The electrode lowering method of the in situ radiotracer technique provides a unique opportunity for the understanding of both the kinetics and the mechanism of contamination, corrosion and electrocatalytic phenomena. The advanced version of the technique, the thin gap method was originally developed for the investigation of sorption phenomena on smooth metal surfaces. This fact greatly limits the applicability of the method both with species of low specific activity and in case of surfaces of industrial specimens. As the first part of an article series the adaptation of the original method for the investigation of compact, porous surfaces with high surface roughness is demonstrated. The basic equations of the improved method are described, with the help of which the description of sorption phenomena on rough surfaces can be characterized. The optimized preparation parameters of the porous platinum black layer for detection of 360 labelled chloride ions are given. It is shown that the sensitivity of the in situ thin gap radiotracer method was substantially increased by the application of porous electrodes. (C) 2013 Elsevier Ltd. All rights reserved.