Solar thermochemical production of hydrogen using metal oxide redox systems

Abstract

A method to analyze the hydrogen production potential (HPP) of photoelectrochemical systems, based on the lumped equivalent circuit model of a photocell driving a current dependent electrochemical load, is presented. Selection of the appropriate circuit and characteristic junction parameters allows analysis of single and multijunction photoelectrodes including those utilizing a semiconductor-electrolyte junction. In this paper, the HPP of single and multijunction photoelectrodes fabricated from high quality crystalline III–V materials is compared with that of the lower cost amorphous silicon and crystalline-amorphous silicon hybrid junction electrodes. The analysis shows that single junction photoelectrodes, even those with exceptional diode characteristics, require semiconductor bandgaps greater than 2.0 eV for efficient operation when realistic catalyst performance is considered. Multiphoton systems are shown to have higher HPP and exhibit greater operational stability when load mismatches, such as would occur from changes in junction characteristics or catalyst properties, are introduced.