Publication
Ca2Fe2O5 is a p-type semiconductor with properties suitable for potential application as a photocathode in photoelectrochemical water splitting. However, it suffers from poor stability under working conditions that is still not completely understood. In this work, we investigate the degradation mechanism of thermochemically prepared Ca2Fe2O5 thin film photoelectrodes and examine the effect of surface protective layers. The magnitude of the sacrificial photocurrent generated by Ca2Fe2O5 photocathodes (ca. 0.1 mA cm-2 under 1 sun) strongly decreases after exposure to electrolyte under applied potential for several hours in the dark, and this decline was not found to be preventable using standard protective overlayers. However, electrochemical and in situ UV-vis experiments reveal a dual aspect of the degradation due to both iron reduction and calcium leaching. Kinetically controlling these aspects reveals that a degraded photocathode can be regenerated if only iron reduction occurs but also shows that the degradation is irreversible and leads to a conversion of the Ca2Fe2O5 to iron oxide when calcium leaching prevails.