Metallic impurities in black phosphorus nanoflakes prepared by different synthetic routes

The allotropes of elementary phosphorus materials, such as black phosphorus and its single layer form phosphorene have recently regained scientific attention due to their outstanding properties suitable for applications in electronics, optical devices, and energy applications. As with many other materials, there is a fundamental question of the presence of impurities in these materials and their influence on the properties. Such impurities are expected to dramatically influence the electronic and electrochemical properties of black phosphorus in a way similar to the way they do in the case of graphene. Here, we synthesize black phosphorus from commercially available red phosphorus via different techniques. We utilize high-pressure conversion of red phosphorus to black phosphorus and vapor phase growth of black phosphorus using a gold/tin alloy-like solvent for red phosphorus. We show that both methods lead to black phosphorus containing a large number of metallic impurities. We show that the classical tin-based method for preparing black phosphorus adds a significant amount of tin and that the metallic impurities present have an observable effect on the electrochemical properties of black phosphorus.