NOVELTY - Bipolar plate for electrochemical cells comprises two compartments divided by a separator and respectively containing two electrodes or current distributor. The bipolar plate comprises a single wall (1), perimetrical flanges and feeding mechanism for feeding reactants and extracting products. The perimetrical flanges comprise a preassembled frame (5) with a planar abutment surface (6) for welding with the single wall.    USE - For electrochemical cells, electrolyzer or stack of fuel cells (claimed).    ADVANTAGE - The welding between wall and perimetrical frame on the abutment surface of the frame is carried out by diode-laser technique, allowing to obtain a robust connection but without a complete melting of the sheet, thus eliminating the risk of process fluid leakage to the external environment. The bipolar plate design is simplified in folding and/or molding procedures and in welding, and has a high quality standard as regards the planarity of the finished bipolar plate and the absence of defects capable of permitting the outflow of the process fluids to the external environment.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for method for the manufacturing of the bipolar plate, comprising folding or molding a sheet strip to form the frame with U-shaped profile and with planar abutment surface or by drafting quadrangular elements to form the frame with closed quadrangular profile and with planar abutment surface; preassembly of strip-shaped supports; molding projections on one side only of single wall; positioning the perimetrical edge of single wall on the planar abutment surface of the frame and welding with diode laser technique; optional positioning of devices for improving the circulation of biphasic fluids on the single wall and fixing by electric resistance welding, or electric arc welding or laser welding; housing the preassembled supports in the recesses of the projections of the welded frame-single wall element, positioning the first electrode or current distributor in contact with the apex of the projections and execution of first single series of welds (7) by electric arc welding or laser welding technique; and positioning the second electrode or current distributor in contact with the free terminal surfaces of the supports and execution of second single series of welds by electric resistance welding or electric arc welding or laser welding technique.    DESCRIPTION OF DRAWING(S) - The figure is a front view of the assembly resulting from the welding of the frame and side section of the assembly.    Single wall (1)    Frame (5)    Abutment surface (6)    Welds (7)    Projections (9)