The present invention relates to cofactor regeneration systems, components and uses thereof and methods for generating and regenerating cofactors. The cofactor regeneration system comprises a first electron transfer component selected from a polypeptide comprising a NADH:acceptor oxido-reductase or NADPH:acceptor oxido-reductase, a second electron transfer component selected from a hydrogenase moiety and/or non-biological nanoparticles and an electronically conducting surface. The first and second electron transfer components are immobilised on the electrically conducting surface, and the first and second electron transfer components do not occur together in nature as an enzyme complex.