Maintaining the proper low work function surface in steady‐state high‐current‐density negative ion sources is difficult, due to intense ion bombardment of the surface. Experiments were performed in which liquid cesium was forced through a porous molybdenum converter in order to obtain a low work function, while at the same time allowing the surface to be cooled. In a small steady‐state hollow cathode discharge source, the H−yield from a porous molybdenum converter was five fold higher than from a solid molybdenum converter which relied on the conventional method of cesium coverage by vapor deposition.