Role of Pt-probe pseudo-reference electrode in impedance measurements of Pt and polyaniline (PANI) modified Pt electrodes

Analysis of high-frequency distortions in impedance spectra of conducting polyaniline film modified Pt-electrode measured with different cell configurations

“…For almost all curves presented as Bode plots in Fig. 2b, however, some distortions of impedance spectra are at the highest frequencies seen as unexpected shifts of phase angle parts from zero [9,10,12,13,[16][17][18]. For impedance spectra A-1 and B-1 measured in conventional three-electrode cell, increase of log |Z| at the highest frequencies [16][17][18] can also be observed in Fig.…”

“…After formation, the PANI film modified Pt electrodes were thoroughly rinsed and left overnight in 0.5 mol dm −3 H 2 SO 4 electrolyte solution at −0.15 V versus SCE in an order to attain their protonated, leucoemeraldine form [23]. For impedance measurements, PANI film modified Pt electrodes were polarized at +0.35 V versus SCE, where conducting, emeraldine PANI was formed [9,10,12,13,21,22]. Experiments with 0.05 mol dm −3 H 2 SO 4 were performed with the same PANI film electrode after replacing 0.5 mol dm −3 H 2 SO 4 with 0.05 mol dm −3 H 2 SO 4 .…”

“…A Pt wire (∼0.07 cm 2 in superficial area) was applied as PRE and in an order to avoid additional content of experimental artefacts involved by outside position of PRE versus RE [13], PRE was similarly to [4,7,24] placed within HL capillary of RE.…”

“…Overlapping between various impedance responses was found particularly evident in measurements of either highly resistive WE branch (electrode and solution of low conductivity) [3,4,7,8], or highly conductive WE branch (electrode and solution of high conductivity) [9][10][11][12][13]. In both cases, distortions originating not only from reference (RE) and counter (CE) electrodes and their geometrical arrangement [3,4,7,8,13], but also from measuring instrumentation and wirings [9][10][11], have been recognized as main sources of additional impedances termed as experimental artefacts. Although impedance measurements in two-electrode configuration are generally free from experimental artefacts caused by electrical couplings between electrodes [1,5,6,14], some contributions from stray capacities and inductivities were found pronounced in measurements of (very) high and (very) low impedance cells, respectively [6,14,15].…”

“…In already presented impedance spectra of low impedance and highly capacitive WE such as conducting form of polyaniline (PANI) film modified electrodes and/or PANI membranes in acidic solutions, relatively high extent of distortions could be noticed in high frequency parts of impedance spectra measured in either conventional three-electrode cell [16][17][18], in three-electrode cell with RE connected with pseudo-reference electrode (PRE) [9,10,12,13], or in four-electrode cell with two RE's [17,19]. Since in the case of highly capacitive and low impedance WE, presence of parasitic impedances and/or reflections of RE and CE in measured impedance spectra could hardly be avoided, even after using PRE placed close to RE [9,10,12,13], it seems to be of high importance to distinguish and separate their frequency response from the frequency response of impedance branch containing conducting PANI film WE. Characterization, distinguishing and separation of overlapping impedances at high frequencies might be relevant not only for recognition and characterization of all processes influencing short-time response of conducting PANI films what is important for a number of conducting PANI films applications [20], but for definition of physical origins and possible control of the content of experimental artefacts in impedance measurements too.…”