Electricity-mediated biological hydrogen production

Anaerobic bacteria have the ability to produce electricity from the oxidation of organic substrates. They also may use electricity to support chemical reactions that are energetically unfavorable. In the fermentation of sugars, hydrogen can be formed as one of the main products. However, a yield of only four hydrogen per molecule of glucose can be achieved. Potentially, eight additional hydrogen molecules could be produced when the other main fermentation product acetate is converted further, which however is energetically not possible. By the input of electricity, acetate can be oxidized further to form hydrogen. This paper reviews the scarce knowledge of how electricity can be used to produce hydrogen in the microbial oxidation of acetate or other substrates. The technological design concepts and their performance are presented, and the biochemical mechanisms of electron transfer are discussed.