Realizing high performance solar water oxidation for Ti-doped hematite nanoarrays by synergistic decoration with ultrathin cobalt-iron phosphate nanolayers

Abstract Hematite (α-Fe 2 O 3 ) is one of the most promising photoanode materials for solar-to-hydrogen (STH) energy conversion by photoelectrochemical (PEC) water splitting. However, the practical application of hematite in PEC water splitting is severely hindered by the intrinsically low charge separation efficiency and sluggish water oxidation kinetics. Here, we reported Ti-doped hematite photoanode nanoarrays decorated with cobalt-iron phosphate (CoFePi) ultrathin nanolayers greatly enhanced bulk and surface charge separation efficiency, as well as passivate surface states for promoting the PEC water oxidation activity. The synergistic interactions of CoFePi nanolayers with the Ti-Fe 2 O 3 photoanode yield current densities of 1.75 mA/cm 2 and 2.15 mA/cm 2 in 0.1 M KOH and 1 M KOH respectively at 1.23 V RHE under AM 1.5 G illumination, which is 2.3 and 3.1 fold higher than bare hematite photoanode, and also even higher than Ti-Fe 2 O 3 and Ti-Fe 2 O 3 coated with cobalt phosphate (CoPi), iron phosphate (FePi), phosphate (Pi), respectively. A low turn-on voltage of 0.68 V RHE and high incident photon-to-electron conversion efficiency of 46.6% (IPCE, 1.23 V RHE , λ = 340 nm) are achieved with the Ti-Fe 2 O 3 /CoFePi photoanode. Collectively, the results demonstrated that the synergistic Ti-Fe 2 O 3 /CoFePi photoanode is promising for PEC water oxidation for hydrogen production.