Post-Test Raman Investigation of Silver Based Gas Diffusion Electrodes

Abstract

Gas diffusion electrodes are used to overcome mass transport limitations of the electrochemical conversion of CO2. Long-time stability remains one of the key challenges for industrial application. A deactivation mechanism is the formation of carbon on the electrode surface, blocking the active sites of the catalyst. We investigated the effect of 100 h of electrochemical CO2 reduction at a current density of 100 mA cm−2 on a silver based gas diffusion electrode by means of Raman microscopy. Although there was no degradation in electrochemical performance, a darkening of the electrode surface was observed. Raman measurements of the darkened surface revealed intensive carbon signals. Both the darkened surface as well as the carbon signals persisted after washing. However, a surface darkening could also be observed for silver electrodes used for electrolysis in carbon free, aqueous media. This suggests that a formation of nanostructures on the electrode surface rather than the formation of a carbon layer is causing the surface darkening. Such structures enable Surface Enhanced Raman Scattering (SERS) and cause signal enhancement of environmental carbon on the electrode. The changes in surface structure were confirmed with scanning electron microscopy (SEM), and SERS experiments were carried out for verification of the enhancement effect.