Evaluation of the suitability of different materials for use as stable references in the application of Kelvin probe under gas change conditions

• New inert KP tips were developed for environments with changing partial pressures of hydrogen and water. • Ni/Cr and Alumel tips react with H₂ and are not good for stable measurements. • Graphite and Ag/AgCl tips stay stable under changing hydrogen pressure. • Dry Ag/AgCl stays stable (∼250 mV vs SHE) from 0 % to 98 % humidity. • Ag/AgCl inertness is due to non-oriented water adsorption on its surface. The Kelvin probe technique is a powerful tool for the investigation of the electrochemical activity of metal or semiconductor surfaces covered with just ultra-thin water layers or at buried interfaces (e.g., beneath organic coatings). While Kelvin probe-based studies of coating delamination are well established, more insight can be obtained by gas change experiments, where partial pressures of oxygen, hydrogen, and water are systematically varied and the effect on the work function -interpreted here as electrode potential- is monitored by Kelvin probe. However, under such dynamic atmospheres, probe tips made from inert materials maintaining a constant potential despite humidity and gas changes are required. This study evaluates Ni80/Cr20, Alumel alloy, Ag/AgCl, and graphite for use as Kelvin probe tip materials under hydrogen and water-containing environments. Nickel-based materials such as Ni80/Cr20 and Alumel show changes of potential upon changes of partial pressures of hydrogen and water, rendering them unsuitable as stable references. Their reactivity causes inconsistent measurements due to simultaneous changes of both the tip and sample. In contrast, graphite and Ag/AgCl tips used here for the first time in hydrogen atmospheres showed remarkable stability in both humid and dry conditions during dynamic measurements. They remain inert to hydrogen over extended periods, ensuring the change of potential measured is solely from the sample, unaffected by the tip. Notably, Ag/AgCl exhibits outstanding stability in water-containing environments, maintaining a constant tip potential (∼250 mV vs SHE) across humidity levels from 0 % to at least 98 % RH. These findings highlight graphite and Ag/AgCl as robust, hydrogen-insensitive reference tips, with Ag/AgCl being particularly effective for environments with varying hydrogen pressures and humidity levels.