Efficient Photoelectrolysis of Water using TiO₂ Nanotube Arrays by Minimizing Recombination Losses with Organic Additives

Electron−hole (e-h) recombination loss is a major practical problem in using TiO 2 as a photocatalyst. This paper describes the use of organic additives to reduce e-h recombination losses which significantly improved the photocurrent density of the integrated TiO 2 nanotube/Ti photoanode. Studies on photoelectrochemical hydrogen generation using nanotubular arrays of TiO 2 photoanodes were carried out in 1 M KOH with the addition of three different organic additives, namely, methanol (one hydroxyl group), ethylene glycol (two hydroxyl groups), and glycerol (three hydroxyl groups) using a simulated solar light. Ethylene glycol was found to be the best among the investigated organic additives to reduce electron hole recombination. The addition of ethylene glycol produced a photocurrent density of 3.3 mA/cm 2 at 0.2 V Ag/AgCl compared to 0.87 mA/cm 2, using a 87 mW/cm 2 light intensity in 1 M KOH solution. On the other hand, methanol and glycerol showed a photocurrent density of 2.43 and 2.55 mA/cm 2 under the same experimental conditions. A high charge carrier density and reduction of recombination losses were observed in the organically modified electrolytes as compared to that in aqueous basic solution.