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Abstract Using both density functional theory (DFT+U) simulations and experiments, we show that the incorporation of an ordered array of oxygen‐vacancies in a perovskite oxide can lead to enhancement of the electrocatalytic activity for the oxygen‐evolution reaction (OER). As a benchmark, LaCoO₃was investigated, where the incorporation of oxygen‐vacancies led to La₃Co₃O₈(LaCoO_2.67), featuring a structural transformation. DFT+U simulations demonstrated the effect of oxygen‐vacancies on lowering the potential required to achieve negative Gibbs Free Energy for all steps of the OER mechanism. This was also confirmed by experiments, where the vacancy‐ordered catalyst La₃Co₃O₈(LaCoO_2.67) showed a remarkable enhancement of electrocatalytic properties over the parent compound LaCoO₃that lacked vacancies. We also synthesized and studied an intermediate system, with a smaller degree of oxygen‐vacancies, which showed intermediate electrocatalytic activity, lower than La₃Co₃O₈and higher than LaCoO₃, confirming the expected trend and the impact of oxygen‐vacancies. Furthermore, we employed additional DFT+U calculations to simulate a hypothetical material with the same formula as La₃Co₃O₈but without the vacancy‐order. We found that the gap between centers of Codand Opbands, which is considered an OER descriptor, would be significantly greater for a hypothetical disordered material compared to an ordered system. 

Abstract Pseudocapacitors promise to fill the gap between traditional capacitors and batteries by delivering reasonable energy densities and power densities. In this work, pseudocapacitive charge storage properties are demonstrated for two isostructural oxides, Sr₂LaFeMnO₇and Sr₂LaCoMnO₇. These materials comprise spatially separated bilayer stacks of corner sharing BO₆units (B=Fe, Co or Mn). The spaces between stacks accommodate the lanthanum and strontium ions, and the remaining empty spaces are available for oxide ion intercalation, leading to pseudocapacitive charge storage. Iodometric titrations indicate that these materials do not have oxygen‐vacancies. Therefore, the oxide ion intercalation becomes possible due to their structural features and the availability of interstitial sites between the octahedral stacks. Electrochemical studies reveal that both materials show promising energy density and power density values. Further experiments through fabrication of a symmetric two‐electrode cell indicate that these materials retain their pseudocapacitive performance over hundreds of galvanostatic charge‐discharge cycles, with little degradation even after 1000 cycles. 

Abstract With the aid of neutron diffraction and electrochemical impedance spectroscopy, we have demonstrated the effect of the increase in lithium concentration and distribution on Li‐ion conductivity. This has been done through the synthesis of a layered oxide Li₂(La_0.75Li_0.25)(Ta_1.5Ti_0.5)O₇, with the so‐called Ruddlesden‐Popper type structure, where bilayer stacks of (Ta/Ti)O₆octahedra are separated by lithium ions, located in inter‐stack spaces. There are also intra‐stack spaces that are occupied by a mixture of La and Li, as confirmed by neutron diffraction. The distribution of lithium over both inter‐ and intra‐stack positions leads to the enhancement of Li‐ion conductivity in Li₂(La_0.75Li_0.25)(Ta_1.5Ti_0.5)O₇compared to Li₂La(TaTi)O₇, which has a lower concentration of lithium ions, located only in inter‐stack spaces. The analyses of real and imaginary components of electrochemical impedance data confirm the enhanced mobility of ions in Li₂(La_0.75Li_0.25)(Ta_1.5Ti_0.5)O₇. While the Li‐ion conductivity needs further improvement for practical applications, the success of the strategy implemented in this work offers a useful methodology for the design of layered ionic conductors. 

Abstract Multifunctional materials that are capable of facilitating multiple electrocatalytic processes are highly desirable. This work reports the observation of bifunctional electrocatalytic properties for water‐splitting in layered oxides, featuring 2‐dimensional layers of octahedrally coordinated transition metals separated by alkaline‐earth or rare‐earth metals. Remarkably, these materials are able to catalyze both half‐reactions of water‐splitting,i. e., oxygen‐evolution reaction (OER) and hydrogen‐evolution reaction (HER). Electrical charge‐transport studies of SrLaFe_1‐xCo_xO_4‐δin a wide range of temperatures, 25 to 800 °C, indicate semiconducting behavior for all three compounds, where there is a systematic increase in electrical conductivity as a function of temperature. The end member of the series, SrLaCoO_4‐δ, exhibits the highest electrical charge transport and best electrocatalytic activity toward both OER and HER. This catalyst also features the highest degree of polyhedral distortion as well as the presence of oxygen‐vacancies. In addition, the transition metals in this material have a favorable electronic configuration for enhanced electrocatalytic activity.