Reliability of electrochemical noise measurements: Results of round-robin testing on electrochemical noise

Abstract

Sixteen laboratories have performed electrochemical noise (EN) measurements based on two systems. The first uses a series of dummy cells consisting of a "star" arrangement of resistors in order to validate the EN measurement equipment and determine its baseline noise performance, while the second system, based on a previous round-robin in the literature, examines the corrosion of aluminium in three environments. All participants used the same measurement protocol and the data reporting and analysis were performed with automatic procedures to avoid errors. The measurement instruments used in the various laboratories include commercial general-purpose potentiostats and custom-built EN systems. The measurements on dummy cells have demonstrated that few systems are capable of achieving instrument noise levels comparable to the thermal noise * Corresponding author 1 ISE member 2 of the resistors, because of its low level. However, it is of greater concern that some of the instruments exhibited significant artefacts in the measured data, mostly because of the absence of anti-aliasing filters in the equipment or because the way it is used. The measurements on the aluminium samples involve a much higher source noise level during pitting corrosion, and most (though not all) instruments were able to make reliable measurements. However, during passivation, the low level of noise could be measured by very few systems. The round-robin testing has clearly shown that improvements are necessary in the choice of EN measurement equipment and settings and in the way to validate EN data measured. The results emphasise the need to validate measurement systems by using dummy cells and the need to check systematically that the noise of the electrochemical cell to be measured is significantly higher than the instrument noise measured with dummy cells of similar impedance.

Analysis of electrochemical noise measurement on an organically coated metal

“…Each ENM experiment gathered 1024 data points at 2 Hz sampling frequency. The instrument was assessed according to the guidelines given in references [35,36] to check the significance of instrumental noise on the gathered electrochemical data. Resistors with resistance values similar to the coating resistances were used in a dummy cell with "star-arrangement" (see reference [35] for more detail).…”

A critical review of electrochemical noise measurement as a tool for evaluation of organic coatings

“…In principle the noise generated by the dummy cell is very low; in the thermal noise range of the resistor used in the construction of dummy cell which often cannot be measured by commercial noise measurement devices. For example (theoretical) σ(v) and σ(i) generated by a dummy cell based on 100 Ω resistors are 1.1 nV and 6.3 pA respectively [51]. Therefore the noise measured with the dummy cell connected to WEs and RE is essentially the noise level generated by the instrument.…”

“…However, since the current noise generated by the instrument is a function of source impedance, the current noise of the 7 instrument should be checked using a dummy cell with comparable impedance to the system being studied. A protocol describing the procedure of measuring electrochemical noise with a dummy cell is given in reference [51]. In principle the noise generated by the dummy cell is very low; in the thermal noise range of the resistor used in the construction of dummy cell which often cannot be measured by commercial noise measurement devices.…”

“…corroding metal or coating/metal system) should be significantly higher than the noise level measured with a dummy cell of comparable impedance to the electrochemical system [51]. …”

Modeling data acquisition during electrochemical noise measurements for corrosion studies

“…Additionally, given that the measurement of the analog signal is performed at a specific rate, the noise above the Nyquist frequency can potentially result in aliasing in the digitalized signal. A possible solution to this problem is the use of analog low-pass filtering before the digitalization of the signal (Bosch et al, 2014;Ritter et al, 2012).…”