NOVELTY - Treatment of stainless steel substrate surface having metal oxide involves contacting the substrate surface with an acidic solution having a pH of 0-4 and containing halogen ion(s) present in the solution at concentration of less than 1x10-1-lx10-6 molarity. The solution reacts with the metal oxide in the absence of an impressed electrical current. The anion reacts with the metal oxide to form a metal halide species soluble in the solution.    USE - The method is used for treating surface of stainless steel substrate useful as an electrically conductive element for use in an electrochemical cell (claimed), i.e. fuel cell. The fuel cell is used as power source for electric vehicles.    ADVANTAGE - The treated substrate provides an electrically conductive element that reduces the metal substrate contact resistance. The electrically conductive element maintains electrical conductivity, resist the fuel cell aggressive environment, and improve overall operational efficiency of the fuel cell.    DETAILED DESCRIPTION - Treatment of stainless steel substrate surface having metal oxide involves contacting the substrate surface with an acidic solution having a pH of 0-4 and containing halogen ion(s) present in the solution at a concentration of less than 1x10-1-lx10-6 molarity. The solution reacts with the metal oxide in the absence of an impressed electrical current. The anion reacts with the metal oxide to form a metal halide species soluble in the solution. The metal halide species and the acidic solution are separated from the surface to reduce the amount of the metal oxide on the surface. INDEPENDENT CLAIMS are also included:    (a) method of treating an electrically conductive element (8) comprising stainless steel having metal oxides on a surface of the steel, comprising contacting the surface with an acidic solution having fluoride ions, in which the reaction forms a metal fluoride species soluble in the solution and separating the metal fluoride and the acidic solution from the surface to remove the portion of the metal oxides and to reduce electrical resistance of the surface thus improving electrical conductivity of the element; and    (b) method of activating a substrate surface comprising providing a stainless steel alloy substrate comprising iron, chromium, nickel, and/or molybdenum forming metal oxide species, determining an instable region of the metal oxide species by thermodynamic phase data, creating a solution for removing of the metal oxide species within the instable region, contacting the solution with the substrate surface to react the solution with the metal oxide species to form a metal halide species soluble in the solution, and separating the metal halide soluble species from the substrate surface to remove the metal oxide species and activating the substrate surface.    The metal oxide species removing solution comprises halogen ion(s) at a concentration so that the solution reacts with the metal oxide species within the instable region.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic, exploded, isometric, illustration of a liquid-cooled proton exchange membrane fuel cell stack.    Conductive element (8)    Clamping terminal plates (10, 12)    End contact fluid distribution elements (14, 16)