THE EFFICIENCY AND PHYSICAL PRINCIPLES OF PHOTOLYSIS OF WATER BY MICROALGAE

By a simple argument, the theoretical upper efficiency of the biophoto lytic splitting of water into molecular hydrogen and oxygen by microal gae is found to be 0.11. By considering non-ideal conditions such as t he transmission and reflection of solar photons, the realistic upper e fficiency is found to be approximately 0.06-0.08. The theoretical effi ciency is further seen in connection to mechanisms securing charge tra nsfer and charge separation (Marcus theory), and the process is primar ily a non-ideal one in a thermodynamic context. The importance of this fact is stressed because it is shown to be essential regarding the fu nctionality under various illumination intensities for photosynthesis in vivo. Fuel-generating processes are discussed from a general thermo dynamic point of view, and are found to differ in a fundamental way re garding the potential and current from those involving photovoltaic so lar cells. Finally, photolysis of water by microalgae is compared with PV-assisted electrolysis and photoelectrochemical cells on the basis of efficiencies.