A Semiconductor‐Mediator‐Catalyst Artificial Photosynthetic System for Photoelectrochemical Water Oxidation

In fabricating an artificial photosynthesis (AP) electrode for water oxidation, we have devised a semiconductor‐mediator‐catalyst structure that mimics photosystem II (PSII). It is based on a surface layer of vertically grown nanorods of Fe 2 O 3 on fluorine doped tin oxide (FTO) electrodes with a carbazole mediator base and a Ru(II) carbene complex on a nanolayer of TiO 2 as a water oxidation co‐catalyst. The resulting hybrid assembly, FTO|Fe 2 O 3 |−carbazole|TiO 2 |−Ru(carbene) , demonstrates an enhanced photoelectrochemical (PEC) water oxidation performance compared to an electrode without the added carbaozle base with an increase in photocurrent density of 2.2‐fold at 0.95 V vs. NHE and a negatively shifted onset potential of 500 mV. The enhanced PEC performance is attributable to carbazole mediator accelerated interfacial hole transfer from Fe 2 O 3 to the Ru(II) carbene co‐catalyst, with an improved effective surface area for the water oxidation reaction and reduced charge transfer resistance.