Calculating Electrochemical Activity of Porous Electrodes of a Filled-up Type with an Immobilized Enzyme and Regular Gas Pores

Abstract

A model for a porous electrode of a filled-up type with an immobilized enzyme, in which a system of regular gas pores is formed, is studied. The system of regular gas pores is in fact a collection of equidistant cylinders whose thicknesses are equal to one grain of the hydrophobizing agent. Usually, the gas reactant passes into a porous electrode via a number of chains that comprise porous grains of the hydrophobizing agent. The latter is distributed in the electrode bulk in a random fashion. In this case, channels for supplying gas are formed at high concentrations of the hydrophobizing agent. As a result, the number of molecules of a catalyst in a porous electrode, and along with it the current, are not great. Should we pass to electrodes with regular gas pores, the required amount of a hydrophobizing agent would decrease. As a result, the number of molecules of the enzyme in the electrode and the current would increase. The calculation of the last quantity is the subject matter to which the paper pays a major attention. The calculation is performed for two versions of distribution of a hydrophobizing agent over the electrode bulk, specifically, a random distribution and a regular distribution. Concrete calculations are carried out for an oxygen porous electrode with an enzyme whose electrochemical characteristics are close to those obtained on laccase. It was assumed in the calculations that the enzyme operates without mediators. It is established that a porous electrode with a quasi-regular structure has a considerable advantage. With an electrode thickness of 13 μm one can manage to obtain currents of nearly 0.74 A cm^–2 as early as at an overvoltage of about 30 mV.