Chapter 8: Photobiological Methods of Renewable Hydrogen; Production

Research output: Chapter in Book/Report/Conference proceedingChapterpeer-review

9 Scopus Citations


Oxygenic photosynthetic microbes such as green algae and cyanobacteria normally absorb sunlight and store the energy in the form of polysaccharides such as starch (in green algae) or glycogen (in cyanobacteria). These storage biomolecules are mobilized, as required, to produce the energy needed to drive microbial metabolism. The conversion of light energy into chemical potential, "the light reactions of photosynthesis", is well described and has been reviewed recently (cf. Ref. 32,132,184, and references therein). Under certain conditions these microbes can use the energy from sunlight to produce H2 gas instead of fixing carbon, and thus are at least partially able to sustain growth and cellular repair function although at lower than normal levels for up to several days.65 However, H2 production is not the normal function of algal and cyanobacterial photosynthesis. Indeed, the H 2-producing enzymes are not even synthesized under normal growth conditions (with the exception of some cyanobacteria), and their genes are only expressed following exposure to specific environmental conditions. Nevertheless, it is this type of biological function that offers the potential to efficiently generate renewable H2 in direct light conversion processes. The photobiological production of H2 by oxygenic, photosynthetic organisms occurs in four major sequential steps: 1. light absorption and transfer of excitation energy to reaction center (RC) molecules; 2. charge separation by the RCs, electron extraction from water, and charge equilibration between the photosystems; 3. transfer of low potential (high energy) electrons to intermediate acceptors such as ferredoxin or some combination of an organic carrier and ferredoxin; and 4. H2 gas release associated with nitrogenase or hydrogenase enzymes. The overall light-conversion efficiency of the process is determined mainly by the absorption spectrum of the organism, the amount of that energy delivered to the H2-producing enzyme, and the energetic requirements of the enzyme catalyzing the H2-evolving step. The purpose of Sections 2 and 3 is to show how green algae and cyanobacteria approach each step and how the process might be mobilized to produce useful amounts of H2. Section 4 will discuss other types of biohydrogen systems, Section 5 will examine the major current scientific issues preventing application of photobiological H2-production technology, and Section 6 will outline some future directions.

Original languageAmerican English
Title of host publicationSolar Hydrogen Generation
Subtitle of host publicationToward a Renewable Energy Future
EditorsK. Rajeshwar, R. McConnell, S. Licht
PublisherSpringer New York
Number of pages43
ISBN (Print)9780387728094
StatePublished - 2008

NREL Publication Number

  • NREL/CH-270-44205


  • hydrogen
  • microbial metabolism
  • photobiological production of hydrogen


Dive into the research topics of 'Chapter 8: Photobiological Methods of Renewable Hydrogen; Production'. Together they form a unique fingerprint.

Cite this