NOVELTY - The electrochemical cell comprises a first electrode, a second electrode, a porous separator disposed between the first and second electrodes, a first channel having an inlet and an outlet, and a second channel having an inlet and an outlet. The first channel is contiguous with the first electrode and the porous separator. The second channel is contiguous with the second electrode and the porous separator. A laminar flow is established in first and second liquids, when a first liquid and a second liquid flow through first and second channels.    USE - The electrochemical cell such as a fuel cell (claimed), battery and photoelectric cell is useful: in cellular phones, laptop computers, DVD players, televisions, palm pilots, calculators, pagers, hand-held video games, remote controls, tape cassettes, compact disk players, amplitude modulation and frequency modulation radios, audio recorders, video recorders, cameras, digital cameras, navigation systems, and wristwatches and other electronics; in automotive and aviation systems; and in aerospace vehicles.    ADVANTAGE - The electrochemical cell has increased resistance, good mass transport characteristics, reduced crossover rate and high power density, and can be economically manufactured with lightweight.    DETAILED DESCRIPTION - The electrochemical cell comprises a first electrode, a second electrode, a porous separator disposed between the first and second electrodes, a first channel having an inlet and an outlet, and a second channel having an inlet and an outlet. The first channel is contiguous with the first electrode and the porous separator. The second channel is contiguous with the second electrode and the porous separator. A laminar flow is established in first and second liquids, when a first liquid and a second liquid flow through first and second channels. A distance measured from the first electrode to the second electrode is 1 cm traversing the porous separator. The first and second electrodes are a gas diffusion electrode. The porous separator has a thickness of 1-100 microns, a pore size of 5 nm to 5 microns, a pore density of 106 to 1011 pores/cm2, and a porosity of 0.1-50%.    DESCRIPTION OF DRAWING(S) - The diagram shows a cross-sectional view of a polymer electrolyte fuel cell.    Polymer electrolyte fuel cell (2)    Anode (4)    Cathode (8)    Cathode catalyst (10)    Polymer electrolyte membrane. (12)