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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]

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 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]

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]

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 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]

Inorganic CsPbI2Br halide perovskite has received extensive attention due to its excellent thermal stability and suitable bandgap for high-performance solar cells. However, CsPbI2Br can easily transform from the perovskite phase to the non-perovskite phase due to a water vapour-induced phase transition under ambient conditions, leading to a rapid degradation of device performance. Herein, we introduced lanthanum (La3+) ions into the lattice to stabilize the perovskite phase in CsPbI2Br-based all-inorganic solar cells. A power conversion efficiency of 8.03% was obtained at an optimized La3+-doping level of 2%, leading to a 27% efficiency improvement. Moreover, the La3+-doped solar cell retained 90% of its efficiency in ambient air for 400 h, showing a significantly enhanced moisture stability compared to that of the pristine (undoped) device. Detailed analysis indicates that La3+-ions can induce lattice shrinking and thus inhibit the formation of a non-perovskite phase, and enhance the charge carrier lifetime, which contribute to the improved moisture stability and efficiency. Our results indicate that highly stable all-inorganic solar cells can be produced in an air atmosphere, showing great potential for future commercialization. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) have gained tremendous research interest in recent several years. To date the power conversion efficiency (PCE) of PSCs has been increased from 3.8% to over 22.1%, showing that they have a promising future as a renewable energy resource to compete with conventional silicon solar cells. However, a crucial challenge of PSCs currently is that perovskite materials and PSCs have limitations of easy degradation and inferior long-term stabilities, thus hampering their future commercial applications. In this review, the degradation mechanisms for instable perovskite materials and their corresponding solar cells are discussed. The stability study of perovskite materials and PSCs from the aspect of experimental tests and theoretical calculations is reviewed. The strategies for enhancing the stability of perovskite materials and PSCs are summarized from the viewpoints of perovskite material engineering, substituted organic and inorganic materials for hole transportation, alternative electrodes comprising mainly carbon and its relevant composites, interfacial modification, novel device structure construction and encapsulation, etc. Various approaches and outlooks on the future direction of perovskite materials and PSCs are highlighted. This review is expected to provide helpful insights for further enhancing the stability of perovskite materials and PSCs in this exciting field. [ABSTRACT FROM AUTHOR]

This article provides a contribution towards the mechanistic understanding of surface phenomena observed during the corrosion of Mg-based substrates particularly in the low anodic polarization range. The concept considers the recent literature explaining cathodic hydrogen evolution from noble acting areas even during global anodic polarization. Heavy metal impurities in the ppm range or intermetallics are always present even in highly pure magnesium. Their potential effect was investigated here in more detail. The experimental results contribute to understanding the role of iron impurities in dark area formation and suggest a way for linking the observed phenomena to the recent literature. The shown enhanced cathodic activity of dark areas especially at the corrosion front and the superfluous hydrogen are linked to an iron re-deposition mechanism due to iron reduction. The proposed mechanism is based on the results obtained from innovative characterisation techniques using magnetic fields, diffraction experiments and transmission electron microscopy, which show the formation of iron rich zones, especially at the corrosion front offering “in statu nascendi” metallic Fe films acting as active cathodes for hydrogen reduction. [ABSTRACT FROM AUTHOR]

A solution-based two-dimensional interfacial reaction between 5,10,15,20-tetra(4-pyridyl)-porphinato zinc(ii) (ZnTPyP, 1) and Cu(NO3)2·3H2O, 2, results in the assembly of uniform preferentially oriented highly crystalline metal–organic framework nanosheets, NAFS-21 that have sub-micron planar size and mono-molecular thickness. [ABSTRACT FROM AUTHOR]