Functional Protection of Exfoliated Black Phosphorus by Noncovalent Modification with Anthraquinone

Few and monolayer black phosphorus (phosphorene) is currently an intensively researched material. Shear exfoliated black phosphorus (BP_SE) nanosheets were functionalized with the redox active antraquinone (AQ) that can provide additional charge storage capacity. The noncovalent interaction of BP with AQ occurs due to van der Waals interactions. X-ray photoelectron spectroscopy results show that AQ coverage of BP_SE nanosheets led to a stabilization against BP_SE degradation. Electrochemistry of the BP_SE-AQ shows that AQ is stably anchored onto BP_SE and exhibits redox peaks stable for more than 100 cycles. The surface coverage by AQ on BP_SE is estimated to be 1.25 nmol AQ/mg BP and electron-transfer rate constant ( k_ET) of 33 s^-1. Furthermore, the proposed modification greatly increases the gravimetric capacitance of BP_SE-AQ with respect to the starting BP_bulk. Such coating of BP not only protects BP from degradation but also brings electroactive functionality to this two-dimensionally layered material.