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

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 H-2 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 H-2 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 H-2 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 H-2 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 H-2 production rate, since agglomeration of the metal nanoparticles takes place at high loading, decreasing the Pd-TiO2 interface where the photoreforming reactions take place.