Controlling the structure of catalysts at the atomic level provides an opportunity to establish detailed understanding of the catalytic form-to-function and realize new, non-equilibrium catalytic structures. Here, advanced thin-film deposition is used to control the atomic structure of La2/3Sr1/3MnO3, a well-known catalyst for the oxygen reduction reaction. The surface and sub-surface is customized, whereas the overall composition and d-electron configuration of the oxide is kept constant. Although the addition of SrMnO3 benefits the oxygen reduction reaction via electronic structure and conductivity improvements, SrMnO3 can react with ambient air to reduce the surface site availability. Placing SrMnO3 in the sub-surface underneath a LaMnO3 overlayer allows the catalyst to maintain the surface site availability while benefiting from improved electronic effects. The results show the promise of advanced thin-film deposition for realizing atomically precise catalysts, in which the surface and sub-surface structure and stoichiometry are tailored for functionality, over controlling only bulk compositions.

Understanding how physicochemical properties of materials affect the oxygen evolution reaction (OER) has enormous scientific and technological implications for the OER electrocatalyst design. We present our investigation on the role of strain on the surface–oxygen interaction and the OER on well-defined single-termination SrIrO3 films. Our approach employs a combination of molecular-beam epitaxy, electrochemical characterizations, ambient-pressure X-ray photoelectron spectroscopy, and density functional theory (DFT). We find that inplane compressive strain weakens the surface oxygen binding strength on SrIrO3; however, it has a negligible effect on the surface oxygen electroadsorption and the OER. We explain this observation, which goes against a commonly held intuition that a change in the surface oxygen binding strength should influence surface oxygen electroadsorption and OER by recognizing that the trend in surface oxygen adsorption measured in the gas phase does not account for the presence of water in the surface oxygen electroadsorption. Inclusions of surface water molecules allow DFT to qualitatively reproduce the electroadsorption trend, highlighting the importance of surface water in the surface–oxygen interaction. Our finding suggests that a commonly held assumption between surface oxygen binding strength (in vacuum, no water) and electroadsorption (requiring water) is not always a simple one-to-one description and calls for a more in-depth investigation on the structure of water at electrochemical interfaces.

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Intravital microscopy is a powerful technique to observe dynamic processes with single-cell resolution in live animals. No intravital window has been developed for imaging the colon due to its anatomic location and motility, although the colon is a key organ where the majority of microbiota reside and common diseases such as inflammatory bowel disease, functional gastrointestinal disorders, and colon cancer occur. Here we describe an intravital murine colonic window with a stabilizing ferromagnetic scaffold for chronic imaging, minimizing motion artifacts while maximizing long-term survival by preventing colonic obstruction. Using this setup, we image fluorescently-labeled stem cells, bacteria, and immune cells in live animal colons. Furthermore, we image nerve activity via calcium imaging in real time to demonstrate that electrical sacral nerve stimulation can activate colonic enteric neurons. The simple implantable apparatus enables visualization of live processes in the colon, which will open the window to a broad range of studies.

Amorphous oxides are one of the most active catalysts for the oxygen evolution reaction (OER). However, very little is known about the structure of the amorphous oxide catalyst during OER, especially the structural detail of the low-atomic number groups (e.g., O, P-containing species). Herein, we report in situ stimulated Raman spectroscopy (SRS) of an amorphous cobalt oxide deposited in phosphate electrolyte (CoPi), one of the most active OER catalysts in neutral pH. In situ SRS reveals the presence of orthophosphates (PO4 3–) in CoPi, despite the species being unstable at the studied pH. 18O labeling of water during the CoPi electrodeposition substantially shifts the vibrational spectra of the phosphate bands, even though the phosphate groups were not labeled. The new vibrational positions match best to the phosphate network, for example, pyrophosphates (P2O7 4–), implying that the phosphates polymerize like a phosphate glass. We propose that the CoPi formation starts by electro-generating high-valence Co that subsequently react with water and phosphate to form CoPi. In 18O water, the kinetic isotope effect slows down the Co reactivity toward water. As a result, the high-valence Co reacts preferably with phosphates, polymerizing them into a phosphate network. Our finding provides a mechanistic view of how the buffer ions affect the structure of an amorphous oxide, which may explain why the activity is sensitive to the deposition procedure.

Two-photon fluorescence microscopy is a nonlinear imaging modality frequently used in deep-tissue imaging applications. A tunable-wavelength multicolor short-pulse source is usually required to excite fluorophores with a wide range of excitation wavelengths. This need is most typically met by solid-state lasers, which are bulky, expensive, and complicated systems. Here, we demonstrate a compact, robust fiber system that generates naturally synchronized femtosecond pulses at 1050 nm and 1200 nm by using a combination of gain-managed and Raman amplification. We image the brain of a mouse and view the blood vessels, neurons, and other cell-like structures using simultaneous degenerate and nondegenerate excitation.

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