An electrochemical generator consisting of an alternation of membrane fuel cells and cooling cells with internal circulation of liquid water is described. The fuel cells are fed in at least one of the two compartments, anodic or cathodic, with dry gas, which is humidified through the passage of water coming from the adjacent cooling cell through a metal porous separating wall. The permeated liquid water contributes to the withdrawal of the heat of reaction by evaporating at least in part inside the fuel cells.