We report on the spectroscopic analysis of iron oxides as a (photo)anode for water oxidation. We are particularly interested in α-hematite type iron oxides and iron perovskite from CaxSr2-xFe2O6-δ series. These materials are particularly attractive as a clean and inexpensive alternative in (photo)electrochemical water oxidation. However, application of these materials in (photo)electrochemical devices is challenging, mainly due to their poor electrical conductivity and sluggish oxygen evolution kinetics. Improvements to electrocatalytic activity for oxygen evolution often address the low hole mobility in these materials which may contribute to their low electrical conductivity and slow kinetics. We have synthesized α-hematite with varying oxygen deficiencies by controlling synthesis atmosphere. Our Raman spectroscopy analysis shows signature features at ca. 1300 cm-1 assigned to higher order scattering which we show correlate with oxygen vacancy content of the material. We use Raman spectroscopy under controlled atmosphere to quantify the time scale of surface events correlated with oxygen vacancy concentration and stability on α-hematite surfaces. We will discuss how oxygen vacancy plays a role in photoelectrochemical activity and electrical properties of α-hematite type materials and how solution conditions influence these effects.

Oxygen vacancy related effects in α-hematite photoanodes for water splitting

ACS Spring 2022

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