Operando identification of electrocatalyst layer generated on lead electrode under oxygen evolution reaction

• Surface catalyst layer on Pb electrode was investigated by in-situ Raman spectroscopy. • α- and β-PbO 2 were generated on Pb electrode under oxygen evolution reaction. • Generated Pb-oxides species depend on the local environment on electrode surface. Lead (Pb)-based materials are conventionally used as electrodes in various electrochemical systems. However, the chemical state of the surface films working as electrocatalysts under the oxygen evoltuion reaction (OER) has not been clarified. In this study, we investigated the chemical state and microstructure of surface films generated on a Pb electrode during OER in a sulfuric acid solution by operando microscopic electrochemical (EC) Raman spectroscopy. The EC-Raman spectra revealed that the Pb-related compounds and crystal structure of the surface films depend on the applied potential and analysis point. Notably, at the main analysis point, a sharp band of β-PbO 2 was detected as the main phase in the potential region for OER and its intensity increased with increase in the applied potential. On the other hand, at another analysis point, the band for β-PbO 2 did not appear in the same potential region. Instead, α-PbO 2 and β-PbO, which have a lower electronic conductivity than β-PbO 2 , were detected, and the band intensities were almost unchanged by increasing the potential. The results indicate that the local environment significantly affects the chemical states of EC-generated surface films on a Pb electrode and β-PbO 2 acts as the main OER active site.