Improving charge transfer kinetics of Ti-doped hematite photoanodes via surface modification with metal phytate complexes as cocatalysts for photoelectrochemical water oxidation

Abstract

Coating metal-based oxide photoelectrodes with oxygen evolution catalysts (OECs) is considered a very effective approach to boost photoelectrochemical (PEC) activity. In the study, metal (Fe, Co, Ni and Mn)-based phytate complexes as OECs were coated on a Ti-doped hematite (Ti–Fe₂O₃) photoanode to promote charge migration and enhance PEC water oxidation performance. As a result, the OEC-modified Fe₂O₃ photoelectrodes yielded improved PEC photocurrent compared with that of the Ti–Fe₂O₃ photoanode, and the Ni-based phytate complex (Ni-PA) decorated on Ti–Fe₂O₃ (TFO) achieved the best photocurrent registered at 0.87 mA cm⁻² and 1.23 V vs. RHE, which is about 1.5- and 21.8-fold higher than the performance of the Ti–Fe₂O₃ (0.57 mA cm⁻²) and pristine Fe₂O₃ (0.04 mA cm⁻²) photoelectrodes, respectively. Besides, the constructed TFO–NiPA photoanode presented a prominent improvement in the long-term PEC stability, incident photon-to-current efficiency (IPCE) and surface charge separation efficiency in contrast to the TFO photoelectrode. The effect of the Ni-PA layer on charge dynamics and PEC efficiency of the Ti–Fe₂O₃ photoanode was further explored, and the results implied the Ni-PA cocatalyst made significant contributions to increasing the charge carrier density, accelerating charge transfer kinetics and improving charge transfer efficiency, which resulted in enhanced charge separation and superior PEC performance. This work guides the rational design of hematite-based photoelectrodes coated with metal phytate cocatalysts to boost solar water oxidation performance.