On the role of metal atom doping in hematite for improved photoelectrochemical properties: a comparison study

Doping with metals is an effective strategy to improve the charge transport and photoelectrochemical (PEC) properties of hematite photoelectrode. Herein, we report a comparison study of various metal atoms doped hematites to look into the effect of metal doping on the physical and chemical properties as well as the PEC performance of planar hematite thin film under the same synthetic and measurement condition. The efficient dopants, Ti, Cr, W, Pb, Sn, Zr and Si were selected and further investigated for their morphological and electronic properties. Nanorod arrays shaped hematite electrodes were also used to investigate the doping effect for the selected typical dopant elements. It was found that Ti, Zr, and Sn doping could greatly improve the photocurrent response, and Ce and Pb doping mildly increased the photocurrent. In contrast, Mo doping had a negative effect on the PEC property of hematite photoelectrodes. Based on the results of Mott-Schottky plots, valence band XPS spectra, electrochemical impedance spectroscopy and photocurrent, it can be found that the improvement of PEC performance of doped hematite is largely due to positively shifted flat band potential, which significantly influence the surface states and interface charge transport property. While for most dopants, the charge carrier densities were not changed and show less influence on the overall performance.