Exploring the Structural Competition between the Black and the Yellow Phase of CsPbI3

The realization of stable inorganic perovskites is crucial to enable low-cost solution-processed photovoltaics. However, the main candidate material, CsPbI3, suffers from a spontaneous phase transition at room temperature towards a photo-inactive orthorhombic δ-phase (yellow phase). Here we used theoretical and experimental methods to study the structural and electronic features that determine the stability of the CsPbI3 perovskite. We argued that the two physical characteristics that favor the black perovskite phase at low temperatures are the strong spatial confinement in nanocrystalline structures and the level of electron doping in the material. Within this context, we discussed practical procedures for the realization of long-lasting inorganic lead halide perovskites.

Spontaneous phase segregation of Sr2NiO3 and SrNi2O3 during SrNiO3 heteroepitaxy

Recent discovery of superconductivity in Nd0.8Sr0.2NiO2 motivates the synthesis of other nickelates for providing insights into the origin of high-temperature superconductivity. However, the synthesis of stoichiometric R1−xSrxNiO3 thin films over a range of x has proven challenging. Moreover, little is known about the structures and properties of the end member SrNiO3. Here, we show that spontaneous phase segregation occurs while depositing SrNiO3 thin films on perovskite oxide substrates by molecular beam epitaxy. Two coexisting oxygen-deficient Ruddlesden-Popper phases, Sr2NiO3 and SrNi2O3, are formed to balance the stoichiometry and stabilize the energetically preferred Ni2+ cation. Our study sheds light on an unusual oxide thin-film nucleation process driven by the instability in perovskite structured SrNiO3 and the tendency of transition metal cations to form their most stable valence (i.e., Ni2+ in this case). The resulting metastable reduced Ruddlesden-Popper structures offer a testbed for further studying emerging phenomena in nickel-based oxides.

Self-supported hierarchical nanoporous Cu/Mo@MoOx hybrid electrodes as robust nonprecious electrocatalysts for high-efficiency hydrogen evolution

Background: The hydrogen evolution reaction is a crucial step in electrochemical water splitting to generate molecular hydrogen with high purity, but it usually suffers from a sluggish reaction kinetics in alkaline media because of additional water dissociation and/or improper adsorption energy of reactive hydrogen intermediates. It is desirable to design highly active and robust nonprecious electrocatalysts as alternatives to state-of-the-art commercially available Pt/C catalyst for large-scale hydrogen production via water-alkali electrolysis. Methods: We develop monolithic nanoporous hybrid electrodes composed of electroactive Mo@MoOx nanoparticles, which are seamlessly integrated on hierarchical nanoporous Cu scaffold (Cu/Mo@MoOx) by making use of a spontaneous phase separation of Mo nanoparticles and subsequently self-grown MoOx in chemical dealloying. Results: Owing to the unique monolithic electrode architecture, in which the constituent Mo@MoOx nanoparticles work as electroactive sites and the hierarchical nanoporous Cu skeleton serves as fast electron-transfer and mass-transport pathways, the monolithic nanoporous Cu/Mo@MoOx hybrid electrode exhibits a superior electrocatalysis in 1 M KOH, with a low Tafel slope of 66 mV dec-1 and outstanding stability. It only takes them ~185 mV overpotential to reach -400 mA cm-2 , ~150 mV lower than that of nanoporous Cu supported Pt/C. Conclusion: The outstanding electrochemical performance and excellent structural stability make nanoporous Cu/Mo@MoOx electrodes attractive alternatives to Pt/C catalysts in alkaline-based devices.

Chloroform-Injection (CI) and Spontaneous-Phase-Transition (SPT) Are Novel Methods, Simplifying the Fabrication of Liposomes with Versatile Solution to Cholesterol Content and Size Distribution

Intricate formulation methods and/or the use of sophisticated equipment limit the prevalence of liposomal dosage-forms. Simple techniques are developed to assemble amphiphiles into globular lamellae while transiting from the immiscible organic to the aqueous phase. Various parameters are optimized by injecting chloroform solution of amphiphiles into the aqueous phase and subsequent removal of the organic phase. Further simplification is achieved by reorienting amphiphiles through a spontaneous phase transition in a swirling biphasic system during evaporation of the organic phase under vacuum. Although the chloroform injection yields smaller Z-average and poly-dispersity-index the spontaneous phase transition method overrides simplicity and productivity. The increasing solid/solvent ratios results in higher Z-average and broader poly-dispersity-index of liposomes under a given set of experimental conditions, and vice versa. Surface charge dependent large unilamellar vesicles with a narrow distribution have poly-dispersity-index < 0.4 in 10 μM saline. As small and monodisperse liposomes are prerequisites in targeted drug delivery strategies, hence the desired Z-average < 200 d.nm and poly-dispersity-index < 0.15 is obtained through the serial membrane-filtration method. Phosphatidylcholine/water 4 μmol/mL is achieved at a temperature of 10°C below the phase-transition temperature of phospholipids, ensuring suitability for thermolabile entities and high entrapment efficiency. Both methods furnish the de-novo rearrangement of amphiphiles into globular lamellae, aiding in the larger entrapped volume. The immiscible organic phase benefits from its faster and complete removal from the final product. High cholesterol content (55.6 mol%) imparts stability in primary hydration medium at 5 ± 3 °C for 6 months in light-protected type-1 glass vials. Collectively, the reported methods are novel, scalable and time-efficient, yielding high productivity in simple equipment.

Chloroform-injection (CI) and Spontaneous-phase-transition (SPT) are Novel Methods, Simplifying the Fabrication Liposomes

Intricate formulation methods and/or use of sophisticated equipment limit the prevalence of liposomal dosage-forms. Simple techniques are developed to assemble amphiphiles into globular lamellae while transiting from immiscible organic to the aqueous phase. Various parameters are optimized by injecting chloroform solution of amphiphiles into the aqueous phase and subsequent removal of the organic phase. Further simplification is achieved by reorienting amphiphiles through a spontaneous phase transition in a swirling biphasic system during evaporation of the organic phase under vacuum. Although the chloroform injection yields smaller size and PDI yet spontaneous phase transition method overrides simplicity and productivity. The size distribution of liposomes and solid/solvent ratio in both or any phases of formulation show direct relation. Surface charge dependant large unilamellar vesicles with a narrow distribution have PDI <0.4 in 10 μM saline. As small and monodisperse liposomes are prerequisites in targeted drug delivery strategies. Hence the desired size distribution <200 d.nm and PDI <0.15 is obtained through serial membrane-filtration method. Phosphatidylcholine/water 4 μmol/ml is achieved at a temperature of 10°C below the phase-transition temperature of phospholipids ensuing suitability for thermolabile entities and high entrapment efficiency. Both methods furnish the de-novo rearrangement of amphophiles into globular lamellae aiding in the larger entrapped volume. The immiscible organic phase facilitates faster and complete removable of the organic phase. High cholesterol content (55.6 mol%) imparts stability in primary hydration medium at 5+3°C for 6 months in light-protected type-1 glass vial. Collectively the reported methods are novel, scalable, time-efficient yielding high productivity in simple equipment.