Hydrogen Interaction (Electrosorption and Evolution) Characteristics of Pd and Pd3Co Alloy Nanoparticles: An In-situ Investigation with Electrochemical Impedance Spectroscopy

Abstract

Electrochemical impedance spectroscopy (EIS) and voltammetry are used to investigate the interaction of hydrogen with Pd and Pd3Co nanoparticles supported on a carbon-matrix. The EIS patterns are recorded in the hydrogen underpotential deposition (UPD) and overpotential deposition (OPD) regions of the voltammogram in acidic electrolyte (0.1M HClO4) where the hydrogen interacts with palladium. The atomic ratio of hydrogen to Pd (n(H/Pd)) estimated from the Hupd region of the voltammogram of Pd nanoparticles suggests a gradual α-β transition unlike the sharp transition reported with bulk Pd thin-films. However, a potential range of this transition can be estimated from the EIS patterns. The diffusion characteristics of hydrogen in the Pd lattice are absent in the EIS patterns (at mid-frequency region) of these nanoparticles due to the very small particle size. The kinetic parameters, those effectively describe the Pd-H system, are estimated from the complex non-linear least square (CNLS) fit of the EIS patterns. A maximum in the charge-transfer resistance with potential, similar to that reported with bulk Pd thin-films, is observed with both Pd and Pd3Co nanoparticles suggesting the trapping mechanism of hydrogen.