Enhanced Oxygen Evolution Reaction Activity of Nanoporous SnO₂/Fe₂O₃/IrO₂ Thin Film Composite Electrodes with Ultralow Noble Metal Loading

Abstract

Abstract A conductive SnO 2 layer and small quantities of IrO 2 surface cocatalyst enhance the catalytic efficiency of nanoporous Fe 2 O 3 electrodes in the oxygen evolution reaction at neutral pH. Anodic alumina templates are therefore coated with thin layers of SnO 2 , Fe 2 O 3 , and IrO 2 by atomic layer deposition. In the first step, the Fe 2 O 3 electrode is modified with a conductive SnO 2 layer and submitted to different postdeposition thermal treatments in order to maximize its catalytic performance. The combination of steady‐state electrolysis, electrochemical impedance spectroscopy, X‐ray crystallography, and X‐ray photoelectron spectroscopy demonstrates that catalytic turnover and e − extraction are most efficient if both layers are amorphous in nature. In the second step, small quantities of IrO 2 with extremely low iridium loading of 7.5 µg cm −2 are coated on the electrode surface. These electrodes reveal favorable long‐term stability over at least 15 h and achieve maximized steady‐state current densities of 0.57 ± 0.05 mA cm −2 at η = 0.38 V and pH 7 (1.36 ± 0.10 mA cm −2 at η = 0.48 V) in dark conditions. This architecture enables charge carrier separation and reduces the photoelectrochemical water oxidation onset by 300 mV with respect to pure Fe 2 O 3 electrodes of identical geometry.