Toward Settling the Debate on the Role of Fe2O3 Surface States for Water Splitting

Understanding the chemical nature and role of electrode surface states is crucial for improved electrochemical cell operation. For iron(III) oxide (alpha-Fe2O3), which is one of the most widely studied anode electrodes used for water splitting, surface states were related to the appearance of a dominant absorption peak during water splitting. The chemical origin of this signature is still unclear, and this open question has provoked tremendous debate. In order to pin down the origin and role of surface states, we perform first-principles calculations with density functional theory + U on several possible adsorbates at the alpha-Fe2O3(0001) surface. We rule out the existence of a stable peroxo Fe-O-O Fe adsorbate and show that the origin of the surface absorption peak could be a Fe-O center dot type bond that functions as an essential intermediate of water oxidation.