Calcination In Air Research Articles

Facile immobilization of polyoxometalates for low-cost molybdenum/tungsten phosphide nanoparticles on carbon black for efficient electrocatalytic hydrogen evolution

Cheap and stable earth-abundant electrocatalysts for hydrogen evolution reaction (HER) is an urgent need to realize industrial production of hydrogen. Herein, we present a “1-methylimidazole-immobilization” method to fix molybdenum and tungsten precursors simultaneously on carbon black for preparation of hybrid molybdenum/tungsten phosphide (Mo-W-P) HER catalysts. The synthesis of Mo-W-P nanoparticles on carbon black was designed as two steps: immobilization and phosphorization. The Mo/W precursors, phosphotungstic acid (H3PW12O40) and phosphomolybdic acid (H3PMo12O40) were first fixed on carbon black by 1-methylimidazole, followed by subsequent calcination in air to form the Mo-W-O precursors, which were further phosphatized with red phosphorus at 850 °C in argon atmosphere to form the Mo-W-P nanoparticles. The HER performance can be effectively tuned by changing the atomic ratio of Mo/W, where the introduction of suitable amount of W into MoP results in dramatic decrease of the overpotential. The optimized sample with Mo/W ratio of 1.8:1 showed excellent electrocatalytic performance for HER with a low onset overpotential of 92 mV, along with a low Tafel slope of 62 mV dec−1 in 0.5 M H2SO4. More importantly, at higher current density of 50 mA cm−2, the optimized Mo-W-P/CB sample showed superior overpotential (231 mV) to that of MoP/CB (287 mV) and WP/CB (333 mV). Meanwhile, the Mo-W-P/CB hybrid nanoparticles also showed good stability and durability in strong acid electrolyte. Our work provides a route for construction of efficient hybrid electrocatalysts by immobilization of inorganic complexes.

Performance controlled via surface oxygen-vacancy in Ti-based oxide catalyst during methyl oleate epoxidation

The catalytic performance with high conversion and high selectivity of Ti-based oxide catalysts have been widely investigated. Besides, stability, which is an essential parameter in the industrial process, lacked fundamental understanding. In this work, we combined computational and experimental techniques to provide insight into the deactivation of P25 and TS-1 Ti-based oxide catalysts during the methyl oleate (MO) epoxidation. The considered deactivation mechanisms are fouling and surface oxygen vacancy (OV). The fouling causes temporary catalyst deactivation through active site blockage but can be removed via calcination in air at high temperature. However, in this work, the OV formation plays an important role in the overall performance of the spent catalyst as the deactivated catalyst after regeneration, cannot be restored to the initial activity. Also, the effects of OV in spent catalysts caused (i) the formation of more Ti3+ species on the surface as evident by XPS and Bader charge analysis, (ii) the activity modification of the active region on the catalyst surface as the reduction in energy gap (Eg) occurred from the formation of the interstates observed in the density of states profiles of spent catalyst modeled by the O-vacant P25 and TS-1 models. This reduction in Eg affects directly the strength of Ti–OOH active site and MO bonding, in which high binding energy contributes to a low conversion because the MO needed an O atom from Ti–OOH site to form the methyl-9,10-epoxy stearate. Hence, the deactivation of the Ti-based oxide catalysts is caused not only by the insoluble by-products blocking the active region but also mainly from the OV. Note that the design of reactive and stable Ti-based oxide catalysts for MO epoxidation needed strategies to prevent OV formation that permanently deactivated the active region. Thus, the interrelation and magnitude between fouling and OV formation on catalyst deactivation will be investigated in future works.

Calcination Effects of Fe Modified MoS2-Carbon Composites for the Improved Degradation Performances of Rhodamine B

The pure MoS2-carbon composites (MoS2-C) and Fe modified MoS2-carbon composites (Fe/MoS2-C) were successfully synthesized through a facile two-step hydrothermal method by adding soft template of CTAB and applied as piezocatalysts to degrade Rhodamine B. The as-obtained catalysts were characterized by the X-ray diffraction (XRD) and scanning electron microscope (SEM). The results indicated the hybrids have large surface area, mesoporous structure, more edges and unsaturated S atoms. By comparing the muffle furnace samples (open air calcination) with the tube furnace one (closed Ar calcination), Fe/MoS2-C catalysts with tube furnace show the higher degradation activities (12.8% versus 5.8%). The possible degradation mechanisms are also discussed.

Production of jet fuel intermediates from biomass platform compounds via aldol condensation reaction over iron-modified MCM-41 lewis acid zeolite

Liquid fuel intermediates could be produced via aldol condensation reaction between furfural or 5-hydroxymethylfurfural (HMF) and acetone. It was found that iron-modified MCM-41 zeolite can be an effective Lewis acid catalyst for C—C bond formation via aldol condensation of furfural or HMF with acetone. The 4-(2-furyl)-3-buten-2-one and 1, 5-di-2-furanyl-1, 4-pentadien-3-one (FAc and F2Ac), or 1, 5-di-2-furanyl-1, 4-pentadien-3-one and 1, 5-bis[(5- hydroxlmethyl)-2-furanyl]-1, 4-pentadien-3-one (HAc and H2Ac), as two main condensation products of furfural with acetone or HMF with acetone, were observed. After 24 h at 160 °C, 86.9% conversion of furfural with 60.0% yield of the FAc as well as 7.5% yield of the F2Ac and 88.9% conversion of the HMF with 41.1% yield of the HAc as well as 3.5% yield of the H2Ac were achieved. Although furfural or HMF conversion was almost same after 24 h at 160 °C, iron-modified MCM-41 zeolite catalyst displayed an enhanced selectivity to condensation products of furfural with acetone. In addition, catalysts showed an improved selectivity to the F2Ac and H2Ac at higher reaction temperature. The reusability and regeneration studies showed that iron-modified MCM-41 zeolite catalyst could not be reused directly, but could be regenerated by calcination in air, and the catalytic performance of regenerated catalyst was acceptable.

Nanosize CaCu3Ti4O12 Green Synthesis and Characterization of a Precursor Oxalate Obtained from Averrhoa carambola Fruit Juice and Its Thermal Decomposition to the Perovskite

Improving on the very high temperatures used in solid-state synthesis routes to prepare CCTO ignited the idea of using oxalate routes which make use of organic solvents in the synthesis of CCTOX as oxalate intermediates to the decomposition product, CCTO. The use of commercial oxalic acids and oxalate has not only recorded a solubility problem which reflects on the size, shape, homogeneity, and morphology of the final product but also has an environmental impact originating from the solvents used. Both the composition and morphology of these inhomogeneities play a role in the behaviour of the final product, pointing out the need to assess the dependence of size, shape, homogeneity, and morphology and the material performance on the sample synthesis history. In this study, nanosized particles of calcium copper titanium oxide, CaCu3Ti4O12 (CCTO), were successfully synthesized by pyrolysis of the corresponding heterometal oxalate precursors obtained via coprecipitation using the edible carambola fruit juice as a precipitating agent and investigated in detail. The precursors were characterized, and the results revealed the formation of a single molecular precursor represented by the formula CaCu3(TiO)4(C2O4)8·9H2O (CCTOX). The decomposition products, obtained via calcination in air, were subsequently subjected to thermal treatments at different temperatures for 4 hours. The morphology and microstructure were characterized, and analysis showed the formation of a single phase, CaCu3Ti4O12 (CCTO) with CuO and CaTiO3 as impurity. It was observed from microscopy that the samples obtained from sintering at 600°C for four hours had discrete particles with regular morphology, limited size distribution, high degree of homogeneity, and multiple dimensions ranging between 10 and 35 nm and showed some degree of ellipticity in shape. Increasing the sintering temperature from 600°C to 700°C and 800°C increased the grain growth in the ceramic as well as the densification. The method makes advantage of the fact that oxalate precursors decomposed at relatively lower temperatures and the fact that the oxalate in the juice is in the solution which downplays both the solubility and environmental pollution problems since no additional solvents are used.

Nanoceria as a recyclable catalyst/support for the cyanosilylation of ketones and alcohol oxidation in cascade

The cyanosilylation of carbonyl compounds is a fundamental reaction in organic synthesis, to give cyanohydrins. Ketones are particularly reluctant to cyanosilane addition and require the action of a catalyst, and despite many soluble Brönsted and Lewis acids have been employed for this task, it is difficult to find in the open literature catalytic solids able to carry out the reaction. Here, we show that commercially available nanoceria catalyzes the cyanosilylation of different ketones (21 examples) at temperatures between 0 and 50 °C, in high yields, under solventless conditions if required. The nanoceria network atoms act in a cooperative way to provide a bifunctional acid-base solid catalyst for the cyanosilylation reaction. The amorphization of nanoceria during reaction, due to acid release, does not hamper the catalytic activity and, indeed, different types of nanoceria, even with supported metal nanoparticles on surface, are active for the reaction, enabling extensive reuses after air calcination and the use of the catalytic material for the aerobic oxidation of alcohols / cyanosilylation reaction.

Modification of Graphite Felt with Lead (II) Formate and Acetate—An Approach for Preparation of Lightweight Electrodes for a Lead-Acid Battery

Lead-acid battery (LAB) weight is a major downside stopping it from being adapted to electric/hybrid vehicles. Lead grids constitute up to 50% of LAB electrode’s weight and it only ensures electric connection to electrochemically active material and provides structural integrity. Using graphite felt (GF) as a current collector can reduce the electrode’s weight while increasing the surface area. Modification of GF with lead (II) oxide using impregnation and calcination techniques and lead (II) formate and acetate as precursors was conducted to produce composite electrodes. It was found that lead (II) formate is not a viable material for this purpose, whereas multiple impregnation in lead (II) acetate saturated solution and calcination in air leads to thermal destruction GF. However, impregnation and calcination under nitrogen atmosphere in three cycles produced a sample of good quality with a mass loading of lead (II) oxide that was 17.18 g g−1 GF. This equates to only 5.5% of the total mass of composite electrode to be GF, which is immensely lower than lead grid mass in traditional electrodes. This result shows that a possible lightweight alternative of LAB electrode can be produced using the proposed modification method.

Sulfated attapulgite for catalyzing the conversion of furfuryl alcohol to ethyl levulinate: Impacts of sulfonation on structural transformation and evolution of acidic sites on the catalyst

Attapulgite (ATTP) is an abundant natural magnesium aluminosilicate mineral that can be used as support for manufacturing cost-effective solid acid catalysts. This study mainly focuses on structural change of ATTP and the formation of Brønsted and Lewis acid sites during sulfonation in H 2 SO 4 . The results indicate that the sulfonation leads to the drastic change of the crystal phases as sulfuric acid not only plays the roles of grafting the sulfur species but also reacts with the CaO, MgO, Al 2 O 3 and Fe 2 O 3 or their salts in ATTP to form the sulfates, resulting in the substantial change of the porous structure of ATTP. In such a process, the Brønsted acidic sites, which are the main active sites for the conversion of furfuryl alcohol (FA) to ethyl levulinate (EL), are introduced, while the abundance/strength of the Lewis acid sites are enhanced. The yield of EL up to 95.4% is achieved over the H 2 SO 4 /ATTP catalyst. The Fe 2 (SO 4 ) 3 and MgSO 4 in the catalyst leaches in ethanol but does not affect the catalytic stability. The formed polymer also does not affect much the catalytic activity after their removal via the calcination in air. • Sulfated attapulgite (ATTP) is prepared for conversion of furfuryl alcohol (FA) in ethanol. • Sulfonation transforms CaO, MgO, Al 2 O 3 and Fe 2 O 3 phase, changing structure in ATTP. • Sulfonation destroys Al–OH–Al, Si–O–Al and carbonate functionalities in ATTP. • Sulfonation enhanced abundance/strength of Brønsted and Lewis acid sites. • Leaching of sulfates does not affect the sulfur species that generate acidic sites.

Biotemplate synthesis of mesoporous α-Fe2O3 hierarchical structure with assisted pseudocapacitive as an anode for long-life lithium ion batteries

The oriented biotemplate synthesis of nanostructured metal oxides as anode materials for lithium-ion batteries (LIBs) has recently attracted widespread attentions. Herein, mesoporous α-Fe2O3 hierarchical tubes (named as Fe-400) were successfully prepared by facile iron salt impregnation and air calcination at 400 °C using waste poplar branch as biotemplate. The hierarchical structure of Fe-400 is constructed from cross-linked small nanoparticles (~29 nm), which then results in large specific surface area (37.7 m2 g−1) and uniform mesoporous size distribution (12.2 nm). As anode material for LIBs, Fe-400 displays reversible capacity of 880.7 mA h g−1 after long-cycle of 800th at 1 A g−1, indicating that this material has high capacity retention and good long-cycle stability. The prominent electrochemical properties are mainly ascribed to the large specific surface area, unique homogeneous mesopores, and the assisted pseudocapacitive behaviors of Fe-400. In view of the low-cost, environment-friendly and easily large-scale synthesis of Fe-400 electrode material, the present biotemplate strategy can present useful reference for the synthesis of other transition metal oxide-based anode materials for LIBs.

α or β?-hemihydrates transformed from dihydrate calcium sulfate in a salt-mediated glycerol–water solution

α-and β-hemihydrate calcium sulfate (HH), the most important calcium sulfate phases, are usually achieved by autoclave hydrothermal reaction and calcination in air, respectively. Herein, we report an investigation on preparation of HH from dihydrate calcium sulfate(DH) in a salt-mediated glycerol-water solution. We found that both α-HH and β-HH in forms of apparently single crystals could be obtained at 110 ℃ only by tuning the concentrations of glycerol, Na2EDTA, and NaCl. TG-DSC, XRD, SEM, and Raman spectroscopy were used to identify and characterize the product crystals. The results indicate that the high relative supersaturation of HH could be the key factor determining the generation of β-HH crystal in solution. Glycerol and NaCl generally decrease the water activity, enhance the crystallization kinetics, and therefore allow the presence of a metastable HH phase (especially for compact α-HH bulk crystal). But too high concentration of glycerol (i.e., ≥70%) and NaCl (i.e., ≥0.2 M) would be favorable for β-HH crystallization with obviously defective crystal morphology due to the dramatically increased local relative supersaturation. Na2EDTA could retard the recrystallization but well regulate the morphology of HH bulk crystals.

Sol–gel synthesized ZnO/Mn–TiO2 core–shell nanocomposite and its elevated activity for methyl orange degradation

Photocatalysis is a new advanced oxidation process based on the irradiation of semiconductors such as TiO2 and ZnO for photodegradation of contaminants. In this process, the semiconductor absorbs the photon energy of ultraviolet radiation, generating highly reactive species for the degradation of organic compounds. It has been reported that doping of transition metals (e.g., Cu, Ni, Co, and Mn) into the structure of oxide semiconductors can reduce the band gap and expand their adsorption properties to the visible solar spectrum. Accordingly, a new hybrid photocatalyst of Mn-doped TiO2 / ZnO with an Mn content of 1 to 5 wt. % was synthesized via the sol–gel process followed by thermal calcinations in air at 500°C. The prepared photocatalyst powder was characterized in terms of crystalline structure, thermal property, surface morphology, and band gap energy level. Its photocatalytic performance was then assessed based on photodegradation of methylene orange under visible light irradiation. Compared with the pure TiO2 / ZnO, the lattice of Mn-doped TiO2 / ZnO was found to be more thermally stable, and thus phase transformation of anatase to rutile was postponed to a higher calcination temperature. The photocatalysis evaluation showed an increased activity of Mn–ZnO / TiO2 compared with pure TiO2 and TiO2 / ZnO under visible light irradiation. Accordingly, the highest degradation of 98% was obtained by the Mn–ZnO / TiO2 with 3 wt. % Mn.

Self‐Supported Electrocatalysts Derived from Nickel‐Cobalt Modified Polyaniline Polymer for H2‐Evolution and O2‐Evolution Reactions

AbstractThe water splitting aims to produce H2 for fuel cells and a number of industrial processes such as the ammonia synthesis and the metals refining. There is actually a major limitation about the development of cost‐effective and efficient electrocatalysts to lower the cell voltage that must be overcome to perform sequentially the overall reaction that is 2H2O →2H2+O2. In the present study, we combined Ni and Co as the promising alternative catalytic metals to Pt‐group metals as well as N and S as the doping elements to fabricate self‐supported electrocatalysts for hydrogen evolution (HER) and oxygen evolution (OER) in alkaline media. To these ends, the polymerization of the aniline into polyaniline (PANI) in the presence of Ni(II) and Co(II) followed by calcination in air resulted in the formation of heterogeneous catalytic materials self‐supported onto a matrix made of C, N, S, Ni and Co. Enhanced activity and durability were recorded for the hybrid and bimetallic PANI‐NiCo composite.

Gallium and tin exchanged Y zeolites for glucose isomerisation and 5-hydroxymethyl furfural production

This study demonstrates the use of gallium and tin modified Y zeolites as catalysts for the conversion of glucose into fructose, mannose and 5-Hydroxymethyl furfural. These catalysts can be synthesised via a simple and scalable procedure that uses commercially available Y zeolite. The catalysts were characterised by various techniques including elemental analysis, electron microscopy, nitrogen physisorption, X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet-visible spectroscopy, solid state nuclear magnetic resonance spectroscopy and X-ray absorption near edge spectroscopy. It is found that tin containing Y zeolite generate a glucose conversion of 36 % and total product yield of 17 % in water. Meanwhile, gallium containing Y zeolite shows an HMF yield of 33 % when reactions were conducted in DMSO. The recyclability of tin and gallium containing Y zeolites were studied in DMSO and the activities of both materials were shown to remain stable. Furthermore, the spent catalysts can be regenerated via calcination in air.

Structural changes of Nd- and Ce-doped ammonium diuranate microspheres during the conversion to U1−yLnyO2±x

The structural changes of ammonium diuranate (ADU) microspheres, prepared by the sol–gel route via internal gelation, were investigated during thermal treatments in oxidative and reducing conditions. In particular, in-situ simultaneous thermogravimetric analyses and in-situ high-temperature scanning electron microscopy investigations were carried out on un-doped ADU microspheres, and ADU microspheres doped with 10 mol% neodymium or 10 mol% cerium. Calcination in air caused the surface of the particles to crack, but with increasing temperature up to 900 °C some healing, and additionally, shrinkage occurred. The extent of the fractures and the amount of shrinkage was, however, significantly more pronounced in a particle prepared with a tetravalent Ce precursor, as compared to particles prepared with a trivalent Nd or Ce precursor. The macroscopic behaviour could be related to the release of volatile decomposition products and the calcined compositions were identified as (Ln-doped) α−U3O8by X-ray powder diffraction. During thermal treatment in reducing conditions a transition from a (Ln-doped) α−U3O8phase to a (Ln-doped) UO2±x phase was observed. After exposure to a hydrogen containing gas mixture, this transition occurred rapidly in un-doped particles, and in particles prepared with trivalent Nd or Ce dopant precursors at 700 °C. Despite the fast reduction reaction, severe fractures appeared in the particles above temperatures of 850 °C, indicating that such behaviour is mainly attributed to sintering effects and less to the phase transition. In contrast, a more delayed reduction reaction was observed in particles prepared with a tetravalent dopant precursor and the described effects appeared less severe.

Poplar branch bio-template synthesis of mesoporous hollow Co3O4 hierarchical architecture as an anode for long-life lithium ion batteries

Mesoporous hollow hierarchical structures play an important role in enhancing the lithium storage performances of Co3O4 anode materials. In this work, Co3O4 with mesoporous hollow structure has been successfully fabricated by simple impregnation and subsequently air calcination using poplar branch as bio-template. The product calcined at 600 °C (PB-Co600) perfectly duplicates the 3D aligned microchannels structure of poplar branch. Importantly, the wall of aligned microchannels in PB-Co600 is constructed by a lot of irregular cross-linked Co3O4 nanoparticles and there are abundant mesopores on the surface. As an anode, it exhibits high reversible capacity and remarkable long-cycle stability. At 0.1 A g-1, it can deliver a high specific capacity of 1153.7 mA h g-1 after 100 cycles, and even at 1 A g-1, the reversible specific capacity of 555.7 mA h g-1 can be retained after cycling 1000 times. The excellent lithium storage performance of PB-Co600 may be attributed to its unique hierarchical structure, which is not only favorable to the rapid transfer of substances and Li+ ion diffusion, but also alleviates the volume change during the charge/discharge cycle. Furthermore, the existence of oxygen vacancies and pseudo-capacitance also contributes significantly to the superior lithium storage performance of the PB-Co600 electrode. Therefore, the PB-Co600 prepared by a large-scale and eco-friendly route can be used as a potential candidate anode for LIBs.

Atomic-level understanding on the evolution behavior of subnanometric Pt and Sn species during high-temperature treatments for generation of dense PtSn clusters in zeolites

To achieve high-loading of stable subnanometric metal clusters on solid carriers is a challenge since those small metal clusters have strong tendency to sinter into larger nanoparticles. Development of facile synthesis methodologies to obtain subnanometric metal catalysts with high metal loading and high stability against sintering at high temperature (>500 °C) in reductive atmosphere (such as H2) is critical for the practical applications. In this work, we will present and discuss the generation of high-loading (~1.4 wt%) subnanometric Pt clusters confined in the sinusoidal channels of MFI zeolite, on the basis of the atomic-level understanding on the evolution of Pt and Sn species during high-temperature oxidation–reduction treatments. It will be shown that the structural evolution of Pt and Sn species is dependent on the post-synthesis treatments. The Pt particles on the external surface can disintegrate into subnanometric Pt species and get stabilized in the zeolite channels during high-temperature calcination in air while Sn species migrate from surface region to internal region during high-temperature reduction treatment at 650 °C. The resultant material containing bimetallic PtSn clusters confined in the 10MR sinusoidal channels of the purely siliceous MFI zeolite show excellent catalytic activity and stability, as demonstrated for dehydrogenation of light alkanes at high reaction temperature.

Ferromagnetic metal conversion directly from two-dimensional nickel hydroxide

We have demonstrated a direct metallic conversion from nickel hydroxide nanosheets to nickel metal nanostructures by thermal annealing in vacuum. The metal transition of the single-layer nanosheets deposited on a Si substrate was revealed by x-ray absorption near edge structure (XANES) measurements. The XANES signal significantly changed at annealing temperatures above 250 °C. The metal transition temperature coincides with the reported temperatures at which layered nickel hydroxide nanosheets are converted to nickel oxide nanosheets by calcination in air. Auger measurements confirmed that a dissociation of oxygen from the hydroxide nanosheet induces the metallic conversion. The converted nickel metallic structures exhibit ferromagnetic behavior revealed by x-ray magnetic circular dichroism (XMCD) measurement. Atomic force microscopy measurements indicate that diffusions of nickel atoms on the substrates leads to a structural change from a 2D-like structure to a particle-like structure.

Effect of Alkali-Free Synthesis and Post-Synthetic Treatment on Acid Sites in Beta Zeolites.

Beta zeolites with Si/Al around 14 were prepared using three new alkali-free synthesis methods based on the application of amorphous aluminosilicate precursor and calcined in ammonia or air. All samples exhibit structural and textural properties of standard beta zeolite. Comprehensive study by 27Al and 29Si MAS NMR, together with FTIR adsorption of d3-acetonitrile and pyridine were used to characterize the influence of both the synthesis and calcination procedure on the framework Al atoms and related Brønsted and Lewis acid sites. While calcination in ammonia preserves all framework Al atoms, calcination in air results in 15% release of framework Al, but without restrictions of the accessibility of the beta zeolite channel system for bulky pyridine molecules. Terminal (SiO)3AlOH groups present in the hydrated zeolites were suggested as a precursor of framework Al-Lewis sites. Surprisingly, the mild dealumination of the air-calcined zeolites result in an increase of the concentration of Brønsted acid sites and a decrease of the total concentration of Lewis sites with the formation of the extra-framework ones.

Lanthanum Ferrites-Based Exsolved Perovskites as Fuel-Flexible Anode for Solid Oxide Fuel Cells.

Exsolved perovskites can be obtained from lanthanum ferrites, such as La0.6Sr0.4Fe0.8Co0.2O3, as result of Ni doping and thermal treatments. Ni can be simply added to the perovskite by an incipient wetness method. Thermal treatments that favor the exsolution process include calcination in air (e.g., 500 °C) and subsequent reduction in diluted H2 at 800 °C. These processes allow producing a two-phase material consisting of a Ruddlesden–Popper-type structure and a solid oxide solution e.g., α-Fe100-y-zCoyNizOx oxide. The formed electrocatalyst shows sufficient electronic conductivity under reducing environment at the Solid Oxide Fuel Cell (SOFC) anode. Outstanding catalytic properties are observed for the direct oxidation of dry fuels in SOFCs, including H2, methane, syngas, methanol, glycerol, and propane. This anode electrocatalyst can be combined with a full density electrolyte based on Gadolinia-doped ceria or with La0.8Sr0.2Ga0.8Mg0.2O3 (LSGM) or BaCe0.9Y0.1O3-δ (BYCO) to form a complete perovskite structure-based cell. Moreover, the exsolved perovskite can be used as a coating layer or catalytic pre-layer of a conventional Ni-YSZ anode. Beside the excellent catalytic activity, this material also shows proper durability and tolerance to sulfur poisoning. Research challenges and future directions are discussed. A new approach combining an exsolved perovskite and an NiCu alloy to further enhance the fuel flexibility of the composite catalyst is also considered. In this review, the preparation methods, physicochemical characteristics, and surface properties of exsoluted fine nanoparticles encapsulated on the metal-depleted perovskite, electrochemical properties for the direct oxidation of dry fuels, and related electrooxidation mechanisms are examined and discussed.

In situ synthesis of exfoliation TiO2@C hybrids with enhanced photocatalytic hydrogen evolution activity

TiO2 is an ideal semiconductor material for photocatalytic applications. However, inadequate visible light response and fast recombination of charge carriers restrict its photocatalytic performance. Constructing a junction structure between TiO2 and carbon nanomaterials can solve the above shortcomings. In the present work, two-dimensional (2D) transition metal carbides (Ti3C2) were synthesized from the Ti3AlC2 MAX phase firstly. Then the porous carbon-supported TiO2 (TiO2@C) hybrids were in-situ synthesized by calcination in air. Also, the pristine Ti3C2 was exfoliated by intercalation with dimethyl sulfoxide (DMSO). The exfoliation TiO2@C catalyst was in-situ prepared by freeze-drying and calcining, and it delivered an enhanced visible-light-driven photocatalytic H2 evolution rate of 160.42 µmol·h−1·g−1, 13 times higher than the primary TiO2@C catalyst. The enhanced photocatalytic activity results from the increased specific surface area, facilitating charge separation and elevated conduction band. The paper indicates that MXene oxidation can further apply in the visible light photocatalysis.