Solar photoproduction of hydrogen: A review

The concept of using solar energy to drive the conversion of water into hydrogen and oxygen has been examined, from the standpoints of: potential and ideal efficiencies; measurement of (and how to calculate) solar hydrogen production efficiencies; a survey of the state-of-the-art and a technological assessment of various solar hydrogen options. The analysis demonstrates that the ideal limit of the conversion efficiency for 1 sun irradiance is ∼31% for a single photosystem scheme and ∼42% for a dual photosystem scheme. However, practical considerations indicate that real efficiencies will not likely exceed ∼10% and ∼16% for single and dual photosystem schemes, respectively. Four types of solar photochemical hydrogen systems have been identified: photochemical systems, semiconductor systems, photobiological systems and hybrid and other systems. A survey of the state-of-the-art of these four types has been presented. The four system types (and their sub-types) have been examined in a technological assessment, where each has been examined as to efficiency, potential for improvement and long-term functionality. Four solar hydrogen systems have been selected as showing sufficient promise for further research and development: (1) photovoltaic cells plus an electrolyzer; (2) photoelectrochemical cells with one or more semiconductor electrodes; (3) photobiological systems; and (4) photodegradation systems. Several recommendations have been made for future work in this area.