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The interactions between metal ions and graphene oxide (GO) nanosheets were investigated by in situ two-dimensional grazing incidence X-ray diffraction (GIXRD). We found that metal cations (Mn2+, Co2+, Cu2+, Fe3+) and GO can self-assemble into a hydroxide/GO superlattice by drop-casting a metal chloride and GO solution due to the electrostatic interactions between the positively charged hydroxide and the negatively charged GO nanosheets and the interlayer spacing of the superlattice can be controlled by the cation species. Moreover, based on this superlattice template, graphene-based metal oxide nanosheets can be facilely obtained by subsequent annealing. The growth mechanism and structural evolution of the GO/cation systems can be described in four stages: (1) hydrated cation intercalation of the GO interlayer in an aqueous solution; (2) metal hydroxide growth between the GO layers during annealing, with the formation of a superlattice structure at approximately 250 °C; (3) metal oxide nucleation between the reduced GO (rGO) interlayers with increasing temperature; and (4) complete graphene layer decomposition at a temperature of 600 °C, along with metal oxide nanosheet formation. This work gives a new perspective for understanding the interactions between and growth behaviour of metal cations and GO. We employed the in situ two-dimensional grazing incidence X-ray diffraction (GIXRD) technique to understand the interaction between and growth behaviour of metal cations (Mn2+, Co2+, Cu2+, Fe3+) and GO layers. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper addresses the heating/cooling-induced formation, dissociation and phase separation during thermal oxidation of Sm 2 (Co, Fe, Cu, Zr) 17 alloys at 298.15 K-973 K, using real-time and room-temperature measurements. Whereas, Fe 3 O 4 forms at 673 K ≤ T ≤ 773 K, it transforms to CuFe 2 O 4 at 823 K ≤ T ≤ 973 K because of the incorporation of Cu+2 into the octahedral Fe+2 lattice sites in Fe 3 O 4. CuFe 2 O 4 dissociates instantaneously upon cooling, and separates into layered structure of Cu-oxides at oxide-surface and Fe 3 O 4 underneath. A detailed discussion on possible reaction pathways leading to these phenomena during the heating/cooling cycle is presented here. [Display omitted] • Real-time, in-situ x-ray diffractograms are recorded during oxidation of Sm 2 Co 17. • Fe 3 O 4 transforms to CuFe 2 O 4 in 823 K ≤ T ≤ 973 K due to Cu+ 2 inclusion in Fe 3 O 4. • Upon cooling from 973 K, CuFe 2 O 4 dissociates instantaneously into Fe 3 O 4 and CuO. • Phase separation happens forming Cu oxides at the surface and Fe 3 O 4 in interior. • Increased bulk copper content leads to dense, compact copper oxide surface layer. [ABSTRACT FROM AUTHOR]

Highlights: [•] Effect of volume fractions on change in the size of embedded silver nanoparticles. [•] Surface plasmon resonance study to understand the dipolar interactions. [•] Study provides data for the development of non-equilibrium thermodynamics. [ABSTRACT FROM AUTHOR]

Solar-driven hydrogen generation is one of the promising technologies developed to address the world's growing energy demand in an sustainable way. While, for hydrogen generation (otherwise water splitting), photocatalytic, photoelectrochemical, and PV-integrated water splitting systems employing conventional semiconductor oxides materials and their electrodes have been under investigation for over a decade, lead (Pb)- halide perovskites (HPs) made their debut in 2016. Since then, the exceptional characteristics of these materials, such as their tunable optoelectronic properties, ease of processing, high absorption coefficients, and long diffusion lengths, have positioned them as a highly promising material for solar-driven water splitting. Like in solar photovoltaics, a solar-driven water splitting field is also dominated by Pb-HPs with ongoing efforts to improve material stability and hydrogen evolution/generation rate (HER). Despite this, with the unveiling potential of various Pb-free HP compositions in photovoltaics and optoelectronics researchers were inspired to explore the potential of these materials in water splitting. In this current review, we outlined the fundamentals of water splitting, provided a summary of Pb HPs in this field, and the associated issues are presented. Subsequently, Pb-free HP compositions and strategies employed for improving the photocatalytic and/or electrochemical activity of the material are discussed in detail. Finally, this review presents existing issues and the future potential of lead-free HPs, which show potential for enhancing productivity of solar-to-hydrogen conversion technologies. [ABSTRACT FROM AUTHOR]

In situ and operando X-ray techniques have emerged as powerful tools for unravelling the complex mechanisms underlying photoelectrochemical transformations. These techniques offer real-time insights into the dynamic processes occurring at the electrode–electrolyte interface during solar-driven water splitting and other PEC reactions. The present work aims to summarise the latest advances in in situ and operando X-ray absorption spectroscopy (XAS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) for the characterisation of photoelectrocatalytic systems and materials for the generation of solar fuels and value-added chemicals. This review highlights the recent advancements achieved using these techniques for elucidating the structural, chemical, and electronic properties of photoelectrocatalytic materials and interfaces during operation. Besides, this review provides technical guidance for performing these measurements, considering the experimental requirements for each of these spectroscopies. Further, we provide an overview of different state-of-the-art synchrotron-based techniques employed for the characterisation of photoelectrocatalytic materials, focusing on the possibilities of the studied techniques, cell designs and more relevant results. [ABSTRACT FROM AUTHOR]

Solution‐processable perovskite‐based devices are potentially very interesting because of their relatively cheap fabrication cost but outstanding optoelectronic performance. However, the solution spin‐coating process involves complicated processes, including perovskite solution droplets, nucleation of perovskite, and formation of intermediate perovskite films, resulting in complicated crystallization pathways for perovskite films under annealing. Understanding and therefore controlling the fabrication process of perovskites is difficult. Recently, synchrotron radiation‐based in situ grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) techniques, which possess the advantages of high collimation, high resolution, and high brightness, have enabled to bridge complicated perovskite structure information with device performance by revealing the real‐time crystallization pathways of perovskites during the spin‐coating process. Herein, the developments of synchrotron radiation‐based in situ GIWAXS are discussed in the study of the crystallization process of perovskites, especially revealing the important crystallization mechanisms of state‐of‐the‐art perovskite optoelectronic devices with high performance. At the end, several potential applications and challenges associated with in situ GIWAXS techniques for perovskite‐based devices are highlighted. [ABSTRACT FROM AUTHOR]

Ge–Sb–Se–Te chalcogenides, namely Se-substituted Ge–Sb–Te, have been developed as an alternative optical phase change material (PCM) with a high figure-of-merit. A need for the integration of such new PCMs onto a variety of photonic platforms has necessitated the development of fabrication processes compatible with diverse material compositions as well as substrates of varying material types, shapes, and sizes. This study explores the application of chemical solution deposition as a method capable of creating conformally coated layers and delves into the resulting modifications in the structural and optical properties of Ge–Sb–Se–Te PCMs. Specifically, we detail the solution-based deposition of Ge–Sb–Se–Te layers and present a comparative analysis with those deposited via thermal evaporation. We also discuss our ongoing endeavor to improve available choice of processing-material combinations and how to realize solution-derived high figure-of-merit optical PCM layers, which will enable a new era for the development of reconfigurable photonic devices. [ABSTRACT FROM AUTHOR]

Pyrometallurgical slags are a valuable secondary resource for several technologically important critical materials/elements. A promising cost-efficient recovery currently under research depends on the incorporation of the element of interest into a specific compound. This new approach under research to recover these elements from the slag is called the "Engineered Artificial Minerals" (EnAM) concept. Optimization of slag system and cooling conditions potentially allow enrichment of a desired element in only one phase. Studying EnAM-formation requires multi model characterization of the slag at different states of formation. This includes bulk as well as microscopic elemental, structural, and species analytical tools and modeling approaches. Here, a characterization strategy mainly studying the formation of potential EnAMs for the recovery of lithium from battery recycling slags is reviewed. LiAlO2 as well as lithium manganates were identified as promising EnAMs. The manganese oxidation state was identified a decisive parameter. For a knowledge-based design of slags, it is necessary to understand the processes leading to oxidation state variability. Hence, besides structural, compositional characterization, speciation of redox active elements is discussed here using molecular dynamics simulations, powder X-ray diffraction, electron probe microanalysis, X-ray absorption near edge structure, micro-X-ray fluorescence, micro-X-ray diffraction, and micro-X-ray absorption near edge structure. [ABSTRACT FROM AUTHOR]

In the electrocatalytic CO2 reduction reaction (CO2RR), metal catalysts with an oxidation state generally demonstrate more favorable catalytic activity and selectivity than their corresponding metallic counterparts. However, the persistence of oxidative metal sites under reductive potentials is challenging since the transition to metallic states inevitably leads to catalytic degradation. Herein, a thorough review of research on oxidation-state stabilization in the CO2RR is presented, starting from fundamental concepts and highlighting the importance of oxidation state stabilization while revealing the relevance of dynamic oxidation states in product distribution. Subsequently, the functional mechanisms of various oxidation-state protection strategies are explained in detail, and in situ detection techniques are discussed. Finally, the prevailing and prospective challenges associated with oxidation-state protection research are discussed, identifying innovative opportunities for mechanistic insights, technology upgrades, and industrial platforms to enable the commercialization of the CO2RR. [ABSTRACT FROM AUTHOR]

The classic solvent system can't sufficiently separate one‐dimensional edge‐sharing SnI2 crystals in solution, which severely restricts the fabrication of high‐quality tin‐based perovskite film. Herein, a strong Lewis base (hexamethylphosphoramide, HMPA) has been introduced to coordinate Sn2+ to modulate solvation behaviours on perovskite precursor and regulate crystallization kinetics. The large molecular volume of HMPA and stronger bind energy of SnI2 ⋅ 2HMPA (−0.595 eV vs −0.118 eV for SnI2 ⋅ 2DMSO) change the solvation structure of SnI2 from edge‐sharing cluster to monodisperse adduct, which contributes to uniform nucleation sites and prolongs crystal growth process. Delightfully, a fully‐covered perovskite film is formed on the large‐area substrate and tin‐based perovskite solar cells processed with HMPA exhibit an excellent efficiency of 13.46 %. This research provides novel insights and directions for the solution preparation of smooth and uniform large‐area tin‐based perovskite film. [ABSTRACT FROM AUTHOR]

The black phase of formamidinium lead iodide (FAPbI3) perovskite shows huge promise as an efficient photovoltaic, but it is not favoured energetically at room temperature, meaning that the undesirable yellow phases are always present alongside it during crystallization1–4. This problem has made it difficult to formulate the fast crystallization process of perovskite and develop guidelines governing the formation of black-phase FAPbI3 (refs. 5,6). Here we use in situ monitoring of the perovskite crystallization process to report an oriented nucleation mechanism that can help to avoid the presence of undesirable phases and improve the performance of photovoltaic devices in different film-processing scenarios. The resulting device has a demonstrated power-conversion efficiency of 25.4% (certified 25.0%) and the module, which has an area of 27.83 cm2, has achieved an impressive certified aperture efficiency of 21.4%.The black phase of formamidinium lead iodide perovskite is used to make highly efficient solar cells, and a technique to improve its purity and stability by controlling crystal nucleation could make them even better. [ABSTRACT FROM AUTHOR]

The ubiquity of solid–liquid interfaces in nature and the significant role of their atomic-scale structure in determining interfacial properties have led to intensive research. Particularly in electrocatalysis, however, a molecular-level picture that clearly describes the dynamic interfacial structures and organizations with their correlation to preferred reaction pathways in electrochemical reactions remains poorly understood. In this review, CO2 electroreduction reaction (CO2RR) is spatially and temporally understood as a result of intricate interactions at the interface, in which the interfacial features are highly relevant. We start with the discussion of current understandings and model development associated with the charged electrochemical interface as well as its dynamic landscape. We further highlight the interactive dynamics from the interfacial field, catalyst surface charges and various gradients in electrolyte and interfacial water structures at interfaces under CO2RR working conditions, with emphasis on the interfacial-structure dependence of catalytic reactivity/selectivity. Significantly, a probing energy-dependent "in situ characterization map" for dynamic interfaces based on various complementary in situ/operando techniques is proposed, aiming to present a comprehensive picture of interfacial electrocatalysis and to provide a more unified research framework. Moreover, recent milestones in both experimental and theoretical aspects to establish the correct profile of electrochemical interfaces are stressed. Finally, we present key scientific challenges with related perspectives toward future opportunities for this exciting frontier. [ABSTRACT FROM AUTHOR]

Reducing the lead (Pb) toxicity has remained a huge challenge toward the commercial development of the mainstream Pb-based halide perovskites. Tin (Sn) has been considered as one of the most promising candidates to replace the Pb component, but it still suffers from severe oxidation of Sn2+ and poor perovskite morphology. In this work, bifunctional additive engineering by incorporating nicotinohydrazide (NHD) with two effective groups (–N2H3 and –C＝O) into the perovskite is employed for improving the device performance of Sn-based PeLEDs. The Sn2+ oxidation is greatly suppressed due to the reducibility of –N2H3 and strong interaction between –C＝O and Sn2+. Meanwhile, the perovskite film morphology is apparently optimized owing to the distinctly retarded crystallization process. Consequently, a pure-red PeLED emitting at 628 nm is achieved with elevated electroluminescence efficiency and stability, and the CIE coordinates match the BT.2020 standard. These results provide an effective strategy for the development of lead-free PeLEDs. [ABSTRACT FROM AUTHOR]

Metal halide perovskite materials have demonstrated significant potential in various optoelectronic applications, such as photovoltaics, light emitting diodes, photodetectors, and lasers. However, the stability issues of perovskite materials continue to impede their widespread use. Many studies have attempted to understand the complex degradation mechanism and dynamics of these materials. Among them, in situ and/or operando approaches have provided remarkable insights into the degradation process by enabling precise control of degradation parameters and real-time monitoring. In this review, we focus on these studies utilizing in situ and operando approaches and demonstrate how these techniques have contributed to reveal degradation details, including structural, compositional, morphological, and other changes. We explore why these two approaches are necessary in the study of perovskite degradation and how they can be achieved by upgrading the corresponding ex situ techniques. With recent stability improvements of halide perovskite using various methods (compositional engineering, surface engineering, and structural engineering), the degradation of halide perovskite materials is greatly retarded. However, these improvements may turn into new challenges during the investigation into the retarded degradation process. Therefore, we also highlight the importance of enhancing the sensitivity and probing range of current in situ and operando approaches to address this issue. Finally, we identify the challenges and future directions of in situ and operando approaches in the stability research of halide perovskites. We believe that the advancement of in situ and operando techniques will be crucial in supporting the journey toward enhanced perovskite stability. [ABSTRACT FROM AUTHOR]

Electrons can enhance SiO2 atomic layer deposition (ALD) at low temperatures using disilane (Si2H6) and either ozone (O3/O2) or water (H2O) as reactants. SiO2 electron-enhanced ALD (EE-ALD) was demonstrated at 35 °C by exposing the sample to sequential electron, oxygen reactant, and Si2H6 exposures. The reaction sequence was electron beam exposure for 3 s, purge for 5 s, O3/O2 or H2O exposure at 0.5–1.0 Torr for 3 s, purge for 10 s, Si2H6 exposure at 100 mTorr for 1 s, and purge for 15 s. The electron exposure was an electron current of ∼150 mA for 3 s. The electrons were produced by a hollow cathode plasma electron source typically operating with a grid bias of ≈−300 V. These electrons could irradiate a sample area of ∼2 × 2 cm2. In situ spectroscopic ellipsometry measurements determined that SiO2 EE-ALD films nucleated rapidly and deposited linearly versus number of EE-ALD cycles. The SiO2 EE-ALD growth rate was 0.89 Å/cycle using O3/O2 and 0.88 Å/cycle using H2O. The SiO2 growth rate was also self-limiting at higher electron and Si2H6 exposures. In addition, SiO2 EE-ALD films were grown by changing the reaction sequence or codosing the electrons with the oxygen reactant. The SiO2 EE-ALD films could be grown on conducting silicon wafers or insulating SiO2 films. SiO2 EE-ALD is believed to be possible on insulating SiO2 films because the secondary electron yield for SiO2 at electron energies of ∼100–300 eV is greater than unity. Under these conditions, the SiO2 film charges positive during electron exposure and then pulls back secondary electrons to maintain charge neutrality. The SiO2 EE-ALD films had properties that were comparable with thermal SiO2 oxides. The refractive indices of the SiO2 EE-ALD films were similar at n = 1.44 ± 0.02 for various process conditions and equivalent to the refractive index of a wet thermal SiO2 oxide film. In addition, all the SiO2 EE-ALD films yielded etch rates in dilute buffered oxide etch solution that were only slightly higher than the etch rate of a thermal SiO2 oxide film. SiO2 EE-ALD should be useful to deposit high-quality SiO2 films for various applications at low temperatures. [ABSTRACT FROM AUTHOR]

Solar energy technologies are among the most promising renewable energy sources. The massive growth of global solar generating capacity to multi-terawatt scale is now a requirement to mitigate climate change. Perovskite solar cells (PSCs) are one of the most efficient and cost-effective photovoltaic (PV) technologies with efficiencies reaching the 26% mark. They have attracted substantial interest due to their light-harvesting capacity combined with a low cost of manufacturing. However, unsolved questions of perovskite stability are still a concern, challenging the potential of widespread commercialization. Thus, it is imperative to advance in the understanding of the degradation mechanism of PSCs under in situ and operando conditions where variable and unpredictable stressors intervene, in parallel or sequentially, on the device stability. This review aims to debate the advantages behind in situ and operando characterization to complement stability-testing of PV parameters in the strive to achieve competitive stability and reproducibility in PSCs. We consider the impact of applying single and multi-stressors under constant monitoring of alterations observed in PSC components or complete devices. We outline key future research directions to achieve the long-term stability necessary for the successful commercialization of this promising PV technology. [ABSTRACT FROM AUTHOR]

In situ micro-Raman studies are reported to monitor the evolution of the tetragonal phase in a monoclinic zirconium oxide thin film under swift heavy ion irradiation with increasing ion fluences. Structural changes in the irradiated film are observed as compared to the virgin sample, evident from an evolution of the tetragonal phase beyond critical ion fluence. The interpretation of experimental data allows for an in-depth understanding of irradiation induced stiffening of phonon and crystalline-to-crystalline phase transformation in ZrO2 thin films. Irradiation induced peak broadening and uniform shifting of fundamental Raman modes are observed mainly in the anion (i.e., oxygen atom) dominant frequency region and give a direct indication of the accumulation of structural disorder in the oxygen sublattice of the ZrO2 film. A qualitative approach is followed to understand the kinetics of such a crystalline-to-crystalline phase transformation. Experimental results reveal that the cascade overlap model with the requirement of about six multiple ion impacts provides an excellent fit to data, and the same is further confirmed by x-ray diffraction data. Thus, this study suggests that such in situ studies envisage a better and more authentic insight into the kinetics of phase transformations under similar nonequilibrium conditions. [ABSTRACT FROM AUTHOR]

Organometal halide perovskites have recently emerged as an appealing candidate in photovoltaic devices due to their excellent properties. Therefore, intense efforts have been devoted to find the ideal organics for perovskite solar cells. In response, we investigate the doping effect of CH3SH organic on the structure and related performance of a CH3NH3PbI3 perovskite solar cell, via in situ synchrotronbased grazing incidence X-ray diffraction (GIXRD), together with scanning electron microscopy (SEM). In situ GIXRD investigations clearly illustrated the transformation and modification of the perovskite structure induced by the organic dopant, which subsequently led to the enhancement of the power conversion efficiency of fabricated solar cells. Notably, nanoporous morphology and nanocrystalline structures were discovered in the perovskite film by SEM; they were also confirmed by the increase in broadening peaks/features in the GIXRD measurements. Overall, our study may ultimately result in an attractive strategy for the fabrication of high performance perovskite solar cells. [ABSTRACT FROM AUTHOR]

The in situ polymerization controlled growth of perovskites has been demonstrated as a general strategy to effectively repair grain boundary defects. However, the highly active, volatile, and brittle cross-linked scaffolds of small molecular monomers simultaneously limit the efficiency and mechanical endurance of perovskite solar cells (PSCs). Here, we first adopt macromonomer poly(ethylene glycol)dimethacrylate (PEGDMA) to achieve an effective in situ cross-linking polymerization for flexible PSCs. PEGDMA can chemically anchor at the grain boundaries during thermal annealing of perovskite films, thus effectively regulating the crystallization and reducing grain boundary defects. In addition, the in situ cross-linking of PEGDMA can limit the thermal expansion of perovskites during thermal annealing, which releases the residual strain to enhance the mechanical stability of the perovskite film. Overall, the power conversion efficiency (PCE) of the rigid and flexible PSCs with PEGDMA reaches 23.15% and 21.41%, respectively, retaining over 90% of the initial PCE after 3500 h of storage in a glove box. Furthermore, the efficiency retention of the PSCs is maintained at more than 86% after 5000 bending cycles (bending radius: 5 mm), which is of great significance for the practical application of PSCs in portable and wearable electronics. [ABSTRACT FROM AUTHOR]

In the past decade, organic–inorganic hybrid perovskite solar cells (PSCs) have made unprecedented progress and recently achieved high efficiency of over 25%, comparable with commercial silicon solar cells. However, PSCs still face poor long‐term stability hindering their commercial application. Because PSCs undergo severe degradation under environmental stress factors, such as moisture, heat, light, and electrical bias. Thus, exploring and evaluating the degradation pathways of perovskites and the degradation mechanisms of PSCs is quite essential. In situ diagnostic techniques can track the real‐time changes of structure, morphology, and optoelectronic properties of the materials in the device during the degradation process. Herein, the progress on in situ characterization for understanding the degradation in PSCs is reviewed, including advanced characterization techniques in the aspects of electron microscopy, X‐Ray, and optoelectronic spectroscopy. Besides, in situ characterization tracking the degradation process of perovskite material films from typical methylamine (MA) perovskite to formamidinium (FA)–cesium (Cs) mixed‐cation perovskite and PSCs dependent on external factors is also discussed. This overview can provide a further understanding of the stability of PSCs and solve the problems on their road to commercialization. Finally, the future perspectives of in situ characterization for understanding the degradation of PSCs are provided at the end of this review. [ABSTRACT FROM AUTHOR]

Formamidinium (FA) based perovskites are considered as one of the most promising light‐absorbing perovskite materials owing to their narrower band gap and better thermal stability compared to conventional methylammonium‐based perovskites. Constant improvement by using various additives stimulates the potential application of these perovskites. Amine molecules with different structures have been widely used as typical additives in FA‐based perovskite solar cells, and decent performances have been achieved. Thus, a systematic review focusing on structural regulation and functional construction of amines in FA‐based perovskites is of significance. Herein, we analyze the construction mechanism of different structural amines on the functional perovskite crystals. The influence of amine molecules on specific perovskite properties including defect conditions, charge transfer, and moisture resistance are evaluated. Finally, we summarize the design rules of amine molecules for the application in high‐performance FA‐based perovskites and propose directions for the future development of additive molecules. [ABSTRACT FROM AUTHOR]

Porous organic polymers (POPs), a versatile class of materials that possess many tunable properties such as high chemical absorptivity and ionic conductivity, are emerging candidate electrode materials, permselective membranes, ionic conductors, interfacial stabilizers and functional precursors to synthesize advanced porous carbon. Based on their crystal structure features, the emerging POPs can be classified into two subclasses: amorphous POPs (hyper cross-linked polymers, polymers with intrinsic microporosity, conjugated microporous polymers, porous aromatic frameworks, etc.) and crystalline POPs (covalent organic frameworks, etc.). This tutorial review provides a brief introduction of different types of POPs in terms of their classification and functions for tackling the remaining challenges in various types of Li-chemistry-based batteries. In situ and ex situ characterization studies are also discussed to highlight their importance and applicability for the structural investigation of POPs to reveal the underlying mechanism of POPs over the course of the electrochemical process. Although some revolutionary advances have been achieved, the development of POPs in Li-chemistry-based batteries is still in its infancy. Perspectives regarding future application and mechanistic insights of POPs in battery studies are outlined at the end. [ABSTRACT FROM AUTHOR]

The increasing global demand for sustainable energy sources and emerging environmental issues have pushed the development of energy conversion and storage technologies to the forefront of chemical research. Electrochemical carbon dioxide (CO2) conversion provides an attractive approach to synthesizing fuels and chemical feedstocks using renewable energy. On the path to deploying this technology, basic and applied scientific hurdles remain. Copper, as the only metal catalyst that is capable to produce C2+ fuels from CO2 reduction (CO2R), still faces challenges in the improvement of electrosynthesis pathways for highly selective fuel production. In this regard, mechanistically understanding CO2R on Cu‐based electrocatalysts, particularly identifying the structure–function correlation, is crucial. Here, a broad view of the variable structural parameters and their complex interplay in CO2R catalysis on Cu was given, with the purpose of providing deep insights and guiding the future rational design of CO2R electrocatalysts. First, this Review described the progress and recent advances in the development of well‐defined nanostructured catalysts and the mechanistic understanding on the influences from a particular structure of a catalyst, such as facet, defects, morphology, oxidation state, composition, and interface. Next, the in‐situ dynamic restructuring of Cu was presented. The importance of operando characterization methods to understand the catalyst structure‐sensitivity was also discussed. Finally, some perspectives on the future outlook for electrochemical CO2R were offered. [ABSTRACT FROM AUTHOR]

Quasi‐2D metal halide perovskite light emitting diodes (PeLEDs) have attracted a lot of attentions in recent years, while their potential applications in displays and lighting are limited by the device stability. Although defect passivation in PeLEDs is an effective method to ameliorate the unstable problem, the underlying mechanisms need to be further explored. Herein, organic spacer cations with different charge distributions and formation energies in quasi‐2D CsPbBr3 perovskites are utilized to unravel the defect passivation mechanisms, including phenylmethanamine, 2‐phenylethanamine bromide, and 4‐phenylbutylammonium. The experimental findings and density functional theory calculation reveal that the defect passivation occurs by the electrostatic interaction between defective PbBr64− octahedrons and proper organic spacer cations during the annealing process, particularly at the grain boundaries. The thermal stability of the perovskite films and device performance are improved after the effective defect passivation process. The exploration of the defect passivation process in perovskites will be beneficial to the development of high‐performance PeLEDs. [ABSTRACT FROM AUTHOR]

Thin, porous films of WO3 were fabricated by solution-based synthesis via spin-coating using polyethylene glycol (PEG), a block copolymer (PIB50-b-PEO45), or a combination of PEG and PIB50-b-PEO45 as structure-directing agents. The influence of the polymers on the composition and porosity of WO3 was investigated by microwave plasma atomic emission spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, X-ray diffraction, and gas sorption analysis. The electrochromic performance of the WO3 thin films was characterized with LiClO4 in propylene carbonate as electrolyte. To analyze the intercalation of the Li+ ions, time-of-flight secondary ion mass spectrometry, and X-ray photoelectron spectroscopy were performed on films in a pristine or reduced state. The use of PEG led to networks of micropores allowing fast reversible electrochromic switching with a high modulation of the optical transmittance and a high coloration efficiency. The use of PIB50-b-PEO45 provided isolated spherical mesopores leading to an electrochromic performance similar to compact WO3, only. Optimum characteristics were obtained in films which had been prepared in the presence of both, PEG and PIB50-b-PEO45, since WO3 films with mesopores were obtained that were interconnected by a microporous network and showed a clear progress in electrochromic switching beyond compact or microporous WO3. [ABSTRACT FROM AUTHOR]

Renewable energy conversion and storage are crucial in aiding the worldwide efforts to replace fossil fuels and achieve carbon neutrality. In particular, electrocatalytic water splitting to obtain H2 and CO2 reduction to high‐value‐added fuels can lead to an epoch of hydrogen energy and a closed‐loop carbon cycle. Although many reported electrocatalysts have demonstrated outstanding performance at the laboratory scale, the origin of the superior electrocatalytic activity and selectivity and the structural evolution of these catalysts remain ambiguous. For this purpose, operando techniques are able to combine the characterizations of the catalyst with measurement of its performance under real working conditions. Herein, a critical overview of recent developments in understanding the underlying mechanisms of water splitting and CO2 reduction is presented, emphasizing the advanced operando X‐ray absorption spectroscopy characterization of these two electrocatalytic reactions. Some perceptions of the rising X‐ray technique directions and the foreground in this field are also presented. [ABSTRACT FROM AUTHOR]

The addition of molten alkali metal salts drastically accelerates the kinetics of CO2 capture by MgO through the formation of MgCO3. However, the growth mechanism, the nature of MgCO3 formation, and the exact role of the molten alkali metal salts on the CO2 capture process remain elusive, holding back the development of more-effective MgO-based CO2 sorbents. Here, we unveil the growth mechanism of MgCO3 under practically relevant conditions using a well-defined, yet representative, model system that is a MgO(100) single crystal coated with NaNO3. The model system is interrogated by in situ X-ray reflectometry coupled with grazing incidence X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. When bare MgO(100) is exposed to a flow of CO2, a noncrystalline surface carbonate layer of ca. 7-Å thickness forms. In contrast, when MgO(100) is coated with NaNO3, MgCO3 crystals nucleate and grow. These crystals have a preferential orientation with respect to the MgO(100) substrate, and form at the interface between MgO(100) and the molten NaNO3. MgCO3 grows epitaxially with respect to MgO(100), and the lattice mismatch between MgCO3 and MgO is relaxed through lattice misfit dislocations. Pyramid-shaped pits on the surface of MgO, in proximity to and below the MgCO3 crystals, point to the etching of surface MgO, providing dissolved [Mg2+...O2-] ionic pairs for MgCO3 growth. Our studies highlight the importance of combining X-rays and electron microscopy techniques to provide atomic to micrometer scale insight into the changes occurring at complex interfaces under reactive conditions. [ABSTRACT FROM AUTHOR]

We elucidate the role of subsurface oxygen on the production of C2 products from CO2 reduction over Cu electrocatalysts using the newly developed grand canonical potential kinetics density functional theory method, which predicts that the rate of C2 production on pure Cu with no O is ∼500 times slower than H2 evolution. In contrast, starting with Cu2O, the rate of C2 production is >5,000 times faster than pure Cu(111) and comparable to H2 production. To validate these predictions experimentally, we combined time-dependent product detection with multiple characterization techniques to show that ethylene production decreases substantially with time and that a sufficiently prolonged reaction time (up to 20 h) leads only to H2 evolution with ethylene production ∼1,000 times slower, in agreement with theory. This result shows that maintaining substantial subsurface oxygen is essential for long-term C2 production with Cu catalysts. [ABSTRACT FROM AUTHOR]

Thermal annealing is critical in governing the phase distribution, and ultimately the electrical properties, of ferroelectric hafnium oxide films. In particular, rapid thermal annealing (RTA) has been shown to favor the formation of ferroelectric crystal phases, but the dynamic behavior of the film over the course of the anneal is not well understood. Herein, synchrotron X‐ray diffraction is used to characterize the phase distribution of HfO2 films deposited by atomic layer deposition (ALD) in situ during RTA, revealing complex phase transformations occurring on the scale of seconds. All samples investigated here transform into a nonmonoclinic phase, which is required for ferroelectric films. However, this phase often converts into the more stable monoclinic phase as annealing proceeds. The kinetic barrier to the transformation to the monoclinic phase during heating is higher than 1 eV f.u.−1 The initial crystallization into the ferroelectric phase and relatively high barrier to transformation to the nonferroelectric phase suggests that careful control of the thermal annealing profile can greatly increase the ferroelectric fraction of the film. By using a fast ramp rate and a short annealing time above the ferroelectric crystallization temperature, the remanent polarization of a pure HfO2 film can be increased more than twofold. [ABSTRACT FROM AUTHOR]

The crystallization mechanism of the perovskite crystals inside the mesopores of printable mesoscopic perovskite solar cells is demonstrated by in situ grazing-incidence X-ray diffraction. Ionic liquids can universally tune the crystallization process of different perovksites in the mesopores regradless of the precursor solvents, resulting in enhanced efficiency. [ABSTRACT FROM AUTHOR]