A method is for producing seals on faces of electrochemical reactor components intended to be stacked in order to form an electrochemical reactor Each component is in the form of a plate and having a first face and an opposing second face. The first face is designed to receive a first seal and the second face is designed to receive a second seal. The method includes shaping the first seals on the first faces of the components, the first seals being at least partially polymerized; depositing the second seals on the second face of the components; and shaping the second seals by compressing a stack formed from the components alternating with molding plates. Each molding plate has a bearing face pressed against the first face of a component and includes a groove designed to receive, without deforming, the first seal previously formed on the first face of said component, and a molding face pressed against the second face of another component and having a molding surface for shaping the second seal deposited on the second face of said other component as a result of compressing the stack. The method also includes at least partially polymerizing the second seals.