AN ATTEMPT TO EXPLAIN THE HIGHER EFFICIENCY OF GAS-GENERATING ELECTRODES COMPARED WITH GAS-ABSORBING ELECTRODES

The mechanisms governing operation of the gas-generating (electrolyzer s) and gas-absorbing (fuel cells) porous electrodes differ in a number of significant features, namely, in the nature of the gas-phase and e lectrolyte-phase distributions across the electrode thickness, in the way the pores are filled with gas, etc. There is one more difference, which is the subject of this paper. As the overvoltage in the electrol yte pore increases, the operation of gas-generating systems can change from the inner-diffusion mode to the kinetic mode; whereas during the gas-burning process, the reverse transition occurs. That is why the u se of the catalyst in the porous electrodes of electrolyzers becomes m ore efficient with the growing overvoltage; whereas the catalyst effic iency in the fuel cells drops. We show in this paper that this phenome non can be used to explain the known experimental fact that the thickn esses of porous electrodes in fuel cells (millimeters) are much greate r than those in electrolyzers (tens and hundreds of microns).