The real-area scaling factor in electrocatalysis and in charge storage by supercapacitors

In comparative evaluation of high-area, porous electrocatalyst materials, an important "scaling factor" arises connected with the real-to-apparent area ratio, R, of the material. At a given operating current in a fuel-cell or electrolyser system, the polarisation and hence power consumption of the system is determined by the real current-density, taking into account the scaring factor R. In the case of comparative evaluation of various porous electrode materials, e.g. for H-2 evolution electrocatalysis, it is important to know the extent to which improvements to performance are due to intrinsic changes of electrocatalysis on account of fine-particle structure or are simply due to large R values. Procedures for real area evaluation are reviewed and experimental applications are made to evaluation of effectiveness of several electrodeposited composite materials for improvement of cathodic H-2 evolution performance in the water electrolysis process. Conditions under which real area determinations at porous electrodes can be made by the "doubIe-layer" capacitance method are critically examined and a resulting satisfactory procedure is described. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.