Photocatalytic H₂O-to-H₂O₂ and -H₂ affected by Pd-TiO_2-δ/TiO₂

The 21st Conference of Parties suggested that a significant increase in solar-driven electricity could assist in the practicable reduction of the continuously increasing global CO₂ concentrations. Since the conversion efficiencies of TiO₂ for photocatalytic H₂O-to-H₂O₂ were relatively low (ie, 0.14 mmole H₂O₂/gTiO₂/min), the novel Pd-TiO_2-δ/TiO₂ photocatalysts for H₂O-to-H₂O₂ and -H₂ were, thus, prepared by dispersion of palladium (36-86 ppm) on the Ti³⁺ self-doped TiO₂ (Pd-TiO_2-δ/TiO₂). Specifically, a feasibility study for photocatalytic H₂O_(l)-to-H₂O_2(aq) and -H_2(g) affected by the Pd-TiO_2-δ/TiO₂ photocatalysts for green energy was carried out in the present work. Note that H₂O₂ and H₂ can be yielded through the photocatalytic two-electron transfer reactions (O₂ + 2H⁺ + 2e⁻ → 2H₂O₂ and 2H⁺ +2e⁻ → H₂) that are thermodynamically feasible. Palladium on TiO₂ surfaces could effectively retard the recombination of photoexcited charges and facilitated the simultaneous formation of H₂O₂ and H₂ from H₂O. The photoactive Ti⁴⁺ on the TiO₂ surface could form peroxo-species (Ti⁴⁺-O₂H⁻) that further induced the formation of H₂O₂. In the presence of the Pd-TiO_2-δ/TiO₂ photocatalyst, under UV light irradiation for 90 min, very high yields of naturally separated H₂O_2(aq) (0.45 mmole/gTiO₂/min) and H_2(g) (0.16 mmole/gTiO₂/min) could be obtained simultaneously. A relatively high photo-conversion efficiency (14%) for the Pd-TiO_2-δ/TiO₂ photocatalysts was achieved. This work demonstrates that using the unlimited solar energy, the effective Pd-TiO_2-δ/TiO₂ photocatalysts can enhance H₂O_(l)-to-H₂O_2(aq) and -H_2(g) for green energy.