Investigation of Ni2+-doped ceria nanorods as the anode catalysts for reduced-temperature solid oxide fuel cells

Tailoring the surface chemistry of oxides has been widely used to adjust their catalytic behavior in the energy conversion and storage devices. Herein, nanorods of Ni²⁺-doped ceria (Ce_1-xNi_xO_2-δ, x = 0, 0.05, 0.1, 0.15) are synthesized via a modified hydrothermal method, and evaluated as the anode catalysts for reduced-temperature solid oxide fuel cells (SOFCs). X-Ray diffraction patterns of as-synthesized powders in air imply successful incorporation of Ni²⁺ into the fluorite lattice of ceria for x = 0.05 and 0.1, with a secondary phase of NiO observed for x = 0.15. Transmission electron microscopy (TEM) examination confirms a rod-like morphology with a diameter of 10–13 nm and a length of 55–105 nm. Exposure of these powders in H₂ at 600°C results in exsolution of some spherical Ni particles of 11 nm in diameter. Electrochemical measurements on both symmetrical anode fuel cells and functioning cathode-supported fuel cells show an order of the catalytic activity toward hydrogen oxidation - CeO_2-δ < Ce_0·95Ni_0·05O_2-δ < Ce_0·9Ni_0·1O_2-δ. The anode polarization resistances in 97% H₂ – 3% H₂O are 0.24, 0.31 and 0.37 Ω?cm² for Ce_0·9Ni_0·1O_2-δ, Ce_0·95Ni_0·05O_2-δ and CeO_2-δ at 600°C, respectively. Thin (La_0·9Sr_0.1) (Ga_0.8Mg_0.2)O_3-δ-electrolyte fuel cells with nanostructured SmBa_0.5Sr_0·5Co₂O_5+δ cathodes and Ce_0·9Ni_0·1O_2-δ anodes yield the highest power densities among the investigated series of anodes, e.g., 820 mW?cm^?2 in 97% H₂ – 3% H₂O and 598 mW?cm^?2 in 68% CH₃OH - 32% N₂. XPS analyses of reduced nanorods indicate that the highest catalytic activities of Ce_0·9Ni_0·1O_2-δ toward fuel oxidation reactions should be correlated to the presence of highly active Ni nanoparticles and increased surface active oxygen, as confirmed by substantially facilitated extraction of the lattice oxygen on the surface by H₂ in temperature-programmed reduction (TPR) measurements.     

Hydrogen production from oxidative steam reforming of ethanol over rhodium catalysts supported on Ce–La solid solution

The catalytic behaviors of Rh catalysts supported on Ce–La solid solution in H₂ production from the oxidative steam reforming (OSR) of ethanol were studied for the first time. 1%Rh/Ce_0.7La_0.3O_y exhibits 100% ethanol conversion at 573 K with H₂ yield rate 214 μmol g-cat⁻¹ s⁻¹, which is 150 K lower than that required for comparable performance with 1%Rh/CeO₂. La doping also enhanced the stability by accelerating CH₃COCH₃ conversion and gave low CO selectivity due to the high water gas shift activity. X-ray diffraction and Raman spectroscopy characterizations indicate the formation of Ce–La solid solutions and oxygen vacancies. H₂ temperature-programmed reduction and thermo-gravimetric measurement results confirmed that the redox properties of Rh/CeO₂ were greatly enhanced by La doping, which accelerated ethanol conversion, promoted H₂ yield, and maintained good long–term activity for the OSR reaction.     

Hydrogen production from oxidative steam reforming of ethanol over Ir catalysts supported on Ce–La solid solution

The Ce_1?xLa_xO_2?δ solid solution (CL) supported Ir (nIr/CL, n = 2, 5 and 10 wt.%) catalysts are studied for H₂ production from ethanol oxidative steam reforming (OSR). The Ir dispersion, surface area, oxygen vacancy density and carbon deposition resistance of nIr/CL catalysts are greatly enhanced compared with Ir/CeO₂. Among the tested catalysts, 5%Ir/CL shows the best catalytic performance, exhibiting >99.9% ethanol conversion at 400 °C with H₂ yield rate of 323 μmol·g_cata^?1·s^?1 and no obvious carbon deposition after used. The 5%Ir/CL catalyst contains the highest amount of reducible interface Ce⁴⁺, leading to a strong interaction with surface Ir species at the metal-support interface during the OSR reaction. The strong interaction induces Ir to be well dispersed on the CL support, and is associated with more redox-active sites (interface Ce⁴⁺/Ce³⁺), to guarantee high activity.     

Dry reforming over mesoporous nanocrystalline 5% Ni/M-MgAl2O4 (M: CeO2, ZrO2, La2O3) catalysts

In this article mesoporous nanocrystalline 5 wt%M-95 wt%MgAl₂O₄ (M: CeO₂, ZrO₂, La₂O₃) powders were prepared by a novel on-step sol-gel process and employed as a support for the synthesis of 5 wt%Ni catalysts for synthesis gas production via dry reforming. The magnesium aluminate spinel prepared with this sol-gel method possessed a high BET area of 264 m² g⁻¹ with a high pore volume of 0.436 cm³ g⁻¹. The results indicated that the addition of promoters (CeO₂, ZrO₂, La₂O₃) to magnesium aluminate improved the BET area and pore volume and also decreased the crystallite size. Among the prepared powders and catalysts, 5 wt%La₂O₃-95 wt%MgAl₂O₄ and 5 wt%Ni/5 wt%CeO₂-95 wt%MgAl₂O₄ exhibited the highest BET area of 306 m² g⁻¹ and 263 m² g⁻¹, respectively. The catalytic results indicated that the 5 wt%Ni/5 wt%CeO₂-95 wt%MgAl₂O₄ catalyst exhibited the highest activity and the lowest carbon formation among the prepared catalysts with the same content of the promoter. The influence of the CeO₂ content on the textural and catalytic performance was also investigated and the results illustrated that the increment in CeO₂ content improved the methane conversion and reduced the amount of deposited carbon, which could be related to the redox properties of the catalyst support.     

Ba2+/Ti4+- co-doped layered perovskite BаLaInO4: The structure and ionic (O2−, H+) conductivity

The new complex oxides Ba_1·1La_0·9In_0·9Ti_0·1InO₄ and Ba_1·1La_0·9In_0·95Ti_0·05O_3.98 with Ruddlesden-Popper structure were obtained for the first time. Ba²⁺ and Ti⁴⁺- co-doping of BаLaInO₄ both with and without change in the oxygen stoichiometry led to an increase in oxygen-ionic and protonic conductivity. It was proved that both factors (geometric and defect concentration) effect the ionic transport in the block-layered structures. The sample Ba_1·1La_0·9In_0·95Ti_0·05O_3.98 demonstrates the increase in the protonic conductivity by one order of magnitude and it is ~90% proton conductor below 400 °C.     

The optimization of Ni–Al2O3 catalyst with the addition of La2O3 for CO2–CH4 reforming to produce syngas

A series of La₂O₃–NiO–Al₂O₃ catalysts promoted by different loading of lanthanum were prepared via the hydrolysis-deposition method to improve the catalytic performance of nickel-based catalyst for CO₂–CH₄ reforming. The catalysts were characterized by N₂ adsorption - desorption, XRD, H₂-TPR, TG-DTG, TEM, Raman and TPH techniques. Results showed that the precursor of active component was mainly in the form of NiAl₂O₄ spinel, which almost disappeared after reduction process from XRD characterization, suggesting well reduction performance. The catalyst with La loading of 0.95 wt% (La–Ni-1) presented a small average Ni grain size of 7.71 nm and exhibited well catalytic performance at 800 °C, with CH₄ conversion of 94.37%, CO₂ conversion of 97.15%, H₂ selectivity of 75.01% and H₂/CO ratio of 0.92. The Ni grain size of La–Ni-1 increased only 5.84% to 8.16 nm after performance test, which was lower than that of others and indicated a well structure stability. Additionally, the strong carbon diffraction peak over La–Ni-0.5 and La–Ni-2 catalysts suggested the presence of crystalline carbon species accumulated on the catalysts, while there was no carbon peak over La–Ni-1 sample. A 150 h stability test for La–Ni-1 demonstrated that the conversion of CH₄ was around 95%, higher than that of La–Ni-0 (without lanthanum addition) and La–Ni-4 (with La content of 3.82 wt%). The carbon deposition rate of La–Ni-1 was only 1.63 mg/(g_cat·h), lower than that of La–Ni-4 (2.20 mg/(g_cat·h)), showing both high activity and well stability. Therefore, the “confinement effect” of La₂O₃ to Ni crystalline grain would inhibit the sintering of active component, prevent the carbon deposition, and improve the catalytic reforming performance.     

Preparation of Cu0.1-xNixCe0.9O2-y catalyst by ball milling and its CO catalytic oxidation performance

A series of Cu_0.1-xNi_xCe_0.9O_2-y catalysts with different Cu/Ni molar ratios were prepared by the ball milling method. The obtained catalytic materials were characterized by XRD, H₂-TPR, BET, XPS and Ramen and the effects of different Cu/Ni content on the structure, properties and CO catalytic oxidation performance of the catalysts were explored. The results evidenced the formation of Cu–Ni–Ce mixed oxide solid solution in all ternary catalysts. In addition, there is a synergistic interaction between Cu and Ni in ternary catalysts, resulting in more oxygen vacancies and improved reduction performance, and hence demonstrating better CO catalytic oxidation activity in the ternary catalysts than binary ones. Under a GHSV of 60000 mL·g_cat⁻¹·h⁻¹, the required reaction temperature for reaching less than 10 ppm CO is lowed from 160 °C with Cu_0·1Ce_0·9O_2-y to 130 °C with Cu_0·07Ni_0·03Ce_0·9O_2-y.     

Gd,La co-doped CeO2 as an active support for Fe2O3 to enhance hydrogen generation via chemical looping water gas shift

Support materials are indispensable to promote the durability of iron oxides for chemical looping applications. However, the dilution effect of supports on the active phase would lead to decreased bulk oxygen conduction, thus leading to compromised activity. Here, we propose several Gd³⁺, La³⁺ and Nd³⁺ doped CeO₂ as active supports for iron oxides and investigate the support effect to improve hydrogen generation via chemical looping water gas shift. The characterizations show that the dopants improve the oxygen vacancy concentration in the CeO₂ lattice and Fe₂O₃/Ce_0.8Gd_0.1La_0.1O_2-δ exhibits the most oxygen vacancy concentration among all the oxygen carriers. Pulse reactions of oxygen carriers show that an abundance of oxygen vacancy concentration can promote the lattice oxygen transfer in bulk, thus contributing to improved redox reactions. The high oxygen conductivity mitigates the dilution effect on the active phase. Therefore, Fe₂O₃/Ce_0.8Gd_0.1La_0.1O_2-δ shows the highest hydrogen yield (～9.49 mmol^?1.g^?1) and hydrogen generation rate (～0.632 mmol.g^?1.min^?1) with only a slight decrease at 650 °C over 100 cycles. Overall, this work highlights the influence of support properties on the redox reactivity of iron oxides for chemical looping applications.     

Supported mesoporous Cu/CeO2-δ catalyst for CO2 reverse water–gas shift reaction to syngas

The design and development of a high performance hydrogenation catalyst is an important challenge in the utilization of CO₂ as resources. The catalytic performances of the supported catalyst can be effectively improved through the interaction between the active components and the support materials. The obtained results demonstrated that the oxygen vacancies and active Cu⁰ species as active sites can be formed in the Cu/CeO_2-δ catalysts by the H₂ reduction at 400 °C. The synergistic effect of the surface oxygen vacancies and active Cu⁰ species, and Cu⁰–CeO_2-δ interface structure enhanced catalytic activity of the supported xCu/CeO_2-δ catalysts. The electronic effect between Cu and Ce species boosted the adsorption and activation performances of the reactant CO₂ and H₂ molecules on the corresponding Cu/CeO_2-δ catalyst. The Cu/CeO_2-δ catalyst with the Cu loading of 8.0 wt% exhibited the highest CO₂ conversion rate in the RWGS reaction, reaching 1.38 mmol·g_cat⁻¹ min⁻¹ at 400 °C. Its excellent catalytic performance in the RWGS reaction was related to the complete synergistic interaction between the active species via Ce³⁺-□-Cu⁰ (□: oxygen vacancy). The Cu/CeO_2-δ composite material is a superior catalyst for the RWGS reaction because of its high CO₂ conversion and 100% CO selectivity.     

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.     

Sustainable and selective hydrogen production by steam reforming of bio-based ethylene glycol: Design and development of Ni–Cu/mixed metal oxides using M (CeO2, La2O3, ZrO2)–MgO mixed oxides

Hydrogen (H₂) production in a clean and green manner via renewable sources is at present of great interest. Ethylene glycol, a bio-based feedstock, offers a sustainable route for high purity H₂ production. In the current investigation, MgO based mixed metal oxides containing CeO₂, La₂O₃ and ZrO₂ were synthesized and used to support 20 wt% Ni–Cu (1:1). The impacts of altering support characteristics on catalytic behavior have been studied and compared in H₂ synthesis via ethylene glycol steam reforming (SR), employing various characterization techniques such as XRD, SEM, EDX, TEM, H₂-TPR, H₂-TPD, TG-DSC and BET. Further, high resolution XPS studies were performed to explore the valence states and effectiveness of surface engineering of the catalysts. Assessment of the efficacy of catalysts was done via several parameters such as reactant conversion, H₂ concentration and long-term stability. All the synthesized materials produced encouraging results with high H₂ yield and conversion under the said operating conditions [T- 623 to 773 K; GHSV - 3120 to 6240 h^?1; P - 0.1 MPa; S/C - 3 to 7.5 mol/mol]. Amongst the three catalysts, Ni–Cu/La₂O₃–MgO and Ni–Cu/CeO₂–MgO exhibited superior behavior for high H₂ production. Ni–Cu/La₂O₃–MgO was better in comparison to Ni–Cu/CeO₂–MgO in terms of reactant conversion whereas Ni–Cu/CeO₂–MgO showed highest H₂ concentration (98 mol %) and improved stability along with absence of carbon deposition owing to its high mobile oxygen vacancies in its lattice. The highly active cubic CeO₂ species and its long-term durability (up to 8 cycles) owing to its exceptional redox property further justified its efficacy. The optimized process showed that at T = 773 K, GHSV = 3120 h^?1, S/C = 4.5 mol/mol for Ni–Cu/La₂O₃–MgO and Ni–Cu/CeO₂–MgO and at T = 773 K, GHSV = 3120 h^?1, S/C = 6 mol/mol and for Ni–Cu/ZrO₂–MgO, maximum H₂ concentration was obtained. At the end, reaction pathway followed by the catalysts was proposed.     

Production of high-purity H2 through sorption-enhanced water gas shift over a combination of two intermediate-temperature CO2 sorbents

Sorption-enhanced water gas shift (SEWGS) that integrates the WGS reaction and in situ CO₂ removal in one reactor is a promising technology for producing high-purity hydrogen. In this study, a series of Mg–Al hydrotalcite-based CO₂ sorbents were prepared, characterized, and evaluated at low CO₂ pressure (0.01 bar). It shows that the layered double oxide prepared at pH = 10 (abbr. LDO_10) has a higher CO₂ adsorption uptake at 30–400 °C than other LDO_x, owing to its large surface area. After doping with M₂CO₃ (M = Li, Na, K, or Cs), the resulting M-LDO_10 sorbents exhibit different CO₂ uptake, with Li-LDO_10 the lowest and K-LDO_10 the highest. It is considered that the high total basicity contributed to the high CO₂ uptake of K-LDO_10. A single-layered reactor (physically mixed Cu/Ce_0·6Zr_0·4O₂ (catalyst) and K-LDO_10) can realize a stable production of high-purity H₂ in 10 SEWGS cycles, but the duration time is rather short (≤1 min). By combining our previously developed MgO-based sorbent (AMS-Mg₉₅Ca₅) with K-LDO_10 in a four-layered configuration, i.e., three (Cu/Ce_0·6Zr_0·4O₂|AMS-Mg₉₅Ca₅) layers followed by one (Cu/Ce_0·6Zr_0·4O₂ + K-LDO_10) layer, high-purity H₂ (>99.9%) without CO contamination is stably produced with extended duration time (22–31 min) in 10 SEWGS cycles (300 °C, 12 bar, and H₂O/CO molar ratio of 1.5).     

Modified CeO2 as active support for iron oxides to enhance chemical looping hydrogen generation performance

Chemical looping hydrogen generation (CLG) is a promising pathway that can offer both the high purity hydrogen as well as the efficient CO₂ capture capability. However, this process was significantly hindered by the lack of active oxygen carriers at relatively low temperatures. Mixed ionic-electronic (MIEC) supported iron oxides exhibit desirable redox performance for the improved oxygen-ion conductivity. In this work, we prepared several A_xCe_1-xO_2-δ (A = Gd, La; x = 0, 0.1, 0.3) supported Fe₂O₃ for hydrogen production at 750 °C. It was shown that Fe₂O₃/Gd_0.3Ce_0.7O_2-δ shows the highest hydrogen generation performance and stability over 50 redox cycles. The reactivity follows the sequence of: Fe₂O₃/Gd_0.3Ce_0.7O_2-δ > Fe₂O₃/La_0.1Ce_0.9O_2-δ > Fe₂O₃/Gd_0.1Ce_0.9O_2-δ > Fe₂O₃/La_0.3Ce_0.7O_2-δ. The fundamental investigation shows that the doping of rare earth (Gd, La) into CeO₂ contributes to the formation of oxygen vacancies, thus improving the lattice oxygen diffusion. The enhanced hydrogen generation performance attributes to the high lattice oxygen diffusion to improve the reactivity and inhibiting outward diffusion of Fe. The roughly linear relation between the oxygen vacancy concentration and chemical looping performance can be extended to predict the performance of oxygen carriers for other chemical looping applications, methane reforming, combustion, and ethane dehydrogenation, etc.     

Facile fabrication of mesoporous In2O3/LaNaTaO3 nanocomposites for photocatalytic H2 evolution

The incorporation of In₂O₃ nanoparticles on mesoporous La_0.02Na_0.98TaO₃ photocatalysts is very interesting for promoting the H₂ production under UV illumination in the presence of [10%] glycerol as a hole scavenger. It is demonstrated that an outstanding mesoporous In₂O₃/La_0.02Na_0.98TaO₃ photocatalyst can be constructed by incorporating In₂O₃ nanoparticles (0-2 wt%) and mesoporous La_0.02Na_0.98TaO₃ nanocomposites for highly promoting photocatalytic H₂ evolution. The maximum yield of H₂ ~ 2350 μmol g⁻¹ was obtained over mesoporous 1%In₂O₃/La_0.02Na_0.98TaO₃ nanocomposite. The mesoporous 1%In₂O₃/La_0.02Na_0.98TaO₃ nanocomposite exhibited further enhancement H₂ production, in which the rate of H₂ evolution can be as high as 235 μmol g⁻¹ h⁻¹, 435 times higher than those of mesoporous La_0.02Na_0.98TaO₃. The results showed that the 1%In₂O₃/La_0.02Na_0.98TaO₃ photocatalyst possesses high stability and durability for H₂ evolution by implying almost no photoactivity reduce after five cycles for 45 h continuous illumination. The measurement of photoluminescence spectroscopy, transient photocurrent spectra and UV- diffuse reflectance spectra for all synthesized samples exhibited that the promoted H₂ production is mainly explained by its effective electron-hole separation and broaden photoresponse region due to its compositions and structures of the obtained heterostructures.     

Effect of ZrO2 on the performance of Co–CeO2 catalysts for hydrogen production from waste-derived synthesis gas using high-temperature water gas shift reaction

In this study, highly active and stable CeO₂, ZrO₂, and Zr_(1-x)Ce_(x)O₂-supported Co catalysts were prepared using the co-precipitation method for the high-temperature water gas shift reaction to produce hydrogen from waste-derived synthesis gas. The physicochemical properties of the catalysts were investigated by carrying out Brunauer-Emmet-Teller, X-ray diffraction, CO-chemisorption, Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and H₂-temperature-programmed reduction measurements. With an increase in the ZrO₂ content, the surface area and reducibility of the catalysts increased, while the interaction between Co and the support and the dispersion of Co deteriorated. The Co–Zr_0.4Ce_0·6O₂ and Co–Zr_0.6Ce_0·4O₂ catalysts showed higher oxygen storage capacity than that of the others because of the distortion of the CeO₂ structure due to the substitution of Ce⁴⁺ by Zr⁴⁺. The Co–Zr_0.6Ce_0·4O₂ catalyst with high reducibility and oxygen storage capacity exhibited the best catalytic performance and stability among all the catalysts investigated in this study.     

Powder and structured Pt/Ce0.75Zr0.25O2-based catalysts: Water gas shift performance and quasi in situ XPS studies

The data on the performance in water gas shift reaction of a powder 5 wt% Pt/Ce_0.75Zr_0.25O₂ and a structured 0.33 wt% Pt/Ce_0.75Zr_0.25O₂/θ-Al₂O₃/FeCrAl catalysts are reported in this work. For the powder one the lowest outlet CO concentrations were shown to be 0.5, 0.9 and 1.5 vol% corresponding to the initial ones of 5, 10 and 15 vol%, respectively; the temperature required to reach these values did not exceed 310 °C. The quasi in situ XPS data have shown that doping CeO₂ with Zr enhances the reducibility of the oxide allowing Ce³⁺ formation without any treatment. Additionally, it was found that there are 20–30% of nonmetallic Pt atoms on the surface even after a treatment in CO at 300 °C. For the structured catalyst the downward temperature gradient along the monolith was observed with a dispersion of 50–60 °C. The lowest CO concentrations were observed at the temperatures at the catalyst's back point of 280 °C–3.9 and 4.3 vol% CO in the dry gas for 15,700 and 31,400 cm³·g_cat⁻¹·h⁻¹, respectively, for 10 vol% CO in the feed gas.     

Ruthenium substituted pyrochlore metal oxide catalysts Y2Ce2-xRuxO7-δ (x = 0–0.4) for oxidative steam reforming of ethanol

Metal oxides Y₂Ce_2-xRu_xO_7-δ (x = 0–0.4) with partial substitution of Ruⁿ⁺ cations in the host structure were synthesized to study their catalytic activity on oxidative steam reforming of ethanol (OSRE). The samples were characterized using X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) and temperature-programmed reduction (TPR). The performances investigated by varied temperatures, Ru ion content, carbon-to-oxygen ratios and long-term stability. The lowest activation temperature on OSRE is 300 °C, which is significantly lower than that of La₂Ce_2-xRu_xO_7-δ (400 °C). The cell dimension of Y₂Ce_2-xRu_xO_7-δ was reduced compare to La₂Ce_2-xRu_xO_7-δ for the replacement of the Y³⁺ ion with La³⁺ ion. The reduced unit cell in the host structure not only increase the surface composition of the Ce⁴⁺ ions, but also induce the synergetic effect of Ruⁿ⁺/Ru⁴⁺ (n > 4) and Ce⁴⁺/Ce³⁺, which lead to the enhanced OSRE activity. The optimized catalyst Y₂Ce_1.6Ru_0.4O_7-δ showed selectivity of hydrogen S_H2 = 84(4)% (Y_H2 = 2.5(1) mol/mol EtOH) and carbon monoxide S_CO = 48(1)% for long-term stability test at T = 300 °C, C/O = 0.5, and O₂/C₂H₅OH = 1.5.     

Hydrogen production via chemical looping steam reforming of ethanol by Ni-based oxygen carriers supported on CeO2 and La2O3 promoted Al2O3

This work studies the effects of Ce⁴⁺ and/or La³⁺ on NiO/Al₂O₃ oxygen carrier (OC) on chemical looping steam reforming of ethanol for hydrogen production - alternating between fuel feed step (FFS) and air feed step (AFS). Suitable amount of Ce- and La-doping increases OC carbon tolerance. The solubility limit is found at 50 mol% La in solid solution. At higher La-doping, La₂O₃ disperses on the surface and adsorbs CO₂ forming La₂O₂CO₃ during FFS. From the 1st cycle, 12.5 wt%Ni/7 wt%La₂O₃-3wt%CeO₂–Al₂O₃ (N/7LCA) displays the highest averaged H₂ yield (3.2 mol/mol ethanol) with 87% ethanol conversion. However, after the 5th cycle, 12.5 wt%Ni/3 wt%La₂O₃-7wt%CeO₂–Al₂O₃ (N/3LCA) exhibits more stability and presents the highest ethanol conversion (88%) and H₂ yield (2.7 mol/mol ethanol). Amorphous coke on the OCs decreases with increasing La³⁺ content and can be removed at 500 °C during AFS; nevertheless, fibrous coke and La₂O₂CO₃ cannot be eliminated. Therefore, after multiple redox cycles, highly La-doped OCs exhibits rather low stability.     

Boosting hydrogen evolution under simulated sunlight via constructing close electron transfer interface between 1D CdxZn1-xS nanorod and 2D MoS2@MoOy nanosheet

Designing an efficient non-noble metal photocatalyst, which utilizes solar energy, has great potential to produce clean energy hydrogen. The microstructural refinement of 1D Cd_0.2Zn_0.8S nanorod was induced by doping with 2D MoS₂@MoO_y layer during microwave hydrothermal treatment. The maximum H₂ production rate of the composite prepared at optimum conditions was 186 mmol g⁻¹ h⁻¹, which increased by 34.8% compared with that of Cd_0.2Zn_0.8S (138 mmol g⁻¹ h⁻¹). The apparent quantum yields of the optimized composite were 10.3% and 15.6% at 365 and 420 nm, respectively. The tight S-scheme heterojunction contributed to the separation of photogenerated electron-hole pairs effectively, as confirmed by the characterization analysis of ·OH and ·O⁻₂ radicals, surface potential under illumination and darkness and in situ XPS spectra. Moreover, the active species of sulfur coordinated-Mo⁵⁺ as low-coordinate center promoted the dissociation of water and decreased the over potential of H₂ production. Furthermore, the optimal composite showed excellent stable catalytic activity for hydrogen evolution, and the H₂ production rate was 176.7 mmol g⁻¹ h⁻¹ after five cycles (95% of the first cycle). Overall, this work provides a promising strategy for improving the effectiveness of H₂ production by preparing non-noble metal composite photocatalysts.     

A high-performance cobalt-free Ruddlesden-Popper phase cathode La1·2Sr0·8Ni0·6Fe0·4O4+δ for low temperature proton-conducting solid oxide fuel cells

Ruddlesden-Popper typological (R-P type) layered material La₂NiO₄ is known for the excellent ionic conductivity and fast oxygen kinetics, but limited by its electronic conductivity as a single-phase cathode for low-temperature proton-conducting solid oxide fuel cells (LT H-SOFC). Cobalt-doping can improve the electro-catalytic capability, accompanied with an increased thermal expansion coefficient (TEC), which would lead to the delamination at the cathode/electrolyte interface. In this assignment, strontium and iron co-doped R-P phase cathode La_1·2Sr_0·8Ni_0·6Fe_0·4O_4+δ (LSNF), exhibiting fine oxygen conduction, sufficient electronic conductivity and compatible TEC with the electrolyte, is investigated thoroughly. The single cell with LSNF cathode based on BaZr_0·1Ce_0·7Y_0·2O_3-δ (BZCY) electrolyte achieves a maximum power density (MPD) of 781 mW cm⁻² with the low interfacial polarization resistance (R_p) of 0.078 Ω cm² at 700 °C. Interestingly, the single cell can also possess an eximious power output of 138.5 mW cm⁻² at relatively low temperature of 500 °C. Moreover, the excellent long-term stability with no observable performance degradation for almost 100 h at 600 °C could also indicate that the single-phase R-P layered material LSNF is a preeminent cathode candidate for LT H-SOFC.