Uncovering Energetic Positions of Surface Trap States in α‐Fe2O3 Treated with Cobalt Phosphate (Co−Pi) Using Charge Carrier‐Selective Heterodyne Transient Grating Technique

Abstract

AbstractNear‐field heterodyne transient grating (NF‐HD‐TG) responses of hematite (α‐Fe2O3) 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‐Fe2O3. One of them named r‐SS2, of which potential was similar to that of r‐SS1 in the surface of α‐Fe2O3, 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‐Fe2O3 but lower than those of r‐SS1 and r‐SS2.