On the modeling of electrochemical systems with simultaneous gas evolution. Case study: The zinc deposition mechanism

Electrodeposition of zinc with simultaneous hydrogen evolution in an aqueous acidic sulphate solution is investigated in an Inverted Rotating Disk Electrode (IRDE) reactor. A simulation tool, based on the MITReM (Multi-Ion Transport and Reaction Model) model is used to describe the electrochemical behavior. This model can account for mass transport by convection, diffusion and migration and for the presence of homogeneous reactions. The electron transfer at the electrode is described by a Butler–Volmer relation. A reaction mechanism is proposed from surface analysis of the deposited zinc layer. Field Emission Auger Electron Spectroscopy (FE-AES) in combination with Factor Analysis (FA) is used to determine the compositional structure of the formed zinc layer. The model parameters such as diffusion coefficients, rate constants and transfer coefficients are determined by comparison of experimental and simulated polarization curves and current efficiency profiles for different rotation speeds of the IRDE and concentrations of supporting electrolyte. The importance of the homogeneous reactions is shown. The influence of gas bubble evolution (induced micro-stirring effects, reduced electrolyte conductivity and surface blockage) on the electrodeposition process is elucidated.