Electrocatalytic reduction of Cr(VI) over heterophase MoS2 film electrode

Abstract

Electrochemical reduction and treatment of Cr(VI)-contaminated wastewater normally suffer from a high overpotential, due to the extravagant consumption of electrons by the adverse reactions of hydrogen evolution and oxygen reduction. In this work, the MoS2 film electrode prepared by electrochemical deposition-annealing method was applied into the electrochemical reduction of Cr(VI), with the aim to suppress the over-potential of the reduction and improve the utilization of electrons. Results demonstrated that the 2H/1T′ heterostructure of MoS2 enhanced the reduction efficiency of Cr(VI) up to 99% at a lower potential of −1.0 V vs. Ag/AgCl. The in-situ electrochemically generated hydrogen peroxide was found to play a critical role in accelerating the reduction of Cr(VI). Selective oxygen reduction reaction (ORR) via a two-electron pathway on the MoS2 cathode was responsible for the formation of hydrogen peroxide, where the MoS2 film electrode annealed at 700 °C can obtain a high productivity of 360 μM hydrogen peroxide within 60 min. The plenty of preserved interfaces between 2H and 1 T′ in the heterophase MoS2 were crucial to the selective electrocatalytic activity. In addition, this electrode also presented an excellent electrocatalytic activity in hydrogen evolution reaction (HER), which could form atomic hydrogen on the surface of cathode to facilitate the reduction of Cr(VI) under the anoxic condition. This study paves a novel pathway to in-situ deposit the MoS2 film electrode for the sustainable electrochemical reduction and treatment of Cr(VI)-containing wastewater.