NOVELTY - A fuel cell comprises substrate having first (11) and second grooves (21); electrolyte membrane (3) lying on substrate to define first (11a) and second flow channels (21a); and catalyst-bearing current collector layer sections (12, 22). A fuel liquid (11b) flows through first channel to undergo anodic reaction, an oxidant liquid (21b) flows through second channel to undergo cathodic reaction, hydrogen ions migrate from first channel to second channel through the electrolyte membrane. The oxidant liquid is an aqueous hydrogen peroxide solution.    USE - Used as e.g. direct methanol fuel cell.    ADVANTAGE - The use of hydrogen peroxide water as the oxidant liquid can feed the oxidant to the cathode at a high efficiency. Thus, current density and power density are enhanced, indicating an efficient fuel cell. The fuel cell avoids the phenomenon that oxygen gas produced by decomposition of hydrogen peroxide stagnates within pores in the gas diffusion layer to inhibit further supply of the oxidant liquid; and does not employ the conventional membrane electrode. An ultra-compact-size fuel cell can be manufactured using similar process to the well-known semiconductor fabrication. This reduces the cost of mass-scale production.    DETAILED DESCRIPTION - A fuel cell comprises a substrate having first and second grooves formed in juxtaposition, the grooves each having an opening and an inner wall; an electrolyte membrane lying on the substrate so as to cover the openings of the first and second grooves to define first and second flow channels; and catalyst-bearing current collector layer sections disposed on the inner wall of the first groove or the inside surface of the electrolyte membrane defining the first channel and the inner wall of the second groove or the inside surface of the electrolyte membrane defining the second channel, respectively. A fuel liquid flows through the first channel to undergo anodic reaction, an oxidant liquid flows through the second channel to undergo cathodic reaction, hydrogen ions migrate from the first channel to the second channel through the electrolyte membrane, and the oxidant liquid is an aqueous hydrogen peroxide solution.    DESCRIPTION OF DRAWING(S) - The figure shows a cross-sectional view of a fuel cell.    Electrolyte membrane (3)    Grooves (11, 21)    Flow channels (11a, 21a)    Fuel liquid (11b)    Current collector layer sections (12, 22)    Second grooves (21)    Flow channels (21a)