EFFECTS OF GAS-BUBBLES ON THE CURRENT AND POTENTIAL PROFILES WITHIN POROUS FLOW-THROUGH ELECTRODES

This paper presents a mathematical model to calculate the distributions of current i(x), potential E(x), gas void fraction epsilon(x) and pore electrolyte resistivity rho(x) within porous flow-through electrodes producing hydrogen. It takes into consideration the following effects: (i) the kinetics of the interfacial charge transfer step, (ii) the effect of the non-uniformly generated gas bubbles on the resistivity of the gas-electrolyte dispersion within the pores of the electrode rho(x) and (iii) the convective transport of the electrolyte through the pores. These effects appear in the form of three dimensional groups i.e. K = i0-alpha-L where i0 is the exchange current density, alpha is the specific surface area of the electrode and L its thickness. Phi = rho-0L where rho-0 is the pore electrolyte resistivity and tau = sigma/lambda-Q where sigma is a constant. LAMBDA tortuosity/porosity of the porous electrode and Q is the superficial electrolyte volume flow rate within it. Two more dimensionless groups appear: i.e. the parameter of the ohmic effect DELTA = K-phi/b and the kinetic-transport parameter I = K-tau. The model equations were solved for i(x), E(x), epsilon(x) and rho(x) for various values of the above groups.