Passivation of Hematite Surface States to Improve Water Splitting Performance

Abstract Hematite is considered a promising photoanode material for solar water splitting; however, its photoelectrochemical (PEC) water splitting performance is limited by a high‐density surface state. In this study, we achieved passivation of a hematite surface using In 2 O 3 nanoparticles. We characterized the passivation effect by analyzing the Mott‐Schottky curves. The resulting compound exhibited a negative shift of 0.1 eV in the onset potential compared to pure hematite, strongly indicating that the defect surface state of hematite was effectively passivated. Furthermore, the addition of NiFe(OH) x as a cocatalyst enhanced the oxygen evolution reaction kinetics. The optimal Ti−Fe 2 O 3 /In 2 O 3 /NiFe(OH) x compound photoanode achieved a superior photocurrent density of 2.6 mA cm −2 at 1.23 V vs. RHE, which is more than six times that of pure hematite (0.41 mA cm −2 ). This finding highlights a potential avenue for overcoming the issue of a high surface‐state density as the limiting condition for photoelectrodes.