Photoelectrochemical decomposition of water using modified monolithic tandem cells

Photovoltaic tandem cells, consisting of a gallium indium phosphide (GaInP2 ) homojunction grown epitaxially on a gallium arsenide (GaAs) homojunction with a GaAs tunnel diode interconnect, were modified with an additional top player of GaInP2. These cells were used as electrodes to photoelectrochemi cally decompose water into hydrogen and oxygen in 1M, 5M and 11M KOH electr olyte solutions. The hydrogen reaction was catalyzed at the semiconductor s urface with a photoelectrochemically deposited thin layer of platinum and r uthenium. Gas chromatography and electrochemical experiments demonstrate th at the modified tandem cells produce hydrogen and oxygen with a light-to-hy drogen conversion efficiency of up to 6%. Both the efficiency and the stabi lity of these cells are discussed. (C) 1999 International Association for H ydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.