Water electrolysis has attracted significant attention for large-scale production of green hydrogen as next-generation clean fuels. Recently, the development of graphdiyne (GDY), a new member of carbon allotropes, has been promisingly offering novel alternatives for acquisition of inexpensive and efficient catalysts in the water electrolyzer. The unique atomic arrangement in GDY architecture leads to coexistence of sp– and sp2–C, correspondingly brings numerous intriguing features such as heterogeneous electron distribution, wide tailorable natural bandgap, rapid electron/mass transport and rich chemical bonds. These unique intrinsic natures of GDY provide brilliant inspirations for scientists to design new-concept electrocatalyst toward cathodic hydrogen evolution reaction, anodic oxygen evolution reaction and the overall water-splitting. Based on the immense progress, in this short perspective, current principal design strategies of GDY-based catalysts are systematically summarized, including interface engineering, individual atom fixation, induced constrained growth and bottom-up fabrication. With abundant implementation examples for achieving highly efficient water electrolysis, in particular we focus on clarifying the decisive role of GDY on these design strategies with comprehensive theoretical and experimental evidences. The future direction in developing GDY-based electrocatalysts in hydrogen energy field is also depicted with the urgent anticipation of deeper understanding of structure-performance relationship and catalytic mechanism, especially those in real industry water electrolyzers.

Multiferroic materials with strong coupling between different degrees of freedom are prone to exhibit giant multicaloric effects resulting from the application or removal of diverse external fields. These materials exhibit a synergic response to the combined action of two fields when the monocaloric effects are both conventional (or both inverse), while a non-synergic response occurs when one of the monocaloric effects is conventional and the other is inverse. In all cases, the multicaloric properties (isothermal entropy and adiabatic temperature changes) do not result from the simple addition of the corresponding monocaloric quantities because there is a contribution from the interplay between degrees of freedom (cross-coupling term). In this paper, we analyse in detail the contribution of the cross-coupling term to the multicaloric entropy values obtained for both synergic and non-synergic multicaloric materials. We first introduce basic thermodynamic concepts accounting for the multicaloric effects, and next the contribution from the cross-coupling term is illustrated via several model examples. We finally analyse the realistic situation for two prototype materials with synergic and non-synergic multicaloric effects.

A critical design criterion for future fusion reactor components is low activation. The equiatomic multi-principal element alloy VCrMnFe is comprised solely of low activation elements and forms a single-phase solid solution at temperatures over 1000 °C. However, at lower temperatures it forms detrimental sigma phase. In this work, compositional gradients of Ga, Sn or Al were induced in VCrMnFe using only a furnace to investigate their effect on intermetallic formation. By examining how the microstructure changed across a region with varying composition, phase stability limits could be assessed. For example, all three elements were found to prevent sigma phase from forming within the alloy when they were present at relatively low concentrations (2–5 at%). Al was found to be the most promising addition (in terms of not causing embrittlement), and the approach used enabled the characterisation of the VCrMnFe–Al pseudo binary phase diagram up to 50 at% Al after heat treatment of 800 °C/240 h followed by ageing at 600 °C/240 h, with numerous ordered phases found using electron diffraction. The level of Al addition required to suppress the sigma phase has been identified more precisely, which will be useful for future alloy development work.

Despite the high capacitance and low cost, transition metal oxides have the limitation of low electrical conductivities and structural instability. In order to resolve these problems, herein, we propose a one-pot facile synthesis approach to construct a hierarchically structured nanohybrid material, where carbon nanotube (CNT) branches encapsulate NiO nanoparticles inside the tubes and interconnect them with steam-activated reduced graphene oxide. This unique hierarchical structure is attributed to large accessible surface areas, rapid electronic conduction, fast ion diffusion, and buffering effects. Moreover, the mixed Ni and NiO particles acts as catalysts to grow CNT branches and high capacitance redox active materials. In particular, the resulting composite electrode deliver a high specific capacitance of up to 1605.81 F g−1 at a current density of 1 A g−1 as well as, an excellent cycle stability with 71.56% capacitance retention after more than 10 000 cycles. Consequently, this research provides a rational material design chemistry to construct hierarchical architectures and multiple compositions of CNT/graphene/metal oxide nanoparticle hybrids for high-capacitance electrodes of composite capacitors.

Vanadium doped indium sulphide, In2S3:V, is studied as a potential absorber material for intermediate band (IB) solar cells. Based on electronic considerations, it is usually assumed that V occupies octahedrally coordinated In sites, although geometrical considerations would favour tetrahedral In sites. In this study, we therefore combined experimental x-ray diffraction and x-ray absorption spectroscopy with ab initio theoretical calculations of both α and β phase to elucidate the incorporation of V in In2S3:V thin films grown with different V content and different growth temperatures. Comparing shape and position of the measured and calculated x-ray absorption edge of V, comparing experimentally determined and calculated V–S bond lengths, and evaluating the calculated heat of solution of V on different lattice sites all indicate that V is incorporated on octahedral rather than tetrahedral sites in the In2S3 matrix. For this material system, the electronic benefit of octahedral coordination thus outweighs the mechanical stress of the associated lattice relaxation. Finally, we studied the electronic structure of V-substituted α - In2S3 using hybrid density functional calculations and find that for a concentration of 1.9 at %, V on octahedrally coordinated In sites forms an empty IB isolated from valence band and conduction band (CB). By increasing the V content to 3.8 at %, however, the gap between IB and CB closes, which results in a reduction of the band gap. This differs from the electronic structure calculated for β - In2S3 :V and clearly demonstrates that both crystal structure and V incorporation site affect the resulting electronic material properties.

Sodium-ion batteries (SIBs) see intensive research and commercialization efforts, aiming to establish them as an alternative to lithium-ion batteries. Among the reported cathode material families for SIBs, Na-deficient P2-type layered oxides are promising candidates, benefiting from fast sodium diffusion and therefore high charge/discharge rates. However, upon sodium extraction at high potentials, a transition from the P2 to O2 phase occurs, with the corresponding change in cell volume resulting in particle fracture and capacity degradation. A possible solution to this is to increase configurational entropy by introducing more elements into the transition-metal layer (so-called high-entropy concept), leading to some kind of structural stabilization. In this work, the acoustic emission (AE) of a series of P2-type layered oxide cathodes with increasing configurational entropy [Na0.67(Mn0.55Ni0.21Co0.24)O2, Na0.67(Mn0.45Ni0.18Co0.24Ti0.1Mg0.03)O2 and Na0.67(Mn0.45Ni0.18Co0.18Ti0.1Mg0.03Al0.04Fe0.02)O2] is recorded during SIB operation and correlated to the materials properties, namely change in c lattice parameter and cracking behavior. A structure-property relationship between entropy, manifested in the extent of phase transition, and detected AE is derived, supported by the classification of signals by peak frequency. This classification in combination with microscopy imaging allows to distinguish between inter- and intragranular fracture. Relatively more intergranular and less intragranular crack formation is observed with increasing configurational entropy.

MXenes, which are graphene-like two-dimensional transition metal carbides and nitrides, have tunable compositions and exhibit rich surface chemistry. This compositional flexibility has resulted in exquisitely tunable electronic, optical, and mechanical properties leading to the applications of MXenes in catalysis, electronics, and energy storage. The work function of MXenes is an important fundamental property that dictates the suitability of MXenes for these applications. We present a series of machine learning models to predict the work function of MXenes having generic compositions and containing surfaces terminated by O*, OH*, F*, and bare metal atoms. Our model uses the basic chemical properties of the elements constituting the MXene as features, and is trained on 275 data points from the Computational 2D Materials Database. Using 15 different features of the MXene as inputs, the neural network model predicts the work function of MXenes with a mean absolute error of 0.12 eV on the training data and 0.25 eV on the testing data. Our feature importance analysis indicates that properties of atoms terminating the MXene surface like their electronegativity, most strongly influence the work function. This sensitivity of the work function to the surface termination is also elucidated through experimental measurements on Ti3C2. We introduce reduced-order models comprising of ten-, eight-, and five-features to predict the work function. These reduced-order models exhibit easier transferability to new materials, while exhibiting a marginal increased mean average error. We demonstrate the transferability of these reduced order models to new materials, by predicting the work function of MXenes having surface terminations beyond the original training set, like Br*, Cl*, S*, N*, and NH*. Predicting electronic properties like the work function from the basic chemical properties of elements, paves the way towards rapidly identifying tailored MXenes having a targeted range of properties that are required for a specific application.

Numerous catalysts have been reported with enhanced performance, e.g. longer lifetime and improved selectivity, for the electrochemical CO2 reduction reaction (CO2RR). Respectively little is, however, known about the influence of the electrode structuring and pre-treatment on this reaction for catalytic layers. Thus, we herein report on the modification of the catalyst environment of a Cu-ZnO-carbon black catalyst by variation of the ink composition and subsequent electrode treatment before performing CO2RR. We furthermore provide insight into the impact of different solvents, ionomer, and additives like pore forming agents used for the ink preparation as well as post-treatment steps in terms of pressing and sintering of the generated electrodes on the CO2RR performance. Although using the same catalyst for all electrodes, remarkable differences in hydrophobicity, surface morphology, and electrochemical performance with respect to stability and product distribution were observed. Our study reveals the critical role of the catalytic layer assembly aside from using proper catalysts. We furthermore show that the parasitic hydrogen formation and flooding behavior can be lowered and C2+ product formation can be enhanced when operating in optimized gas diffusion electrodes.

Internet-of-thing (IoT) is an assembly of devices that collect and share data with other devices and communicate via the internet. This massive network of devices, generates and communicates data and is the key to the value in IoT, allowing access to raw information, gaining insight, and making an intelligent decisions. Today, there are billions of IoT devices such as sensors and actuators deployed. Many of these applications are easy to connect, but those tucked away in hard-to-access spots will need to harvest ambient energy. Therefore, the aim is to create devices that are self-report in real-time. Efforts are underway to install a self-powered unit in IoT devices that can generate sufficient power from environmental conditions such as light, vibration, and heat. In this review paper, we discuss the recent progress made in materials and device development in power- and, storage units, and power management relevant for IoT applications. This review paper will give a comprehensive overview for new researchers entering the field of IoT and a collection of challenges as well as perspectives for people already working in this field.

Ionomers are used in polymer electrolyte fuel cells (PEFCs) catalyst layers to improve proton conduction. Recent analytical studies have clarified that the adsorption of the ionomer on the surface of a Pt catalyst deteriorates the catalytic activity for the oxygen reduction reaction and oxygen transport properties near the catalyst surface. These findings have led to the development of new materials, such as mesoporous carbon support and highly oxygen-permeable ionomer, which are now commercially used. In this review article, we summarize recent analytical studies of the Pt/ionomer interface focusing on half-cell experiments with single-crystal electrodes. We also present promising approaches for mitigating ionomer adsorption, as well as the remaining challenges in the application of these approaches to PEFCs.

As a consequence of the issues resulting from global climate change many nations are starting to transition to being low or net zero carbon economies. To achieve this objective practical alternative fuels are urgently required and hydrogen gas is deemed one of the most desirable substitute fuels to traditional hydrocarbons. A significant challenge, however, is obtaining hydrogen from sources with low or zero carbon footprint i.e. so called ‘green’ hydrogen. Consequently, there are a number of strands of research into processes that are practical techniques for the production of this ‘green’ hydrogen. Over the past five decades there has been a significant body of research into photocatalytic (PC)/photoelectrocatalytic processes for hydrogen production through water splitting or water reduction. There have, however been significant issues faced in terms of the practical capability of this promising technology to produce hydrogen at scale. This road map article explores a range of issues related to both PC and photoelectrocatalytic hydrogen generation ranging from basic processes, materials science through to reactor engineering and applications for biomass reforming.

Electrochemical hydrodynamic techniques typically involve electrodes that move relative to the solution. Historically, approaches involving rotating disc electrode (RDE) configurations have become very popular, as one can easily control the electroactive species’ mass transport in those cases. The combination of cyclic voltammetry and RDE is nowadays one of the standard characterization protocols in electrocatalysis. On the other hand, impedance spectroscopy is one of the most informative electrochemistry techniques, enabling the acquisition of information on the processes taking place simultaneously at the electrode/electrolyte interface. In this work, we investigated the hydrogen evolution reaction (HER) catalyzed by polycrystalline Pt (Pt(pc)) and Pt5Gd disc electrodes and characterized them using RDE and electrochemical impedance spectroscopy techniques simultaneously. Pt5Gd shows higher HER activities than Pt in acidic and alkaline media due to strain and ligand effects. The mechanistic study of the reaction showed that the rotation rates in acidic media do not affect the contribution of the Volmer–Heyrovsky and Volmer–Tafel pathways. However, the Volmer–Heyrovsky pathway dominates at lower rotation rates in alkaline media. Besides, the HER in acidic solutions depends more strongly on mass diffusion than in alkaline media. In addition to simple and clearly defined systems, the combined method of both techniques is applicable for systems with greater complexity, such as Pd/C nanostructured catalysts. Applying the above-presented approach, we found that the Volmer–Tafel pathway is the dominating mechanism of the HER for this catalytic system.

The growing interest in phase-change materials (PCM) is related to their possible role in thermal energy storage and thermal management. The choice of materials depends strongly on the required temperature range, whereas the latent heat of solid–liquid phase transition has to be as high as possible. Among other organic PCM, sugar alcohols have gained some attention due to their availability and certain advantageous properties. However, the thermal processes in these materials still require investigation. In the present work, we focused on the materials with solid–liquid phase change within 80 °C–100 °C. A comprehensive literature survey was conducted to elucidate the available sugar alcohols relevant to this range. It was found that the use of pure materials of this type is not very practical, because of their scarcity in the required range and their specific features, like difficulties with crystallization and solidification. On the other hand, based on the literature, we have discerned three eutectic mixtures of erythritol with other organic materials, namely, erythritol–xylitol, erythritol–urea and erythritol– trimethylolethane (TME). In all those cases, it is remarkable that while the components commonly have rather high melting temperatures, the eutectic mixtures had the phase transitions in the required range. Still, each of these mixtures has its own peculiar features, especially at cooling and solidification. An extensive experimental study was performed to provide detailed visualization of these major processes. The results revealed the melting temperature and latent heat of the mixtures to be: 84 °C and 190 J g−1 for erythritol–xylitol, 82 °C and 227 J g−1 for erythritol–urea. Erythritol–TME has two phase transitions at 82 °C and 97 °C, with total latent heat of 198 J g−1. Based on the present findings, the erythritol–urea mixture is the best PCM candidate for the melting range within 80 °C–100 °C.

Temperature is one of the most crucial outdoor variables that influence the photovoltaic performance and stability of carbon perovskite solar cells (CPSCs), although not many reports are there on temperature-dependent CPSCs performance based on various mesoscopic structures. This study demonstrates the temperature coefficient (T C) of carbon-based triple and double mesoscopic devices having MAPICL [MAPbI3−x Cl x ] and CSFAMA [Cs0.05(FA0.83MA0.17)0.95Pb(I0.83Br0.17)3] to understand the performance compatibility of different CPSC configurations despite the thermal treatment (MA = methylammonium, FA = formamidinium). While treating a single device in the range of 5 °C–65 °C, MAPICL-based CPSC maintained a power conversion efficiency (PCE) of ∼9%–11.7%. In contrast, CSFAMA-based double mesoscopic devices showed a PCE variation of ∼14%–16% in the same temperature window. The interesting fact of this analysis is that the average T C values for MAPICL and CSFAMA are in the order of 10−4, implying better retention of performance for both mesoscopic devices despite thermal stress. A photoluminescence analysis has been done to understand the temperature-dependent charge transfer properties between the perovskite and transport layer. To the best of our knowledge, this analysis, for the first time, provides insight into the temperature coefficient of different CPSC mesoscopic structures to promote suitable future development.

The emergent evolution of first-order phase transitions from magneto-structural to magneto-elastic and magnetocaloric effect (MCE) have been investigated by X-ray diffraction, differential scanning calorimetry and magnetization measurements. Applying the isostructural alloying principle, the martensitic transition temperature (T M) increases effectively and the Curie temperatures of the two phases increase slightly by substituting the Si content (x). With an appropriate amount of Fe and Si content, an emergent first-order antiferromagnetic–ferromagnetic magnetoelastic transition with thermal hysteresis in the martensitic state occurs for MnCo0.7Fe0.3Ge1–x Si x (x = 0.15–0.40) alloys, which results from the decrease in the nearest-neighbor Mn–Mn distance. Moreover, the values of magnetic entropy change (ΔS M), refrigeration capacity (RC) and temperature-averaged entropy change (TEC, 10 K) with ΔH = 50 kOe reach −12.2 J kg−1 K−1, 112.8 J kg−1 and 11.4 J kg−1 K−1 for MnCo0.7Fe0.3Ge0.8Si0.2 undergoing the ferromagnetic magneto-structural transition in the Curie temperature window. The results facilitate the magnetocaloric/magnetoelastic performance and tunability of multiple phase states in a wider temperature range.

Nuclear data, describing neutron reaction probabilities (cross sections) and decay behaviour, are critical to the design and operation of fusion experiments and future fusion power plants. Equally vital, are the inventory codes that use the data to predict neutron-induced activation and transmutation of materials, which will define the radiological hazards that must be managed during reactor operation and decommissioning. Transmutation, including gas production, combined with the neutron-induced displacement damage, will also cause the properties of materials to degrade, for example through swelling and embrittlement, eventually limiting the lifetime of components. Thus validated and accurate nuclear data and inventory codes are essential. For data validation there are decay heat measurements performed at FNS in Japan more than 20 years ago. The experiments produced an invaluable database for benchmarking of nuclear data libraries; the latest versions of several international libraries perform well against this data during tests with the FISPACT-II inventory code, although there is still scope for improvement. A recent attempt to provide fusion-relevant validation based on γ-spectroscopy data from neutron-irradiated material samples tests produced predictions for short-lived (several hours or less) radionuclides. The detailed analysis performed for molybdenum demonstrates how these data could eventually provide a new benchmark, and also illustrates the potential benefits of further experiments targeting the longer-lived radionuclides relevant to maintenance and decommissioning timescales. There are also some successful tests of transmutation predictions with FISPACT-II. These direct validations of inventory simulations are critical for lifetime predictions and future experiments should learn lessons from the examples described for tungsten, which demonstrate the importance of an accurate description of the neutron spectrum in experiments. More novel experimental techniques are needed to measure helium production in materials such as Fe and C, but the need to validate the nuclear data evaluations used by simulations should motivate future experimental efforts.

In most cases, substitution studies that aim to optimize magnetic properties are performed at the magnetic atomic site. However, in the case of MnB, magnetic substitutions at the Mn site significantly decrease the once promising magnetocaloric and magnetic properties. This study employs computationally directed search to optimize the magnetocaloric properties of MnB where partial substitutions of boron atoms (Mn50B50− x Si x and Mn50B50− x Ge x where x = 3.125, 6.25, and 12.5) reveal new compounds with a greater magnetocaloric effect than pure MnB at the same Curie temperature. These new compounds were obtained by arc melting the pure elements and further characterized. The computationally driven screening process is based on density functional theory calculations that do not require large databases of known compounds. This work demonstrates that using simple computational screening procedures to search for new magnetocaloric materials with improved properties can be done quickly, cost-effectively, and while maintaining reliability.

Magnetocaloric hydrogen liquefaction could be a ‘game-changer’ for liquid hydrogen industry. Although heavy rare-earth based magnetocaloric materials show strong magnetocaloric effects in the temperature range required by hydrogen liquefaction (77–20 K), the high resource criticality of the heavy rare-earth elements is a major obstacle for upscaling this emerging liquefaction technology. In contrast, the higher abundances of the light rare-earth elements make their alloys highly appealing for magnetocaloric hydrogen liquefaction. Via a mean-field approach, it is demonstrated that tuning the Curie temperature (T C) of an idealized light rare-earth based magnetocaloric material towards lower cryogenic temperatures leads to larger maximum magnetic and adiabatic temperature changes (ΔS T and ΔT ad). Especially in the vicinity of the condensation point of hydrogen (20 K), ΔS T and ΔT ad of the optimized light rare-earth based material are predicted to show significantly large values. Following the mean-field approach and taking the chemical and physical similarities of the light rare-earth elements into consideration, a method of designing light rare-earth intermetallic compounds for hydrogen liquefaction is used: tuning T C of a rare-earth alloy to approach 20 K by mixing light rare-earth elements with different de Gennes factors. By mixing Nd and Pr in Laves phase (Nd, Pr)Al2, and Pr and Ce in Laves phase (Pr, Ce)Al2, a fully light rare-earth intermetallic series with large magnetocaloric effects covering the temperature range required by hydrogen liquefaction is developed, demonstrating a competitive maximum effect compared to the heavy rare-earth compound DyAl2.

Caloric cooling enlisting solid-state refrigerants is potentially a promising eco-friendly alternative to conventional cooling based on vapor compression. The most common refrigerant materials for elastocaloric cooling to date are Ni-Ti based superelastic shape memory alloys. Here, we have explored tuning the operation temperature range of Ni50.8Ti49.2 for elastocaloric cooling. In particular, we have studied the effect of thermal treatments (a.k.a. aging) on the transformation temperature, superelasticity, and elastocaloric effects of Ni50.8Ti49.2 shape memory alloy tubes. The isothermal compressive test revealed that the residual strain of thermally-treated Ni-Ti tubes at room temperature approaches zero as aging time is increased. Short-time aging treatment at 400 °C resulted in good superelasticity and elastocaloric cooling performance with a large tunable austenite finish (A f) temperature range of 24.7 °C, as determined from the A f temperature of the samples that were aged 5–120 min. The main reason of the property change is the formation of a different amount of Ni4Ti3 precipitates in the NiTi matrix. Our findings show that it is possible to tailor the A f temperature range for development of cascade elastocaloric cooling systems by thermally treating a starting single composition Ni-Ti alloy.

The excellent theoretical specific charge (lithium) storage capacity and rich abundance of silicon (Si), and the good mechanical and electrical properties of titanium based MXene (Ti3C2T x ) nanosheets promise high performance composites (Si/Ti3C2T x ) for negative electrodes (negatrodes) in future lithium ion battery (LIB) applications. In particular, the Si/Ti3C2T x composites have been preliminarily shown to offer large and stable cyclic capacity, good rate capability and a highly profitable market prospect. To better understand and help further improve the electrochemical performance of these composites, this review focuses on the electrochemical processes occurring in Si/MXene composites from a material perspective. Different cells used for electrochemical measurements, the related materials properties and the reaction processes and kinetics of Si/MXene composites as negatrode in LIB are reviewed. The perspective is also discussed for practical applications in flexible electronic devices and automobiles.