Effect of kinetic reversibility on the voltammetric response in room temperature ionic liquids

• A systematic simulation study compares the sensitivity of SWV vs LSV • Optimized SWV parameters were applied experimentally for six redox couples • The sensitivity is strongly related to the redox kinetics and reversibility • Fast reversible redox systems have enhanced SWV currents – positive feedback loop • LSV is superior for irreversible systems, while quasi-reversible currents are enhanced with larger SWV amplitudes Square wave voltammetry (SWV) and linear sweep voltammetry (LSV) are widely used electrochemical techniques in electroanalytical applications, but their relative sensitivity for redox systems with different electron transfer kinetics is not fully understood. In this work, an extensive simulation study is performed to investigate the effect of SWV parameters, such as step potential, amplitude, and frequency on the electrochemical response of different redox processes with varying electrochemical reversibility kinetics. The optimized set of SWV parameters obtained from the simulation study – including a step potential of 5 mV, amplitude of 50 mV, and frequency of 20 Hz – were then applied experimentally to investigate the SWV vs LSV performance for different solid and gaseous analytes in the room temperature ionic liquid [C₂mim][NTf₂] using conventional home-made Pt microdisk vs thin-film macrodisk electrodes. The analytes include ferrocene (reversible), Cl₂, HCl, H₂, and O₂ (quasi-reversible), and NH₃ (irreversible), allowing for direct comparison between the SWV vs LSV responses, which make a clear correlation between the redox kinetics and the signal outputs. The combined simulation and experimental results demonstrate that the voltammetric response is strongly governed by the reversibility of the redox couple. For fast reversible redox couples such as ferrocene, SWV gave significantly higher currents than LSV due to the formation of the positive feedback loop. For quasi-reversible species, the SWV current response was also higher than LSV but could be further improved by employing higher amplitude values to enhance the redox cycling. However, for irreversible redox processes such as ammonia, where no backward reaction or positive feedback loop occurs, LSV is always considered to be the superior technique, consistently giving stronger and more distinct current signals. Thus, this study provides valuable insights and practical guidance on how to select and tune the electrochemical technique depending on the redox nature of the analyte.