Engineering Palladium Surfaces to Enhance the Electrochemical Storage of Hydrogen

Wednesday, 31 May 2017: 12:00
Grand Salon C - Section 15 (Hilton New Orleans Riverside)
S. C. Hamm, D. L. Knies, O. Dmitriyeva, R. Cantwell, and M. McConnell (Coolescence LLC)
Materials can be engineered to have enhanced hydrogen storage capabilities during electrolysis by modifying the composition of the first few surface layers at the electrolytic interface. The proper choice of surface layer can radically affect the electrochemical insertion of hydrogen. To this end, between 1 μg cm−2 and 23 μg cm−2 of Pb was deposited onto Pd cathodes during galvanostatic experiments in the 0.1 M LiOH electrolyte. The optimum surface doping level 2.9 μg cm−2 (~1.4 mass equivalent monolayers) of Pb was found to achieve the highest quantity of inserted hydrogen at a potential of approximately −0.5 V vs RHE. Additionally, the hydrogen content increased from PdH0.75 to PdH0.86 with increasing Pb amounts up to 2.9 μg cm−2 at a constant current of −14.5 mA cm−2. For comparison, the same change in hydrogen content from pressurized gas loading experiments would require an increase in hydrogen fugacity from about 6 to 1420 atm. Furthermore, the addition of a small amount of Pt co‑deposited with the Pb resulted in a further increase in hydrogen content to PdH0.89 at −14.5 mA cm−2. Preliminary analysis suggests the Pb and Pt are changing the balance between the Volmer, Heyrovsky, and Tafel reaction rates, which changes the chemical potential of the adsorbed hydrogen, and ultimately controls the hydrogen insertion. This work provides a fundamental basis for the future design of surface alloys yielding enhanced electrochemical hydrogen insertion in Pd and other hydrogen absorbing materials.