Direct water electrolysis was achieved with a novel, integrated, monolithic photoelectrochemical-photovoltaic design. This photoelectrochemical cell, which is voltage biased with an integrated photovoltaic device, splits water directly upon illumination; light is the only energy input. The hydrogen production efficiency of this system, based on the short-circuit current and the lower heating value of hydrogen, is 12.4 percent.

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With an eye toward developing a photoelectrochemical system for water splitting using p-GaInP2, the electrochemical stability of p-GaInP2 was studied in 10 M KOH, 3 M H2504, and a phosphate buffer of pH 7. It was found that inthe dark, the p-GaInP2 electrode is susceptible to corrosion in all investigated solutions. Upon illumination, the anodic corrosion current increases. Under cathodic polarization in 10 M KOH, the p-GaInP2 electrode shows saturated photocurrent density, however the photocurrent slowly decreases with time due to the precipitation of an indium-enriched oxide. In 3 M H,S04, the anodic process can be inhibited under relatively low cathodic potentials, and stable photocurrents can be obtained. In neutral solution, p-GaInP2 is covered by a semi-insulating oxide film and the observed photocurrent densities are much lower than those in 10 M KOH and 3 M H2504.

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Anodizing of magnesium was studied in solutions containing 3MKOH+0.6MKF+0.21MNa3PO4 , with and without addition of 0.4 M and 1.1 M of aluminate. At constant applied current, the process occurs in two stages. First, the voltage rises linearly until an initial breakdown occurs. A thin and compact oxide film is formed at this stage. In the second stage an intense continuous spark is maintained on the metal surface. A thick oxide film is formed at the site of sparking. The formation of the film is accompanied by voltage oscillation and gas evolution. The anodic films formed under continuous breakdown conditions are rough and porous and enriched in aluminum. Anodic films formed in a bath containing 1.1 M aluminate at 15 normalmA/cm2 are composed of a single oxide phase MgAl2O4 spinel. © 1999 The Electrochemical Society. All rights reserved.