indicated that the material has small particles with a diameter of ~1.8 nm and a specific surface area above 60 m² g^?1. The optical properties revealed semiconducting properties with band gap energy of 1.74 eV, showing an efficient visible light absorption. The cyclic voltammetry indicated that the photoelectrochemical response of the material is characterized by type p conductivity. Furthermore, the solid exhibited a high photoactivity toward the reduction of water, which is attributed to the efficient separation and transportation of the photogenerated charge carriers. Under visible light, the best performance is achieved at pH 10 with a hydrogen liberation amount and quantum efficiency of 223 mol and 0.5%, respectively, after 1 h of irradiation. Copyright © 2014 John Wiley & Sons, Ltd.