Determination of photo conversion efficiency of nanotubular titanium oxide photo-electrochemical cell for solar hydrogen generation

Anodized and annealed titanium oxide nanotubes show enhanced photo activity and can be used as photo anodes for water electrolysis in hydrogen generation. Application of an external potential to the photo anode is required for enhancement of the photocurrent. This additional electrical energy input complicates the photo conversion efficiency calculation. In this investigation, the photo-electrochemical behavior of anodized titanium oxide nanotubular arrays have been characterized in various electrolytes. Increase in the applied potential increased the photocurrent under illumination with visible light. A simple experimental method for calculating the photo conversion efficiency has been proposed. According to this method, the potential difference between the photo anode and cathode is measured with and without light illumination. The product of the photocurrent and the increase in potential due to light irradiation is considered as the net power output. The photocurrent and the conversion efficiency increased with increase in the pH of the electrolyte. TiO2 nanotubular arrays annealed at 350 °C for 6 h in nitrogen atmosphere showed a maximum photo conversion efficiency of ∼4% in 1 M KOH electrolyte and ∼3% in 3.5 wt.% sodium chloride solution. The results indicate that nanotubular TiO2 can be potentially used for the photo electrolysis of seawater to generate hydrogen.