Transforming waste gases of steel making operations into valuable products through both thermo- and electrocatalytic processes, involves design and optimization challenges of both catalysts and reaction cells. In that sense, developing a set of local sensing tools is essential, so that local pH, temperature and reagent concentration near the reaction surface can be monitored, reaction pathways and mechanisms of CO2 reduction can be revealed and the activity and selectivity of catalysts can be fine-tuned.
Figure: (a) Variation of the current density and interfacial pH recorded during cyclic voltammetry in CO2-saturated 0.1 M NaHCO3, b) interfacial pH as function of the logarithm of the current density during the cyclic voltammetry from a).
Using a rotating ring-disk electrode (RRDE) as a real-time pH and CO2 sensor, successful measurements of the interfacial pH as well as faradaic efficiency during the carbon dioxide reduction reaction (CO2RR) were performed, making it possible to unravel the influence of interfacial environment on the competition between CO2RR and the hydrogen evolution reaction. This research signifies the remarkable difference between interfacial and bulk parameters. The interfacial environment in acidic media can be highly alkaline even with a strong buffer (e.g., phosphate) under forced convection. The RRDE sensor used here allows to trace the change of competition between multiple reactions with the evolving interfacial environment during reactions, which might be a promising alternative for studies in other electrochemical systems.