Controlling fragmentation pathways in boron toward borophene-like nanoflakes: impact on morphology, properties, and surface accessibility

In this study, we investigated how successive fragmentation, centrifugation, and drying method affect the morphology, structure, and electrochemical behavior of boron-derived nanoflakes. Bulk boron was first ultrasonicated for 24 h (physical route) and then subjected to dichromate-assisted treatment (chemical route). AFM analysis showed that the mean thickness decreased from 15.0 nm for the starting boron to 10.1 nm after ultrasonication and 4.9 nm after chemical treatment, together with a narrower thickness distribution. TEM and XRD analyses revealed that crystalline features were retained after fragmentation, despite changes in diffraction peak widths. Subsequent centrifugation yielded thinner nanoflake fractions with mean thicknesses ranging from 2.15 to 2.98 nm. Compared with conventional drying, freeze-drying slightly increased the apparent AFM thickness while maintaining a comparable BET surface area. However, t-plot analysis suggested an increased contribution from non-microporous surfaces after freeze-drying. The freeze-dried sample also exhibited the most favorable cathodic polarization response among the investigated materials. Overall, these findings demonstrate that fragmentation and post-processing conditions can influence the morphology, surface characteristics, and electrochemical behavior of boron-derived nanoflakes.