Regulating the Interfacial Electron Density of La0.8Sr0.2Mn0.5Co0.5O3/RuOx for Efficient and Low-Cost Bifunctional Oxygen Electrocatalysts and Rechargeable Zn-Air Batteries

Inducing Bifunctionality by Mechanical Blending of Oxygen Evolution Reaction- and Oxygen Reduction Reaction-Active 3D Perovskite Electrocatalysts for Zinc-Air Batteries

Bifunctional electrocatalysts for oxygen electrocatalysis are typically developed by combining separate oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) electrocatalysts to form composites, often requiring complex synthesis methods. In this study, a simplified approach is presented by mechanical blending of BaSr2CoTiSbO9 (BSCTS), an OER catalyst, with BaSr2MnTiSbO9 (BSMTS), an ORR catalyst, to construct a composite bifunctional electrocatalyst. The density-functional theory calculation supports superior ORR activity of BSMTS due to an uplifted Mn d-band center than the Co d band and its proximity to the Fermi level, whereas the greater OER activity of BSCTS is due to the uplifted O 2p band center. While microstructural similarity of BSCTS and BSMTS facilitates efficient mixing for composite formation, the mechanical blending avoids intervention of complex synthesis procedures. The resulting bifunctional composite electrocatalyst demonstrates excellent performance with a bifunctional index of 0.72 V and a peak power density of 125 mW cm-2 when used as an air-cathode electrocatalyst in Zn-air battery (ZAB). This approach underscores the importance of mechanical blending of microstructurally compatible OER and ORR catalysts in designing practical bifunctional electrocatalysts for ZABs.

Perovskite Type ABO3 Oxides in Photocatalysis, Electrocatalysis, and Solid Oxide Fuel Cells: State of the Art and Future Prospects

Since photocatalytic and electrocatalytic technologies are crucial for tackling the energy and environmental challenges, significant efforts have been put into exploring advanced catalysts. Among them, perovskite type ABO3 oxides show great promising catalytic activities because of their flexible physical and chemical properties. In this review, the fundamentals and recent progress in the synthesis of perovskite type ABO3 oxides are considered. We describe the mechanisms for electrocatalytic oxygen evolution reactions (OER), oxygen reduction reactions (ORR), hydrogen evolution reactions (HER), nitrogen reduction reactions (NRR), carbon dioxide reduction reactions (CO2RR), and metal-air batteries in details. Furthermore, the photocatalytic water splitting, CO2 conversion, pollutant degradation, and nitrogen fixation are reviewed as well. We also stress the applications of perovskite type ABO3 oxides in solid oxide fuel cells (SOFs). Finally, the optimization of perovskite type ABO3 oxides for applications in various fields and an outlook on the current and future challenges are depicted. The aim of this review is to present a broad overview of the recent advancements in the development of perovskite type ABO3 oxides-based catalysts and their applications in energy conversion and environmental remediation, as well as to present a roadmap for future development in these hot research areas.

Flexible Nanogenerators Based on Enhanced Flexoelectricity in Mn3O4 Membranes

Atomically thin, few-layered membranes of oxides show unique physical and chemical properties compared to their bulk forms. Manganese oxide (Mn3O4) membranes are exfoliated from the naturally occurring mineral Hausmannite and used to make flexible, high-performance nanogenerators (NGs). An enhanced power density in the membrane NG is observed with the best-performing device showing a power density of 7.99 mW m-2 compared to 1.04 µW m-2 in bulk Mn3O4. A sensitivity of 108 mV kPa-1 for applied forces <10 N in the membrane NG is observed. The improved performance of these NGs is attributed to enhanced flexoelectric response in a few layers of Mn3O4. Using first-principles calculations, the flexoelectric coefficients of monolayer and bilayer Mn3O4 are found to be 50-100 times larger than other 2D transition metal dichalcogenides (TMDCs). Using a model based on classical beam theory, an increasing activation of the bending mode with decreasing thickness of the oxide membranes is observed, which in turn leads to a large flexoelectric response. As a proof-of-concept, flexible NGs using exfoliated Mn3O4 membranes are made and used in self-powered paper-based devices. This research paves the way for the exploration of few-layered membranes of other centrosymmetric oxides for application as energy harvesters.