Introduction to Biohydrogen: Advancements, Challenges, and Perspectives of the Cleanest Fuel

Hydrogen, the simplest fuel, is also the one with the highest energy density, and the only one whose combustion produces only water as a byproduct. Because it is non-polluting and can be produced sustainably, it is gaining importance and is the object of new developments backed by government policies worldwide. Although most of the so-called green hydrogen is not bio-based, the same fuel, aptly called biohydrogen, can be produced using bioprocesses. Waste biomass, an unavoidable product of human existence even in the most sustainable societies, can be used to produce biohydrogen via dark fermentation with no additional energy input. Other approaches, such as biophotolysis or microbial electrolysis, require an energy input—ideally renewable—to reclaim even more chemical energy from organic matter. One kilogram of carbohydrate-based organic matter can produce up to 1.5 kWh worth of hydrogen via dark fermentation while producing a stream of diluted organic acids that can be reclaimed for sustainable processing. Biohydrogen is not only a fuel; it can be used in industry as a reducing agent and a raw material for ammonia production. This chapter describes the basics of biohydrogen production technology and the trends and challenges to its widespread production soon.