Electrochemical reduction of carbon dioxide (CO2) to carbon monoxide (CO) has been widely studied in a membrane electrolysis cell. In the cell, a proton exchange membrane has been used as diaphragm to separate the catholyte from the anolyte. However, owing to the high cost of the proton exchange membrane, the practical utilization of the cell has been limited. In present work, we propose a non-membrane electrolysis cell for CO2 reduction to CO. In this cell, tetrabutylammonium perchlorate (Bu4NClO4)/propylene carbonate (PC) solution is used as the catholyte, H2SO4 aqueous solution is used as the anolyte. Owing to the hydrophobic nature of Bu4NClO4/PC, a liquid-liquid interface exists between the catholyte and the anolyte. Thus, electrochemical reduction of CO2 is carried out in organic media, while H2O electro-oxidation is carried out in aqueous solution. Such designed cell has three important advantages over than the membrane electrolysis cell: 1) Owing to the elimination of membrane, the cost of the electrolysis cell is reduced; 2) Because the cell voltage is lowered, the energy efficiency for CO formation is increased; 3) H2O generated from CO2 reduction can transport into the aqueous anolyte without obstacle, the removal of H2O from the catholyte is avoided. (C) 2018 The Electrochemical Society.