Separation of hydrogen adsorption and absorption on Pd thin films (original) (raw)

Hydrogen sorption in Pd monolayers in alkaline solution

2009

Hydrogen adsorption/absorption at palladium monolayers (ML) deposited on monocrystalline Au(1 1 1) electrode was studied in 0.1 M NaOH solution. H charge isotherms demonstrated that adsorption started at potentials more positive than at thicker nanometric Pd/Au(polycrystal) deposits. Due to 3-dimensional deposit growth, absorption could be seen at all deposits thicker than 1 ML. Besides, H sorption at Pd/Au(1 1 1) monolayers was more reversible than at nanometric Pd/Au(polycrystal) deposits. Strong geometric and electronic effects due to the Au substrate were observed up to 5 Pd ML. Influence of benzotriazole (BTA) on H sorption was also investigated. BTA blocked H adsorption above 250 mV vs. RHE. At less positive potentials adsorbed BTA layer seemed to undergo a reorientation allowing H adsorption. Stationary and dynamic electrochemical impedance spectroscopy was used to obtain double layer capacitance and charge transfer resistance. BTA also promoted kinetically H sorption into Pd/Au(1 1 1) monolayer and Pd/Au(polycrystal) nanometric deposits.

Investigation of Hydrogen Adsorption and Absorption in Palladium Thin Films

Journal of The Electrochemical Society, 2004

ABSTRACT The electrochemical impedance of palladium films of various thicknesses, deposited on a gold electrode, was measured in the potential range where hydrogen absorbs in palladium. The kinetic and diffusion parameters of the whole electrochemical process were determined. One of the main results was the observation of a maximum on the curves of charge-transfer resistance vs. electrode potential. At this maximum the charge-transfer resistance decreased with the increase of film thickness. This finding is in agreement with the model proposed in Part I, where such a behavior is found to be related to the trapping of the hydrogen atoms in a sublayer just under the electrode surface and a direct exchange of the trapped hydrogen with the electrolyte. (C) 2004 The Electrochemical Society.

Mechanism of hydrogen adsorption/absorption at thin Pd layers on Au(111)

Electrochimica Acta, 2007

ABSTRACT Hydrogen adsorption and absorption at thin palladium deposits of 0.8–10 monolayers (ML) on Au(1 1 1) was studied in 0.1 M H2SO4 and HClO4 using cyclic voltammetry, ac voltammetry, and impedance spectroscopy in the absence and in the presence of poison, crystal violet. Hydrogen adsorption on palladium is more reversible in sulfuric acid than in perchloric acid but it occurs at potentials 30 mV more positive in latter. The charge-transfer resistance exhibits a minimum at ∼0.27 V versus RHE and decreases with increasing in Pd deposit thickness in both acids. Adsorption capacitance at 0.8 ML Pd reaches maximum at the same potential. At other deposits the pseudo-capacitance starts to increase at lower overpotentials indicating the beginning of absorption, even at 2 ML Pd. The double layer capacitance is similar for all the deposits in sulfuric acid and it has a sharp maximum at 0.27 V versus RHE. In perchloric acid a broad maximum is observed. Crystal violet inhibits hydrogen adsorption but makes hydrogen absorption more reversible. The results suggest a fast direct hydrogen absorption mechanism that proceeds in parallel with slower hydrogen adsorption and indirect absorption.

Hydrogen adsorption/absorption on Pd/Pt(111) multilayers

Journal of Electroanalytical Chemistry, 2008

One to 20 monolayers of Pd were deposited on Pt(1 1 1) and their electrochemical behavior was studied by cyclic voltammetry and impedance spectroscopy. The hydrogen adsorption and absorption is more reversible at deposits on Pt(1 1 1) as compared to Au(1 1 1), probably due to less strain and/or electronic effects. The quantity of hydrogen adsorbed/absorbed at 10 ML are however comparable at both supports. The charge transfer resistance is lower at 1 Pd ML in perchloric and sulfuric acids than for thicker layers, and it is lower at Pd/Pt(1 1 1) than at Pd/Au(1 1 1). The adsorption pseudocapacitance reaches a maximum at 0.214 V in sulfuric acid for 1 ML and there are two peaks at 0.214 V and 0.255 V for thicker layers. Crystal violet increases the reversibility of hydrogen absorption and inhibits hydrogen adsorption although some residual adsorption remains.

Hydrogen absorption in Pd thin-films

International Journal of Hydrogen Energy, 2014

Hydrogen absorption isotherms for Pd thin films were modeled at atomistic scale by Monte Carlo (MC) simulation in the TPmN ensamble and by Molecular Dynamics (MD) simulations at 300 K. The interaction among atoms was modeled by embedded atom method (EAM) potentials. Simulated samples consisted of monocrystalline nanofilms with different thickness (2e8 nm) and two crystallographic surface orientations, (001) and (111). The isotherms were compared to bulk Pd and a few available experimental results. Instead of the plateau corresponding to the a-b PdH equilibrium in the bulk, the isotherms at nanofilms show a two-plateaux behavior: a small one corresponding to a surfaceesubsurface hydride formation, and a larger one for the subsequent bulk hydride formation. This is strongly correlated with the atomic stress distribution induced within the thin film. The equilibrium pressures at the isotherms depend on the thin-film thickness, with pressure being larger for thicker films. The isotherms of the (001) films display lower equilibrium pressures than those for (111) films.

Study of the hydrogen absorption in Pd in alkaline solution

Electrochimica Acta, 2008

Hydrogen adsorption/absorption in palladium thin deposits on gold electrode, in 0.1 M NaOH solution, was studied. The contributions of adsorption and absorption to the total charge of hydrogen are separated from the total isotherms at different deposit thicknesses. The adsorbed hydrogen charge increases to a plateau of ∼73.5 C cm −2 , which corresponds to the surface coverage ratio by adsorbed hydrogen of 0.36. The absorbed hydrogen charge agreed with that obtained from the permeation experiments at 50 m Pd foil, at potentials between +100 and +300 mV vs. RHE. EIS was carried out at thin Pd deposits. The kinetics of hydrogen sorption is slower in alkaline solutions than in acids and the isotherms are shifted towards more negative potentials. address: a.lasia@usherbrooke.ca (A. Lasia).

Hydrogen Adsorption on Palladium and Platinum Overlayers: DFT Study

Advances in Physical Chemistry, 2011

Hydrogen adsorption on twenty different palladium and platinum overlayer surfaces with (111) crystallographic orientation was studied by means of periodic DFT calculations on the GGA-PBE level. Palladium and platinum overlayers here denote either the Pd and Pt mono-and bilayers deposited over (111) crystallographic plane of Pd, Pt, Cu, and Au monocrystals or the (111) crystallographic plane of Pd and Pt monocrystals with inserted one-atom-thick surface underlayer of Pd, Pt, Cu, and Au. The attention was focused on the bond lengths, hydrogen adsorption energetics, mobility of adsorbed hydrogen, and surface reactivity toward hydrogen electrode reactions. Both the ligand and strain effects were considered, found to lead to a significant modification of the electronic structure of Pd and Pt overlayers, described through the position of the d-band center, and tuning of the hydrogen adsorption energy in the range that covers approximately 120 kJmol −1 . Mobility of hydrogen adsorbed on studied overlayers was found to be determined by hydrogen-metal binding energy. Obtained results regarding Pd layers on Pt(111) and Au(111) surfaces, in conjunction with some of the recent experimental data, were used to explain its electrocatalytic activity towards hydrogen evolution reaction.

ELECTROCHEMICAL HYDROGEN INSERTION INTO PALLADIUM AND PALLADIUM-NICKEL THIN FILMS

Electrochimica Acta, 1991

Abatraet-A generator-detector mode with the rotating nng-dlsk electrode has been used to determme the &fference between Pd and Pt electrode behavior and the ongm of the larger overpotentials at Pd-hydrogen evolving cathodes The use of thm film Pd disk electrodes has allowed full hydrogen or deutenum chargmg of the metal phase m short ties The electrode system has made feasible emultaneous measurements of the hydrogen uptake m PdH, lilms where the-mum composition reached was PdH, 8, Alloymg NI mto Pd decreases the maxlmum hydrogen absorption by sohd solution Pd-Nl films to near zero at 17% NI The outgassmg of hydrogen on open cxcmt from vanously charged electrodes can be followed m real time and shows the losses associated with transfer of specimens to post-analysis (w 6% m 5 mm)

On the influence of the way of thin gold films preparation on the character of hydrogen adsorption

Surface Science, 1987

Thermal desorption (TD) and surface potential (SP) measurements were applied in studying the adsorption process of molecular and atomized hydrogen on evaporated thin gold films. It has been found that H 2 is adsorbed dissociatively on thin gold films deposited at 78 K and not sintered, while the H 2 adsorption on the same films but sintered at T >/320 K was not detected. The course of atomized hydrogen adsorption on sintered and unsintered Au films is also reported.