Plasma-Enabled Process with Single-Atom Catalysts for Sustainable Plastic Waste Transformation.

In this study, we present a novel plasma-enabled strategy for the rapid breakdown of various types of plastic wastes, including mixtures, into high-value carbon nanomaterials and hydrogen. The H2 yield and selectivity achieved through the catalyst-free plasma-enabled strategy are 14.2 and 5.9 times higher, respectively, compared to those obtained with conventional thermal pyrolysis. It is noteworthy that this catalyst-free plasma alone approach yields a significantly higher energy yield of H2 (gH2/kWh) compared to other pyrolysis processes. By coupling plasma pyrolysis with thermal catalytic process, employing of 1 wt.% M/CeO2 atomically dispersed catalysts can further enhance hydrogen production. Specifically, the 1 wt.% Co/CeO2 catalyst demonstrated excellent catalytic performance throughout the 10 cycles of plastic waste decomposition, achieving the highest H2 yield of 46.7 mmol/gplastic (equivalent to 64.4% of theoretical H2 production) and nearly 100% hydrogen atom recovery efficiency at the 7th cycle. Notably, the H2 yield achieved over the atomically dispersed Fe on CeO2 surface in the integrated plasma-thermal catalytic process is comparable to that obtained with Fe particles on CeO2 surface (10 wt.%). This innovative and straightforward approach provides a promising and expedient strategy for continuously converting diverse plastic waste streams into high-value products conducive to a circular plastic economy.

Nanoscale Imaging and Measurements of Grain Boundary Thermal Resistance in Ceramics with Scanning Thermal Wave Microscopy.

Material thermal conductivity is a key factor in various applications, from thermal management to energy harvesting. With microstructure engineering being a widely used method for customizing material properties, including thermal properties, understanding and controlling the role of extended phonon-scattering defects, like grain boundaries, is crucial for efficient material design. However, systematic studies are still lacking primarily due to limited tools. In this study, we demonstrate an approach for measuring grain boundary thermal resistance by probing the propagation of thermal waves across grain boundaries with a temperature-sensitive scanning probe. The method, implemented with a spatial resolution of about 100 nm on finely grained Nb-substituted SrTiO3 ceramics, achieves a detectability of about 2 × 10-8 K m2 W-1, suitable for chalcogenide-based thermoelectrics. The measurements indicated that the thermal resistance of the majority of grain boundaries in the STiO3 ceramics is below this value. While there are challenges in improving sensitivity, considering spatial resolution and the amount of material involved in the detection, the sensitivity of the scanning probe method is comparable to that of optical thermoreflectance techniques, and the method opens up an avenue to characterize thermal resistance at the level of single grain boundaries and domain walls in a spectrum of microstructured materials.

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.

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.

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.

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.

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.

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.

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.

Natural wood templated hierarchically cellular NbC/Pyrolytic carbon foams as Stiff, lightweight and High-Performance electromagnetic shielding materials.

Hierarchically cellular, stiff, and lightweight niobium carbide (NbC)-pyrolytic carbon (PyC) monolithic foam composites possessing excellent electromagnetic interference shielding effectiveness (EMI SE) were developed via a natural wood template-based method. Pyrolytic carbon derived from the decomposed cellulose in the wood worked as the carbon source for the growth of NbC phase, and the NbC-PyC heterogeneous nano-interface formed between the residual PyC and the freshly formed NbC. Multi-loss mechanisms (e.g. conductive loss, dipole polarization loss, and especially interface polarization loss) were established by controlling the NbC content and residual PyC phase in the NbC-PyC foams, which significantly improved the absorption capability. Compared to 28.0 dB of PyC monolith, the EMI SE of NbC-PyC foam can reach 54.8 dB when the thickness is 0.5 mm, which outperforms the other porous-based shielding materials. Due to the highly porous structure of pristine wood, the resulting NbC-PyC foam exhibited a low density of 0.48 g/cm3, which is ~ 1/16 of dense NbC (7.78 g/cm3). Generally, this work introduces innovative ideas for designing novel and advanced transition metal carbide-carbon composite materials.

Effects of Doping Ni on the Microstructures and Thermoelectric Properties of Co-Excessive NbCoSn Half-Heusler Compounds.

The half-Heusler (HH) compound NbCoSn with 18 valence electrons is a promising thermoelectric (TE) material due to its appropriate electrical properties as well as its suitable thermal and chemical stability. Nowadays, doping/substitution and tailoring of microstructures are common experimental approaches to enhance the TE performance of HH compounds. However, detailed theoretical insights into the effects of doping on the microstructures and TE properties are still missing. In this work, the microstructure of NbCoSn was tailored through precipitating the full-Heusler phases in the matrix by changing the nominal ratio of Co and Ni on the Co sites, focusing on the resulting TE properties. Further, first-principles calculations were employed to understand the relationship between the microstructure and the TE properties from the thermodynamic point of view. Detailed analysis of the electronic structure reveals that the presence of excess Co/Ni contributes to the increasing carrier concentration. Through an increase in the electrical conductivity and a reduction in the thermal conductivity, the TE performance is improved. Therefore, the present work offers a new pathway and insights to enhance the TE properties by modifying the microstructure of HH compounds via tailoring the chemical compositions.

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.

Synthesis and Characterization of 40 wt % Ce0.9Pr0.1O2-δ-60 wt % NdxSr1-xFe0.9Cu0.1O3-δ Dual-Phase Membranes for Efficient Oxygen Separation.

Dense, H2- and CO2-resistant, oxygen-permeable 40 wt % Ce0.9Pr0.1O2-δ-60 wt % NdxSr1-xFe0.9Cu0.1O3-δdual-phase membranes were prepared in a one-pot process. These Nd-containing dual-phase membranes have up to 60% lower material costs than many classically used dual-phase materials. The Ce0.9Pr0.1O2-δ-Nd0.5Sr0.5Fe0.9Cu0.1O3-δ sample demonstrates outstanding activity and a regenerative ability in the presence of different atmospheres, especially in a reducing atmosphere and pure CO2 atmosphere in comparison with all investigated samples. The oxygen permeation fluxes across a Ce0.9Pr0.1O2-δ-Nd0.5Sr0.5Fe0.9Cu0.1O3-δ membrane reached up to 1.02 mL min-1 cm-2 and 0.63 mL min-1 cm-2 under an air/He and air/CO2 gradient at T = 1223 K, respectively. In addition, a Ce0.9Pr0.1O2-δ-Nd0.5Sr0.5Fe0.9Cu0.1O3-δ membrane (0.65 mm thickness) shows excellent long-term self-healing stability for 125 h. The repeated membrane fabrication delivered oxygen permeation fluxes had a deviation of less than 5%. These results indicate that this highly renewable dual-phase membrane is a potential candidate for long lifetime, high temperature gas separation applications and coupled reaction-separation processes.

Effects of Nanodomains on Local and Long-Range Phase Transitions in Perovskite-Type Eu0.8Ca0.2TiO3-δ.

The determination of reversible phase transitions in the perovskite-type thermoelectric oxide Eu0.8Ca0.2TiO3-δ is fundamental, since structural changes largely affect the thermal and electrical transport properties. The phase transitions were characterized by heat capacity measurements, Rietveld refinements, and pair distribution function (PDF) analysis of the diffraction data to achieve information on the phase transition temperatures and order as well as structural changes on the local level and the long range. On the long-range scale, Eu0.8Ca0.2TiO3-δ showed a phase transition sequence during heating from cubic at 100 < T < 592 K to tetragonal and finally back to cubic at T > 846 K. The phase transition at T = 592 K (diffraction)/606 K (thermal analysis) was reversible with a very small thermal hysteresis of about 2 K. The local structure at 100 K was composed of a complex nanodomain arrangement of Amm2- and Pbnm-like local structures with different coherence lengths. Since in Eu0.8Ca0.2TiO3-δ the amount of Pbnm domains was too small to percolate, the competition of ferroelectrically distorted octahedra (Amm2 as in BaTiO3) and rigid, tilted octahedra (Pbnm as in CaTiO3) resulted in a cubic long-range structure at low temperatures.

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 Tantalum as a Potential Dopant to Promote the Thermoelectric Performance of Zinc Oxide.

Zinc oxide (ZnO) has being recognised as a potentially interesting thermoelectric material, allowing flexible tuning of the electrical properties by donor doping. This work focuses on the assessment of tantalum doping effects on the relevant structural, microstructural, optical and thermoelectric properties of ZnO. Processing of the samples with a nominal composition Zn1-xTaxO by conventional solid-state route results in limited solubility of Ta in the wurtzite structure. Electronic doping is accompanied by the formation of other defects and dislocations as a compensation mechanism and simultaneous segregation of ZnTa2O6 at the grain boundaries. Highly defective structure and partial blocking of the grain boundaries suppress the electrical transport, while the evolution of Seebeck coefficient and band gap suggest that the charge carrier concentration continuously increases from x = 0 to 0.008. Thermal conductivity is almost not affected by the tantalum content. The highest ZT~0.07 at 1175 K observed for Zn0.998Ta0.002O is mainly provided by high Seebeck coefficient (-464 V/K) along with a moderate electrical conductivity of ~13 S/cm. The results suggest that tantalum may represent a suitable dopant for thermoelectric zinc oxide, but this requires the application of specific processing methods and compositional design to enhance the solubility of Ta in wurtzite lattice.

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.

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.