Adsorption and Absorption Energies of Hydrogen with Palladium

Abstract

Thermal recombinative desorption rates of HD on Pd(111) and Pd(332) are reported from transient kinetic experiments performed between 523 and 1023 K. A detailed kinetic model accurately describes the competition between recombination of surface-adsorbed hydrogen and deuterium atoms and their diffusion into the bulk. By fitting the model to observed rates, we derive the dissociative adsorption energies ( E 0, ads H 2 = 0.98 eV; E 0, ads D 2 = 1.00 eV; E 0, ads HD = 0.99 eV) as well as the classical dissociative binding energy ϵ ads = 1.02 ± 0.03 eV, which provides a benchmark for electronic structure theory. In a similar way, we obtain the classical energy required to move an H or D atom from the surface to the bulk (ϵ sb = 0.46 ± 0.01 eV) and the isotope specific energies, E 0, sb H = 0.41 eV and E 0, sb D = 0.43 eV. Detailed insights into the process of transient bulk diffusion are obtained from kinetic Monte Carlo simulations.

Correlating Experimentally Determined Hydrogen Binding Energy with Hydrogen Evolution Activity over Metal Monolayers on Molybdenum Nitride

“…The DFT-calculated Δ E H aligns well with the TPD-determined Δ H ad,H (Table ) via a linear relationship (red line, R 2 = 0.93 in Figure ), showing the binding strength increasing from Pt(111), Pt/Mo 2 N < Pd(111), Pd/Mo 2 N < Mo 2 N. A reasonable agreement between Δ H ad,H and Δ E H is observed for Pt(111), Pt-modified Mo 2 N(111), and Pd-modified Mo 2 N(111) (Table ). In comparison, a more pronounced discrepancy is seen for Pd(111), which can be attributed to the competition between the recombination of surface adsorbed hydrogens and their diffusion into the bulk as reported in a previous study . Nevertheless, the trend in hydrogen binding energy going from Pt-based surfaces to Pd-based surfaces to Mo 2 N(111) still holds, which captures well the trend observed for HER activity, as will be demonstrated below.…”

“…In comparison, a more pronounced discrepancy is seen for Pd(111), which can be attributed to the competition between the recombination of surface adsorbed hydrogens and their diffusion into the bulk as reported in a previous study. 43 Nevertheless, the trend in hydrogen binding energy going from Pt-based surfaces to Pdbased surfaces to Mo 2 N(111) still holds, which captures well the trend observed for HER activity, as will be demonstrated below.…”

Binding Energy and Diffusion Barrier of Formic Acid on Pd(111)

“…Recently, the velocity-resolved kinetics (VRK) method has demonstrated determinations of adsorption energies that are at least as accurate as those obtained with SCAC. − By measuring accurate desorption rates, statistical rate modeling and detailed balance can be applied to obtain binding energies. In this work, we demonstrate the capability of VRK to determine binding energies in reactive systems; specifically, we present work from which the binding energy of formic acid on Pd(111) is derived, under conditions where molecular desorption competes with decomposition to CO 2 and H 2 .…”

Spiers Memorial Lecture: New directions in molecular scattering

“…In fact, the kinetic data were even sensitive to hydrogen diffusion between the surface and the bulk; hence, the bulk absorption energy could also be obtained. 394 Where comparison is possible, the binding energies obtained above compare well with results from single-crystal adsorption micro-calorimetry. 398,399 One advantage of VRK (or for that matter any accurate desorption kinetics measurement) is that, in addition to binding energies, accurate diffusion barriers can be derived.…”