CO-dehydrogenase [1-3] is a very promising enzyme for production of fuel from renewable resources by catalytic conversion of carbon dioxide. The knowledge of the catalysis mechanisms of this enzyme is highly important. Our group has studied the mechanism of this enzyme using protein film voltammetry (PFV) [1]. Unfortunately, the rotating disk electrode (RDE) classically used for these studies is almost useless due to the insufficient transport of the chemical species to match its very high activity; this blurs the enzymatic response and prevents mechanistic studies [4]. To overcome this issue, using numerical tools, a full extensive study of the mass transport of different configurations guided us to create new geometries of apparatus to improve and control the flow of species towards the electrode with the respect of our specific constraints imposed by theses enzymes.