Electrochemical synthesis of sulfur-doped iron oxide in aqueous ferrous sulfate solution

Energy storage devices and conversion systems have attracted more and more attention with the rapid development of clean energy. Iron oxide is widely used as electrode materials and electrocatalysts because of its abundant resource, low cost, and superior electrical and catalytic properties. Doping sulfur in iron oxide is an effective method to improve electrochemical and photocatalytic performance. The common synthesis method of sulfur-doped iron oxide is a three-step method of co-precipitation, hydrothermal, and calcination. This method has to be performed under high pressure and high temperature, so it needs to consume more energy. In this work, the electrochemical synthesis of sulfur-doped iron oxide was investigated under atmospheric pressure and temperature in the aqueous ferrous sulfate solution that was used as the precursors of sulfur, iron and oxygen. The influences of solution pH on the electrochemical synthesis process and the composition and morphology of deposits were investigated by the analyses of electrochemical reaction and SEM-EDS of deposits. It was found that the oxygen content in the deposit decreased as the pH value of the solution increased. There were three electrochemical reduction processes in sequence from positive to negative potential, followed by the underpotential deposition of iron on the platinum electrode, hydrogen evolution and sulfur doping. The sheet sulfur-doped iron oxide was successfully prepared by electrodeposition under a potential more negative than -1.70 V vs MSE. The kinetics of the electrochemical reaction of iron ions on the platinum electrode was investigated. The reduction process was a quasi-reversible process controlled by diffusion. The heterogeneous charge transfer rate constant k(s) and the diffusion coefficient D were obtained.