Structural Studies of Porous Electrodes

Abstract

Nondestructive techniques are described for the measurement of total electrode surface area, microporosity and pore size distribution, total porosity, and fraction of total porosity consisting of open pores. These measurements have been applied to a class of composite porous electrode structures based on platinum black, Teflon, and a metal screen current collector. They have been shown to correlate with electrochemical performance on the basis of exponential relationships of the type i=aexp)(normalbS or bσV where i is the current or limiting current density based on the geometric electrode area, S is the total (BET) surface area, σV is the cumulative micropore volume, and a and b are constants depending on the type of electrode and experimental conditions. The electrochemical performance of the electrodes was shown to increase with an increase in the percentage of total open (i.e., accessible) porosity consisting of micropores. It is not clear, at present, whether the relative importance of the micro‐ and macro‐pore structures is actually conducive to maximum or asymptote‐type of optimum structure, since no macropore size distribution data are now available. Within the micro‐ pore range of 25–350Aå pore radius it was shown that the range 25–200 is performance‐determining for the class of composite electrode that was studied.