Photobiohydrogen Production and Strategies for H Yield Improvements in Cyanobacteria.

Hydrogen gas (H) is one of the potential future sustainable and clean energy carriers that may substitute the use of fossil resources including fuels since it has a high energy content (heating value of 141.65 MJ/kg) when compared to traditional hydrocarbon fuels [1]. Water is a primary product of combustion being a most significant advantage of H being environmentally friendly with the capacity to reduce global greenhouse gas emissions. H is used in various applications. It generates electricity in fuel cells, including applications in transportation, and can be applied as fuel in rocket engines [2]. Moreover, H is an important gas and raw material in many industrial applications. However, the high cost of the H production processes requiring the use of other energy sources is a significant disadvantage. At present, H can be prepared in many conventional ways, such as steam reforming, electrolysis, and biohydrogen production processes. Steam reforming uses high-temperature steam to produce hydrogen gas from fossil resources including natural gas. Electrolysis is an electrolytic process to decompose water molecules into O and H. However, both these two methods are energy-intensive and producing hydrogen from natural gas, which is mostly methane (CH) and in steam reforming generates CO and pollutants as by-products. On the other hand, biological hydrogen production is more environmentally sustainable and less energy intensive than thermochemical and electrochemical processes [3], but most concepts are not yet developed to production scale.