An electrochemical sensor is described for the nondestructive determination of the activity of mobile elemental hydrogen in a wide range of metals, like steel and palladium. The sensor is based on the principle of a concentration cell. In this cell one of the electrodes is either the sample metal to be investigated or an ultrathin palladium layer in direct contact with the sample, acting as a sensing electrode. The other electrode functions as the reference, for which we have used palladium hydride or molybdenum bronze. The electrolyte is a liquid or preferably solid proton conductor. A version, using molybdenum bronze and thin palladium film (20 nm) electrodes and hydrogen uranyl phosphate tetrahydrate, has been found to be especially valuable because of its selectivity and long-term stability.

Various metal samples from research and industry have been investigated to yield significant potential differences between samples containing (mobile) hydrogen and those which were low in hydrogen content. The qualitative and quantitative information from these hydrogen measurements may be used for many purposes provided that suitable calibration procedures are carried out.