Real surface area measurements in electrochemistry

Electrode reaction rates and most double layer parameters are extensive quantities and have to be referred to the unit area of the interface. Knowledge of the real surface area of electrodes is therefore needed. Comparison of experimental data with theories or of experimental results for different materials and/or from different laboratories to each other is physically groundless without normalization to unit real area of the electrode surface. Different methods have been proposed to normalize experimental data specifically with solid electrodes. Some of them are not sufficiently justified from a physical point of view. A few of them are definitely questionable. The purpose of this document is to scrutinize the basis on which the various methods and approaches rest, in order to assess their relevance to the specific electrochemical situation and, as far as possible, their absolute reliability. Methods and approaches are applicable to (a) liquid electrodes, (b) polycrystalline and single crystal face solids, (c) supported, compressed and disperse powders. The applicability of the various techniques to each specific case is to be verified. After an introductory discussion of the “concept” of real surface area, fifteen methods, eleven applied in situ and four ex situ, are scrutinized. For each of them, after a description of the principles on which it is based, limitations are discussed and recommendations are given.