The cobalt phosphate water oxidation catalyst (Co–Pi WOC) stabilized, CdS sensitized TiO2 nanowire arrays for nonsacrificial solar water splitting are reported. In this TiO2/CdS/Co–Pi photoanode, the Co–Pi WOC acts as hole transfer relay to accelerate the surface water oxidation reaction, CdS serves as light absorber for wider solar spectra harvesting, and TiO2 matrix provides direct pathway for electron transport. This triple TiO2/CdS/Co–Pi hybrid photoanode exhibits much enhanced photocurrent density and negatively shifts in onset potential, resulting in 1.5 and 3.4 times improved photoconversion efficiency compared to the TiO2/CdS and TiO2 photoanode, respectively. More importantly, the TiO2/CdS/Co–Pi shows significantly improved photoelectrochemical stability compared to the TiO2/CdS electrode, with ≈72% of the initial photocurrent retained after 2 h irradiation. The reason for the promoted performance is discussed in detail based on electrochemical measurements. This work provides a new paradigm for designing 1D nanoframework/light absorber/WOC photoanode to simultaneously enhance light absorption, charge separation, and transport and surface water oxidation reaction for efficient and stable solar fuel production.

Cobalt-phosphate water oxidation catalysts were successfully deposited onto TiO 2 /ZnSe core/shell nanowire arrays by photo-assisted electrodeposition methods. Photoelectrochemical (PEC) properties of the resulting composite photoanodes were studied for solardriven water splitting under back side illumination in 0.5 M Na 2 SO 3 electrolyte. Compared with pristine TiO 2 and TiO 2 /ZnSe nanowire arrays, the photoconversion efficiency in TiO 2 /ZnSe/Co-Pi composite photoanode was increased by 1.5 and 3.8 times at a bias voltage of 0.6 V vs. Ag/AgCl. More attractive, this triple TiO 2 /ZnSe/Co-Pi photoanodes show significantly improved PEC stability compared with the TiO 2 /ZnSe electrode, remaining 56% initial photocurrent after 4000 seconds persistent light irradiation. By using the electrochemical measurements, the reason for the improved performance of TiO 2 /ZnSe/Co-Pi is discussed in detail. It is proposed that the TiO 2 provided direct channel for electron transport, ZnSe photosensitizer extended the spectral response to the visible region, and the Co-Pi acts as hole transfer relay to accelerate the surface water oxidation reaction. The strategy for designing photoanode in this work is low-cost but effective, and could be extended to prepare other hybrid photoanode with elaborate textural characteristics.To cope with the ever increasing global energy crisis and environmental concerns, it is becoming urgent to seek clean and sustainable fuels. Hydrogen is one of the most promising candidates due to its carbon-neutral, high energy density and easy to portable properties. It releases energy after combustion with oxygen and leaves the only water by-product. Particularly, it is meaningful to extract hydrogen from water using solar light through photoelectrochemical (PEC) devices, which enables recyclable use of hydrogen fuel in a clean and renewable way. The PEC performances is heavily dependent upon light absorption, charge separation/migration, charge recombination and stability in aqueous solution of the photocatalysts. 1,2 Frustratingly, considerable efforts have proven to be impossible to optimize a single semiconductor material for all these processes so far. Titanium oxide (TiO 2 ) is one of the most commonly used wide bandgap semiconductors for PEC application due to its high catalytic activity, good stability and low cost. However, the large bandgap of TiO 2 limits its light absorption within the UV part of the solar spectrum, which strictly prevents the efficient utilization of the solar energy in the visible region. 3,4 Lots of efforts have been made to enhance the visible light harvesting ability of TiO 2 . For example, transition metal or nonmetal ions doping can extend its light absorption into the visible light region. [5][6][7][8] Alternatively, by combining short bandgap semiconductors such as ZnSe, CdS, CdSe, Zn x Cd 1-x Se with TiO 2 can also enhance the visible light harvest ability, which is widely studied in quantum dot sensitized solar cells (QDSC) and solar water splitting. 9-13,14-16 More i...