Real time in-situ microscopy imaging of surface structure and atom dynamics of heterogeneous catalysts is an important step for understanding reaction mechanisms. Here, using in-situ environmental transmission electron microscopy (ETEM), we directly visualize surface atom dynamics at manganite perovskite catalyst surfaces for oxygen evolution reaction (OER), which are ≥20 times faster in water than in other ambients. Comparing (001) surfaces of La0.6Sr0.4MnO3 and Pr0.67Ca0.33MnO3 with similar initial manganese valence state and OER activity, but very different OER stability, allows us to distinguish between reversible surface adatom dynamics and irreversible surface defect chemical reactions. We observe enhanced reversible manganese adatom dynamics due to partial solvation in adsorbed water for the highly active and stable La0.6Sr0.4MnO3 system, suggesting that aspects of homogeneous catalysis must be included for understanding the OER mechanism in heterogeneous catalysis.

The stability of perovskite oxide catalysts for the oxygen evolution reaction (OER) plays a critical role in their applicability in water splitting concepts. Decomposition of perovskite oxides under applied potential is typically linked to cation leaching and amorphization of the material. However, structural changes and phase transformations at the catalyst surface were also shown to govern the activity of several perovskite electrocatalysts under applied potential. Hence, it is crucial for the rational design of durable perovskite catalysts to understand the interplay between the formation of active surface phases and stability limitations under OER conditions. In the present study, we reveal a surface-dominated activation and deactivation mechanism of the prominent electrocatalyst La0.6Sr0.4CoO3−δ under steady-state OER conditions. Using a multiscale microscopy and spectroscopy approach, we identify the evolving Co-oxyhydroxide as catalytically active surface species and La-hydroxide as inactive species involved in the transient degradation behavior of the catalyst. While the leaching of Sr results in the formation of mixed surface phases, which can be considered as a part of the active surface, the gradual depletion of Co from a self-assembled active CoO­(OH) phase and the relative enrichment of passivating La­(OH)3 at the electrode surface result in the failure of the perovskite catalyst under applied potential.

Thermally induced structural transformation of 2D materials opens unique avenues for generating other 2D materials by physical methods. Imaging these transitions in real time provides insight into synthesis routes and property tuning. We have used in situ transmission electron microscopy (TEM) to follow thermally induced structural transformations in layered CoSe2. Three transformation processes are observed: orthorhombic to cubic-CoSe2, cubic-CoSe2 to hexagonal-CoSe, and hexagonal to tetragonal-CoSe. In particular, the unit-cell-thick orthorhombic structure of CoSe2 transforms into cubic-CoSe2 via rearrangement of lattice atoms. Cubic-CoSe2 transforms to hexagonal-CoSe at elevated temperatures through the removal of chalcogen atoms. All nanosheets transform to basal-plane-oriented hexagonal 2D CoSe. Finally, the hexagonal to tetragonal transformation in CoSe is a rapid process wherein the layered morphology of hexagonal-CoSe is broken and islands of tetragonal-CoSe are formed. Our results provide nanoscopic insights into the transformation processes of 2D CoSe2 which can be used to generate these intriguing 2D materials and to tune their properties by modifying their structures for electro-catalytic and electronic applications.

Heterogeneous copper catalysis enabled photoinduced C−H arylations under exceedingly mild conditions at room temperature. The versatile hybrid copper catalyst provided step‐economical access to arylated heteroarenes, terpenes and alkaloid natural products with various aryl halides. The hybrid copper catalyst could be reused without significant loss of catalytic efficacy. Detailed studies in terms of TEM, HRTEM and XPS analysis of the hybrid copper catalyst, among others, supported its outstanding stability and reusability.

The synthesis of efficient molecular water oxidation catalysts (WOCs) and their stable anchoring on suitable electron acceptor supports are crucial, yet challenging, steps for the development of artificial photosynthesis schemes. Here, a highly active diruthenium complex based on the bis­(bipyridyl)­pyrazolate (bbp–) ligand scaffold is anchored on electronically conducting multiwall carbon nanotubes (MWCNTs) using a pyrene group attached to either the pyrazolate backbone (2) or to multiple axial ligand positions (1). High-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) show the presence of >75% sp2 hybridization of the MWCNTs and an increase of spectral weight of π–π* transitions upon immobilization of the pyrene-modified ligand or diruthenium complex, supporting pyrene anchoring via π–π interactions. Upon electrochemical oxidation the pyrene groups confined to the MWCNT-modified electrodes are rapidly converted to redox-active surface-bound quinone species. The water oxidation performance of the hybrid systems is studied by cyclic voltammetry and rotating ring disk electrode (RRDE) experiments under acidic aqueous condition (triflic acid, pH 1). Whereas the complex anchored at the backbone position shows higher initial catalytic activity, the complex anchored via four axial ligand positions features a higher stability. X-ray photoemission (XPS) data before and after electrochemical measurements reveal that the chemical structure of the immobilized complex remains intact under catalytic conditions. The results suggest that anchoring of Ru2 complexes by differently located pyrene groups on MWCNTs offers good performance for electron transfer, however, a single pyrene group at the pyrazolate backbone does not provide sufficiently strong surface attachment. The distinct experimental results for MWCNT hybrids with anchored 1 and 2 are further discussed in terms of the preferred attachment position at the pyrazolate-based Ru2 scaffold and the orientation of the catalyst’s active site with respect to the supporting surface.