Ultrathin CoOx nanolayers derived from polyoxometalate for enhanced photoelectrochemical performance of hematite photoanodes

Abstract

Molecular oxygen evolution catalysts, particularly polyoxometalates (POMs), have been rarely reported for improving the performance of semiconductor photoanodes. Herein, a Co-based POM was investigated for modifying Fe₂O₃ photoanodes. The photogenerated carriers of Fe₂O₃ have a fundamental effect on Co₈POM. Ultrathin CoO_x overlayer derived from Co₈POM is confirmed as the true active species, which was prepared by a simple photodeposition method. This CoO_x nanolayer effectively restrains the surface states on the hematite nanorod and reduces the water oxidation overpotential. Our CoO_x(POM)/Fe₂O₃ composite photoanode affords the best PEC performance and the highest photovoltage when compared with pristine Fe₂O₃ photoanode and CoO_x(salt)/Fe₂O₃ photoanode prepared by a simple cobalt salt. The photocurrent density of CoO_x(POM)/Fe₂O₃ photoanode is 2.2 times higher than that of pristine Fe₂O₃ photoanodes. Meanwhile, the CoO_x(POM)/Fe₂O₃ composite photoanode achieves faster transient photoresponse and an improved charge injection efficiency of 80%.