Water Oxidation at Hematite Photoelectrodes with an Iridium-Based Catalyst

• Published in: Journal of physical chemistry. C 2013-02, Vol.117 (8), p.3826-3833
• Main Authors: Badia-Bou, Laura, Mas-Marza, Elena, Rodenas, Pau, Barea, Eva M, Fabregat-Santiago, Francisco, Gimenez, Sixto, Peris, Eduardo, Bisquert, Juan
• Format: Article
• Language: English
• Subjects: Catalysis; Catalytic reactions; Chemistry; Exact sciences and technology; General and physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp311983n

The iridium complex [Cp*Ir(H2O)3](SO4) was used as an organometallic source for the electrodeposition of iridium oxide onto Fe2O3. The new iridium-containing electrode allowed us to study the coupling between the photocatalytic properties of hematite and the electrocatalytic properties of the iridium-based material. A cathodic shift of the photocurrent for water oxidation upon electrodeposition of the iridium complex was observed, which increased with increasing surface concentration of IrO x on Fe2O3. The shift for the highest surface concentration of iridium tested amounts to 300 mV at 200 μA·cm–2 current density. The catalytic mechanism of the IrO x layer was unveiled by impedance spectroscopy measurements fitted to a physical model and can be explained on the basis of a highly capacitive layer, which enhances charge separation and stores photogenerated holes at Fe2O3, subsequently oxidizing water. These findings improve our understanding of the mechanism of water oxidation by heterogeneous Ir-based catalysts coupled to semiconductor electrodes.