Visible‐Light Photooxidation of Water to Oxygen at Hybrid TiO₂–Polyheptazine Photoanodes with Photodeposited Co‐Pi (CoO_x) Cocatalyst

Abstract

A cobalt oxide-based oxygen-evolving cocatalyst (Co-Pi) is photodeposited by visible-light irradiation onto nanocrystalline TiO(2)-polyheptazine (TiO(2)-PH) hybrid photoelectrodes in a phosphate buffer. The Co-Pi cocatalyst couples effectively to photoholes generated in the surface polyheptazine layer of the TiO(2)-PH photoanode, as evidenced by complete photooxidation of water to oxygen under visible-light (λ>420 nm) irradiation at moderate bias potentials. In addition, the presence of the cocatalyst also reduces significantly the recombination of photogenerated charges, particularly at low bias potentials, which is ascribed to better photooxidation kinetics resulting in lower accumulation of holes. This suggests that further improvements of photoconversion efficiency can be achieved if more effective catalytic sites for water oxidation are introduced to the surface structure of the hybrid photoanodes.

Enabling visible-light water photooxidation by coordinative incorporation of Co(II/III) cocatalytic sites into organic-inorganic hybrids: quantum chemical modeling and photoelectrochemical performance

“…Following a similar concept, we have been recently developing photoanodes (figure 1) based on a hybrid absorber layer comprising of nanocrystalline TiO 2 and polyheptazine, "PH", more precisely poly(aminoimino)heptazine or melon, a CN x H y polymeric s-heptazine derivative, also often referred to as "graphitic carbon nitride" or "g-C 3 N 4 " in the literature [22][23][24][25][26]. A remarkable feature of PH is its very high thermal and chemical stability, making it a material of choice for photo(electro)catalytic applications [22,27,28].…”

CNT-TiO2−δ Composites for Improved Co-Catalyst Dispersion and Stabilized Photocatalytic Hydrogen Production

“…Control experiments were performed in either pure water or a water-methanol mixture under UV irradiation and in the presence of photocatalysts (i.e., pristine TiO2, TiO2−δ or CNT-TiO2−δ-60) without Pt co-catalyst. The protocol for the preparation of electrodes for photocurrent measurements was described elsewhere [42]. Briefly, a suspension containing 100 mg of powder sample in 1 mL of ethanol was sonicated for 15 min and then evenly deposited onto ITO glass by doctor blading using scotch tape as the frame and spacer.…”

Water Oxidation by Co‐Based Oxides with Molecular Properties

“…In order to optimize the absorption of visible light, it has been coupled with molecular dye sensitizers [109]. Bledowski and coworkers [117] reported a polyheptazine-coated nanocrystaline TiO 2 in which a CoCat was deposited. This catalyzed water oxidation under visible-light illumination and moderate bias potential and improved photocatalytic water oxidation by photo-excitation with UV light [64,118].…”

“…The mechanism of this improvement is still debated, however. Bledowski and coworkers [117] suggested that it was the result of the improved photooxidation kinetics in the presence of the CoCat cocatalyst; another alternative is that the passivation of TiO 2 surface states resulted in increased hole lifetime and thus improved energy conversion efficiency [118]. [108] Tungsten oxide (WO 3 ) is another n-type semiconductor (Figure 9.10).…”