More recently, defect-engineering has been demonstrated as a facile but effective route to boost electrocatalytic performance. In this work, an activity-enhanced MnO₂ catalyst with abundant oxygen vacancies and edges is developed by Ar-plasma strategy to enhance the electrochemical performance of Al-air batteries. Based on the detailed morphology and structure analysis, rich defects are successfully induced on the surface of MnO₂ nanowires, and the defect-engineered MnO₂ catalyst displays higher activities (more positive reduction potential and larger reduction current density) towards oxygen reduction reaction (ORR) compared with pristine MnO₂. However, excessively high defects can work against the ORR catalytic enhancement due to the structure distortion. The resultant Al-air battery displays higher voltage, larger power density and better durability. The remarkable ORR activity is due to the formation of defective active sites, which is beneficial for the oxygen species adsorption and activation of O-O bond, confirmed by DFT calculation. This strategy represents a new route for the development of non-noble Electrocatalyst for Al-air batteries.

Read more at Nature: https://www.nature.com/articles/s41586-019-1175-6

Microcavity-based frequency combs, or ‘microcombs’ have enabled many fundamental breakthroughs through the discovery of temporal cavity-solitons. These self-localized waves, described by the Lugiato-Lefever equation, are sustained by a background of radiation usually containing 95% of the total power. Simple methods for their efficient generation and control are currently being investigated to finally establish microcombs as out-of-the-lab tools. Here, we demonstrate microcomb laser cavity-solitons.

Laser cavity solitons are intrinsically background-free and have underpinned key breakthroughs in semiconductor lasers. By merging their properties with the physics of multimode systems, we provide a new paradigm for soliton generation and control in microcavities. We demonstrate 50-nm-wide bright soliton combs induced at average powers more than one order of magnitude lower than the Lugiato–Lefever soliton power threshold, measuring a mode efficiency of 75% versus the theoretical limit of 5% for bright Lugiato–Lefever solitons. Finally, we can tune the repetition rate by well over a megahertz without any active feedback.

Read more at Nature Photonics: https://www.nature.com/articles/s41566-019-0379-5