Highly oriented Ge-doped hematite nanosheet arrays for photoelectrochemical water oxidation

We report a simultaneous strategy of impurity doping and crystal growth for building highly oriented Ge-doped α-Fe2O3 nanosheet arrays vertically aligned on fluorine-doped tin oxide (FTO) glass substrates in hydrothermal environments, by using β-FeOOH nanorod arrays as sacrificial templates and highly reactive Ge colloidal solutions as dopant source. Microstructure characterization and elemental analysis reveal the preferential growth orientation, distribution of dopants, and doping level of Ge-doped α-Fe2O3 nanosheet arrays. Based on the doping of Ge atoms, proper feature size of nanosheets (with thickness <10 nm) and preferential growth orientation within (001) basal plane of perpendicular nanosheet arrays, Ge-doped α-Fe2O3 nanosheet arrays show a photocurrent density of 1.4 mA cm−2 at 1.23 V vs. RHE, which is more than 50 times of the undoped α-Fe2O3 nanorod arrays. Moreover, we find that the annealing temperature remarkably affects the majority carrier density and optical absorption efficiency, which enabled the determination of photocurrent density of hematite nanostructure arrays.