Promotion of Hydrogen Desorption from Palladium Surfaces by Fluoropolymer Coating

Abstract

The catalytic activity of Pd surfaces towards hydrogen desorption was significantly improved by a nanometer‐thin polytetrafluoroethylene (PTFE) layer, as shown by an enhancement in the permeability of a Pd membrane coated on the permeate side. The origin of this effect was found to be due to a lowering of the barrier for hydrogen desorption, as evidenced by a change in the rate‐limiting mechanism of hydrogen permeation through the membrane from desorption (un‐coated) to diffusion controlled. In situ X‐ray photoelectron spectroscopy (XPS) revealed the electronic structure of the sputtered PTFE. Apart from C–Fn subunits (n=1, 2, 3), we found that nonsaturated carbon atoms became hydrogenated during hydrogen permeation, which was indicative of an interaction between Pd and PTFE. This interaction was weak; no Pd−F bonds were formed. We thus attributed the effect to an increase in the hydrophobicity of the surface by the porous PTFE layer and to a promoter effect of hydrogen desorption as a result of electrostatic interactions between chemisorbed hydrogen and physisorbed PTFE.

Physical Separation of H2 Activation from Hydrogenation Chemistry Reveals the Specific Role of Secondary Metal Catalysts

“…These hydrogen flux measurements also point to the secondary catalysts changing the rate‐limiting step of hydrogen permeation. In the absence of the secondary catalyst, the rate‐limiting step for a 25‐μm thick Pd membrane is expected to be the desorption of adsorbed H atoms from the membrane surface [34, 35] . We observed that catalysts with weaker M–H binding yielded a higher hydrogen flux through the membrane, which is consistent with the desorption step being accelerated by the catalyst (Figure 7 a, b).…”

Dynamic plasmonic colour display

“…Careful material engineering and optimization using Mg alloys 25 26 27 can be carried out to further improve the display durability for real world applications. In addition, polytetrafluoroethylene protective coating can be applied to avoid water staining on the display surface 31 32 . Our technique suggests promising avenues for applications in actively tunable displays 8 9 10 11 and filters 7 8 9 33 , plasmonic holograms 34 35 , plasmonic colourimetric sensing 36 , advanced optical data storage 14 , security tagging and cryptography 15 , as well as realization of plasmonic movies with subwavelength resolution in the future.…”

Metal–polymer hybrid nanomaterials for plasmonic ultrafast hydrogen detection

“…These results, along with similar kinetics acceleration observed for metal-organic framework-coated Pd sensors measured in vacuum/hydrogen 26 and in air 31 , imply that the kinetics-accelerating effect of such coatings may be generic. To this end, a number of different explanations of the origin of the accelerated kinetics is given in the literature, such as the modification of surface chemical 27,32 and electronic states 26,27,33 , physical force/stress imposed by the coating layer 33 and the removal of competing molecules reacting on the surface 31 . Employing DFT calculations to capture the experimentally observed trends, we show that the measured decrease in E a induced by the polymer coating is connected to the absorption and desorption processes at the nanoparticle-polymer interface ( Fig.…”