Depth probing of the hydride formation process in thin Pd films by combined electrochemistry and fiber optics-based in situ UV/vis spectroscopy

Abstract

We demonstrate a flexible combined electrochemistry and fiber optics-based in situ UV/vis spectroscopy setup to gain insight into the depth evolution of electrochemical hydride and oxide formation in Pd films with thicknesses of 20 and 100 nm. The thicknesses of our model systems are chosen such that the films are thinner or significantly thicker than the optical skin depth of Pd to create two distinctly different situations. Low power white light is irradiated on the sample and analyzed in three different configurations; transmittance through, and, reflectance from the front and the back side of the film. The obtained optical sensitivities correspond to fractions of a monolayer of adsorbed or absorbed hydrogen (H) and oxygen (O) on Pd. Moreover, a combined simultaneous readout obtained from the different optical measurement configurations provides mechanistic insights into the depth-evolution of the studied hydrogenation and oxidation processes.

Selective Electrochemical Reduction of Nitrogen to Ammonia by Adjusting the Three-Phase Interface

“…Compared with pristine Pd/ACC and a reference sample prepared by heating Pd/ACC in a tube furnace with a N 2 flow, the catalyst after NRR showed diffraction peaks slightly shifted toward lower diffraction angles in the XRD pattern and enlarged lattice distances in the HRTEM image, suggesting that Pd hydride might form after the NRR test (Figures ). The solid-state NMR measurement further confirmed it (), consistent with the above DFT results and the previous reports that H atoms can enter into the lattice of Pd to form stable PdH under operating potentials [42, 43].…”

Role of Hydride Formation in Electrocatalysis for Sustainable Chemical Transformations

“…74 UV−visible spectroscopy can identify hydride formation via changes in electronic structure that lead to differences in optical transitions. This has been demonstrated in situ for PdH x formation, as shown in Figure 3F (bottom panel), 73 but again presents an area (and depth) averaged, semiquantitative picture. 4.3.…”

Ambient ammonia synthesis via palladium-catalyzed electrohydrogenation of dinitrogen at low overpotential

“…In comparison, such a significant difference in both N 2 RR activity and selectivity clearly indicates that Pd is a unique catalyst for N 2 RR. Actually, Pd can readily absorb H atoms in its lattice, forming Pd hydrides under operating conditions 41 . The cathodic current observed at 0.10 and 0.05 V is similar to the data in a previous study 42 , and the unaccounted current at the two potentials (see Supplementary Fig.…”