Surface passivation of hematite photoanodes using iron phosphate

Abstract

Deposition of passive layers containing covalently bonded oxygen is an effective strategy to suppress the surface states of α-Fe₂O₃ (hematite). In this research, hematite films were first grown using the electric field assisted liquid phase deposition (EA-LPD). The deposited films were then heat-treated at 800 °C for 20 minutes. Thin layers of iron phosphate (FePO₄·2H₂O) in both crystalline and amorphous forms were deposited on the films using the liquid phase deposition (LPD). Photoelectrochemical (PEC) studies indicated that the hematite films modified with an FePO₄·2H₂O surface passivation layer show higher photocurrent density than pristine hematite. The highest photocurrent density, ∼0.71 mA cm⁻², was obtained at 1.23 V vs. reversible hydrogen electrode (RHE) for the hematite films modified with amorphous FePO₄·2H₂O, ∼36% more than pristine hematite. Under solar radiation, FePO₄·2H₂O facilitates the oxygen evolution reaction (OER) by reducing the onset potential from ∼0.82 V vs. RHE for pristine hematite to 0.74 V vs. RHE for the hematite modified with FePO₄·2H₂O layer.