Iron precipitated onto ceria-zirconia nanoparticle mixtures for the production of hydrogen via two-step thermochemical water splitting

Several novel materials were synthesized by precipitating iron oxide (using the previously optimized 10% Fe loading by weight) onto mixtures of nanoparticle zirconia and ceria to investigate the effects of adding CeO₂ to FeO_x/ZrO₂ materials in the thermochemical water splitting reaction. At water splitting temperatures of 1000 °C (after thermal reduction at 1450 °C), the stability of the CeO₂-containing materials was lower than for the FeO_x/ZrO₂ material, and there was no advantage to adding CeO₂ to the FeO_x/ZrO₂ material. However, when operating at a water splitting (WS) temperature of 1200 °C, the stability increased and the hydrogen production was significantly higher over most materials compared with a water splitting temperature of 1000 °C. At a WS temperature of 1200 °C the FeO_x/Zr₇₅Ce₂₅O₂ (75% Zr₇₅O₂ and 25% CeO₂ by weight) and FeO_x/Zr₅₀Ce₅₀O₂ materials performed slightly better than the FeO_x/ZrO₂ material, and X-ray photoelectron spectroscopy data revealed that the surface concertation of iron is less important compared with water splitting at 1000 °C. The temperature programmed reduction data indicated that the FeO_x-CeO₂ interactions were weaker compared with FeO_x-ZrO₂ interactions, since the FeO_x reduction occurred at lower temperatures for the CeO₂-containing materials. The weaker interactions can explain why the stability was lower for the materials containing CeO₂ (sintering of FeO_x was likely more pronounced) The X-ray diffraction data revealed that ZrO₂-CeO₂ solid solutions formed after activation at 1450 °C and lattice volume calculations indicated that iron did incorporate into the ZrO₂-CeO₂ matrices. More incorporation was observed after water-splitting at 1200 °C compared with a lower temperature (1000 °C), and likely explains why the materials were more stable during water-splitting at 1200 °C.     

Effects of substrate temperatures on the thermal stability of AlxOy/Pt/AlxOy multilayered selective solar absorber coatings

We report the effects of substrate temperatures on the thermal stability of Al_xO_y/Pt/Al_xO_y multilayered selective solar absorber coating (MSSAC). The samples were deposited at different substrate temperatures (from room temperature up to 250 °C), and then annealed at various temperatures (300–600 °C) in air for 2 h. Characterizations are made via X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), Atomic Force Microscopy (AFM), Raman Spectroscopy, UV–Vis and emissometeric measurements. These coatings were found to be thermally stable up to 500 °C with good spectral selectivity of 0.930/0.11. Furthermore, the observed decrease in the spectral selectivity 0.883/0.13 at 600 °C is attributed to the diffusion of Cu and the formation of CuO phase. Such phase formation was confirmed using XRD and Raman spectral analysis. The insensitiveness of the thermal stability of such coatings on the substrate temperature is demonstrated.     

Enhanced low temperature catalytic activity of Ni/Al–Ce0.8Zr0.2O2 for hydrogen production from ammonia decomposition

Ammonia decomposition is an effective way for high purity hydrogen production, yet the increase of catalytic activity at low temperatures remains a big challenge for this process. In this paper, a CeO₂–ZrO₂ composite with Al as the secondary dopant was synthesized by the co-precipitation method, which was used as the carrier of nickel metal for ammonia decomposition. The experimental results showed that an obvious increase in catalytic activity of the ammonia decomposition at the relatively low temperature range of 450–550 °C was achieved over the nickel catalyst with CeO₂–ZrO₂ composite as the metal carrier. Specifically, the complete decomposition of ammonia was achieved at 580 °C for Ni/Al–Ce_0.8Zr_0.2O₂ catalyst, while only 92% of ammonia was decomposed at 600 °C over the reference Ni/Al₂O₃ catalyst. The characterization results indicated that the introduction of Al as the secondary dopant of ceria not only increases the specific surface area and oxygen defects on the surface, but also enhances the nickel metal dispersion and metal-support interaction, thus enhances the catalytic performance of Ni/Al–Ce_0.8Zr_0.2O₂ catalyst in the ammonia decomposition.     

Enhanced low-temperature activity for CO2 methanation over Ru doped the Ni/CexZr(1−x)O2 catalysts prepared by one-pot hydrolysis method

A series of 30 wt%Ni/Ce_xZr_1?xO₂ catalysts doped with Ru ranging from 0 to 5 wt% were prepared by one-pot hydrolysis of metal nitrates with ammonium carbonate for carbon dioxide methanation at low temperature range of 150–310 °C. The influences of Ce/Zr molar ratios and Ru contents on the physicochemical properties and catalytic activities of prepared catalysts were systematically investigated. The addition Ru can improve the Ni dispersion and the basicity of the yRu-30Ni/Ce_0.9Zr_0.1O₂ catalysts surface. As a result, their low-temperature catalytic activity had been enhanced over these doped Ru promoted catalysts. The optimal catalyst was 3Ru-30Ni/Ce_0.9Zr_0.1O₂ on which the CO₂ conversion reached theoretical equilibrium value as high as 98.2% with the methane selectivity of 100% at a reaction temperature as low as 230 °C. Moreover, there was almost no deactivation for the 3Ru-30Ni/Ce_0.9Zr_0.1O₂ catalyst during 300 h at 230 °C indicating excellent catalytic stability and coke resistence ability. It was also found that the low-temperature activity of 3Ru-30Ni/Ce_0.9Z_r0.1O₂ catalyst prepared by one-pot hydrolysis method was much higher than the one prepared by impregnation method.     

Impact of substrate material and annealing conditions on the microstructure and chemistry of yttria-stabilized-zirconia thin films

Si-diffusion from Si-based substrates into yttria-stabilized-zirconia (YSZ) thin films and its impact on their microstructure and chemistry is investigated. YSZ thin films used in electrochemical applications based on micro-electrochemical systems (MEMS) are deposited via spray pyrolysis onto silicon-based and silicon-free substrates, i.e. Si_xN_y-coated Si wafer, SiO₂ single crystals and Al₂O₃, sapphire. The samples are annealed at 600 °C and 1000 °C for 20 h in air. Transmission electron microscopy (TEM) showed that the Si_xN_y-coated Si wafer is oxidized to SiO_z at the interface to the YSZ thin film at temperatures as low as 600 °C. On all YSZ thin films, silica is detected by X-ray photoelectron spectroscopy (XPS). A particular large Si concentration of up to 11 at% is detected at the surface of the YSZ thin films when deposited on silicon-based substrates after annealing at 1000 °C. Their grain boundary mobility is reduced 2.5 times due to the incorporation of SiO₂. YSZ films on Si-based substrates annealed at 600 °C show a grain size gradient from the interface to the surface of 3 nm to 10 nm. For these films, the silicon content is about 1.5 at% at the thin film's surface.     

Plasma sprayed coatings for low-temperature SOFC and high temperature effects on Lix(Ni,Co)yO2 catalyst layers

In this paper, a new plasma spray technology working in low pressure condition has been successfully applied to deposit Li_x(Ni,Co)_yO₂ catalyst/electrode layers for low-temperature solid oxide fuel cells (LT-SOFCs). The low pressure induced distinctive phenomena were illustrated for presenting the characteristics and advances of such coating technique. Micro-nano crystalline microstructure was generated on the plasma sprayed coatings simultaneously with phase transformation taking place. To study the effect of high temperature on such catalyst material, sintering experiments were carried out at 600–1000 °C. The results show that the ratio of x/y decreased when increasing temperature and sintering time because of the degradation of Li from Li_x(Ni,Co)_yO₂ phase. The catalytic property and stability of the Li_x(Ni,Co)_yO₂ at various temperatures were also discussed.     

Biohydrogen synthesis from catalytic steam gasification of furniture waste using nickel catalysts supported on modified CeO2

Present study evaluated the catalytic steam gasification of furniture waste to enhance the biohydrogen production. To do this, 10 wt% nickel loaded catalysts on the variety of supports (Al₂O₃, CeO₂, CeO₂-La₂O₃, and CeO₂–ZrO₂) were prepared by the novel solvent deficient method. The hydrogen selectivity (vol%) order of the catalysts was achieved as Ni/CeO₂–ZrO₂>Ni/CeO₂>Ni/Al₂O₃?Ni/CeO₂-La₂O₃. The best catalytic activity of Ni/CeO₂–ZrO₂ catalyst (~82 vol % H₂ at 800 °C) was ascribed to the smaller size of nickel crystals, finely dispersed Ni on the catalyst surface, and Ce_1-xZr_xO_2-δ solid solution. The role of Ce_1-xZr_xO_2-δ solid solution in Ni/CeO₂–ZrO₂ catalyst was observed as bi-functional; acceleration of water-gas-shift and oxidation of carbon reaction. The high resistance of Ni/CeO₂–ZrO₂ towards the coke formation showed its potential to establish a cost-effective commercial-scale biomass steam gasification process. This study is expected to provide a promising solution for the disposal of furniture wastes for production of clean energy (biohydrogen).     

Deoxygenation of oleic acid over Ce(1–x)Zr(x)O2 catalysts in hydrogen environment

Ce_(1–x)Zr_(x)O₂ catalysts were prepared by co-precipitation method for deoxygenation (DO) of oleic acid. The CeO₂/ZrO₂ ratio was systematically varied to optimize Ce_(1–x)Zr_(x)O₂ catalysts. Ce_0.6Zr_0.4O₂ exhibited the highest oleic acid conversion as well as high selectivity to C₉ ∼ C₁₇ compounds (diesel fuel range) at the reaction temperature of 300 °C. The high activity/selectivity of Ce_0.6Zr_0.4O₂ catalyst was correlated to its reducibility, oxygen storage capacity and crystallite size.     

Optical properties and thermal stability of pulsed-sputter-deposited AlxOy/Al/AlxOy multilayer absorber coatings

Spectrally selective Al_xO_y/Al/Al_xO_y multilayer absorber coatings were deposited on copper (Cu) and molybdenum (Mo) substrates using a pulsed sputtering system. The Al targets were sputtered using asymmetric bipolar-pulsed DC generators in Ar+O₂ and Ar plasmas to deposit an Al_xO_y/Al/Al_xO_y coating. The compositions and thicknesses of the individual component layers were optimized to achieve high solar absorptance (α=0.950-0.970) and low thermal emittance (ε=0.05-0.08). The X-ray diffraction data in thin film mode showed an amorphous structure of the Al_xO_y/Al/Al_xO_y coating. The X-ray photoelectron spectroscopy data of the Al_xO_y/Al/Al_xO_y multilayer absorber indicated that the Al_xO_y layers present in the coating were non-stoichiometric. The optical constants (n and k) of the multilayer absorber were determined from the spectroscopic ellipsometric data. Drude's free-electron model was used for generating the theoretical dispersion of optical constants for Al films, while the Tauc-Lorentz model was used for modeling optical properties of the dielectric Al_xO_y layers. In order to study the thermal stability of the Al_xO_y/Al/Al_xO_y coatings, they were subjected to heat treatment (in air and vacuum) at different temperatures and durations. The multilayer absorber deposited on Cu substrates exhibited high solar selectivity (α/ε) of 0.901/0.06 even after heat-treatment in air up to 400 °C for 2 h. At 450 °C, the solar selectivity decreased significantly on Cu substrates (e.g., α/ε=0.790/0.07). The coatings deposited on Mo substrates were thermally stable up to 800 °C in vacuum with a solar selectivity of 0.934/0.05. The structural stability of the absorber coatings heat treated in air (up to 400 °C) and vacuum (up to 800 °C) was confirmed by micro-Raman spectroscopy measurements. Studies on the accelerated aging tests suggested that the absorber coatings on Cu were stable in air up to 75 h at 300 °C and the service lifetime of the multilayer absorber was predicted to be more than 25 years. Further, the activation energy for the degradation of the multilayer absorber heat treated for longer durations in air is of the order of 64 kJ/mol.     

Hydrogen production by steam reforming of liquefied natural gas (LNG) over Ni/Al2O3–ZrO2 xerogel catalysts: Effect of calcination temperature of Al2O3–ZrO2 xerogel supports

Al₂O₃–ZrO₂ (AZ) xerogel supports prepared by a sol-gel method were calcined at various temperatures. Ni/Al₂O₃–ZrO₂ (Ni/AZ) catalysts were then prepared by an impregnation method for use in hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of calcination temperature of AZ supports on the catalytic performance of Ni/AZ catalysts in the steam reforming of LNG was investigated. Crystalline phase of AZ supports was transformed in the sequence of amorphous γ-Al₂O₃ and amorphous ZrO₂ → θ-Al₂O₃ and tetragonal ZrO₂ → (θ + α)-Al₂O₃ and (tetragonal + monoclinic) ZrO₂ → α-Al₂O₃ and (tetragonal + monoclinic) ZrO₂ with increasing calcination temperature from 700 to 1300 °C. Nickel oxide species were strongly bound to γ-Al₂O₃ and θ-Al₂O₃ in the Ni/AZ catalysts through the formation of solid solution. In the steam reforming of LNG, both LNG conversion and hydrogen composition in dry gas showed volcano-shaped curves with respect to calcination temperature of AZ supports. Nickel surface area of Ni/AZ catalysts was well correlated with catalytic performance of the catalysts. Among the catalysts tested, Ni/AZ1000 (nickel catalyst supported on AZ support that had been calcined at 1000 °C) with the highest nickel surface area showed the best catalytic performance. Well-developed and pure tetragonal phase of ZrO₂ in the AZ1000 support played an important role in the adsorption of steam and the subsequent spillover of steam from the support to the active nickel.     

Methanol steam reforming for hydrogen production over ternary composite ZnyCe1Zr9Ox catalysts

Developing the catalysts for methanol steam reforming (MSR) via interfacial construction still remains many challenges. In this study, the effects of ZnO content on the performance of Zn_yCe₁Zr₉O_x were studied for MSR. The best-performing Zn₁Ce₁Zr₉O_x catalyst exhibited full methanol conversion and higher H₂ production rate of 0.31 mol·h⁻¹·g_cat⁻¹ at 400 °C. Characterization results revealed the synergistic effect among ZnO, CeO₂ and ZrO₂ after forming a solid solution and the incorporation of Zn²⁺ into Ce₁Zr₉O_x matrix not only modulate the ratio of surface O_Latt/O_Ads, but also generate new Zn–O–Zr interfacial structure corresponding to the lattice/bridge oxygen to increase the selectivity of CO₂. The excess oxygen vacancies on the samples surface favor the decomposition of methanol to generate the undesired CO. This study proposes a new design strategy for developing highly efficient composite MSR catalysts by control of the lattice/bridge oxygen and surface oxygen vacancy.     

Thermodynamic and experimental study on the reduction and carbonization of TiO2 through gas‐solid reaction

Titanium oxycarbide (TiC_xO_y) has attracted much attention recently as a soluble anode used in the USTB (University of Science and Technology Beijing) or MER (Materials and Electrochemical Research) molten‐salt electrolysis process to produce sponge titanium. The present study aimed to investigate the production of titanium oxycarbide from TiO₂ by using CH₄–H₂ gas mixture, and both thermodynamic and experimental studies were carried out. First, thermodynamic analysis in the TiO₂–CH₄–H₂ system was performed by the method of equilibrium calculation. The analysis indicated that TiO₂ could be ultimately reduced and carbonized to TiC_xO_y by CH₄ and H₂ gas at temperature above 1200°C, and the increase of temperature was theoretically favorable to the final carbonization extent of TiC_xO_y. The experimental process involved the reduction of both pure TiO₂ powder and TiO₂ with additives using methane–hydrogen gas mixture in the temperature range from 1200°C to 1450°C. Experimental results showed that pure TiO₂ could be reduced completely to TiC_xO_y at 1350°C and above after 8‐hour reduction. It was also found that the reduction extent of TiO₂ increased with increasing time and temperature when at a low temperature range; however, a much higher temperature (above 1350°C) would hinder further carbonization for the production of deposited carbon. Addition of iron oxides to TiO₂ powders strongly facilitated the reduction reaction, even prompting the reaction of TiO₂ to TiC_xO_y completely at only 1200°C after 8‐hour reduction. The gas‐solid reaction provided a simple and quick way to produce titanium oxycarbide.     

Ethanol dry reforming over Ni supported on modified ceria-zirconia catalysts– the effect of Ti and Nb dopants

In this work complex metal-oxide catalysts with the general formula 5 wt% Ni/Ce_0·75Zr_0.25-x(Nb,Ti)_xO_2-δ were synthesized by the solvothermal method using supercritical alcohols followed by nickel deposition. The catalysts were characterized and studied in ethanol dry reforming reaction (EDR) in the temperature range 600–750 °C. XRD and TEM showed that the synthesis method provides incorporation of doping cations into the ceria-zirconia fluorite structure, leading to mixed oxides formation. The effect of doping cations on structural and surface properties of 5 wt% Ni/Ce_0·75Zr_0.25-x(Nb,Ti)_xO_2-δ and activity in the EDR reaction was investigated. Oxygen deficiency δ increases with the introduction of titanium and niobium cations, which contributes to the bifunctional reforming mechanism implementation with rapid oxidation of coke precursors and activation of СО₂ at surface oxygen vacancies. TPO-O₂ analysis after reaction showed no carbon formation above 700 °C, and a few carbon deposits (not exceeding 4%) even after significant catalyst deactivation at 600 °C.     

Deposition of ZrO2 film by liquid phase deposition

In this study, undoped ZrO₂ thin films were deposited on single-crystal silicon substrates using liquid phase deposition. The undoped films were formed by hydrolysis of zirconium sulfate (Zr(SO₄)₂·4H₂O) in the presence of H₂O. A continuous oxide film was obtained by controlling adequate (NH₄)₂S₂O₈ concentration. The deposited films were characterized by SEM, FT-IR, XRD and DTA. Typically, the films showed excellent adhesion to the substrate with uniform particle diameter about 150 nm. The thicknesses of ZrO₂ film were about 200 nm after 10 h deposition at 30 °C. These films shows single tetragonal phase after heat treated at 600 °C. High annealing temperature (e.g. 750 °C) may result in the phase transformation of (t)-ZrO₂ into (m)-ZrO₂.     

Crystal structure and functional properties of Nd1.6Ca0.4Ni1-yCuyO4+δ as prospective cathode materials for intermediate temperature solid oxide fuel cells

Complex oxides Nd_1.6Ca_0.4Ni_1-yCu_yO_4+δ (y = 0.0–0.4) have been prepared by a pyrolysis of glycerol-nitrate compositions. According to the X-ray diffraction analysis, the materials are single-phase up to y = 0.3 and crystallize in an orthorhombic structure (Bmab) at room temperature. High-temperature studies assert that they all undergo a phase transition from orthorhombic to tetragonal (I4/mmm) structure in a range of 300–400 °C. With Cu doping, the over-stoichiometric oxygen content δ decreases from 0.07 (y = 0.0) down to 0.00 (y = 0.3). The studies on the compact samples reveal the maximum value of total conductivity (165 S cm^?1 at 420 °C) and the minimum value of the linear coefficient of thermal expansion (11.9·10^?6 K^?1 in a range of 400–1000 °C in air) at y = 0.2. Chemical compatibility of the Nd_1.6Cа_0.4Ni_1-yCu_yO_4+δ (y = 0.0, 0.2) oxides with oxygen- and proton conducting electrolytes (Ce_0.9Gd_0.1O_1.95, Ce_0.8Sm_0.2O_1.9 and BaCe_0.5Zr_0.3Y_0.1Yb_0.1O_3-δ) up to a temperature of 1100 °C is demonstrated.     

Optical properties of sol–gel deposited Al2O3 films

Highly transparent, uniform and corrosion resistant Al₂O₃ films were prepared on stainless-steel and quartz substrates by the sol–gel process from stable coating solutions using aluminum-sec-butoxide, Al(OBu^s)₃ as precursor, acetylacetone, AcAcH as chelating agent and nitric acid, HNO₃, as catalyzer. Films up to 1000 nm thick were prepared by multiple spin coating deposition, and were characterized by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), optical spectroscopy and micro Vickers hardness test. XRD of the film heat treated at 400°C showed that they had an amorphous structure. XPS confirmed that they were stoichiometric Al₂O₃. The refractive index (n) and extinction coefficient (k) were found to be n=1.56±0.01 and k=0.003±0.0002 at 600 nm, respectively. The surface microhardness and corrosion resistance investigations showed that Al₂O₃ films improved the surface properties of stainless-steel substrates.     

Optical properties of electrochromic all-solid-state devices

We have investigated the optical properties of an all-thin-film electrochromic device, with a thin film of ZrO₂ acting as an ion conductor. The device also employed electrochromic layers of amorphous or crystalline WO₃ and NiV_xO_yH_z. Transmission (T) and reflection (R) spectra were recorded in the wavelength range 300–2500 nm at different intercalation levels, both for single films and complete devices. The results show that T decreases significantly upon intercalation in the WO₃ thin films as well as in the devices. The reflectance only shows minor changes.     

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.     

Preparation,characterization of ZrOxNy/C and its application in PEMFC as an electrocatalyst for oxygen reduction

In this paper, a noble-metal-free electrocatalyst based on carbon-supported zirconium oxynitride (ZrO_xN_y/C) was prepared by ammonolysis of carbon-supported zirconia (ZrO₂/C) at 950 °C and investigated as cathode electrocatalyst towards oxygen reduction reaction (ORR) in PEMFCs. The electrocatalyst was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. The catalytic activity of the catalyst towards ORR was investigated by using the rotating disk electrode (RDE) technique in an O₂-saturated 0.5 M H₂SO₄ solution. The ZrO_xN_y/C electrocatalyst presented attractive catalytic activity for ORR. The onset potential of ZrO_xN_y/C electrocatalyst for oxygen reduction was 0.7 V versus RHE and the four-electron pathway for the ORR was achieved on the surface of ZrO_xN_y/C electrocatalyst. The ZrO_xN_y/C electrocatalyst showed a comparatively good cell performance to ORR in PEMFCs, especially when operated at a comparatively high temperature.     

Synthesis of BaCe0.9-xZrxY0.1O3-δ nanopowders and the study of proton conductors fabricated on their basis by low-temperature spark plasma sintering

Using a citrate-nitrate process, BaCe_0.9-xZr_xY_0.1O_3-δ (x = 0, 0.5, 0.6, 0.7 and 0.8) nanopowders were synthesized, on the basis of which proton-conducting solid electrolytes (average size of coherent scattering region (CSR) - 15–53 nm) were obtained by spark plasma sintering (SPS) at a low temperature (900°С). The dependence of phase composition, microstructure and electrophysical properties of the obtained samples on ZrO₂ content and consolidation conditions was established. It was found that the BaCe_0.4Zr_0,5Y_0.1O_3-δ solid solution had the highest electrical conductivity among zirconium-containing ceramic materials in the studied concentration range. It was shown that SPS is a promising method for obtaining solid electrolytes for proton-conducting solid oxide fuel cells (PCFC) at lower temperatures (by 400–500°С), compared to traditionally-used temperature conditions (1400–1800 °C).