The objective of this study was to improve butanol yield and productivity by redox modulation and immobilization of Clostridium acetobutylicum B3 cells. Stoichiometric network analysis revealed that NAD(P)H that had escaped from the fermentation as H-2 limited the butanol yield and led to the accumulation of oxidation byproducts, e.g., acetone. Methyl viologen was used as an electron carrier to divert the electron flow away from H-2 production and to reinforce the NAD(P)H supply. Butanol yield was increased by 37.8% with severely diminished acetone production. Immobilization of the cells by adsorption onto a fibrous matrix improved their butanol tolerance and production rate. An average of 15.6 g/L butanol was achieved within 12 h with a solvent productivity of 1.88 g/L/h in repeated batch fermentation. To our knowledge, this is the highest solvent productivity with a relatively high butanol titer produced by a Clostridium strain in batch fermentation. (C) 2012 Elsevier Ltd. All rights reserved.