Multiplying Oxygen Permeability of a Ruddlesden-Popper Oxide by Orientation Control via Magnets.

Ruddlesden-Popper-type oxides exhibit remarkable chemical stability in comparison to perovskite oxides. However, they display lower oxygen permeability. We present an approach to overcome this trade-off by leveraging the anisotropic properties of Nd2 NiO4+δ . Its (a,b)-plane, having oxygen diffusion coefficient and surface exchange coefficient several orders of magnitude higher than its c-axis, can be aligned perpendicular to the gradient of oxygen partial pressure by a magnetic field (0.81 T). A stable and high oxygen flux of 1.40 mL min-1 cm-2 was achieved for at least 120 h at 1223 K by a textured asymmetric disk membrane with 1.0 mm thickness under the pure CO2 sweeping. Its excellent operational stability was also verified even at 1023 K in pure CO2 . These findings highlight the significant enhancement in oxygen permeation membrane performance achievable by adjusting the grain orientation. Consequently, Nd2 NiO4+δ emerges as a promising candidate for industrial applications in air separation, syngas production, and CO2 capture under harsh conditions.

Shielding Protection by Mesoporous Catalysts for Improving Plasma-Catalytic Ambient Ammonia Synthesis.

Plasma catalysis is a promising technology for decentralized small-scale ammonia (NH3) synthesis under mild conditions using renewable energy, and it shows great potential as an alternative to the conventional Haber-Bosch process. To date, this emerging process still suffers from a low NH3 yield due to a lack of knowledge in the design of highly efficient catalysts and the in situ plasma-induced reverse reaction (i.e., NH3 decomposition). Here, we demonstrate that a bespoke design of supported Ni catalysts using mesoporous MCM-41 could enable efficient plasma-catalytic NH3 production at 35 °C and 1 bar with >5% NH3 yield at 60 kJ/L. Specifically, the Ni active sites were deliberately deposited on the external surface of MCM-41 to enhance plasma-catalyst interactions and thus NH3 production. The desorbed NH3 could then diffuse into the ordered mesopores of MCM-41 to be shielded from decomposition due to the absence of plasma discharge in the mesopores of MCM-41, that is, "shielding protection", thus driving the reaction forward effectively. This promising strategy sheds light on the importance of a rational design of catalysts specifically for improving plasma-catalytic processes.

Holistic View on Materials Development: Water Electrolysis as a Case Study.

In view of rising ecological awareness, materials development is primarily aimed at improving the performance and efficiency of innovative and more elaborate materials. However, a materials performance figure of merit should include essential aspects of materials: environmental impact, economic constraints, technical feasibility, etc. Thus, we promote the inclusion of sustainability criteria already during the materials design process. With such a holistic design approach, new products may be more likely to meet the circular economy requirements than when traditional development strategies are pursued. Using catalysts for water electrolysis as an example, we present a modelling method based on experimental data to holistically evaluate processes.

Realizing p-type NbCoSn half-Heusler compounds with enhanced thermoelectric performance via Sc substitution.

N-type half-Heusler NbCoSn is a promising thermoelectric material due to favourable electronic properties. It has attracted much attention for thermoelectric applications while the desired p-type NbCoSn counterpart shows poor thermoelectric performance. In this work, p-type NbCoSn has been obtained using Sc substitution at the Nb site, and their thermoelectric properties were investigated. Of all samples, Nb0.95Sc0.05CoSn compound shows a maximum power factor of 0.54 mW/mK2 which is the highest among the previously reported values of p-type NbCoSn. With the suppression of thermal conductivity, p-type Nb0.95Sc0.05CoSn compound shows the highest measured figure of merit ZT = 0.13 at 879 K.

Exploring the Thermoelectric Performance of BaGd2NiO5 Haldane Gap Materials.

One-dimensional Haldane gap materials, such as the rare earth barium chain nickelates, have received great interest due to their vibrant one-dimensional spin antiferromagnetic character and unique structure. Herein we report how these 1D structural features can also be highly beneficial for thermoelectric applications by analysis of the system CaxBaGd2-xNiO5 0 ≤ x ≤ 0.25. Attractive Seebeck coefficients of 140-280 µV K-1 at 350-1300 K are retained even at high acceptor-substitution levels, provided by the interplay of low dimensionality and electronic correlations. Furthermore, the highly anisotropic crystal structure of Haldane gap materials allows very low thermal conductivities, reaching only 1.5 W m-1 K-1 at temperatures above 1000 K, one of the lowest values currently documented for prospective oxide thermoelectrics. Although calcium substitution in BaGd2NiO5 increases the electrical conductivity up to 5-6 S cm-1 at 1150 K < T < 1300 K, this level remains insufficient for thermoelectric applications. Hence, the combination of highly promising Seebeck coefficients and low thermal conductivities offered by this 1D material type underscores a potential new structure type for thermoelectric materials, where the main challenge will be to engineer the electronic band structure and, probably, microstructural features to further enhance the mobility of the charge carriers.

Band structure modification of the thermoelectric Heusler-phase TiFe2Sn via Mn substitution.

Doping (or substitution)-induced modification of the electronic structure to increase the electronic density of states (eDOS) near the Fermi level is considered as an effective strategy to enhance the Seebeck coefficient, and may consequently boost the thermoelectric performance. Through density-functional theory calculations of Mn-substituted TiFe2-xMnxSn compounds, we demonstrate that the d-states of the substituted Mn atoms induce a strong resonant level near the Fermi energy. Our experimental results are in good agreement with the calculations. They show that Mn substitution results in a large increase of the Seebeck coefficient, arising from an enhanced eDOS in Heusler compounds. The results prove that a proper substitution position and element selection can increase the eDOS, leading to a higher Seebeck coefficient and thermoelectric performance of ecofriendly materials.

Tailoring the structure and thermoelectric properties of BaTiO3via Eu2+ substitution.

A series of Ba1-xEuxTiO3-δ (0.1 ≤ x ≤ 0.9) phases with ∼40 nm particle size were synthesized via a Pechini method followed by annealing and sintering under a reducing atmosphere. The effects of Eu2+ substitution on the BaTiO3 crystal structure and the thermoelectric transport properties were systematically investigated. According to synchrotron X-ray diffraction data only cubic perovskite structures were observed. On the local scale below about 20 Å (equal to ∼5 unit cells) deviations from the cubic structure model (Pm3[combining macron]m) were detected by evaluation of the pair distribution function (PDF). These deviations cannot be explained by a simple symmetry breaking model like in EuTiO3-δ. The best fit was achieved in the space group Amm2 allowing for a movement of Ti and Ba/Eu along 〈110〉 of the parent unit cell as observed for BaTiO3. Density functional calculations delivered an insight into the electronic structure of Ba1-xEuxTiO3-δ. From the obtained density of states a significant reduction of the band gap by the presence of filled Eu2+ 4f states at the top of the valence band was observed. The physical property measurements revealed that barium-europium titanates exhibit n-type semiconducting behavior and at high temperature the electrical conductivity strongly depended on the Eu2+ content. Activation energies calculated from the electrical conductivity and Seebeck coefficient data indicate that at high temperatures (800 K < T < 1123 K) the conduction mechanism of Ba1-xEuxTiO3-δ (0.1 ≤ x ≤ 0.9) is a polaron hopping when 0 < x ≤ 0.6 and is a thermally activated process when 0.6 < x < 1. Besides, the thermal conductivity increases with increasing Eu2+ concentration. Due to a remarkable improvement of the power factor, Ba0.1Eu0.9TiO3-δ showed a ZT value of 0.24 at 1123 K.

The electrodeposition of FeCrNi stainless steel: microstructural changes induced by anode reactions.

The FeCrNi alloy, whose composition is close to that of stainless steel 304, was prepared by electrodeposition and characterized. Nanocrystalline FeCrNi (nc-FeCrNi) was obtained by employing a double-compartment cell where the anode is separated from the cathode compartment, while amorphous FeCrNi (a-FeCrNi) was deposited in a conventional single electrochemical cell. The carbon content of nc-FeCrNi was found to be significantly lower than that of a-FeCrNi, suggesting that carbon inclusion is responsible for the change in the microstructure. The major source of carbon is associated with the reaction compounds at the anode electrode, presumably decomposed glycine. Crystal structure analysis by XRD and TEM revealed that the as-deposited nc-FeCrNi deposits consist of α-Fe which transforms to γ-Fe upon thermal annealing. Nanoindentation tests showed that nc-FeCrNi exhibits higher hardness than a-FeCrNi, which is consistent with the inverse Hall-Petch behavior.

Recycling and Reusing of Graphite from Retired Lithium-ion Batteries: A Review.

The proliferation of rechargeable lithium-ion batteries (LIBs) over the past decade has led to a significant increase in the number of electric vehicles (EVs) powered by these batteries reaching the end of their lifespan. With retired EVs becoming more prevalent, recycling and reusing their components, particularly graphite, has become imperative as the world transitions toward electric mobility. Graphite constitutes ≈20% of LIBs by weight, making it a valuable resource to be conserved. This review presents an in-depth analysis of the current global graphite mining landscape and explores potential opportunities for the "second life" of graphitefrom depleted LIBs. Various recycling and reactivation technologies in both industry and academia are discussed, along with potential applications for recycled graphite forming a vital aspect of the waste management hierarchy. Furthermore, this review addresses the future challenges faced by the recycling industry in dealing with expired LIBs, encompassing environmental, economic, legal, and regulatory considerations. In conclusion, this review provides a comprehensive overview of the developments in recycling and reusing graphite from retired LIBs, offering valuable insights for forthcoming large-scale recycling efforts.

Emergent superstructural dynamic order due to competing antiferroelectric and antiferrodistortive instabilities in bulk EuTiO3.

Microscopic structural instabilities of EuTiO3 single crystals were investigated by synchrotron x-ray diffraction. Antiferrodistortive (AFD) oxygen octahedron rotational order was observed alongside Ti derived antiferroelectric distortions. The competition between the two instabilities is reconciled through a cooperatively modulated structure allowing both to coexist. The combination of electric and magnetic fields increases the population of the modulated AFD order, illustrating how the origin of the large magnetoelectric coupling derives from the dynamic equilibrium between AFD and polar instabilities.

Surface deformations as a necessary requirement for resistance switching at the surface of SrTiO3:N.

Atomic force microscopy (AFM), conductive AFM and electrochemical strain microscopy were used to study the topography change at the defect surface of SrTiO3:N, breakdown in the electrical conduction of the tip/sample/electrode system and ionic motion. The IV curves show resistance switching behavior in a voltage range ±6 V < U <± 10 V and a current of maximum ±10 nA. A series of sweeping IV curves resulted in an increase in ionically polarized states (surface charging), electrochemical volume (surface deformations) and sequential formations of stable surface protrusions. The surface deformations are reversible (U <± 5 V) without IV pinched hysteresis and remained stable during the resistance switching (U >± 6 V), revealing the additional necessity (albeit insufficient due to 50% yield of working cells) of surface protrusion formation for resistance switching memory.

Synchrotron high energy X-ray methods coupled to phase sensitive analysis to characterize aging of solid catalysts with enhanced sensitivity.

X-ray absorption spectroscopy and X-ray diffraction are suitable probes of the chemical state of a catalyst under working conditions but are limited to bulk information. Here we show in two case studies related to hydrothermal aging and chemical modification of model automotive catalysts that enhanced detailed information of structural changes can be obtained when the two methods are combined with a concentration modulated excitation (cME) approach and phase sensitive detection (PSD). The catalysts are subject to a modulation experiment consisting of the periodic variation of the gas feed composition to the catalyst and the time-resolved data are additionally treated by PSD. In the case of a 2 wt% Rh/Al2O3 catalyst, a very small fraction (ca. 2%) of Rh remaining exposed at the alumina surface after hydrothermal aging at 1273 K can be detected by PSD. This Rh is sensitive to the red-ox oscillations of the experiment and is likely responsible for the observed catalytic activity and selectivity during NO reduction by CO. In the case of a 1.6 wt% Pd/Al2O3-Ce(1-x)Zr(x)O2 catalyst, preliminary results of cME-XRD demonstrate that access to the kinetics of the whole material at work can be obtained. Both the red-ox processes involving the oxygen storage support and the Pd component can be followed with great precision. PSD enables the differentiation between Pd deposited on Al2O3 or on Ce(1-x)Zr(x)O2. Modification of the catalyst by phosphorous clearly induces loss of the structural dynamics required for oxygen storage capacity that is provided by the Ce(4+)/Ce(3+) pair. The two case studies demonstrate that detailed kinetics of subtle changes can be uncovered by the combination of in situ X-ray absorption and high energy diffraction methods with PSD.

Perovskite-related oxynitrides in photocatalysis.

Over the last decades photocatalytic water splitting has become of increasing importance for fundamental and applied research, since the direct conversion of sunlight into chemical energy via the production of H2 has the potential to contribute to the world's energy needs without CO2 generation. One of the unsolved challenges consists of finding a highly efficient photocatalyst that is cheap, environmentally friendly, contains exclusively abundant elements, is (photo)chemically stable and absorbs visible light. Photocatalytic efficiency is closely connected to both structural properties like crystallinity, particle size and surface area and to electronic properties like the band gap and the quantum efficiency. Hence extensive control over a large parameter field is necessary to design a good photocatalyst. A material class where the structure-composition-property relations and the influence of substitution effects are well studied is the perovskite-type family of compounds. The perovskite-related oxynitrides belong to this very flexible compound family where many of the necessary characteristics for a photocatalyst are already given and some of the intrinsic properties like the band gap can be tuned within the same crystal structure by substitution. In this work we present materials' design concepts to improve the photocatalytic efficiency of a perovskite-type catalyst and describe their effects on the photocatalytic activity.

Quantitative Characterization of Local Thermal Properties in Thermoelectric Ceramics Using "Jumping-Mode" Scanning Thermal Microscopy.

Thermoelectric conversion may take a significant share in future energy technologies. Oxide-based thermoelectric composite ceramics attract attention for promising routes for control of electrical and thermal conductivity for enhanced thermoelectric performance. However, the variability of the composite properties responsible for the thermoelectric performance, despite nominally identical preparation routes, is significant, and this cannot be explained without detailed studies of thermal transport at the local scale. Scanning thermal microscopy (SThM) is a scanning probe microscopy method providing access to local thermal properties of materials down to length scales below 100 nm. To date, realistic quantitative SThM is shown mostly for topographically very smooth materials. Here, methods for SThM imaging of bulk ceramic samples with relatively rough surfaces are demonstrated. "Jumping mode" SThM (JM-SThM), which serves to preserve the probe integrity while imaging rough surfaces, is developed and applied. Experiments with real thermoelectric ceramics show that the JM-SThM can be used for meaningful quantitative imaging. Quantitative imaging is performed with the help of calibrated finite-elements model of the SThM probe. The modeling reveals non-negligible effects associated with the distributed nature of the resistive SThM probes used; corrections need to be made depending on probe-sample contact thermal resistance and probe current frequency.

A facile strategy for reclaiming discarded graphite and harnessing the rate capabilities of graphite anodes.

Graphite negative electrodes are unbeaten hitherto in lithium-ion batteries (LiBs) due to their unique chemical and physical properties. Thus, the increasing scarcity of graphite resources makes smart recycling or repurposing of discarded graphite particularly imperative. However, the current recycling techniques still need to be improved upon with urgency. Herein a facile and efficient hydrometallurgical process is reported to effectively regenerate aged (39.5 %, 75 % state-of-health, SOH) scrapped graphite (SG) from end-of-life lithium-ion batteries. Ultimately, the first cycle reversible capacity of SG1 (SOH = 39.5 %) improved from 266 mAh/g to 337 mAh/g while 330 mAh/g (98 %) remain after 100 cycles at 0.5 C. The reversible capacity for the first cycle of SG2 (SOH = 75 %) boosted from 335 mAh/g to 366 mAh/g with the capacity retention of 99.3 % after 100 cycles at 0.5 C, which is comparable with the benchmark commercial graphite. The regenerated graphites RG1 and RG2 exhibit excellent output characteristics even increasing the rate up to 4 C. This is the best rate level reported in the literature to date. Finally, the diffusion coefficient of Li ions during deintercalation and intercalation in the regenerated graphites have been measured by galvanostatic intermittent titration technique (GITT), determining values 2 orders-of-magnitude higher than that of the spent counterparts. Taking advantage of the synergistic effect of acid leaching and heat treatment, this strategy provides a simple and up-scalable method to recycle graphitic anodes.

Hydrogen-Tolerant La0.6Ca0.4Co0.2Fe0.8O3-d Oxygen Transport Membranes from Ultrasonic Spray Synthesis for Plasma-Assisted CO2 Conversion.

La0.6Ca0.4Co1-xFexO3-d in its various compositions has proven to be an excellent CO2-resistant oxygen transport membrane that can be used in plasma-assisted CO2 conversion. With the goal of incorporating green hydrogen into the CO2 conversion process, this work takes a step further by investigating the compatibility of La0.6Ca0.4Co1-xFexO3-d membranes with hydrogen fed into the plasma. This will enable plasma-assisted conversion of the carbon monoxide produced in the CO2 reduction process into green fuels, like methanol. This requires the La0.6Ca0.4Co1-xFexO3-d membranes to be tolerant towards reducing conditions of hydrogen. The hydrogen tolerance of La0.6Ca0.4Co1-xFexO3-d (x = 0.8) was studied in detail. A faster and resource-efficient route based on ultrasonic spray synthesis was developed to synthesise the La0.6Ca0.4Co0.2Fe0.8O3-d membranes. The La0.6Ca0.4Co0.2Fe0.8O3-d membrane developed using ultrasonic spray synthesis showed similar performance in terms of its oxygen permeation when compared with the ones synthesised with conventional techniques, such as co-precipitation, sol-gel, etc., despite using 30% less cobalt.

Synthesis, characterization, electronic and gas-sensing properties towards H2 and CO of transparent, large-area, low-layer graphene.

Low-layered, transparent graphene is accessible by a chemical vapor deposition (CVD) technique on a Ni-catalyst layer, which is deposited on a <100> silicon substrate. The number of graphene layers on the substrate is controlled by the grain boundaries in the Ni-catalyst layer and can be studied by micro Raman analysis. Electrical studies showed a sheet resistance (R(sheet)) of approximately 1435 Ω per □, a contact resistance (R(c)) of about 127 Ω, and a specific contact resistance (R(sc)) of approximately 2.8×10(-4) â€…Ω cm(2) for the CVD graphene samples. Transistor output characteristics for the graphene sample demonstrated linear current/voltage behavior. A current versus voltage (I(ds)-V(ds)) plot clearly indicates a p-conducting characteristic of the synthesized graphene. Gas-sensor measurements revealed a high sensor activity of the low-layer graphene material towards H(2) and CO. At 300 °C, a sensor response of approximately 29 towards low H(2) concentrations (1 vol %) was observed, which is by a factor of four higher than recently reported.

Perovskite-supported palladium for methane oxidation - structure-activity relationships.

Palladium is the precious metal of choice for methane oxidation and perovskite-type oxides offer the possibility to stabilize it as PdO, considered crucial for catalytic activity. Pd can adopt different oxidation and coordination states when associated with perovskite-type oxides. Here, we review our work on the effect of perovskite composition on the oxidation and coordination states of Pd and its influence on catalytic activity for methane oxidation in the case of typical Mn, Fe and Co perovskite-based oxidation catalysts. Especially X-ray absorption near edge structure (XANES) spectroscopy is shown to be crucial to fingerprint the different coordination states of Pd. Pd substitutes Fe and Co in the octahedral sites but without modifying catalytic activity with respect to the Pd-free perovskite. On LaMnO(3) palladium is predominantly exposed at the surface thus bestowing catalytic activity for methane oxidation. However, the occupancy of B-cation sites of the perovskite structure by Pd can be exploited to cyclically activate Pd and to protect it from particle growth. This is explicitly demonstrated for La(Fe, Pd)O(3), where catalytic activity for methane oxidation is enhanced under oscillating redox conditions at 500 °C, therefore paving the way to the practical application in three-way catalysts for stoichiometric natural gas engines.

Hot-Water Hemicellulose Extraction from Fruit Processing Residues.

Hemicelluloses are an abundant biopolymer resource with interesting properties for applications in coatings and composite materials. The objective of this investigation was to identify variables of industrially relevant extraction processes that increase the purity of hemicelluloses extracted from fruit residues. Our main finding is that extraction with subcritical water, followed by precipitation with alcohol, can be adjusted to yield products with a purity of at least 90%. Purity was determined based on the total concentration of glucose, galactose, xylose, arabinose, and mannose after hydrolysis with sulfuric acid. In the first experimental design (DoE methodology), the effects of extraction temperature (95-155 °C) and time (20-100 min) on yield and purity were studied. A clear trade-off between yield and purity was observed at high temperatures, indicating the selective removal of impurities. In the second experimental design, the influence of extract pH and alcohol concentration on yield and purity was investigated for the raw extract and a concentrate of this extract with 1/6 of the original volume. The concentrate was obtained by ultrafiltration through ceramic hollow-fiber membranes. The highest purity of 96% was achieved with the concentrate after precipitating with 70% alcohol. Key factors for the resource efficiency of the overall process are addressed. It is concluded that extraction with subcritical water and ultrafiltration are promising technologies for producing hemicelluloses from fruit residues for material applications.