Co/Fe Oxyhydroxides Supported on Perovskite Oxides as Oxygen Evolution Reaction Catalyst Systems.

Co/Fe oxyhydroxide catalysts have been deposited onto the surface of amorphous carbons or different perovskite oxides. By performing electrochemical characterizations and operando X-ray absorption spectroscopy measurements, novel insights into Co/Fe oxyhydroxide catalysts and their interactions with perovskite oxides have been revealed. The addition of Fe into Co oxyhydroxide catalysts greatly enhances the oxygen evolution reaction (OER) activity by stabilizing the Co cations into a lower oxidation state under operative conditions compared to the case of undoped Co oxyhydroxide. A beneficial Co/Fe electronic interaction for OER can also be achieved by depositing Co oxyhydroxide on Fe-containing oxide supports, such as the LaFeO3 perovskite. Finally, it was found that, despite the lower Fe content in the Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) perovskite structure, Co oxyhydroxides supported on this perovskite exhibit the highest OER activity. Therefore, our findings suggest that perovskite structures presenting a large content of oxygen vacancies and undergoing surface reconstruction, such as BSCF, offer the best interface for Co oxyhydroxides. Finally, profiting from the beneficial Co/Fe electronic interaction and perovskite interface interaction, the highest OER activity has been achieved by depositing Co/Fe oxyhydroxide on the surface of BSCF perovskite.

Functional Role of Fe-Doping in Co-Based Perovskite Oxide Catalysts for Oxygen Evolution Reaction.

Perovskite oxides have been at the forefront among catalysts for the oxygen evolution reaction (OER) in alkaline media offering a higher degree of freedom in cation arrangement. Several highly OER active Co-based perovskites have been known to show extraordinary activities and stabilities when the B-site is partially occupied by Fe. At the current stage, the role of Fe in enhancing the OER activity and stability is still unclear. In order to elucidate the roles of Co and Fe in the OER mechanism of cubic perovskites, two prospective perovskite oxides, La0.2Sr0.8Co1- xFe xO3-δ and Ba0.5Sr0.5Co1- xFe xO3-δ with x = 0 and 0.2, were prepared by flame spray synthesis as nanoparticles. This study highlights the importance of Fe in order to achieve high OER activity and stability by drawing relations between their physicochemical and electrochemical properties. Ex situ and operando X-ray absorption spectroscopy (XAS) was used to study the local electronic and geometric structure under oxygen evolving conditions. In parallel, density function theory computational studies were conducted to provide theoretical insights into our findings. Our findings show that the incorporation of Fe into Co-based perovskite oxides alters intrinsic properties rendering efficient OER activity and prolonged stability.

In-Vitro Mechanical Performance Study of Biodegradable Polylactic Acid/Hydroxyapatite Nanocomposites for Fixation Medical Devices.

Osteoconductive, biocompatible, and resorbable organic/inorganic composites are most commonly used in fixation medical devices, such as suture anchors and interference screws, because of their unique physical and chemical properties. Generally, studies on biodegradable composites have focused on their mechanical properties based on the composition and the individual roles of organic and inorganic biomaterials. In this study, we prepared biodegradable organic/inorganic nanocomposite materials using the solvent mixing process and conventional molding. We used polylactic acid (PLA) as the matrix and nano-sized hydroxyapatite (nano-HAp) as the osteoconductive filler. The content of nano-HAp was varied in 0-30 wt% and its influence on the In-Vitro mechanical performance of PLA/HAp nanocomposites was evaluated. The In-Vitro mechanical properties of nanocomposites were evaluated using standardized tensile and flexural tests after different immersion times in simulated body fluid.

Dynamic surface self-reconstruction is the key of highly active perovskite nano-electrocatalysts for water splitting.

The growing need to store increasing amounts of renewable energy has recently triggered substantial R&D efforts towards efficient and stable water electrolysis technologies. The oxygen evolution reaction (OER) occurring at the electrolyser anode is central to the development of a clean, reliable and emission-free hydrogen economy. The development of robust and highly active anode materials for OER is therefore a great challenge and has been the main focus of research. Among potential candidates, perovskites have emerged as promising OER electrocatalysts. In this study, by combining a scalable cutting-edge synthesis method with time-resolved X-ray absorption spectroscopy measurements, we were able to capture the dynamic local electronic and geometric structure during realistic operando conditions for highly active OER perovskite nanocatalysts. Ba0.5Sr0.5Co0.8Fe0.2O3-δ as nano-powder displays unique features that allow a dynamic self-reconstruction of the material's surface during OER, that is, the growth of a self-assembled metal oxy(hydroxide) active layer. Therefore, besides showing outstanding performance at both the laboratory and industrial scale, we provide a fundamental understanding of the operando OER mechanism for highly active perovskite catalysts. This understanding significantly differs from design principles based on ex situ characterization techniques.