Charge Transfer Mechanism on a Cobalt-Polyoxometalate-TiO<sub>2</sub> Photoanode for Water Oxidation in Acid
Fengyi Zhao, Ting Cheng, Xinlin Lu, Nandan Ghorai, Yiwei Yang, Yurii V. Geletii, Djamaladdin G. Musaev, Craig L. Hill, Tianquan Lian
Abstract
High Resolution Image Download MS PowerPoint Slide We constructed a photoanode comprising the homogeneous water oxidation catalyst (WOC) Na 8 K 8 [Co 9 (H 2 O) 6 (OH) 3 (HPO 4 ) 2 (PW 9 O 34 ) 3 ] ( Co 9 POM ) and nanoporous n -type TiO 2 photoelectrodes (henceforth “TiO 2 – Co 9 POM ”) by first anchoring the cationic 3-aminopropyltrimethoxysilane (APS) ligand on a metal oxide light absorber, followed by treatment of the metal oxide-APS with a solution of the polyoxometalate WOC. The resulting TiO 2 – Co 9 POM photoelectrode exhibits a 3-fold oxygen evolution photocurrent enhancement compared to bare TiO 2 in aqueous acidic conditions. Three-element (Co 2p, W 4f, and O 1s) X-ray photoelectron spectroscopy and Raman spectroscopy studies before and after use indicate that surface-bound Co 9 POM retains its structural integrity throughout all photoelectrochemical water oxidation studies reported here. Extensive charge-transfer mechanistic studies by photoelectrochemical techniques and transient absorption spectroscopy elucidate that Co 9 POM serves as an efficient WOC, extracting photogenerated holes from TiO 2 on the picosecond time scale. This is the first comprehensive mechanistic investigation elucidating the roles of polyoxometalates in POM-photoelectrode hybrid oxygen evolution reaction systems.