Solar Water Splitting by TiO2/CdS/Co–Pi Nanowire Array Photoanode Enhanced with Co–Pi as Hole Transfer Relay and CdS as Light Absorber

Abstract

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.