Electrochemical Reduction of Bromate by a Pd Modified Carbon Fiber Electrode: Kinetics and Mechanism

The electroreduction of bromate (BrO3-) was investigated at a Pd modified carbon fiber (Pd/C) electrode prepared from PdCl2 via electrodeposition method. Pd particles distributed on the carbon fiber substrate uniformly. Under various cathode potentials, electroreduction removal of BrO3- at pure carbon fiber electrode and the Pd/C electrode were firstly compared. It was observed that nearly no BrO3- removal was observed within the bias potential of -2.0V at the carbon fiber electrode. At the Pd/C electrode, the removal efficiency of BrO3- was sharply increased from 24.0% to 58.4% at the cathode potential of -1.0 to -1.5 V, which was further increased to be 87.2% at -2.0 V. The electrochemical reduction of BrO3- was strongly pH-dependent at -0.5 V and the reduction rate could be enhanced at low pH. While at the potential of -2.0 V, a slight pH effect was observed. BrO3- electroreduction follows pseudo first-order kinetics; the rate constant k was firstly increased from 0.016 to 0.031 min(-1) with the increase of the Pd loading amount from 0.31 to 0.73 mg/cm(2), and then was decreased to 0.018 min(-1) at a higher Pd loading amount of 1.05 mg/cm(2). The Pd(0) nanoparticles played a significant role in forming atomic H* to realize indirect BrO3- reduction. The electrochemical reduction of BrO3- produces accumulated intermediates of HOBr and OBr-, which were subsequently reduced to Br- with the time evolution. (C) 2014 Elsevier Ltd. All rights reserved.