Electrochemical reactors employing catalytic films of the cobalt corrin vitamin B-12 hexacarboxylic acid [B-12(COOH)(6)] attached to poly(L-lysine) (PLL) covalently bound to carbon cloth electrodes were optimized for the reduction of 1,2-dibromocyclohexane (DBCH) to cyclohexene in a microemulsion. An improved initial electrode oxidation method enabled attachment of films with higher surface concentrations of catalyst than previously. A parallel plate flow reactor containing a catalyst-coated carbon cloth cathode gave sixfold larger turnover rates compared to a simple stirred batch reactor, especially for 20 and 90 nm thick films of B-12(COOH)(6)-PLL. The 90 nm thick films showed high turnover rates in the flow reactor while maintaining 100% current efficiency, whereas in the batch reactor current efficiency dropped well below 100% at the higher applied currents. Significantly thicker films of B-12(COOH)(6)-PLL on carbon cloth than reported in previous work were shown to operate efficiently in microemulsions for catalyzing DBCH conversion to cyclohexene. The key factor was eliminating mass transport limitations in the microemulsion by using an efficient flow reactor, resulting in turnover rates up to 3000 min(-1) at 100% current efficiency.