Taking the electrocatalytic hydrogenation of ethylene as an example, we show that the cavity microelectrode allows the study of the surface processes occurring on powder materials. The electrocatalytic current can be observed at scan rate (upsilon) up to a few tens of mV s(-1), while with a standard composite electrode, upsilon must be lower than a few fractions of mV s(-1). The extent of the scan rate range is around two to three magnitudes. Therefore, it is possible to construct significant voltammogram characteristics (peak intensity, peak potential, and peak area) scan rate profiles, which are related to processes underlying the electrocatalysis. However, their quantitative exploitation needs a theoretical model, which can be built up by (i) applying the chemical and electrochemical kinetics to the various involved processes and (ii) taking into account the geometry proper to a composite electrode. Direct analysis of the model allows qualitatively explaining the variation of the ratio electrolytic-current/H chemisorption current observed on cavity microelectrode vs. the scan rate, when compared to that of the spherically shaped platinum electrode.