Gradient
FeO<sub><i>x</i></sub>(PO<sub>4</sub>)<sub><i>y</i></sub> Layer on Hematite
Photoanodes: Novel Structure for Efficient Light-Driven Water Oxidation
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Abstract
Hematite has been receiving increasing
attention for its application in photoelectrochemical (PEC) water
oxidation but usually exhibits poor efficiency. We fabricated a stable
gradient-structured FeO<sub><i>x</i></sub>(PO<sub>4</sub>)<sub><i>y</i></sub> layer on hematite by diffusively incorporating
phosphate onto the surface layer of hematite films at a low temperature.
X-ray photoelectron spectroscopy depth profile and Fe K-edge grazing-incidence
X-ray absorption near-edge structure and extended X-ray absorption
fine structure analysis demonstrated the formation of a ∼50
nm overlayer with a gradient phosphorus distribution and structural
evolution from the outer surface to the depth. The as-prepared photoanodes
showed highly improved PEC water oxidation performance. Up to 8.5-fold
enhancement in the photocurrent density at 1.23 V versus reversible
hydrogen electrode was achieved relative to the pristine anode. This
strategy is applicable for hematite photoanodes prepared by different
methods and with different morphologies and structures. The improvement
in the water oxidation activity is mainly attributed to the enhanced
separation of photogenerated electron–hole pairs, which is
derived from the increased hole diffusion length in the gradient-structured
overlayer. This work develops a simple and universal method to boost
the PEC water oxidation efficiency with versatile hematite photoanodes