Uncovering Energetic Positions of Surface Trap States in α-Fe2 O3 Treated with Cobalt Phosphate (Co-Pi) Using Charge Carrier-Selective Heterodyne Transient Grating Technique

Near-field heterodyne transient grating (NF-HD-TG) responses of hematite (α-Fe2 O3 ) treated with cobalt phosphate (Co-Pi) were measured with the burn lasers inducing the depletion of the response by the removal of the trapped charge carriers in the target state, which is called charge carrier-selective heterodyne transient grating (CS-HD-TG) spectroscopic technique. We found that two distinct trap states co-existed in Co-Pi loaded on the surface of α-Fe2 O3 . One of them named r-SS2, of which potential was similar to that of r-SS1 in the surface of α-Fe2 O3 , acted as a recombination centre but could increase the lifetime of the trapped holes by the charge separation. We also revealed that the energetic position of the other (i-SS2), which has been regarded as the intermediate state for oxygen evolution reaction with low overpotential, was higher than that of i-SS1 in α-Fe2 O3 but lower than those of r-SS1 and r-SS2.

Development of Charge Carrier-Selective Heterodyne Transient Grating Spectroscopic Technique and Its Application in the Distinction of the Surface Trap States in Hematite

We newly developed a spectroscopic technique which is named charge carrier-selective heterodyne transient grating (CS-HD-TG) method for the distinction of the surface trap states existing in the photocatalysts and photovoltaic...