Gas-Generating Porous Electrodes: Calculating Complete Polarization Curves

Abstract

A complete set of equations that allow one to estimate the maximum electrochemical activity of gas-generating porous electrodes (GGPE) is derived. The equations are valid if all stages that restrict the electrochemical process of gas generation are removed. The equations also allow one to calculate polarization curves throughout the entire range of variations in the overvoltage, provided no ohmic limitations are present in the system. The derivation is based on the lattice model describing the gas and electrolyte distributions over the GGPE thickness. The model was tested in previous works of the authors. Other basic characteristics of porous electrodes are calculated as well. These include, the overvoltage dependences of the oversaturation of electrolyte with gas, the electrolyte and gas porosities, the electrolyte-wetted specific surface area that takes part in the electrochemical gas evolution process, the average distance between neighboring pores, etc. The calculation makes use of constants close to those inherent in the chlorine generation process on DSA. The calculated polarization curves exhibit a clearly pronounced low-polarizability portion, which is the region of a rapid current increase in GGPE, which follows the linear Tafel portion. The presented theory gives one a chance to point out ways to change the structure of the porous space of GGPE and, in particular, DSA, in order to optimize characteristics of DSA and GGPE of other types in the future.