An increase in hydrogen production from light and ethanol using a dual scale porosity photocatalyst

Abstract

The stable photocatalytic production of hydrogen is demonstrated under simulated solar irradiation from the aqueous solutions of ethanol over a dual porosity 3D TiO₂ nanotube array (TNTA). The photocatalytic material consists of a uniform layer of TNTAs grown on each titanium fiber of a commercial sintered titanium web (TNTA-web). Under simulated solar irradiation, a stable H₂ production rate of 40 mmol h⁻¹ m⁻² is observed. In comparison, TNTAs grown on a flat titanium foil (TNTA-foil) do not produce H₂ under the same conditions. The addition of small (4–5 nm) and well distributed Pd nanoparticles to the TNTA-web increases the production of hydrogen to 130 mmol h⁻¹ m⁻² with a solar-to-fuel efficiency of 0.45%. The same Pd loading on the TNTA-foil support resulted in a H₂ production rate of 10 mmol h⁻¹ m⁻². Each catalytic material is characterized by a combination of SEM, HR-TEM, XRD, XPS and Raman spectroscopy. The enhancement in H₂ production is attributed to the increased light absorption properties of the TNTA-web material enabled by its unique dual porosity. The analysis of the reaction by-products shows that ethanol is transformed into acetaldehyde as a single oxidation product. Additionally, it is shown that an optimal Pd loading maximizes the H₂ production rate, since agglomeration of the metal nanoparticles takes place at high loading, decreasing the Pd–TiO₂ interface where the photoreforming reactions take place.