Carbonate-Enhanced Photoelectrochemical Corrosion Limits the CO ₂ Reduction Reactivity on CuFeO ₂ Delafossite Photocathodes

CuFeO2 delafossite materials have been researched for their promising photoactivity for CO2 reduction (CO2R) due to their intrinsic p-type conductivity. However, its practical application is limited by its poor stability and low photocurrent densities. In this work, we investigated the mechanistic origin of CuFeO2 degradation under CO2R conditions. Through photoelectrochemical measurements combined with ex situ X-ray photoelectron spectroscopy and in situ surface-enhanced Raman spectroscopy, we show that CO2-saturated sodium bicarbonate electrolytes enhance photoelectrochemical corrosion by facilitating iron leaching from the catalyst. Systematic control experiments reveal that this instability is not governed solely by thermodynamic surface stability but arises from a nonequilibrium interfacial speciation of CO2, bicarbonate, and carbonate. The presence of carbonate species at the catalyst interface facilitates iron(II) complexation and degrades the CuFeO2 surface. These findings establish carbonate-driven photoelectrochemical corrosion as a key degradation pathway for CuFeO2 and underscore the importance of speciation at the interface-electrolyte in dictating the long-term performance of a catalyst for CO2R.