Unveiling the mass transport dynamics in PEDOT:PSS films: Insights from a probe beam deflection analysis

• Redox conversion of PEDOT:PSS monitored by Probe Beam Deflection. • Data gathered by Probe Beam Deflection dynamically treated by temporal convolution. • PEDOT:PSS prepared galvanostatically at 0 °C shown a dominating exchange of Na + . • Transport numbers of cation and anion in the PEDOT:PSS conversion were determined. • Solvent participation as non-faradaic mass transfer in the conversion quantified. The redox conversion of PEDOT:PSS synthesised potentiostatically and galvanostatically at 0 °C was monitored by in-situ Probe Beam Deflection (PBD) in NaClO 4 /CH 3 CN. The analysis of the redox current and laser beam deflection, as a function of time, is carried out by applying a mathematical treatment based on individual temporal convolutions with specific transfer functions for each species moving between the electrode surface and the solution. A quantitative determination of the extent of the ion transfer involvement in the redox conversion process has been carried out, allowing to dynamically estimate the relative proportion of each species during the oxidation and reduction process of the polymer film through the respective transport numbers. It was confirmed that the conversion process is dominated by the cation, which validates unequivocally the pseudocationic doping of films synthesised galvanostatically at 0 °C (approximately 77% Na + compared to approximately 23% ClO 4 ⁻). By complementing the information obtained through PBD with the electromicrogravimetric technique, the quantitative contribution of each species involved in the conversion process was determined for the first time, confirming the significant participation of solvent accompanying the charge-transfer-dependent ions.