Understanding the fundamental electrical and photoelectrochemical behavior of a hematite photoanode

Abstract

Hematite is considered to be the most promising material used as a photoanode for water splitting and here we utilized a sintered hematite photoanode to address the fundamental electrical, electrochemical and photoelectrochemical behavior of this semiconductor oxide. The results presented here allowed us to conclude that the addition of Sn⁴⁺ decreases the grain boundary resistance of the hematite polycrystalline electrode. Heat treatment in a nitrogen (N₂) atmosphere also contributes to a decrease of the grain boundary resistance, supporting the evidence that the presence of oxygen is fundamental for the formation of a voltage barrier at the hematite grain boundary. The N₂ atmosphere affected both doped and undoped sintered electrodes. We also observed that the heat treatment atmosphere modifies the surface states of the solid–liquid interface, changing the charge-transfer resistance. A two-step treatment, with the second being performed at a low temperature in an oxygen (O₂) atmosphere, resulted in a better solid–liquid interface.