The Quantum Yield of Photolysis of Water on TiO₂ Electrodes

Abstract

The qu;intuni yield of the photo-currents in the electrochemical cell. n-TiO,jelectrolyte/Pt, was measured under monochromatic illumination of TiO, at various electrode potentials, It has been found that the quantum yield is very small ( -10- ') in case where no voltage was applied from outside, getting smaller with illumination intensity. The results of measurements of the quantum yield. together with those of the electrode potential of T i 0 2 . at various conditions are explained from the energy level scheme of the semi-conductor and redox potentials in thc solution. The very small efficiency of this photo-galvanic cell as a light energy converter has been attributed to the sniall difference between the flat-band potential of the TiO, electrode and the reduction potential of H' .Die Chiantenausbeute der Photostrijme in der elektrochemischen Zelle, n-TiO,/Elektrolyt/Pt. wird bei monochromer Beleuchtung von TiO, bei verschiedenen Elektrodenpotentialen geniessen. Es ergibt sich, dal) die ohne AuOenspannung gemessene Quantenausbeutc sehr klein I -10-') ist und sich niit zunehmender Lichtintensitit vermindert. Die Ergebnisse der Messungen der Quantenausbeute bei verschiedeneu Elektrodenpotentialen des TiO, erkliren sich aus den1 Energieniveauschema des Halbleiters und den Redoxpotentialen in1 Elektrolytcii. Der sehr kleine Wirkungsgrad der photogalvanischen Zelle als Lichtenergiekonverter ist auf die geringe Differenz zwischen den1Flachbandpotential der Ti0,-Elektrode und dem Reduktionspotential von H ' zuriickzufuhren. I . IntroductionAfrcr the pioneering work on germanium electrodes by B r a t t i n and Garrett [I]. the electrochemical and photoelectrochemical behaviors of semi-conductor electrodes have been c\lensively studied [ 2 . 3 ] . Recently. H o n d a a n d Fujishinia found that the n-type TiO, electrode is electrochemically stablc and the electrode reaction under illumination is the deconiposition of water into oxygen a n d hydroniuni ions [4]. They also showed that the photo-decomposition of water into oxygen a n d hydrogen occurred in an electrochemical system. TiOJaqueous electrolyte solution/Pt [5]. This systcm has attracted some attention a s a possible solar energy converter in which t h e light energy is transformed into chemical energies. However. a serious difficulty for this system IS pointed out in view of its limited spectral range of light ;I hsorption [6].We have carried out sonie studies on t h e q u a n t u m yields of photolysis of water on the n-type TiOz electrode a s a part of our work on fundamental problems of photo-electrode processes. In this paper. the results a r e reported. ExperimentalSin& crystals of TiO, in the form of wafers. 10. 1 0 . 1 inin. with optically flat (001) surfaces were obtained from Nakazunii Crystal\ Corp. They were treated at 700 C under 4 . 10 'Torr for about 2 hrs to increase the conductivity. Indium was evaporated onto onc face of the crystal to get the ohmic contact, and a copper wire was soldered on it. Then, all surfaces, except the other face of the ...

Comparison of Forward and Reverse Reactions in Hydrogen Generation between GaN, InGaN, Nanocrystalline TiO2 and Pt Electrodes during Water Electrolysis

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