Hydrogen egress from palladium surfaces: A microelectrode-based investigation

Atomic hydrogen could participate in multiple electrochemical reactions during egress from Palladium (Pd) into aqueous environments. Possible reactions include hydrogen recombination to form H-2, the oxygen reduction reaction (ORR) and "hydrogen ionisation" to form H+. Here, bulk measurements and microelectrode-based methods were used to mechanistically investigate such reactions occurring during hydrogen egress from Pd. Significant ORR was detected on hydrogen-charged Pd (Pd-H) surfaces, when using a Platinum (Pt) microelectrode (ME) in the redox competition mode. However, minor hydrogen recombination was also detected while using the Pt ME in the sample generation-tip collection (SG-TC) mode. Hydrogen ionisation is observed to occur when Pd (H) is anodically polarised. These reactions can all be linked to the highly negative equilibrium potential of the atomic H/H+ redox couple. Atomic hydrogen being a strong reducing agent thus tends to efficiently reduce various oxidants in solution resulting in different products, under varying conditions.