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Facile preparation of Al2O3–ZnO nanocomposites, followed by a spark plasma sintering process at high temperature, achieved a thermoelectric ZT value of 0.91 at 860 K.

Organic Phase Change Materials (oPCMs) are practical and efficient materials in regulating temperature changes, with broad applications including building material, textiles, and food packaging. However, their flammability poses the main challenge to their widespread applications. This review summarizes various approaches to reduce the flammability of oPCMs including incorporation of flame retardants in shape stabilized PCMs and microencapsulated PCMs, chemical transformations and surface coating, paying particular attentions to the flammability parameters such as limiting oxygen index (LOI), total heat released (THR), peak heat release rate (pHRR) as well as the mechanisms of fire retardancy. Flame-retardant oPCM for practical applications such as plasterboards and fabrics will be highlighted. Further strategies to enhance flame retardant properties of oPCM, such as, incorporation of synergistic flame retardants, chemical modification of PCM (e.g. intrinsically flame-retardant oPCM), have been proposed and commented in the conclusion of this paper.

Doping high electrical conductivity Nb5Ge3 precipitates into GeTe results in nanoprecipitates phonon scattering, while retaining electrical mobility. As a result, thermoelectric zT of GeTe is drastically enhanced to 2.0 at 723 K.

We advocate triplet–triplet annihilation upconverters as candidates for blue FuLEDs (OLEDs enhanced by triplet-fusion), demonstrating here with the sky-blue DPBF. Its TTA or triplet-fusion behaviour is explored in both solutions and FuLED devices.

Electronic waste (e-waste) recycling is one of the central frameworks of the circular economy.

GeTe is among the best medium-temperature thermoelectrics. Its high performance originates from band convergence at the phase transition and low lattice thermal conductivity due to Peierls distortion. In most studies, the peak performance (zT) in GeTe is achieved by designing and optimizing its electronic and thermal transport properties near its phase transition temperature (700 K). However, for efficient power harvesting, a high average zT (zT(ave)) across a wide temperature range is desirable. This calls for a holistic performance evaluation and enhancement not only near 700 K, but also at room temperature. In this work, we leveraged on the confluence of performance enhancement strategies via Cu2Te alloying and In resonant doping to achieve a record-high room temperature power factor of 2800 mu W mK-2, and an average power factor of 3700 mu W mK-2 between 323 and 773 K. The magnitude of the room temperature power factor is comparable to that of the state-of-the-art Bi2Te3 based compounds. In the optimized sample with Bi doping, a room temperature zT of 0.5 is achieved, highest for lead-free GeTe. Ultimately, a high peak zT of 2.1 at 723 K and single leg power conversion efficiency of 11.8% were achieved between 323 and 745 K, which are among the highest reported for lead-free GeTe. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) The authors acknowledge support from the A*STAR's Science and Engineering Research Council Sustainable Hybrid Lighting System for Controlled Environment Agriculture programme: A19D9a0096. Q. Yan acknowledges Singapore MOE AcRF Tier 2 under Grant No. 2018-T2-1-010, Singapore A*STAR project A19D9a0096. A. S. acknowledges funding from the A*STAR's Career Development Award number C210112022.

Molybdenum disulfide (MoS2) has attracted significant attention due to its good charge carrier mobility, high on/off ratio in field-effect transistors and novel layer-dependent band structure, with potential applications in modern electronic, photovoltaic and valleytronic devices. Despite these advantages, its thermal transport property has often been neglected until recently. In this work, we probe phonon transport in few-layer MoS2 flakes with various point defect concentrations enabled by helium ion (He+) irradiation. For the first time, we experimentally show that Mo-vacancies greatly impede phonon transport compared to S-vacancies, resulting in a larger reduction of thermal conductivity. Furthermore, Raman characterization shows that the in-plane Raman-sensitive peak E2g1 was red-shifted with increasing defect concentration, corresponding to the gradual damage of the in-plane crystalline networks and the gradual reduction in the measured thermal conductivity. Our work provides a practical approach for atomic-level engineering of phonon transport in two-dimensional (2D) layered materials by selectively removing elements, thus holding potential applications in designing thermal devices based on various emerging 2D materials.

Nanostructuring is an effective way to concurrently improve thermal and electrical parameters in some thermoelectric material systems. Herein, we have established that thermoelectric properties of ...

Melt spinning has proven effective in maintaining chemical homogeneity and introducing multiscale microstructures that can reduce the lattice thermal conductivity and consequently enhance the thermoelectric performance of consolidated bulk materials. In this work, p-type Bi0.52Sb1.48Te3 bulk alloys are fabricated by melt spinning (MS) followed by subsequent plasma activated sintering (PAS). The influence of different MS atmospheres (air, Ar, N2, and He) on the morphologies of MS ribbons and the thermoelectric properties of MS-PAS bulk materials has been investigated systematically. Because of the relatively high thermal conductivity, a He atmosphere expedites the heat dissipation in the MS process and results in severe sublimation of tellurium and thus inferior thermoelectric performance. In contrast, an Ar atmosphere can essentially prevent heat loss of the fusant and suppress the sublimation of tellurium. Consequently, the corresponding Bi0.52Sb1.48Te3 sample (MS in Ar atmosphere) presents the highest peak ZT and average ZT values of 1.09 (at 340 K) and 0.81 (in 300-500 K), respectively. The average ZT of the sample prepared using an Ar atmosphere is almost three times the one prepared using a He atmosphere. This reflects the importance of using the appropriate atmosphere during the melt-spinning process. This result, which indicates that melt spinning in an Ar atmosphere is preferable to avoid heat loss, can also be extended to other materials.

Transition metal dichalcogenides (TMDs) possess intrinsic spin–orbit interaction (SOI) with high potential to be exploited for various quantum phenomena. SOI allows the manipulation of spin degree of freedom by controlling the carrier's orbital motion via mechanical strain. Here, strain modulated spin dynamics in bilayer MoS2 field-effect transistors (FETs) fabricated on crested substrates are demonstrated. Weak antilocalization (WAL) is observed at moderate carrier concentrations, indicating additional spin relaxation path caused by strain fields arising from substrate crests. The spin lifetime is found to be inversely proportional to the momentum relaxation time, which follows the Dyakonov–Perel spin relaxation mechanism. Moreover, the spin–orbit splitting is obtained as 37.5 ± 1.4 meV, an order of magnitude larger than the theoretical prediction for monolayer MoS2, suggesting the strain enhanced spin-lattice coupling. The work demonstrates strain engineering as a promising approach to manipulate spin degree of freedom toward new functional quantum devices. Agency for Science, Technology and Research (A*STAR) National Research Foundation (NRF) Published version T.L.acknowledges the Natural Science Foundation of Shanghai (Grant No.22ZR1405700). D.X. acknowledges the National Natural Science Foundation (NSF) of China (Grant No. 62104041) and Shanghai Sailing Program(Grant No. 21YF1402600). J.W. acknowledges the Advanced Manufacturing and Engineering Young Individual Research Grant (AME YIRG Grant No.: A2084c170) and SERC Central Research Fund (CRF). S.G. acknowledges support from National Research Foundation, Prime Minister’s Office, Singapore, under Competitive Research Program (Award No. NRF-CRP13-2014-03).

Two decades after the rapid expansion of photovoltaics, the number of solar panels reaching end-of-life is increasing. While precious metals such as silver and copper are usually recycled, silicon, which makes up the bulk of a solar cells, goes to landfills. This is due to the defect- and impurity-sensitive nature in most silicon-based technologies, rendering it uneconomical to purify waste silicon. Thermoelectrics represents a rare class of material in which defects and impurities can be engineered to enhance the performance. This is because of the majority-carrier nature, making it defect- and impurity-tolerant. Here, the upcycling of silicon from photovoltaic (PV) waste into thermoelectrics is enabled. This is done by doping 1% Ge and 4% P, which results in a figure of merit (zT) of 0.45 at 873 K, the highest among silicon-based thermoelectrics. The work represents an important piece of the puzzle in realizing a circular economy for photovoltaics and electronic waste. Agency for Science, Technology and Research (A*STAR) Ministry of National Development (MND) National Environmental Agency (NEA) A.S. acknowledges funding from A*STAR (Agency of Science, Technology and Research) Career Development Fund (CDF) no. C210112022. J.X acknowledges A*STAR “Sustainable Hybrid Lighting System for Controlled Environment Agriculture programme”: A19D9a0096. Z.L. would also like to express gratitude to the financial support from the A∗STAR’s Science and Engineering Research Council (SERC) Central Research Fund (Use-inspired Basic Research) for this work. N.M. and Q.Y. acknowledge grant award from NEA (National Environmental Agency, Singapore) and Ministry of National Development (MND, Singapore) titled “Singapore–CEA Alliance for Research in Circular Economy (SCARCE, award number USS-IF-2018-4),” which is a joint lab set up between Nanyang Technological University (NTU, Singapore) and the French Alternative Energies and Atomic Energy Commission (CEA, France).

Thermoelectric materials have obtained worldwide attention as they are attractive for waste heat recovery and solid-state cooling. However, their performance is usually sensitive to material compositions, which is less favorable for industrial applications. In this work, we developed composition-insensitive GeTe-based compounds ((100-x-y)%GeTe-x%CuBiSe2-y%PbTe, CBSx-Pby) with high ZTmax as well as ZTave values. The compositional insensitivity can be associated with the persistently high quality factors across the range of compositions. This is largely due to the interplay between electrical and thermal transport caused by the synergy of CuBiSe2 and PbTe alloying. CuBiSe2 alloying can effectively tune the carrier concentrations, while PbTe alloying can significantly decrease the thermal conductivity at a minor sacrifice of electrical properties. The combined effects of CuBiSe2 and PbTe alloying lead to high carrier mobility of 60 cm2V−1s−1 and low thermal conductivities for CBSx-Pby samples simultaneously. Consequently, high ZTave values of 1.4–1.5 in the temperature range of 400 K and 773 K for broad compositions (CBS3-Pby, y = 2 – 8 and CBSx-Pb6, x = 2 – 5) are achieved. A single-leg module is also fabricated, which shows a high power density of 1.46 W/cm2 and an excellent efficiency of 13.4%. The high ZTave with compositional insensitivity and the outstanding module performance demonstrate the promising large-scale application of the developed GeTe-based compositions. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) Submitted/Accepted version This study was supported by the Basic Science Center Project of NSFC under Grant No. 51788104, the National Key R&D Program of China No. 2018YFB0703603, the MOE Tier 1 RG128/21 and Singapore A*STAR project A19D9a0096. A. Suwardi acknowledges funding from Agency for Science, Technology and Research (A*STAR), Singapore Career Development Fund (CDF) C210112022.

Neuromorphic computing provides a means for achieving faster and more energy efficient computations than conventional digital computers for artificial intelligence (AI). However, its current accuracy is generally less than the dominant software-based AI. The key to improving accuracy is to reduce the intrinsic randomness of memristive devices, emulating synapses in the brain for neuromorphic computing. Here using a planar device as a model system, the controlled formation of conduction channels is achieved with high oxygen vacancy concentrations through the design of sharp protrusions in the electrode gap, as observed by X-ray multimodal imaging of both oxygen stoichiometry and crystallinity. Classical molecular dynamics simulations confirm that the controlled formation of conduction channels arises from confinement of the electric field, yielding a reproducible spatial distribution of oxygen vacancies across switching cycles. This work demonstrates an effective route to control the otherwise random electroforming process by electrode design, facilitating the development of more accurate memristive devices for neuromorphic computing.

Non-covalent interactions have gained increasing attention for use as a driving force to fabricate various supramolecular architectures, exhibiting great potential in crystal and materials engineering and supramolecular chemistry. As one of the most powerful non-covalent bonds, the halogen bond has recently received increasing attention in functional nanomaterial design. The present review describes the latest studies based on halogen bonding induced self-assembly and its applications. Due to the high directionality and controllable interaction strength, halogen bonding can provide a facile platform for the design and synthesis of a myriad of nanomaterials. In addition, both the fundamental aspects and the real engineering applications are discussed, which encompass molecular recognition and sensing, organocatalysis, and controllable multifunctional materials and surfaces.

Phase Change Materials (PCM) are efficient materials for thermal management and energy storage due to its high latent heat and recyclability. Many strategies have been employed to form stabilize PCMs through their phase transition; however these materials are almost invariably rigid. Herein a novel flexible form-stable PCM composite was successfully prepared by physical mixing and low temperature curing. They were well characterized in terms of various techniques including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), mechanical and leakage test, etc. A leakage test showed that the composite with 50% octadecane loading was form-stable with only 2.44% leakage. From the differential scanning calorimetry (DSC) results, the octadecane/silicone (Oct/Si) composite was found to possess a latent heat of 103.8 J/g, and an upshift in phase transition temperature was also observed from octadecane's melting point of 30.3 °C to between 34.4 and 37.8 °C, probably due to thermal insulation or microencapsulation by the silicone matrix. Thermogravimetric analysis (TGA) data supported its good thermal stability within this temperature range and mechanical testing of the composites further confirmed its flexibility and durability as evidenced by the Young's Modulus at 388.92 kPa and elongation at 341.42%, making Oct/Si composites useful for application in areas of temperature regulation, cooling, energy harvesting and wearable devices. Agency for Science, Technology and Research (A*STAR) Published version The authors acknowledge the financial support from the Agency for Science, Technology and Research (A*STAR), Science and Engineering Research Council, and A*ccelerate Technologies for this work (Grant No.: GAP/2019/00314).

The discovery of novel materials for thermoelectric energy conversion has potential to be accelerated by data-driven screening combined with high-throughput calculations. One way to increase the efficacy of successfully choosing a candidate material is through its evaluation using transport descriptors. Using a data-driven screening, we selected 12 potential candidates in the trigonal ABX2 family, followed by charge transport property simulations from first principles. The results suggest that carrier scattering processes in these materials are dominated by ionised impurities and polar optical phonons, contrary to the oft-assumed acoustic-phonon-dominated scattering. Using these data, we further derive ground-state transport descriptors for the carrier mobility and the thermoelectric powerfactor. In addition to low carrier mass, high dielectric constant was found to be an important factor towards high carrier mobility. A quadratic correlation between dielectric constant and transport performance was established and further validated with literature. Looking ahead, dielectric constant can potentially be exploited as an independent criterion towards improved thermoelectric performance. Combined with calculations of thermal conductivity including Peierls and inter-branch coherent contributions, we conclude that the trigonal ABX2 family has potential as high performance thermoelectrics in the intermediate temperature range for low grade waste heat harvesting. Agency for Science, Technology and Research (A*STAR) National Research Foundation (NRF) T. D., M. B. S., G. W., and S.-W. Y. acknowledge the support of Agency for Science, Technology and Research (A*STAR) of Singapore (Grant No. 1527200024). J. R.-G., D. V. M. R., P. K., A. A., and K. H. would like to acknowledge the Accelerated Materials Development for Manufacturing Program at A*STAR via the AME Programmatic Fund by the Agency for Science, Technology and Research under Grant No. A1898b0043. K. H. would like to acknowledge funding via the NRF Fellowship NRF-NRFF13-2021. J. R.-G. and I. N. would like to thank A*STAR Graduate Academy's ARAP programme for funding J. R.-G.'s graduate studies in IMRE, A*STAR. M. O. and J. S. would like to acknowledge JSPS KAKENHI (19H00744, 20K14661) and JST CREST (JPMJCR20Q3).

Direct patterning of thermoelectric metal chalcogenides can be challenging and is normally constrained to certain geometries and sizes. Here we report the synthesis, characterization, and direct writing of sub-10 nm wide bismuth sulfide (Bi2S3) using a single-source, spin-coatable, and electron-beam-sensitive bismuth(III) ethylxanthate precursor. In order to increase the intrinsically low carrier concentration of pristine Bi2S3, we developed a self-doping methodology in which sulfur vacancies are manipulated by tuning the temperature during vacuum annealing, to produce an electron-rich thermoelectric material. We report a room-temperature electrical conductivity of 6 S m–1 and a Seebeck coefficient of −21.41 μV K–1 for a directly patterned, substoichiometric Bi2S3 thin film. We expect that our demonstration of directly writable thermoelectric films, with further optimization of structure and morphology, can be useful for on-chip applications.

Effective mass has been touted as an important descriptor in thermoelectric transport. Based on theoretical intuition, some reports demonstrate that low effective mass is preferable in thermoelectrics, while others propose that a large density of states effective mass for high Seebeck is the pathway to better thermoelectric materials. Leveraging on the available data from Materials Project, we present a data-driven conclusion that corroborates the central role of effective mass in high-throughput thermoelectric materials screening. The efficacy of the Fermi surface complexity factor in enhancing power factor is analyzed in relation to the effective mass for a large number of compounds. Here, we show that starting with a low inertial effective mass material, any changes in Fermi surface complexity factor will have a pronounced effect on its thermoelectric power factor and verify this strategy in recently discovered thermoelectric materials. This can be accomplished by employing band engineering using doping, or symmetry distortion, and starting with a base material that intrinsically possesses a low inertial effective mass.

SARS-CoV-2 presence in wastewater has been reported in several studies and has received widespread attention among the Wastewater-based epidemiology (WBE) community. Such studies can potentially be used as a proxy for early warning of potential COVID-19 outbreak, or as a mitigation measure for potential virus transmission via contaminated water. In this review, we summarized the latest understanding on the detection, concentration, and evaluation of SARS-CoV-2 in wastewater. Importantly, we discuss factors affecting the quality of wastewater surveillance ranging from temperature, pH, starting concentration, as well as the presence of chemical pollutants. These factors greatly affect the reliability and comparability of studies reported by various communities across the world. Overall, this review provides a broadly encompassing guidance for epidemiological study using wastewater surveillance.

Thermoelectrics can convert waste heat to electricity and vice versa. The energy conversion efficiency depends on materials figure of merit, zT, and Carnot efficiency. Due to the higher Carnot efficiency at a higher temperature gradient, high-temperature thermoelectrics are attractive for waste heat recycling. Among high-temperature thermoelectrics, silicon-based compounds are attractive due to the confluence of light weight, high abundance, and low cost. Adding to their attractiveness is the generally defect-tolerant nature of thermoelectrics. This makes them a suitable target application for recycled silicon waste from electronic (e-waste) and solar cell waste. In this review, we summarize the usage of high-temperature thermoelectric generators (TEGs) in applications such as commercial aviation and space voyages. Special emphasis is placed on silicon-based compounds, which include some recent works on recycled silicon and their thermoelectric properties. Besides materials design, device designing considerations to further maximize the energy conversion efficiencies are also discussed. The insights derived from this review can be used to guide sustainable recycling of e-waste into thermoelectrics for power harvesting.

Microencapsulated phase change materials (MEPCMs) possess great potential as thermal energy storage materials for heating and cooling applications in industries. However, one important disadvantage of many MEPCMs is their low thermal conductivity. To enhance the thermal conductivity of PCMs, additives with high thermal conductivity are usually added into PCMs. However, these additives might not be mixed uniformly with the PCMs. Herein we report the first use of a polyurethane acrylic lacquer and hardener (PALH) as an adhesive to allow the additives to be uniformly coated on the surface of the shell of MEPCMs. A vacuum filtration assisted drop-casting method was employed to coat nano additives such as nano graphite, copper nanowires, titanium carbide and multi-walled carbon nanotubes (MWCNT) on the shell of commercial MEPCM (MPCM 28D) using PALH. MWCNT was found to be the most effective in improving the thermal conductivity of the MEPCM, giving an 87% increase when just 5 wt.% of MWCNT was added. Field Emission Scanning Electron Microscope (FESEM) images confirm the successful uniform coating of MWCNT on the shell of MPCM 28D, while Differential Scanning Calorimeter (DSC) thermograms show that the phase change properties of MPCM 28D remain largely similar to the pre-coated MPCM 28D. Furthermore, thermal cycling tests indicate that MWCNT do not significantly affect the energy storage and release performance of MPCM 28D. These results indicate that coating MEPCMs with MWCNT can be a simple and effective method to improve their overall thermal conductivity without sacrificing its performance.

Hot corrosions of laser-cladded inconel 625 in molten salt of Na2SO4-MgSO4 mixture have been studied at 900 °C to address its anticorrosion behaviors. Elemental and microstructural characterizations provide direct evidence for the formation of MgO/Cr2O3 external layers and the outward-diffusion of Cr atoms. The Cr-depletion promotes precipitation of δ-Ni3(Nb/Mo), nucleation and accumulation of dislocations, pores, and internal spallation of the corroded alloy. They also provide evidence for the diffusion of sulfur into the near-surface region, leading to the formation of internal sulfide scales (i.e., Nb4−xCrxS6, CrS, and MnCr2S4). Grain boundaries play important roles in the atomic diffusions and sulfide formations.

Thermoelectrics is attractive as a green and sustainable way for harnessing waste heat and cooling applications. Designing high performance thermoelectrics involves navigating the complex interplay between electronic and heat transports. This fundamentally involves understanding the scattering physics of both electrons and phonons, as well as maximizing symmetry-breaking in entropy and electronic transports. In the last two decades, thermoelectrics have progressed in leaps and bounds thanks to parallel advancements in scientific technologies and physical understandings. Figure of merit zT of 2 and above have been consistently reported in various materials, especially Chalcogenides. In this review, we provide a broad picture of physically driven optimization strategies for thermoelectric materials, with emphasis on electronic transport aspect of inorganic materials. We also discuss and analyzes various newly coined metrics such as quality factors, electronics quality factor, electronic fitness function, weighted mobility, and Fermi surface complexity factor. More importantly, we look at the non-trivial interdependencies between various physical parameters even at a very fundamental level. Moving forward, we discuss the outlook for the potential of 3D printing and device oriented research in thermoelectrics. The intuition derived from this review will be useful not only to guide materials selection, but also research directions in the coming years.

Biomaterials is an exciting and dynamic field, which uses a collection of diverse materials to achieve desired biological responses. While there is constant evolution and innovation in materials with time, biomaterials research has been hampered by the relatively long development period required. In recent years, driven by the need to accelerate materials development, the applications of machine learning in materials science has progressed in leaps and bounds. The combination of machine learning with high-throughput theoretical predictions and high-throughput experiments (HTE) has shifted the traditional Edisonian (trial and error) paradigm to a data-driven paradigm. In this review, each type of biomaterial and their key properties and use cases are systematically discussed, followed by how machine learning can be applied in the development and design process. The discussions are classified according to various types of materials used including polymers, metals, ceramics, and nanomaterials, and implants using additive manufacturing. Last, the current gaps and potential of machine learning to further aid biomaterials discovery and application are also discussed.

Phosphide-based thermoelectrics are a relatively less studied class of compounds, primarily due to the presence of light elements, which result in high thermal conductivity and inherent stability problems. In this work, we present a stable phosphide-tetrahedrite, Ag6Ge10P12, which possesses the highest zT (∼0.7) among all known phosphides at intermediate temperatures (750 K). We examine the intrinsic electronic and thermal transport properties of this compound by expressing the transport properties in terms of weighted mobility (μW), transport coefficient (σE0), and material quality factor (B), from which we are able to elucidate that the origin of its high zT can be attributed to the platelike Fermi surface and high level of band multiplicity related to its complex band structure. Finally, we discuss the origin of the low lattice thermal conductivity observed in this compound using experimental sound velocity, elastic properties, and Debye-Callaway model, thus laying the foundation for similar stable phosphides as potentially earth-abundant and nontoxic intermediate-temperature thermoelectric materials.

GeTe is highly sought-after due to its versatility as high-performance thermoelectrics, phase change materials, as well as ferroelectric Rashba semiconductor. Compared to most thermoelectric materials, it has an additional degree of freedom of rhombohedral-cubic phase transition at 673 K. At this temperature, the lattice thermal conductivity approaches theoretical minimum due to ferroelectric instability while the high-energy Σ and low-energy L bands converge to give outstanding electronic properties. Therefore, modulation of the phase transition temperature allows simultaneous and synergistic tuning of electronic and thermal transport properties to achieve high zT. In this work, Sn alloying together with Bi, Sb doping is used to suppress the phase transition to achieve a pure cubic structure with lattice thermal conductivity of around 0.4 W/mK and peak zT of 1.7 at 723 K with average zT of 1.23 between 400 and 800 K. Furthermore, Vickers hardness of 270, and Young’s modulus of 63.5 GPa in Ge0.4Sn0.4Bi0.02Sb0.12Te is by far the highest amongst binary chalcogenides. More importantly, the high quality factor achieved in this work enables ample room for further zT improvements. The fundamental insights drawn from this work provide a pathway towards engineering GeTe-based alloys to achieve high zT at any temperature of interest. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) Accepted version

Developing highly efficient earth-abundant nickel-based compounds is an important step to realize hydrogen generation from water. Herein, the electronic modulation of the semiconducting NiS2 by cation doping for advanced water electrolysis is reported. Both theoretical calculations and temperature-dependent resistivity measurements indicate the semiconductor-to-conductor transition of NiS2 after Cu incorporation. Further calculations also suggest the advantages of Cu dopant to cathodic water electrolysis by bringing Gibbs free energy of H adsorption at both Ni sites and S sites much closer to zero. It is noteworthy that water dissociation on Cu-doped NiS2 (Cu-NiS2 ) surface is even more favorable than those on NiS2 and Pt(111). Thus, the prepared Cu-NiS2 shows noticeably improved performance toward alkaline hydrogen and oxygen evolution reactions (HER and OER). Specifically, it requires merely 232 mV OER overpotential to drive 10 mA cm-2 ; in parallel with Tafel slopes of 46 mV dec-1 . Regarding HER, an onset overpotential of only 68 mV is achieved. When integrated as both electrodes for water electrolysis, Cu-NiS2 needs only 1.64 V to drive 10 mA cm-2 , surpassing the state-of-the-art Ir/C-Pt/C couple (1.71 V). This work opens up an avenue to engineer low-cost and earth-abundant catalysts performing on par with the noble-metal-based one for water splitting.

Atomically thin Bi2 O2 Se has emerged as a new member in 2D materials with ultrahigh carrier mobility and excellent air-stability, showing great potential for electronics and optoelectronics. In addition, its ferroelectric nature renders an ultralow thermal conductivity, making it a perfect candidate for thermoelectrics. In this work, the thermoelectric performance of 2D Bi2 O2 Se is investigated over a wide temperature range (20-300 K). A gate-tunable transition from polar optical phonon (POP) scattering to piezoelectric scattering is observed, which facilitates the capacity of drastic mobility engineering in 2D Bi2 O2 Se. Consequently, a high power factor of more than 400 µW m-1 K-2 over an unprecedented temperature range (80-200 K) is achieved, corresponding to the persistently high mobility arising from the highly gate-tunable scattering mechanism. This finding provides a new avenue for maximizing thermoelectric performance by changing the scattering mechanism and carrier mobility over a wide temperature range.

In recent years, GeTe has received tremendous attention from the research community due to its favorable electronic and thermal properties which make it one of the best performing thermoelectric compounds. In many reports, high performance has often been achieved via various doping/alloying methods, which typically involve more than one type of dopants. In contrast to the widely used co-doping strategies, this work only uses a minute amount of 1% doping, giving rise to one of the highest quality factor (1.30) at 673 K amongst GeTe, with a corresponding zT of 1.5. The high performance is attributed to simultaneously improved electronic properties via carrier concentration optimization as well as reduced thermal conductivity via additional phonon scattering brought about by In-mass fluctuations. More importantly, we elucidate on the importance of preserving the high quality factor via choosing the right dopants to optimize the carrier concentration. Furthermore, we showed that the strategy of evaluating the quality factor can be applied to other material systems, serving as a general guideline for thermoelectric materials design. The quality factor of GeTe in this work is superior to most other high-performing chalcogenides such as PbTe, SnTe, and SnS, revealing the large space for further enhancing its zT. Ministry of Education (MOE) Accepted version The authors acknowledge support from A*STAR’s Science and Engineering Research Council, PHAROS program on Hybrid Thermoelectrics for Ambient Applications: 1527200019, and Agritech program on Sustainable Hybrid Lighting System for Controlled Environment Agriculture: A19D9a0096. DVM. Repaka acknowledges PHAROS 1527200018. Q. Yan acknowledges Singapore MOE AcRF Tier 2 under Grant Nos. 2018-T2-1-010, Singapore A*STAR Pharos Program SERC 1527200022.

Ferromagnetic insulating thin films of Sm(0.34)Sr(0.66)MnO3 (SSMO) on (001) SrTiO3 substrates with a T(C) of 140 K were formed in self-assembled epitaxial nanocomposite thin films. High T(C) ferromagnetism was enabled through vertical epitaxy of the SSMO matrix with embedded, stiff, ∼40 nm Sm2O3 nanopillars giving a c/a ratio close to 1 in the SSMO. In contrast, bulk and single phase SSMO films of the same composition have much stronger tetragonal distortion, the bulk having c/a1 and the films having c/a1, both of which give rise to antiferromagnetic coupling. The work demonstrates a unique and simple route to creating ferromagnetic insulators for spintronics applications where currently available ferromagnetic insulators are either hard to grow and/or have very low T(C).

Self-assembled epitaxial oxide composite films represent a new material form in which very high-quality mesoscopic structures can be created. The main focus has been on coupled electronic devices, but so far, only a very narrow range of compositions and structure types have been explored. Insufficient attention has been paid to the very wide window of possible materials combinations or to the novel materials properties that could be induced. Both of these aspects need to be addressed before we attain mesoscale devices with new properties. In this article, we review the unique materials properties of these epitaxially directed mesoscale composite structures, discussing their very high crystallinity, structural uniformity, and orientation. We also review how the structures can be size-tuned, from ∼2 nm up to ∼50 nm, and how they can be spatially ordered. We discuss how unusual strain states can be induced in the structures, and how epitaxial stabilization of the mesoscale surfaces within the films eliminates problems of surface degradation inherent to “free” nano/mesostructures. Several exemplar systems are given to show that composite films represent an unrivaled new approach to engineering new properties into mesoscale systems.

Auxetic-like strain states were generated in self-assembled nanocomposite thin films of (Ba0.6Sr0.4TiO3)1−x − (Sm2O3)x(BSTO − SmO). A switch from auxetic-like to elastic-like strain behavior was observed for x > 0.50, when the SmO switched from being nanopillars in the BSTO matrix to being the matrix with BSTO nanopillars embedded in it. A simple model was adopted to explain how in-plane strain varies with x. At high x (0.75), strongly enhanced ferroelectric properties were obtained compared to pure BSTO films. The nanocomposite method represents a powerful new way to tune the properties of a wide range of strongly correlated metal oxides whose properties are very sensitive to strain.