Suppressing the electron-hole recombination rate in hematite photoanode with a rapid cooling treatment

The preparation of hematite photoanodes for photoelectrochemical water splitting reactions always involves a high-temperature annealing process. The cooling rate during the annealing process is discovered as an important factor deciding the anode performance. Rapid cooling of the hematite photoanode increased the photocurrent from 0.635 mA cm(-2) for the normally cooled sample to 0.856 mA cm(-2) at 1.23 V vs. RHE. The rapidly cooled hematite nanowires showed decreased diameter, reduced surface disorder, Fe partial reduction, and decreased number of surface OH groups simultaneously with a red shift of light absorption. Both the charge separation and injection efficiencies are improved, confirming the simultaneous decrease of the bulk and surface electron-hole recombination rates. The bulk electron-hole recombination rate depends on the diameter of the nanowires, while the surface electron-hole recombination rate is lowered due to the reduced surface trap states. The photocurrent measurement results with H2O2 as the sacrificial agent indicate that the suppression of surface recombination is more important than that of bulk recombination. In contrast, slow cooling or rapid heating exhibits a negative effect on the performance of the hematite photoanode. (C) 2017 Elsevier Inc. All rights reserved.