Photocatalytic Hydrogen Evolution Over Pt/Co-TiO₂ Photocatalysts

Title:Photocatalytic Hydrogen Evolution Over Pt/Co-TiO₂ Photocatalysts

Volume: 2

Author(s): Soukaina Akel*, Ralf Dillert and Detlef W. Bahnemann*

Affiliation:

• Gottfried Wilhelm Leibniz Universitat Hannover, Institut fur Technische Chemie, Callinstr. 3, D-30167 Hannover,Germany

• Gottfried Wilhelm Leibniz Universitat Hannover, Institut fur Technische Chemie, Callinstr. 3, D-30167 Hannover,Germany

Keywords: Photocatalysis, cobalt-doped titania, H₂ evolution, simulated solar light, EPR spectroscopy, Mott−Schottky method.

Abstract:

Aims: In this study, the photocatalytic hydrogen evolution reaction from aqueous methanol was investigated upon simulated solar light using platinum loaded on cobalt doped TiO₂ (Pt/Co-TiO2) composites.

Background: Controversial results of cobalt-based composites create doubts about their photocatalytic activity. Thus, cobalt doped TiO₂ composites were synthesized differently, and the photocatalytic activity was examined for the photocatalytic hydrogen generation.

Objective: The current study aims to investigate the influence of cobalt doping and platinum loading on the photocatalytic activities of TiO₂ nanoparticles for the photocatalytic H2 generation.

Methods: The 0.5 wt.% Co-TiO₂ and bare TiO₂ photocatalysts were synthesized using two different methods, namely, reflux and hydrothermal synthesis. Additionally, the Pt deposition on the prepared Co-TiO₂ and TiO₂ catalysts (1 wt.% Pt) was performed using a photo-platinization method.

The as-prepared catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy/ energy dispersive X-ray analysis (SEM/EDX), transmission electron microscopy (TEM), ultraviolet- visible spectroscopy (UV-vis), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and electrochemical impedance spectroscopy (EIS).

Results: The XRD and EPR studies clearly indicated that the Co was incorporated into the titanium dioxide lattice. The EIS results suggested that the reduction of protons over Co-TiO₂ and bare TiO₂ materials was possible from a thermodynamic point of view. However, the photocatalytic results revealed that the formed amount of H₂ was extremely low and close to the detection limit. The evolution of H₂ from aqueous methanol (10 vol%) showed higher rates when employing 1 wt.% Pt loaded on 0.5 wt.% Co-TiO₂ photocatalysts under simulated solar light irradiation. A maximum of 317 ± 44 μmol.h-1 was observed over the Pt/Co-TiO₂-HT photocatalyst.

Conclusion: EPR results confirmed that the cobalt ions were introduced into the TiO₂ lattice by trapping the photogenerated conduction band electrons and decreasing the defects in the crystal cell. The Mott−Schottky analysis of electrochemical impedance measurements showed that all catalysts were ntype semiconductors and that cobalt doping induces impurity level within the band gap of TiO₂. The experimental results of photocatalytic H₂ generation from methanol-reforming demonstrated that no significant impact of Co-doping on the photocatalytic H₂ formation was observed neither for bare TiO₂ samples nor for the platinized materials. Based on these experimental findings, a possible mechanism for the continuous photocatalytic activity of Pt/Co-TiO₂ photocatalysts under simulated solar light was proposed.

Cite this article as:

Akel Soukaina*, Dillert Ralf and Bahnemann W. Detlef *, Photocatalytic Hydrogen Evolution Over Pt/Co-TiO₂ Photocatalysts, Journal of Photocatalysis 2021; 2 (1) . https://dx.doi.org/10.2174/2665976X01999200718010443