Mass transfer phenomena induced by surface gas flow rate in the hanging meniscus configuration: A case study of the methanol electro-oxidation reaction on Pt(100)

Abstract

The study of electrochemical systems using single-crystal electrodes under conditions that allow the occurrence of an oscillatory response can be a valuable tool to obtain a proper correlation between structure, composition, and electrocatalytic activity. Measurements with single-crystal electrodes are usually performed in the hanging meniscus configuration, so, it is essential to understand the impact of different experimental parameters on the electrochemical response, mainly under oscillatory regime, which are very sensitive to the electrochemical environment. In this study, we investigated the influence of surface gas flow rate, commonly used to avoid the contribution of the oxygen reduction reaction to the electrochemical response, on the methanol electro-oxidation reaction on Pt(100) electrodes. Controlled experiments were conducted to analyze the effect of this parameter on the electrochemical behavior in the chronoamperometric, voltammetric, and oscillatory responses. The results show that while chronoamperometric and voltammetric profiles remain relatively unaffected by varying gas flow rates, the oscillatory response undergoes significant changes. The induction period, the existence region of potential oscillations, and the transition between oscillatory patterns are notably influenced. The observed effects suggest that the subtle agitation caused by increased gas flow rate enhances mass transfer phenomena near the electrode surface, impacting the presence of soluble species and their role in the oscillatory behavior. In addition, the occurrence of mixed-mode oscillations is attributed to the periodic re-establishment of methanol concentration in the double layer. The findings highlight the importance of controlling the surface gas flow rate to ensure reliable and reproducible results in electrochemical experiments performed in the hanging meniscus configuration.