Photo-electrochemical hydrogen generation from water using solar energy. Materials-related aspects

Abstract

The present work considers hydrogen generation from water using solar energy. The work is focused on the materials-related issues in the development of high-efficiency photo-electrochemical cells (PECs). The property requirements for photo-electrodes, in terms of semiconducting and electrochemical properties and their impact on the performance of PECs, are outlined. Different types of PECs are overviewed and the impact of the PEC structure and materials selection on the conversion efficiency of solar energy are considered. Trends in research in the development of high-efficiency PECs are discussed. It is argued that very sophisticated materials engineering must be used for processing the materials that will satisfy the specific requirements for photo-electrodes. An important issue in the processing of these materials is the bulk vs. interface properties at the solid/solid interfaces (e.g., grain boundaries) and solid/liquid interfaces (e.g., electrode/electrolyte interface). Consequently, the development of PECs with the efficiency required for commercialization requires the application of up-to-date materials processing technology. The performance of PECs is considered in terms of: • excitation of electron–hole pair in photo-electrodes; • charge separation in photo-electrodes; • electrode processes and related charge transfer within PECs; • generation of the PEC voltage required for water decomposition. This work also gives empirical data on the performance of PECs of different structures and materials selection. It is argued that PEC technology is the most promising technology for hydrogen production owing to several reasons: • PEC technology is based on solar energy, which is a perpetual source of energy, and water, which is a renewable resource; • PEC technology is environmentally safe, with no undesirable byproducts; • PEC technology may be used on both large and small scales; • PEC technology is relatively uncomplicated. According to current predictions, the production of hydrogen will skyrocket by 2010 (Morgan and Sissine, Congressional Research Service, Report for Congress. The Committee for the National Institute for the Environment, Washington, DC, 20006-1401, 28 April 1995). Consequently, seed funding already has been allocated to several national research programs aiming at the development of hydrogen technology. The countries having access to this PEC technology are likely to form the OPEC of the future.