Observation of Mercury Underpotential Deposition on an Ir Surface using the Electrochemical Quartz Crystal Microbalance Technique

Development of a technique to measure electrochemical surface area (ECSA) is essential to evaluate the activity and durability of Ir-based catalysts for polymer electrolyte membrane (PEM) water electrolysis. Mercury underpotential deposition (Hg-UPD) on Ir and IrOx in perchloric acid has been reported to be useful for ECSA evaluation. However, previous methods need to be carefully evaluated for reproducibility due to the presence of Hg(II)/Hg(I) redox reactions, and differences in UPD potentials between studies. Here, the electrochemical behavior of an Ir electrode in a mercury nitrate containing solution was investigated using the electrochemical quartz crystal microbalance method. We confirmed that a Hg adatom is reversibly adsorbed and desorbed on an Ir surface at potentials over 0.7 V vs the reversible hydrogen electrode in both perchloric acid and sulfuric acid. These results contribute to the establishment of a reproducible method for ECSA calculations for Ir-based catalysts.

Automated summary

The development of a technique to measure electrochemical surface area (ECSA) is crucial for evaluating the activity and durability of Ir-based catalysts for polymer electrolyte membrane (PEM) water electrolysis. Previous methods using mercury underpotential deposition (Hg-UPD) on Ir and IrOx have shown promise for ECSA evaluation, but reproducibility needs to be carefully evaluated due to the Hg(II)/Hg(I) redox reactions and differences in UPD potentials. In this study, the electrochemical behavior of an Ir electrode in a mercury nitrate solution was investigated, confirming the reversible adsorption and desorption of Hg adatoms on the Ir surface at potentials over 0.7V vs the reversible hydrogen electrode. These results contribute to the establishment of a reproducible method for ECSA calculations for Ir-based catalysts.