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Abstract: NiFe-based compounds are among the most promising catalysts for the oxygen evolution reaction (OER). However, the structural reconstruction of NiFe catalysts during OER is not fully understood. Most existing studies implicitly assume the formation of a homogeneous NiFe (oxy)hydroxide lattice; however, the actual reconstruction process is more likely to generate structurally heterogeneous (oxy)hydroxide phases with local distortions due to the intrinsic mismatch between Fe3+–O and Ni3+–O bond lengths in the bulk NiFe compounds. By constructing atomically dispersed Ni and Fe active sites as precatalysts and combining them with operando spectroelectrochemical studies, we observed an unusual reconstruction pathway in which isolated Ni2+ and Fe atoms can adaptively evolve into a short-range mixed NiFe (oxy)hydroxide local structure through the formation of interconnected M-O-M′ (M/M′ = Ni3+δ, Fe3+) motifs during the OER. At 1.6 V vs RHE, the reconstructed γ-Fe3+OOH clusters are induced to integrate into the high-valent γ-Ni3+δOOH lattice, resulting in a short-range mixed NixFe1–xOOH structure. This new structure is characterized by an unusually short Fe3+–Ni3+δ distance of ∼2.86 Å, which is significantly shorter than the typical Fe3+-Fe3+ distance in Fe3+ (oxy)hydroxides (2.95–3.25 Å). Interestingly, this “induction effect” is absent in Co3+–Fe3+ catalysts, as atomically dispersed Co3+ sites directly transition into γ-Co3+OOH, which lacks structural compatibility with γ-Fe3+OOH. DFT calculations reveal that the unusually short Fe3+-O bond leads to a moderate *O adsorption strength at the Fe site in the catalyst, thereby creating the most favorable conditions for the oxygen evolution reaction (OER).

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Abstract: Mixed-cation lead mixed-halide perovskites are promising materials for applications in photovoltaics; however, it has been suggested that they exhibit instabilities linked to nanoscale heterogeneity. Directly probing the origins of this heterogeneity requires characterization with nanoscale spatial resolution, making transmission electron microscopy (TEM) an essential tool. However, characterizing these materials is challenging due to their extreme sensitivity to electron irradiation. Here, we develop a low-dose, concurrent methodology using four-dimensional scanning transmission electron microscopy (4D-STEM) and energy-dispersive x-ray spectroscopy (EDX) in order to map both the chemical and structural architecture of a (FA0.83Cs0.17)Pb(I0.8Br0.2)3 perovskite film without inducing damage. Our correlative analysis reveals a complex mosaic of coexisting crystal structures in this state-of-the-art LHP film. We establish a direct link between local chemical composition and crystal structure, showing that the formation of undesirable, photovoltaically inactive hexagonal polytypes is predominantly driven by local deficiencies in the stabilizing cesium cation. These findings provide crucial insight into one of the fundamental origins of structural instabilities in mixed composition perovskite thin-films, suggesting that achieving long-term device performance requires the development of fabrication routes that ensure compositional homogeneity at the nanoscale.

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Abstract: Ruthenium oxide is a well-known electrocatalyst for water splitting. Despite many advantages, the reaction mechanism and the structure changes of ruthenium oxide are unclear during catalysis, and the catalytic efficiency of ruthenium oxides remains a concern. In this paper, a needle-shaped copper substrate was synthesized, and the performance of RuOx was optimized. Reversible in situ Raman signals were found during the reaction process, which confirmed from the reversible surface reconstruction of RuOx. Density Functional Theory calculations found that the actual catalytic species is Ru(II)O. A detailed reaction mechanism of the Volmer step on the surface of ruthenium oxide was proposed based on the findings. The results indicate that the needles can lower the overpotentials of RuOx. At a current density of 10 , the overpotential of RuOx@ndl. was 68% lower than that of RuOx@b. f., which is much lower than the overpotential of commercial Pt(20wt.%)/C. This research provides a fundamental understanding of ruthenium oxide's reaction mechanism and gives insight into the design of the hydrogen evolution reaction catalysts.

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Abstract: Organic semiconductors continue to make substantial performance gains from photovoltaics to electronics. However, understanding how differences in solid-state structure give rise to large differences in energy transport properties remains unresolved. We report that microcrystals of two perylene diimide (PDI) derivatives differing only in their terminal groups [cyclohexyl (CH) and 4-heptyl (ST)] have exciton diffusion coefficients differing by more than two orders of magnitude. Applying state-of-the-art techniques for microcrystal structure determination, we report the crystal structures of CH-PDI and two polymorphs of ST-PDI. Scanning electron diffraction reveals a range of crystallographic defects in ST-PDI microcrystals, attributed to polymorph intergrowths, while electron energy loss spectroscopy links these defects to nanoscale electronic structure changes. Computational modeling demonstrates that rotational disorder explains the difference in exciton diffusion coefficients. Our observations establish the importance of defect-induced orientational disorder as a source of extrinsic energetic disorder, highlighting the need for defect management in organic semiconductor technologies.

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Abstract: The formation of inorganic nanomaterials is highly sensitive to the local environment. When environmental conditions are carefully selected, they enable precise control over the composition, shape and dimensionality of inorganic nanostructures, which, in turn, influences their functional properties. In this study, we explore the impact of single-walled carbon nanotubes (SWNTs) on the sequential transformation of triosmium dodecacarbonyl (Os3(CO)12) into osmium iodide (OsI) and subsequently osmium disulphide (OsS2). Initially, the nanotubes form a van der Waals complex with Os3(CO)12, allowing the molecules to retain their structure and properties, unaffected by the presence of the SWNT, as determined by direct imaging using high-resolution transmission electron microscopy (HRTEM) and evaluation of metal atom valence states by X-ray photoelectron spectroscopy (XPS). When iodine is introduced, it triggers a chemical transformation of the metal carbonyl to iodide (OsI) in a NaCl-like cubic phase. The nanotubes play a crucial role by providing electrons from their valence band, as evidenced by resonance Raman spectroscopy. The structure of OsI depends significantly on its position relative to the nanotube: disk-like particles measuring 4–6 nm form on the exterior, while sub-nanometer-wide wires form within the internal cavity, the latter exhibiting tumbling motion within the SWNT, resulting in different projections in HRTEM images. The hybrid OsI-SWNT material shows ionic character and readily reacts with hydrogen sulphide, converting into OsS2. During this reaction, SWNTs regain their electrons and become charge neutral. OsS2 nanoparticles consist of two distinct phases: a standard pyrite-like cubic phase forms the core of the particles, while a hexagonal phase creates the shell (c-OS2@h-OsS2). Inside SWNTs, however, OsS2 forms a nanowire that is one unit cell wide and twists along the length of the nanotube. The nanotube serves as a protective shell for the undercoordinated osmium atoms located at the edges of the nanowire. We showed that in inorganic transformations, the SWNT acts both as a template for the growth of osmium-based nanoparticles and an analytical platform for the detailed characterisation and comparison of nanostructures formed with and without spatial constraints, facilitating the discovery of new crystal phases such as OsI and hybrid nanostructures of c-OS2@h-OsS2 reported in this study.