In this study, we investigated the effect of the design of the cathode flow-field structure on the electrochemical performance of the electrolyzer for the toluene-methylcyclohexane electrocatalytic hydrogenation synthesis system. The patterns of the basic flow-fields; i.e. parallel, interdigit, serpentine and porous-carbon, were investigated based on linear sweep voltammetry (LSV), internal, and cathodic and anodic charge transfer resistances with impedance spectroscopy and current efficiency. The flow-field pattern affected the toluene mass transportation and H-2 gas generation as a side reaction. Based on the LSV curve, the porous-carbon did not affect the overvoltage for the decrease in the toluene concentration, and showed the lowest cell voltage in the all flow-fields. The cathodic charge transfer resistance by impedance analysis and the current efficiency of the porous-carbon showed the highest performance in the all flow-fields over a wide toluene concentration range. (C) 2017 Elsevier Ltd. All rights reserved.