Structural characterization of cage clusters assembled borophene and implication for cathode electrocatalysts in...

The successful fabrication of quasi-freestanding bilayer borophene in experiments, combined with its superior metallic character, has propelled it to a rising star among two-dimensional materials, making it highly promising for applications in micro-electronic devices. Using first-principles calculations, we comprehensively explore and characterize cage cluster assembled borophenes through various methods for experimental references. The simulated scanning tunneling microscope (STM) images under diverse bias voltages exhibit distinct morphologies and closely associated with the partial densities of states (PDOS) of the surface boron atoms. High-resolution and large-scale simulated transmission electron microscope (TEM) images are investigated to detect the internal crystal structures, facilitating better identification of non-monolayer borophenes. The partial densities of states, electronic localization functions and Mulliken bond populations have been calculated to analyze the differences of morphology in STM and TEM images. Furthermore, simulated X-ray diffraction (XRD), Raman, and infrared (IR) spectra are characterized to further assist in distinguishing the phases of borophene. In light of ultrahigh stability and excellent metallic character, cluster assembled borophene of P3¯m1 symmetry act as cathode materials of Li-O₂ battery with lower overpotential in oxygen evolution reaction (OER) than oxygen reduction reaction (ORR) processes. The overpotential is closely related to the adsorption strength of LiO₂ and Li₂O₂ intermediates on surface of boron sheets. These theoretical results offer crucial guidance for the experimental identification of borophenes and suggest that the new type of cluster assembled systems might be suitable for the cathode materials of future Li-O₂ batteries.