Some problems on the resistance method in the in situ measurement of hydrogen content in palladium electrode

Abstract

Some problems on the resistance method in determining the hydrogen content in PdH x electrodes are discussed. First, the resistivity ratio of PdH x , the temperature coefficient of resistivity and the resistance of PdH x , and the resistance of Pd having undergone hydriding–dehydriding cycles are discussed. It is found that the resistivity ratio is somewhat higher than the resistance ratio with the same x value and their difference depends on the internal stress-state arising from hydrogen insertion. Another fact that has been omitted in past work is that the temperature coefficients of PdH x resistance and resistivity increase while x 0.7. The Pd resistance decreases with hydriding–dehydriding cycle number due to the shape deformation of the electrode, which occurs. Second, the effect of the non-uniform distribution of x in the electrode on determining the hydrogen content is discussed theoretically. It is proved that errors are particularly significant when the Pd+H system is in the mixed α+β phase or the resistance is near the maximum value. Finally, we calculate the additional potential drop and hence the apparent resistance of the PdH x electrode caused by the co-conduction of electrolyte, the concentration-cell effect, the collection of electrolysis current and other imperfect configurations of the electrode in the in situ measurement of electrode resistance, using a direct current. It is found that an electrode with a large ratio of length to radius, an active surface, a surrounding electrolyte with high conductance and a high electrolysis current will all induce substantial additional resistance. At the same time, some advice on measuring the PdH x resistance is presented.