Challenges in hydrogen quantification using Kelvin probe technique at different levels of relative humidity

Abstract

Kelvin probe-based contact potential measurements were conducted with in situ electrochemical hydrogen loading of a Pd membrane with a thickness of 100 μm. The theoretical basis of diffusion coefficient calculation based on measured response time of potential drop, arising from hydrogen arriving at the detection side of the Pd membrane, was discussed. In situ hydrogen loading was also utilized for insertion of different amounts of hydrogen into the Pd sample while monitoring the resulting contact potential difference changes. Measurement of contact potential difference at different final values of hydrogen concentration in the Pd membrane was performed at various atmospheric conditions, focusing in this work on increasing relative humidity (4 to 85% rH). Moreover, the effect of humidity changes on hydrogen effusion kinetics at room temperature and low oxygen content (<1%) was studied.

Influence of atmospheric oxygen on hydrogen detection on Pd using Kelvin probe technique

“…In similar manner as potential stability was shown for Pd during variation of relative humidity [57], stability has to be proven for increase of oxygen concentration in the measuring atmosphere. Independence of CPD from measurement conditions ensures reliable hydrogen quantification, as deviations in CPD are, as a consequence, exclusively based on changes in the hydrogen concentration within the investigated material.…”

“…At the highest adjusted oxygen concentration (96%), the detection limit of the utilized oxygen sensor is reached leading to a displayed value of 100%. In comparison to other metals or alloys like steel, Pd shows a very stable potential at various atmospheric conditions, concerning relative humidity [57] as well as oxygen concentration. Therefore, it is a well-suited material for hydrogen quantification as deviations in CPD are only due to changes in concentration of hydrogen absorbed in the metal lattice.…”

“…A 80 × 10 mm sized, 0.1-mm-thick palladium foil (Goodfellow, as rolled, 99.5%) was cleaned ultrasonically with acetone, ethanol and deionized water, before mounting into the experimental setup, described elsewhere [57]. Description of the 3D-printed cell used for in situ hydrogen loading of the Pd foil during Kelvin probe measurements can be found elsewhere [13].…”

“…The fluctuation of oxygen concentration was for each experiment below 5% of the adjusted value. Transients recorded at 1 vol.% O 2 for a freshly prepared Pd sample, which was not hydrogen charged before, as well as for hydrogen pre-charged Pd are not shown in this paper but are presented and discussed in Part I of the present work [57].…”

“…Part 1 of the present work [57] focuses on the influence of relative humidity on the hydrogen detection with KP and explains the fundamental aspects of hydrogen dependence of CPD. Building on these results, the influence of oxygen concentration in the measurement atmosphere is studied.…”