Hydrogen Production by Water Biophotolysis

The reversible potential for the sulfur dioxide electrolysis is only 0.17 V, less than 10% that of water electrolysis (minimum of 1.23V at 298K and 1 bar) [65,69]. However corrosion problems in the electrolysis step are severe due to the presence of high concentration (about 50%) sulfuric acid. The overall thermal efficiency of the process, considering both thermal and electrical energy input derived from the same heat source, is estimated as 48.8% [116]. However, in terms of economics and process complexity the hybrid cycles face tough competition from advanced water electrolyzers. 

Biophotolysis is the process of splitting water into hydrogen and oxygen through a series of biological activities utilizing solar radiation. The overall process can be represented as 

The process of photosynthesis is generally explained by the modified Z-scheme [122-127]. Peso in PS II absorbs light and goes to an excited state. It releases an electron to a primary acceptor named pheophyhn. P eso thus formed receives electrons successively from a 

The light independent reactions take place in the stroma with the help of ATP and NADPH. In a process called the Calvin-Benson cycle, or carbon fixation, carbon dioxide from the atmosphere is captured and converted into carbohydrates [135]. The reaction is catalyzed by the enzyme RuBisCO (ribulose-1,5-biphosphate 

Hydrogenase was named by Stephenson and Stickland in 1931, discovered in their experiments using anaerobic colon bacterium Escherichia Coli that evolved hydrogen [144-146]. Hydrogenase enzymes are metalloproteins that contain sulfur and nickel and/or iron [147]. To date over 80 hydrogenase enzymes have been identified. These enzymes reversibly catalyze hydrogen production/uptake reactions  

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