Membranes in microfluidics have been demonstrated before by sandwiching an ion exchange membrane between two spacers. But this limits flexibility in channel design and precision offered by microfabrication tools and the approach requires that the membrane be integrated during assembly which can complicate the fabrication process. From a microfabrication perspective, a more elegant approach would be to form the membrane after the device is fabricated. Various approaches to in site membrane formation have been demonstrated at the interface between two coflowing reagents streams. In one example, nylon polymer membranes were formed by a polycondensation reaction using an adipoyl chloride in 1,2-dichloroethane and hexamethylenediamine in 0.1 M NaOH solution. In another, freestanding, semipermeable membranes from the biopolymer chitosan was achieved by precipitation following a switch in molecular polarity at the co-flow interface with a basic solution. This technique has subsequently proliferated in the literature as recently reviewed. For example, we previously developed microfluidic methods for creating pure and hybrid chitosan membranes with accurate control over their dimensions. In this study we explore the use of semioccluding chitosan membranes in microfluidic MFCs to separate electrodes with submillimeter spacing. The study is aided by computational electrochemical fluid dynamics and electrochemical impedance spectroscopy. Furthermore, the bioelectrocatalytic performance of the system was investigated with a pure culture Geobacter sulferreduces electroactive biofilm (EAB) and results were compared to a membraneless microfluidic MFC with a larger electrode separation.