The iR drop - well-known but often underestimated in electrochemical polarization measurements and corrosion testing

At first sight the problem of the iR drop and its compensation in electrochemical polarization measurements seems to have only minor significance, but it has actually troubled electrochemists and corrosion scientists for more than a hundred years. For reducing the iR drop in the electrochemical cell, its computation, experimental determination and numerical or automatic electronic compensation numerous scientific and experimental work has been carried out and appropriate suggestions were submitted. These efforts led to commercially available potentiostats with sophisticated facilities for automatic iR compensation. Nevertheless, to date these possibilities have been utilized with a certain hesitancy. Many users underestimate the iR drop, regarding it often merely as a marginal problem, which only has to be taken into account in experiments with very high currents or extremely low conductivity of the electrolyte. Furthermore, there are also doubts and prejudices regarding modern methods of iR compensation, resulting from previous unpleasant experiences or reports on failed experiments with inappropriate equipment or imperfect methods. Reduction or automatic compensation of the iR drop is necessary more frequently than generally assumed and also in most cases possible. On the other hand the application of the different methods is still not completely uncomplicated and requires special experimental experience and care. The aim of the present work is it therefore to give a comprehensive retrospective overview of the ohmic drop problem and the relevant activities to overcome it.