A new route to electrochemical exfoliation of borophene for scalable production

Scalable production of freestanding borophene is of great importance for practical applications. Top-down approaches such as sono-chemical and electrochemical exfoliation are challenging due to complex structure and low electrical conductivity of boron. In this study, we envisaged to add multiwalled carbon nanotubes (MWCNTs) into boron powder to tackle the low conductivity of boron. A few layer borophene sheets down to 0.8 nm thickness were successfully prepared by anodic exfoliation of crystalline boron powder in Na2SO4. + 20 V was found to be the optimum exfoliation voltage as it results in thinner and larger sheets compared to higher voltage values. More than 50% of the exfoliated sheets are less than 10 layers, which indicate the potential of the process for freestanding borophene production. After the exfoliation process, MWCNTs could be effectively removed by a toluene/water system and subsequent filtration through a cellulose membrane. The method proposed here is scalable because the amount of boron powder that can be exfoliated can be increased without a limit as long as sufficient amount of MWCNTs are added to provide enough electrical conductivity. This novel strategy can also be extended to exfoliate other low conductivity materials, promoting future research.