Activation of hematite photoanode synthesized at low temperature by W doping

Hematite is a model semiconductor photocatalyst extensively used for the study of photoelectrochemical (PEC) water splitting. The PEC water oxidation performance of hematite photoanode prepared on FTO (fluorinated tin oxide) increases with the increase of the annealing temperature due to crystallinity enhancement and hence less defects for charge recombination. However, high temperature annealing (i.e., 750 °C) usually induces resistance increase, deterioration or even damage of the FTO substrate. Therefore, it becomes necessary to explore novel methods to improve the intrinsic performance of hematite photoanode fabricated at relatively lower temperatures, aiming at striking the balance between catalytic activity and substrate stability. In this work, we found that facile Na2WO4 solution treatment of as-prepared FeOOH followed by annealing at relatively low temperature of 550 ℃ (W-Fe2O3-550) could improve the PEC water oxidation performance to a level even better than that of hematite prepared at high temperature of 750 ℃ (Fe2O3-750). The results of advanced spectroscopic and electrochemical characterizations demonstrated that the enhancement of the PEC performance of W-Fe2O3-550 arises from efficient charge separation at semiconductor/liquid interface and hence generation of long-lived holes, which is the main reason for enabling the activation of the nearly non-active hematite photoanode synthesized at low temperature of 550 °C. Therefore, doping is an ideal strategy for the improvement of the intrinsic PEC performance of hematite photoanode prepared at low temperature, avoiding higher temperature crystallization and damage of the FTO substrate.