Hydrogen sorption properties of bare and Rh-modified Pd nanofilms grown via surface limited redox replacement reactions

Pd nanofilms were grown using electrochemical atomic layer deposition (E-ALD) and used as a platform for investigations into changes in hydrogen absorption/desorption kinetics as a function of the coverage of Rh. Surface limited redox replacement (SLRR) reactions were used to form Pd atomic layers. That is, Pd atomic layers were grown on polycrystalline Au by first depositing a sacrificial Cu atomic layer using underpotential deposition (UPD), and then exchanging it for PdCl42− ions at open circuit potential (OCP). That cycle was then repeated 15 times to form one of the Pd nanofilms used in this study. Rh was deposited on the 15 cycle Pd films from a RhCl63− solution at constant potential or using an E-ALD procedure, similar to that employed to form the Pd nanofilms. Cyclic voltammetry (CV) of the Pd films modified with various coverages of Rh were compared with unmodified Pd nanofilms. The resulting CVs indicated that the presence of Rh enhanced the rates of hydrogen absorption and desorption into and out of the underlying Pd nanofilm. Rh overlayers formed at 0 V for 60 s produced the greatest kinetic enhancement. Two possible explanations for the observed behavior are proposed and discussed.