Rational Design of CoOOH/α-FeO/SnO for Boosted Photoelectrochemical Water Oxidation: The Roles of Underneath SnO and Surface CoOOH.

Hematite (α-FeO) photoanode is a promising candidate for efficient PEC solar energy conversion. However, the serious charge recombination together with the sluggish water oxidation kinetics of α-FeO still restricts its practical application in renewable energy systems. In this work, a CoOOH/α-FeO/SnO photoanode was fabricated, in which the ultrathin SnO underlayer is deposited on the fluorine-doped tin oxide (FTO) substrate, α-FeO nanorod array is the absorber layer, and CoOOH nanosheet is the surface modifier, respectively. The resulting CoOOH/α-FeO/SnO exhibited excellent PEC water splitting with a high photocurrent density of 2.05 mA cm at 1.23 V vs RHE in the alkaline electrolyte, which is ca. 3.25 times that of bare α-FeO. PEC characterizations demonstrated that SnO not only could block hole transport from α-FeO to FTO substrate but also could efficiently enhance the light-harvesting property and reduce the surface states by controlling the growth process of α-FeO, while the CoOOH overlayer as cocatalysts could rapidly extract the photogenerated holes and provide catalytic active sites for water oxidation. Benefiting from the synergistic effects of SnO and CoOOH, the efficiency of the charge recombination and the overpotential for water oxidation of α-FeO are obviously decreased, resulting in the boosted PEC efficiency for water oxidation. The rational design and simple fabrication strategy display great potentials to be used for other PEC systems with excellent efficiency.