Cuprous oxide has been prepared by the photoelectrochemical reduction of a CuO film formed on a conducting substrate by the anodic deposition from an alkaline solution of a Cu͑II͒-amino acid complex. Both copper oxide films thus prepared are found to be typical p-type semiconductors. The onset of the cathodic photocurrent due to the reduction of O 2 on CuO/ITO ͑ITO, indium tin oxide͒ and Cu 2 O/ITO electrodes give positive shifts of about 0.2 and 0.03 V, respectively, from the dark current rises. Optical bandgap energies of CuO films depend on the amino acids used, 1.56 ͑glycine͒, 1.40 ͑alanine͒, 1.38 ͑isoleucine͒, 1.38 eV ͑valine͒, and the value of E g for the Cu 2 O film is 2.17 eV. The relationship between the flatband potential (V FB ) and the pH for CuO and Cu 2 O films are both linear with the slope of about Ϫ60 mV/pH in agreement with the Nernstian expression for the V FB of a semiconductor.

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The electrochemical formation of spinel-type cobalt oxide has been presented in which the potentiostatic or potentiodynamic oxidation is performed with a Au or Pt electrode in a solution of high pH containing CoSO4 and glycine. The electrochemical quartz crystal microbalance studies indicate that the electrodeposition of cobalt oxide proceeds through the electrochemical oxidation of a cobalt-glycine complex at high pH. The scanning electron microscopy morphology of the deposited film is very compact and quite similar to that of the cobalt oxide prepared by the sol-gel route, followed by the heat-treatment around 300°C. The constituent of the film is determined to be Co3O4 from the electron probe microanalysis and X-ray diffraction measurement. The electric charge of 350 mC cm−2 passed at 1.0 V vs. Ag/AgCl in a solution of pH 10.5 containing 2 mM CoSO4+20 normalmM glycine corresponded to the film thickness of 10 nm. The Co3O4 -deposited Au electrode exhibits two reversible couples in an alkaline solution. The first observed at 0.120 V is attributed to the redox of normalCoOOH/Co3O4, and the second appearing at 0.476 V is equivalent to the CoO2/normalCoOOH couple. © 2002 The Electrochemical Society. All rights reserved.

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p-Type cupric oxide has been deposited electrochemically on platinum and gold electrodes from Cu͑II͒ solutions containing various amino acids, which is very attractive because the procedure is simple and the preparation of large-area film is possible. This indicates that the anodic deposition of CuO takes place simultaneously with the oxygen evolution and the extent of participation of each reaction depends on the stability and structure of Cu͑II͒-amino acid complex, pH, electrode potential, etc. The grain size of CuO obtained in the presence of glycine, which was estimated from the diffraction peak of ͑110͒, was found to be smallest ͑12 nm͒ among those acquired with various amino acids, suggesting that the electrodeposition of CuO from Cu͑II͒-Gly solution leads to the formation of a denser film. Furthermore, it was revealed that the CuO prepared here possesses a property like a p-type semiconductor. The photoelectrochemical reduction of CuO to Cu 2 O was confirmed by analysis with X-ray diffraction.