Observation of Cathodic Photocurrents at Nanocrystalline TiO₂ Film Electrodes, Caused by Enhanced Oxygen Reduction in Alkaline Solutions

Abstract

Nanocrystalline TiO2 (rutile and anatase) film electrodes usually show anodic photocurrents in aqueous electrolytes. Detailed photoelectrochemical studies have revealed that they also show cathodic photocurrents under particular conditions, e.g., in alkaline solutions containing dissolved oxygen under illumination from the TiO2-film side at short wavelengths such as 300 nm. The cathodic photocurrents appear in a potential region about 0.5∼0.9 V more positive than the flat-band potential (U fb) of single-crystal n-TiO2 electrodes. It is shown that the appearance of the cathodic photocurrents can be attributed to efficient electron transfer from the conduction band of TiO2 particles to chemically adsorbed oxygen molecules, the density of which is largely increased in alkaline solutions through a charge-transfer interaction between surface anionic groups such as Ti−O- as an electron donor and oxygen molecules as an electron acceptor. The dependences of the cathodic and anodic photocurrents on the illumination wavelength, the illumination direction, the electrode potential, and the crystal form of TiO2 particles are discussed in relation with the photocatalytic activity of particulate TiO2 films.

The Effect of Chemical Etching by HF Solution on the Photocatalytic Activity of Visible Light-responsive TiO2 Thin Films for Solar Water Splitting

“…7). A possible interpretation of these results is that UV light is mainly absorbed in the rough surface region caused by chemical etching due to the small penetration depth of light with short wavelengths into TiO 2 [33,34].…”

Electrocatalytic properties of polyaniline–TiO2 nanocomposites

“…Titanium dioxide featuring catalytic activity in a number of chemical, electrochemical and photochemical redox processes attracted our attention which eventually led to the development of metal oxide component with CP-based nanocomposites. In particular [8][9][10], various TiO 2 forms can demonstrate electrocatalytic properties in ORR in acidic electrolytes and the prevailing process herewith, according to the two-electron oxygen reduction with the formation of hydrogen peroxide. The CP dopant was chosen to be 12-phosphomolybdic acid, H 3 PMo 12 O 40 (PMA) that features the highest & C. Vedhi cvedhi@rediffmail.com; chinavedhi@yahoo.co.in electrocatalytic activity in ORR among the unsubstituted Keggin-or Dawson-type HPAs [11].…”

Photocurrent generation in a CdS nanocrystals/poly[2-methoxy-5-(2′-ethyl-exyloxy)phenylene vinylene] electrochemical cell

“…Although heterojunctions of organic polymers with semiconductors nanocrystals have been extensively investigated in solid state devices, few information are present in the literature on their photoelectrochemical behaviour in electrolytic solutions [8,9], the data being mainly relative to photoelectrodes of bare polymers [21][22][23][24] or nanocrystals [25][26][27][28][29][30][31].…”