Formation Of Active Phase Research Articles

STUDY OF TECHNOLOGICAL PARAMETERS OF OBTAINING CELSIANE AND SLAWSONITE CERAMICS USING SINGLE-STAGE TECHNOLOGY

On the basis of the RO–Al2O3–SiO2 system, radiotransparent ceramic materials of cordierite, celsian, and anorthite composition, which have low dielectric characteristics, are obtained. These requirements are met by one of the main phases of the BaO–Al2O3–SiO2 system – celsian (BaAl2Si2O8), the melting point of which is 1740 °C, and the beginning of active phase formation occurs at a processing temperature of 1300 °C, as well as one of the main phases of the SrO–Al2O3–SiO2 is slavsonite (SrAl2Si2O8), which undergoes congruent melting at a temperature of 1765 °C, and the beginning of active phase formation occurs at a processing temperature of 1400 °C. The purpose of the work is to study the technological parameters of obtaining celsian and slavsonite ceramics by one-stage technology. According to the subsolidus structure of the three-component system RO–Al2O3–SiO2 (RO = ВаО, SrO), it is advisable to synthesize the necessary phases from pure raw materials and, taking into account the presence of impurities that impair the dielectric characteristics, the synthesis of the necessary crystalline phases is carried out from technical raw materials. Figurative points of the compositions of the selected compounds correspond to their stoichiometric composition (for slavsonite, wt. %: SrO – 31,99; Al2O3 – 30,93; SiO2 – 37,08; for celsian, wt. %: BaO – 40,85; Al2O3 – 27,17; SiO2 – 31,98). It was established that the physical characteristics of the obtained samples improve with an increase in the firing temperature by 100 °C, but they are far from the desired level. The dielectric characteristics of the obtained materials are within the requirements for radio-transparent materials. Taking into account the investigated physical properties and the obtained radiographs of fired samples in order to obtain a densely sintered material, it was decided to investigate model compositions with the addition of intensifying additives and to study their influence on the properties of fired samples

Forming, Confining, and Observing Microtubule-Based Active Nematics

The formation of biopolymer-based active phases has become an important technique for researchers interested in exploring the emerging field of active liquid crystals and their possible roles in cell biology. These novel systems consist of self-driven sub-units that consume energy locally, producing an out-of-equilibrium dynamic fluid. To form the active liquid crystal phase described in this report, purified protein components including biopolymers and molecular motors are combined, and the active nematic phase spontaneously forms in the presence of adenosine triphosphate (ATP). To observe the nematic state, the material must be confined in a suitable geometry for microscopy at a high enough density. This article describes two different methods for the formation of an active nematic phase using microtubules and kinesin motors: assembly of a two-dimensional active layer at an oil and water interface and assembly under an oil layer using an elastomeric well. Techniques to insert the active material into small wells of different shapes are also described.

The formation of active phases in Pt-containing catalysts for bicyclohexyl dehydrogenation in hydrogen storage.

The fundamental role of the carbon carrier Sibunit® in the formation of active and selective phases in low-percentage Pt-containing catalysts Pt/C, Pt/Ni/C, Pt/Ni-Cr/C for the complete dehydrogenation of bicyclohexyl into biphenyl (320 °C, 1 atm) is shown. The Pt/Ni-Cr/C catalyst showed the greatest activity and selectivity in the complete dehydrogenation of bicyclohexyl into biphenyl. Detailed analysis of the catalyst surface by XPS, TEM-HR and EDX methods revealed two main processes associated with the high activity and successful course of the reaction of bicyclohexyl dehydrogenation: the formation of an active carbide Pt1-xCx phase and graphitization of the carbon carrier. Both these processes are realized equally in the Pt/Ni-Cr/C catalyst demonstrating the highest activity. The formation of the Pt1-xCx carbide phase at a low extent of graphitization of the catalyst surface is predominant for the Pt/C catalyst. Graphitization of the carbon carrier is most pronounced for Pt/Ni/C, where the yield of biphenyl is significantly reduced. The formation of graphite for the Pt/Ni/C catalyst at the metal-carrier interface leads to the encapsulation of a metal particle in a graphite shell, which apparently determines its low activity in the conversion of bicyclohexyl.

High polarity catalyst of CoFe alloy/fluoride interconnected by bamboo-like nitrogen-doped carbon nanotubes for efficient oxygen evolution reaction

The easy agglomeration and low conductivity of high polarity catalysts restrict the active phase formation for oxygen evolution reaction (OER) in water-splitting reactions, even for the catalysts with conductive NC species derived from MOFs carbonization. Herein, as a proof of concept, the bamboo-like nitrogen-doped carbon nanotube (N-doped CNT) from dicyandiamide pyrolysis was introduced into MOFs-derived high polarity catalyst of CoFe alloy and fluoride, and the performance for OER can be largely improved to low overpotentials of 231 mV to drive 10 mA cm−2 when loaded on the glassy carbon electrode. The structural evolution induced by the N-doped CNT introduction was carefully studied by both spectroscopic analysis and electrochemical measurements, and it was revealed that forming the structure of carbon nanotube interconnected active sites prevented the active site agglomeration and improved the catalytic conductivity, which improved the mass transfer, and active site exposure. The largely improved performance was attributed to the easy active phase formation by high polarity metal fluoride, the synergy between Fe and Co species, and conductivity improvement by N-doped carbon nanotubes derived from dicyandiamide with high graphitic N. The current work showed some novel contributions to catalytic ability boosting for MOF-derived catalysts in OER catalysis.

Efficient Ternary Mn-Based Spinel Oxide with Multiple Active Sites for Oxygen Evolution Reaction Discovered via High-Throughput Screening Methods.

The discovery of more efficient and stable catalysts for oxygen evolution reaction (OER) is vital in improving the efficiency of renewable energy generation devices. Given the large numbers of possible binary and ternary metal oxide OER catalysts, high-throughput methods are necessary to accelerate the rate of discovery. Herein, Mn-based spinel oxide, Fe10 Co40 Mn50 O, is identified for the first time using high-throughput methods demonstrating remarkable catalytic activity (overpotential of 310mV on fluorine-doped tin oxide (FTO) substrate and 237mV on Ni foam at 10mA cm-2 ). Using a combination of soft X-ray absorption spectroscopy and electrochemical measurements, the high catalytic activity is attributed to 1) the formation of multiple active sites in different geometric sites, tetrahedral and octahedral sites; and 2) the formation of active oxyhydroxide phase due to the strong interaction of Co2+ and Fe3+ . Structural and surface characterizations after OER show preservation of Fe10 Co40 Mn50 O surface structure highlighting its durability against irreversible redox damage on the catalytic surface. This work demonstrates the use of a high-throughput approach for the rapid identification of a new catalyst, provides a deeper understanding of catalyst design, and addresses the urgent need for a better and stable catalyst to target greener fuel.

Dual-purpose nickel-iron layered double hydroxides by controlled lanthanide and phosphide incorporation for promoting overall water splitting efficiency

Developing non-noble metal and binder-free bifunctional electrocatalysts is of paramount importance but challenging for simultaneously promoting oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) processes. In the work, we introduce the dual-purpose utilization of nickel-iron layered double hydroxides (LDH) by a lanthanide and phosphide incorporation strategy for highly efficient overall water splitting (OWS). The screening of lanthanides effect shows that the lanthanide dopants (Ce, La and Nd) greatly contribute to the layer lattice distortion of LDH host structure and strong electronic interaction with Fe2+ species, leading to the increment of OER active species content of α-Ni(OH)2 phase and Fe3+. Specially, the formation of Ce3+/4+ reversible redox species can significantly promote charge transfer efficiency, thus corporately attributing to the excellent OER activity (η10 = 207 mV) and durability (300 mA·cm−2 for 200 h). On the other hand, we found that with further phosphide anions engineering, the HER Volmer step is accelerated in lanthanide and phosphide co-doped LDH, as compared to the solely phosphide doped LDH. The present of co-doped lanthanide can modify the adsorption energy of hydrogen intermediates and the Ce3+/4+ reversible redox species also facilitate the formation of HER active Ni2P phase, resulting in the lowest η10 value of 134 mV. The dual-purpose configuration of the Ce LDH // Ce LDH-P electrodes, provides low OWS potentials of 1.638 and 1.839 V to reach current densities of 10 and 100 mA·cm−2, respectively. These findings could introduce a new way to integrate nonprecious-metal bifunctional electrocatalysts into an efficient OWS system.

Selective synthesis of olefins via CO2 hydrogenation over transition-metal-doped iron-based catalysts

The catalytic hydrogenation of CO2 to olefins has received considerable attention. Herein, transition metal- and sodium-modulated iron-based catalysts were fabricated. Doping with zinc and copper favor the formation of Fe3O4 and Fe5C2 active phases, while adding manganese inhibits the formation of iron carbide. In addition, phase separation between copper and iron species occurs more readily under working conditions. Therefore, a zinc- and sodium-modulated Fe catalyst exhibited the best activity and stability. Moreover, copper was predicted to substantially decrease the energy barrier of the rate-determining step for the secondary hydrogenation of olefins and result in a much lower olefin-to-paraffin ratio. In addition, the ZnO/Fe5C2 interface facilitated the desorption of olefins from the catalyst surface and inhibited the undesirable secondary reaction of olefins, enabling a high selectivity toward olefins of 36.9 % C2–4= and 32.3 % C5+=. This study provides an exemplary new strategy for tuning the product selectivity of catalysts for olefin synthesis.

Atomistic Insights into Activation and Degradation of La0.6Sr0.4CoO3-δ Electrocatalysts under Oxygen Evolution Conditions.

The stability of perovskite oxide catalysts for the oxygen evolution reaction (OER) plays a critical role in their applicability in water splitting concepts. Decomposition of perovskite oxides under applied potential is typically linked to cation leaching and amorphization of the material. However, structural changes and phase transformations at the catalyst surface were also shown to govern the activity of several perovskite electrocatalysts under applied potential. Hence, it is crucial for the rational design of durable perovskite catalysts to understand the interplay between the formation of active surface phases and stability limitations under OER conditions. In the present study, we reveal a surface-dominated activation and deactivation mechanism of the prominent electrocatalyst La0.6Sr0.4CoO3−δ under steady-state OER conditions. Using a multiscale microscopy and spectroscopy approach, we identify the evolving Co-oxyhydroxide as catalytically active surface species and La-hydroxide as inactive species involved in the transient degradation behavior of the catalyst. While the leaching of Sr results in the formation of mixed surface phases, which can be considered as a part of the active surface, the gradual depletion of Co from a self-assembled active CoO(OH) phase and the relative enrichment of passivating La(OH)3 at the electrode surface result in the failure of the perovskite catalyst under applied potential.

Effect of phosphorization temperature on the structure and hydrogen evolution reaction performance of nickel cobalt phosphide electrocatalysts

Nickel cobalt phosphides electrocatalysts have shown great potential for hydrogen evolution reaction (HER) but further improvements are necessary. Here, nickel cobalt phosphide nanosheets were synthesized via electrodeposition followed by phosphorization methodology. The relationships between phosphorization temperature and the structure or hydrogen evolution reaction (HER) activity were studied. The catalyst phosphated at 350 °C (NiCoP-350/CC) displayed excellent HER performance in alkaline media with a low overpotential of 59 mV at the current density of 10 mA cm−2 (η10 = 59 mV). This could be attributed to the formation and better dispersion of active NiCoP crystalline phase on the surface of carbon cloth.

Abundant Dislocation Layered Double Hydroxides Synthesis by Molten Salt with Bound Water Boosting Oxygen Evolution.

Optimizing the adsorption free energy and promoting the active phase transition to further enhance the oxygen evolution reaction (OER) activity remain significant challenges. The adsorption free energy can be optimized by modulating the electronic structure and adjusting the crystal configuration. Meanwhile, the transformation of the active phase can be promoted by introducing strain energy. The theoretical calculations are conducted to verify the rational envisage. However, it is still a great obstacle to introducing strain into the electrocatalysts and avoiding destruction. The stress field caused by dislocation can realize both of the above. Hence, the molten salt with the bound water method is proposed and the abundant dislocation layered double hydroxides (D-NiFe LDH) are constructed. The in situ characterizations further verify the dislocations significantly affect the generation of the active phase and the state of electronic structure. Consequently, the D-NiFe LDH exhibits outstanding OER activity and obtains 10mA cm-2 , only requiring 199mV overpotential with fabulous stability (100mA cm-2 more than 24h). The work paves a new avenue for the rational introduction dislocations to optimize the crystal configuration and boost the active phase formation, significantly enhancing the OER performance.

Theoretical and experimental insights into CO2 formation on Co2C catalysts in syngas conversion to Value-Added chemicals

Cobalt carbide (Co2C) has been discovered as the promising active phase for Fischer–Tropsch to olefins (FTO) process and higher alcohols synthesis (HAS) from syngas, in the form of nanoprisms and nanospheres, respectively. However, CO2 formation is inevitable on Co2C catalysts, especially in FTO process. So far, the mechanism of CO2 formation on Co2C surfaces is less understood. This work provides fundamental insights into CO2 formation on Co2C nanospheres and nanoprisms through computational and experimental study. DFT calculations demonstrate that: Co2C (101) and (020) surfaces exposed on Co2C nanoprisms are basically not active for water gas shift (WGS) reactions but the introduction of Na greatly promotes CO2 formation. CO2 is less favored on Co2C(111) surface which is dominant on Co2C nanospheres, however, the reverse WGS activities can be promoted with Na addition. The experimental results confirmed removing Na from Co2C can efficiently suppress WGS activity, thus reducing CO2 selectivity while the selectivity of light olefins retained. Though previous studies focused on Na addition to promote the yield of light olefins, our work indicates that Na also promotes undesired CO2 formation. Our results suggest that Na is crucial for active phase formation but not necessarily beneficial during the CO hydrogenation reactions.

Elucidating the mechanisms of titanium–induced morphological and structural changes in catalysts on mesoporous Al2O3–TiOx mixed oxides: Effect of non–stoichiometric TiOx phase

In the present work, mesoporous Al 2 O 3 –TiO x composites with different titania loadings (4, 8 and 12 wt%) were synthesized to evaluate the effect of non-stoichiometric TiO x phases on the hydrodesulfurization (HDS) ability of the CoMo/Al 2 O 3 –TiO x catalysts. The activity of the catalysts was evaluated in the dibenzothiophene (DBT) HDS reaction carried out at 593 K, 5.5 MPa in a batch reactor. Regardless of the TiO x content, all sulfided CoMo Al 2 O 3 –TiO x catalysts were more active than the CoMo/Al 2 O 3 catalyst. For all catalysts, DBT HDS occurs mainly through the direct desulfurization (DDS) pathway (95–97% selectivity). The most active catalysts (CoMo-12 and CoMo-4) showed evidence of the presence of non-stoichiometric titanium oxides. The synthesized materials were characterized in depth to evaluate their crystallinity, textural and morphological properties, elemental composition and acidity. Their characterization showed that: (i), the Al 2 O 3 –TiO x interaction increased with decreasing TiO x content; (ii) the strong interaction between TiO x particles and alumina led to the formation of more defined TiO x structures; (iii), an increase in titania content led to the growth of TiO x crystals along the [101] direction (relative to the [001] direction), which in turn, led to the different TiO x morphologies: nanorods → nanotubes → U-shaped nanotubes. The TiCoMoS phase can be formed if the process is performed on Ti 3 O 5 instead of TiO 2 . • Titania loading influenced on the metal–support interaction and the type of titania phases. • Ti–promoted species are related to increase of the direct desulfurization route. • Non–stoichiometric titanium oxides are necessary to formation of TiCoMoS active phase.

A review of Ni based powder catalyst for urea oxidation in assisting water splitting reaction

Water splitting has been regarded as a sustainable and environmentally-friendly technique to realize green hydrogen generation, while more energy is consumed due to the high overpotentials required for the anode oxygen evolution reaction. Urea electrooxidation, an ideal substitute, is thus received increasing attention in assisting water-splitting reactions. Note that highly efficient catalysts are still required to drive urea oxidation, and the facile generation of high valence state species is significant in the reaction based on the electrochemical-chemical mechanisms. The high cost and rareness make the noble metal catalysts impossible for further consideration in large-scale application. Ni-based catalysts are very promising due to their cheap price, facile structure tuning, good compatibility, and easy active phase formation. In the light of the significant advances made recently, herein, we reviewed the recent advances of Ni-based powder catalysts for urea oxidation in assisting water-splitting reaction. The fundamental of urea oxidation is firstly presented to clarify the mechanism of urea-assisted water splitting, and then the prevailing evaluation indicators are briefly expressed based on the electrochemical measurements. The catalyst design principle including synergistic effect, electronic effect, defect construction and surface reconstruction as well as the main fabrication approaches are presented and the advances of various Ni-based powder catalysts for urea assisted water splitting are summarized and discussed. The problems and challenges are also concluded for the Ni-based powder catalysts fabrication, the performance evaluation, and their application. Considering the key influencing factors for catalytic process and their application, attention should be given to structure−property relationship deciphering, novel Ni-based powder catalysts development and their construction in the real device; specifically, the effort should be directed to the Ni-based powder catalyst with multi-functions to simultaneously promote the fundamental steps and high anti-corrosion ability by revealing the local structure reconstruction as well as the integration in the practical application. We believe the current summarization will be instructive and helpful for the Ni-based powder catalysts development and understanding their catalytic action for urea-assisted hydrogen generation via water splitting technique. Advances and challenges of Ni based powder catalyst were reviewed for urea oxidation in assisting water-splitting reaction.

Hetero MOF‐on‐MOF‐derived carbon nanotube interconnected nitrogen‐doped carbon‐encapsulated FeNi/FeF2 for efficient oxygen evolution reaction

AbstractHeterostructures derived from metal–organic frameworks (MOFs) with multicomponent synergism are significant in the energy conversion and catalysis reactions. Herein, we demonstrated such an efficient catalyst with the structure of self‐catalyzed nitrogen‐doped carbon nanotube interconnected FeNi/FeF2 derived from hetero‐zeolite imidazolate frameworks 8 (ZIF‐8) on Fe2Ni MIL (MIL represents Materials of Institut Lavoisier) for oxygen evolution reaction. The obtained catalyst showed efficient synergism of the multicomponents, high polarity, more active sites exposure, increased intrinsic activity, and improved conductivity and stability by a carbon interconnected and confined structure as revealed by the spectroscopic analysis and electrochemical measurements. It required an overpotential of only ca. 240 mV (no iR correction) to reach the current density of 10 mA cm−2 in a KOH solution when loaded on an inert glass carbon electrode, much better than similar kinds of catalysts. The improved catalytic performance can be well correlated to the structural transformation step by step from different MOFs to their derivatives by subsequent carbonation and fluorination. Because of the above‐mentioned structural advantages, good catalysis performance of high activity and stability, faster catalytic kinetics, and facile active phase formation were observed compared to those of other similar materials. This work offers a new platform of derivatives from hetero MOF‐on‐MOF for catalysis reactions.

Highly-selective CO2 conversion through single oxide CuO enhanced NiFe2O4 thermal catalytic activity

The solar-driven thermochemical CO2 conversion is an effective way to achieve the mission of carbon peaking and carbon neutrality. However, finding a material with excellent thermal stability, oxygen exchange capacity, and CO selectivity is one of the most important challenges in the thermochemical CO2 conversion approach. This study investigated the solar thermochemical CO2-splitting characteristics through the synergistic thermal catalytic activity of CuO and NiFe2O4 and the effect of SiC photothermal properties. The thermochemical redox cycling performance of CO2 conversion through thermally activated catalysts was experimentally investigated via thermogravimetric combined quantum chemical calculations to provide comprehensive insights into the physicochemical principles underlying the thermochemical catalytic CO2-splitting. The X-ray diffraction, scanning electron microscopy, and energy spectrum detector technics were developed to gain detail on the crystal structure, surface morphology, and chemical composition changes in the reacting media. The newly synthesized composite material consisting of 25%CuO and 75%NiFe2O4 (CNF-13) coated SiC porous skeleton resulted in higher CO2-splitting catalytic activity with an instantaneous CO production of 10.98mL ⋅ min‐1gCNF‐13−1 and direct CO2-to-CO conversion rate of 33.9% at 1000–1200 K reaction temperature. The thermochemical CO2-splitting activity and redox stability of CNF-13@SiC was promoted by the photothermal properties of SiC support and the formation of Cu2O and Fe3O4 new active material phases easing CO2 reduction at low energy. This study provided experimental and theoretical findings that can be used as guidance for the fundamental research and application of CO2 catalytic conversion into fuels through a solar thermochemical driven strategy.

The Role of the Carbon Carrier in the Formation of Active Surface Phases in Pt-Containing Catalysts for Bicyclohexyl Dehydrogenation

The Role of the Carbon Carrier in the Formation of Active Surface Phases in Pt-Containing Catalysts for Bicyclohexyl Dehydrogenation

Ce/Cr and Ce/Co modified ferrite catalysts for high temperature water-gas shift reaction at elevated pressures

In this work, Ce and Cr/Co co-doped iron oxide (FeCeMOx, where M = Cr or Co) ferrites were investigated for high-temperature water-gas shift (HT-WGS) under industrially relevant pressures (20 bars). The Ce and Cr/Co bi-doping has greatly promoted the catalytic performance in comparison to the single Ce-doping. Especially, the FeCeCoOx ferrite demonstrated the best HT-WGS activity without any deactivation at a steam to CO ratio of 3.5. The ternary FeCeCrOx and FeCeCoOx catalysts also exhibited reasonably stable performance with a slight methanation activity (<2.5%) even under low steam to CO ratio of 1.5. The hematite phase (Fe2-xCex/2Mx/2O3, where M = Cr or Co and × = 0.33) of the fresh (calcined) catalysts became [A(1-δ)Bδ]T[AδB(2-δ)]OO4 type magnetite spinel structure (Fe3-xCex/2Mx/2O4, where M = Cr or Co and × = 0.5) during the activation process, which is regarded as the active phase for the WGS reaction. The co-doping of Cr or Co increased the stability of the active magnetite phase against sintering and suppressed the coke formation during the WGS reaction, which should be responsible for the stable activity. The addition of Cr or Co to iron oxide also delays the formation and over-reduction of active magnetite phase. Mössbauer spectra confirmed that the Cr or Co ions were incorporated into the octahedral sites of [A(1-δ)Bδ]T[AδB(2-δ)]OO4 spinel framework during the activation and modifies the local structure. The superparamagnetic behavior of the spinel ferrites has significantly enhanced upon the co-doping of Ce and Cr/Co into the iron oxide lattice, indicating a high fraction of nanoparticles in the ternary spinel ferrites. The Cr or Co addition resulted in the decreased surface Fe3+/Fe2+ ratio which could be due to the replacement of Fe3+ ions by Cr or Co ions. Most importantly, no evident change was observed in the surface structure of ternary spinel ferrites even after the reaction, which could be responsible the stable performance of the catalysts.

Modification of ZSM-5 mesoporosity and application as catalyst support in hydrodesulfurization of dibenzothiophene: Experimental and DFT studies

The hydrodesulfurization (HDS) efficiency of NiMoS supported on modified H-ZSM-5 was investigated. The support modification was achieved via desilication (DS) in 3 – 5 M NaOH solution for 0.5 – 1 h, at 65 °C. The desilication of H-ZSM-5 increased both its mesoporosity and external surface area. The catalysts acidity and active phase formation and dispersion were influenced by the desilication of the zeolite supports. The NM/B-Z1/2 catalyst shows better HDS performance with dibenzothiophene (DBT) conversion of 87% after 4 h of reaction, while the catalyst formed from pristine ZSM-5 support (NM/Z) recorded the least DBT conversion of 38%. The DFT simulation energetics revealed that the hydrodesulfurization (HDS) process proceeded via the direct desulfurization (DDS) pathway in good correlation with the experimental findings. Extensive characterization techniques were adopted to gain insight into the physico-chemical properties of the support and the catalysts. Surface area and porosity analyzer was used for textural properties information of both the support and the catalyst. The information about surface and type of acidity, the metal-support interaction, morphology, metal charge content and dispersion of active species NiMo-S was explored by FESEM, FETEM, TPD, Pyr-FTIR, FTIR, XRD and XPS

Combined MOF derivation and fluorination imparted efficient synergism of Fe-Co fluoride for oxygen evolution reaction

Novel and efficient MOF derivatives are significant to high-performance catalyst fabrication and application. By combining the MOF derivation and fluorination approaches, herein, we demonstrated an efficient catalyst of ZIF-FeCo MOFs derived FeCo fluoride hybrid with efficient catalytic synergism for electrochemical oxygen evolution reaction (OER). The temperature dependence of fluorination for derivatives is observed by the physical characterization and electrochemical measurements. The optimal catalysts show the best catalytic performance for OER with 250 mV overpotentials (No IR correction) to offer 10 mA cm−2 loaded on glass carbon electrode, which is much better than that of the pristine ZIF-FeCo MOFs and the traditional carbonization derivatives of ZIF-FeCo/C. An efficient synergism of Fe and Co in the catalyst system is demonstrated compared to the single metal MOF-derived fluorides. The specific activity and TOF value at 1.53 V are 2.34 mA cm−2 and 0.055 s−1, respectively, about 17 and 55 times higher than the pristine ZIF-FeCo MOF, and 5 and 14 times higher of ZIF-FeCo/C samples. High catalytic performances of catalytic stability, kinetics, charge transfer ability and active sites efficiency can be attributed to the combined techniques of MOF derivatives and fluorination etching induced high electrochemical surface area, more active site exposure, conductivity improvement and the facile high valence state of Co active phase formation coming from the high polarity of chemical bonds. The current work expands the application of MOF derivatives in the field of energy conversion and catalysis reactions.

Phase development of phosphate‐bonded Al2O3‐MgAl2O4 high‐temperature ceramics: XRD and solid‐state NMR investigations

AbstractThis article describes investigations on the phase development (T ≤ 1500℃) of phosphate‐bonded Al2O3‐MgAl2O4 high‐temperature ceramics by a combination of solid‐state MAS NMR and X‐ray diffraction analyses. The ceramic body was bonded with inorganic hydrogen orthophosphates (Al, Mg, Ca, Zr) with a total binder content of 3 wt.% P2O5. The binding mechanisms of these phosphate‐bonded ceramics could be extensively deduced by analyses of phase developments during hardening, strength development, and high‐temperature phase formation at T ≤ 1500℃: The formation of a network of aluminum phosphate compounds by acid and condensation reactions of the phosphate with the ceramic body is proven to be the active binding process. The binding process is initiated by the formation of active phosphoric acid phosphate phases, which in principle prerequisites water solubility of the binder. Thermal treatment, especially at T ≤ 600℃, promotes the degree of P‐cross‐linking of the phosphate structures. In addition to these phosphate‐ceramic reactions, it was also possible to identify parallel pure phosphate–phosphate conversions of the initial phosphates (via condensation and polymerization) without reactions with ceramic components. The contribution of these structures to the binding effect can be estimated to be minor. Only at temperatures of T ≥ 600℃, these Ca, Mg and Zr phosphates begin to react with the ceramic material to form aluminum phosphates. The phosphate bond has a permanent effect until the formation of the ceramic bond (T &gt; 1000℃). High‐temperature phases are usually crystalline PO4‐sintered structures which are formed by reaction with MgAl2O4.