Dual-Axial Gradient Doping (Zr and Sn) on Hematite for Promoting Charge Separation in Photoelectrochemical Water Splitting.

One of the crucial challenges to enhance the photoelectrochemical water-splitting performance of hematite (α-Fe2 O3 ) is to resolve its very fast charge recombination in bulk. Herein, we describe the design and fabrication of dual-axial gradient-doping on 1D Fe2 O3 nanorod arrays with Zr doping for x-axial and Sn doping for y-axial directions to promote the charge separation. This dual-axial gradient-doping structure fulfills the requirements of a greater electron-carrier concentration for increasing conductivity as well as a higher charge-separation efficiency across the dual-axial direction of Fe2 O3 nanorods, ultimately showing an excellent photocurrent density of 1.64 mA cm-2 at 1.23 V vs. RHE, which is 26.3 times more than that of the bare Fe2 O3 . Furthermore, the remarkably improved photocurrent density, when comparing the uniform Zr-doped Fe2 O3 nanorod arrays (1.0 mA cm-2 at 1.23 V vs. RHE) with dual-axial gradient-doped (Zr and Sn) Fe2 O3 nanorod arrays, highlights the additional charge-separation effect resulting from gradient codoping of Zr and Sn. Hence, this promising design may provide guidelines for dual-axial gradient doping into photoelectrodes to realize efficient PEC water splitting.