Cobalt-Phosphate modified TiO₂/BiVO₄ nanoarrays photoanode for efficient water splitting

Using TiO₂ nanorods as one-dimensional (1D) electron transport tunnel, BiVO₄ as light harvester, and Co-Pi (Cobalt-Phosphate) as co-catalyst, TiO₂/BiVO₄/Co-Pi nanorod arrays were fabricated as efficient photoanode on a FTO substrate for photoelectrochemical (PEC) water splitting cells. It was found that the monoclinic BiVO₄ nanoflakes were mainly vertically attached to the side faces of rutile TiO₂ nanorods with an average size of ∼35 nm and a selective growth direction along <112>. By changing the electrodeposited quantity of BiVO₄, the effect of the loading density of BiVO₄ on the PEC performance was systematically studied, and an optimum photocurrent of ∼1.86 mA cm⁻² at 1.0 V_RHE with an onset potential as small as 0.3 V_RHE and IPCE of 26% (at 450 nm) was obtained for the TiO₂/BiVO₄/Co-Pi anodes. Electrochemical impedance spectroscopy showed that Co-Pi can greatly decrease the charge transfer resistance at the photoanode/electrolyte interface. Along with the band alignment of the 1D nanoarray heterostructure beneficial for the charge separation, a hydrogen production of ∼7.31 μmol cm⁻² h⁻¹ was achieved for the efficient water splitting system. Such a heterostructured 1D nanoarray configuration can be extended to other PEC water splitting systems as well to increase the number of reactive sites and absorption of solar light, and to enhance the OER kinetics.