Photoelectrochemical Analysis of Nanostructured Titanium Oxide Conjugated to Organic Molecules for Hydrogen Evolution

Photocatalytic water splitting using TiO₂ for hydrogen applications has been limited by its inability to absorb wavelengths within the visible light range. TiO₂ covalently linked with folic acid (FA) by the linker molecule 3-aminopropyl)-diethoxy-methylsilane (APTMS) has shown to exhibit photoluminescence under visible light [1]. In this study, functionalized TiO₂ was used as a photocatalyst for water oxidation which was measured using a photoelectrode setup. In order to measure the photoelectric current generated by the catalyst chronoamperometry techniques were employed. In addition, the Butler-Volmer equation was used to model the relationship between the quasi-fermi energy of electron photocarriers, current density, and the ultimately the hydrogen evolution rate.

Experimentation focused on comparing the volume of hydrogen evolution induced by three different photocatalysts: commercially available TiO₂ (P25), sol-gel prepared TiO₂, and functionalized sol-gel prepared TiO₂. P25 was used for a comparison with TiO₂ and TiO₂ functionalized layers. The photochemical cell configuration allowed for the efficient reduction of electron-hole pair recombination and separated hydrogen and oxygen evolution.

Platinum was placed in the acid solution as a cathode (counter electrode) and the nanostructured coatings on stainless steel were placed in the basic solution as an anode (working electrode). The two cells were separated by a nafion 211 cation exchange membrane film and a xenon lamp was directed at the anode through a quartz window in the plexiglass cell. The anode was connected to the cathode using a stainless steel wire which allowed various external bias voltages to be applied to the system. The voltages applied to the system were critical in calculating the hydrogen evolution rates.

Figure 1: Chronoamperometric comparison of P25, TiO₂ , TiO₂-APTMS-FA at .55 V

1. Turkowski, V., et al., Linker-Induced Anomalous Emission of Organic-Molecule Conjugated Metal-Oxide Nanoparticles. ACS Nano, 2012. 6(6): p. 4854-4863.