Nanocube-based hematite photoanode produced in the presence of Na2HPO4 for efficient solar water splitting

• Nanocube structured α-Fe2O3 thin film was synthesized from a hydrothermal process.
• Different synthetic routes for phospahte modified-hematite thin films were compared.
• Two types of phosphate complex were formed on the surface of hematite films.
• The amount and nature of the phosphate complex were discussed.

A thin film of α-Fe2O3 on FTO substrate has been synthesized from hydrothermal process in an aqueous solution of FeCl3 and Na2HPO4. A nanocube structure of α-Fe2O3 is observed within the formed hematite films and coated with phosphate ions on the surface. For comparison, another phosphate modified hematite film has been prepared by soaking the bare hematite film in Na2HPO4 solution. A negative electrostatic field can be built up on the surface of both phosphate modified hematite which will promote charge separation and extraction of photoexcited holes to the electrode surface. It is found that different types of phosphate complex exist in the hematite films, which has been determined by the isoelectric point (IEP) of the hematite films, and consequently influences the formation and strength of the electrostatic field. The effects of phosphate ions on the morphology, surface characteristics and the photoelectrochemical properties of the hematite thin films are investigated and the mechanism is proposed.