Ultrafast Cathodic Exfoliation of Few-Layer Black Phosphorus in Aqueous Solution

Preparing few-layer black phosphorus flakes, in a scalable, fast, and benign way, is a key step to promote both the fundamental research and practical applications of black phosphorus. Although the electrochemically assisted liquid exfoliation of bulk black phosphorus is a promising strategy, it is still challenging to obtain few-layer black phosphorus flakes in polar protic solvent through cathodic exfoliation. In this work, we demonstrate an ultrafast approach to exfoliate bulk black phosphorus, under a cathodic potential, in an aqueous solution of hexadecyltrimethylammonium chloride. Particularly, the exfoliation can be trigged within ∼20 s, and the obtained flakes exhibit satisfactory quality. Further detailed mechanical explorations reveal that the cathodic intercalation of hexadecyltrimethylammonium cations and their subsequent decomposition contribute to the ultrafast expansion and exfoliation of bulk black phosphorus crystals. In addition, the as-exfoliated flakes show improved stability due to the protection of hexadecyltrimethylammonium chloride. This exfoliation method, together with the findings, should shed light on the development of new exfoliation methods for preparing few-layer black phosphorus flakes in various liquid systems, thus facilitating the future applications of black phosphorus.