Palladium hydrides (PdHx) represent a prototypal platform for investigating metal-H interactions, owing to their well-defined phase transition, and are also relevant to molecular hydrogen storage, sensing and (electro)catalysis. It is well-known that the H sorption capacity of Pd nanoparticles (NPs) depends on their size and that H atoms become progressively trapped in Pd after repeated H sorption/desorption cycles. However, the influence of the NP shape on these properties has been much less explored. Herein, by synthesizing carbon-supported Pd nanocubes (NCs) enclosed by {100} facets, we reveal a pronounced size-dependent H sorption capacity, with the H:Pd ratio increasing from 0.55 to 0.68 as the Pd NC size increased from 5.4 to 20.2 nm in 0.1 M H2SO4 at 20 °C. In parallel, a size-dependent H trapping is evidenced, with the fraction of trapped H decreasing from 13.9% to 5.1% as the Pd NC size increases over the same size range. Combining electrochemical measurements on both cubic and spherical Pd NPs with molecular dynamics simulations, we disentangle size and shape effects and demonstrate that both H sorption capacity and H trapping amplitude are primarily governed by the surface-to-volume ratio of the Pd NPs, rather than by their shape.

Poly(allyl diglycol carbonate), CR-39, is a common type of plastic used in detecting and measuring radiation exposure. Incident particles damage the polymer, leaving behind latent tracks. During chemical etching, these tracks are then preferentially etched, resulting in microscale tracks where the particles have passed. In electrochemical cells, pits in CR-39 detectors have been used as evidence for presence of nuclear reactions during palladium-deuterium co-deposition. This research focuses on replicating these measurements and investigating parameters affecting pit formation. With appropriate cell designs, pits can be produced without palladium and/or deuterium in the system. Free radical formation and cavitation are proposed as alternative CR-39 damaging mechanisms. CR-39 response to ultrasound cavitation indicates cavitation as the predominant source of the initial damage on CR-39 surfaces. Pits produced during metal-hydride/deuteride co-deposition and subsequent hydrogen evolution reaction (HER) processes after etching had their diameters distributed into two partially overlapping normal distributions. Comparisons with literature suggested this diametral distribution bifurcation could be the result of cavitation collapse of two types of evolved gas nanobubbles. Spherical nanobubbles and high contact angle surface nanobubbles produce jets during their collapse, creating seed damages relative to their projection, with the spherical bubble collapse producing deeper impressions. Surface damage differences on CR-39 surface are then magnified during the etching process resulting in the observed diametral distributions. The results of this study indicate that work involving CR-39 detectors in systems with gas evolution should take cavitation effects into account, as polymer-damaging cavitation events occur during electrolysis. They also underline that CR-39 detectors can serve as a tool to characterize degradation caused by cavitation in electrolyzers.

The palladium-hydrogen system plays a crucial role in catalysis, hydrogen production and storage, hydrogen embrittlement, and sensing technologies. Understanding the transition of palladium nanocrystals (NCs) from the hydrogen-poor (α) phase to the hydrogen-rich (β) phase is crucial for elucidating hydrogen absorption/desorption mechanisms as well as related phenomena such as hydrogen trapping. In this study, we carefully minimized undesired X-ray beam effects and used in situ Bragg coherent diffraction imaging under electrochemical control to map the strain and lattice parameter distribution within individual palladium NCs across electrochemical potentials relevant to hydrogen absorption and desorption. Lattice parameter changes in both α and β phases are tracked, and reversible strain inversion during the α-to-β phase transition is observed. Through strain and reciprocal space analysis and molecular simulations, a model for the α-to-β phase transition is proposed, which includes a hydrogen-saturated subsurface shell, hydrogen depletion from the α phase during β phase nucleation, and propagation of the β phase in a spherical-cap fashion.

Palladium hydrogen is a useful model in the study of both hydrogen absorption for energy storage, and lattice gas systems for fundamental thermodynamic models. Using in situ time-resolved X-ray nanodiffraction at the fourth generation Extremely Brilliant Source of the European Synchrotron (ESRF-EBS), the kinetics of hydrogen absorption in individual alpha phase Pd nanoparticles is examined. Hydrogen absorption kinetics in a gas reactor and an electrochemical cell are compared. Combining the individual nanoparticle X-ray measurements with chronoamperometry measurements, the kinetics of the ensemble of Pd nanoparticles on the glassy carbon substrate is compared with kinetics at the single nanoparticle level. Hydrogen absorption in alpha phase Pd in the electrochemical system is found to be slower than that of the gas system. Furthermore, the absorption in the electrochemical system slows down as the electrochemical potential is lowered. This slow down is found to be directly related to the increasing hydrogen absorption per step in electrode potential. Furthermore, differences between absorbed-quantity normalized absorption times is seen between the hydrogen and deuterium absorbates. Sieverts's law of absorption is also shown to hold for individual Pd nanoparticles in the alpha phase.

Inductively coupled plasma mass spectrometry (ICP-MS) has become a crucial tool for the real-time analysis of electrochemical processes, such as (photo)corrosion, electrodeposition, and electrocatalytic reactions occurring at high electrode potentials. In this study, we provide insights into a previously unexplored phenomenon: the release of metal from thin-film electrodes composed of metal nanoparticles supported on high-surface-area carbon under hydrogen evolution reaction (HER) conditions. By combining ICP-MS with electrochemistry, we show that the extent of metal release is controlled by the HER activity of the metal: it is more pronounced for Pt than Pd, increases with lower potential limits, and is exacerbated by slower potential sweep rates. Identical-location transmission electron microscopy images reveal that the metal release arises from the detachment of a small fraction of the thin-film electrode and not from metal dissolution or nanoparticle detachment from the carbon support. We recommend strategies to mitigate this adverse effect, such as reducing the catalyst layer thickness and increasing the ionomer-to-carbon ratio. Our findings highlight the risk of misinterpreting catalyst layer detachment as metal dissolution in online ICP-MS studies and are of practical importance for water electrolyzers.

Nanostructured palladium (Pd) is a universal catalyst that is widely used in applications ranging from catalytic converters of combustion engine cars to hydrogenation catalysts in industrial processes. Standard protocols for synthesizing such nanoparticles (NPs) typically use bottom‐up approaches. They utilize special and often expensive physical techniques or wet‐chemical methods requiring organic surfactants. These surfactants should often be removed before catalytic applications. In this article, the synthesis of Pd NPs immobilized on carbon support by electrochemical erosion without using any surfactants or toxic materials is reported. The Pd NPs synthesis essentially relies on a Pd bulk pretreatment, which causes material embrittlement and allows the erosion process to evolve more efficiently, producing homogeneously distributed NPs on the support. Moreover, the synthesized catalyst is tested for hydrogen evolution reaction. The activity evaluations identify optimal synthesis parameters related to the erosion procedure. The electrocatalytic properties of the Pd NPs produced with sizes down to 6.4 ± 2.9 nm are compared with a commercially available Pd/C catalyst. The synthesized catalyst outperforms the commercial catalyst within all properties, like specific surface area, geometric activity, mass activity, specific activity, and durability.

A simple electrochemical surfactant-free top-down methodology for the synthesis of nanowires with non-stoichiometric Magnéli phase Ti9O17 is presented.

The Pd hydride (PdHx) is a typical system to study the fundamentals of solute intercalation and phase transformations or to determine the effect of strain on the rate of electrocatalytic reactions. A crucial methodological aspect, however, involves quantitatively determining the hydrogen-to-palladium atomic ratio (H:Pd) under experimental conditions where various incidental contributions to the total electrode charge are comparable to the charge spent for H adsorption/absorption and desorption. This is the case for electrodes with relatively low (dozens of mu g/cm(2)) loadings of Pd on various porous supports, typically used to study the oxidation of small organic molecules or the reduction of oxygen in acidic or alkaline fuel cells. Ultra-low Pd loadings (often in the range of a few mu g/cm(2)) are also typical for Pd nanoparticles on smooth supports, which are commonly considered as model systems for in situ structural studies of hydrogen sorption. To determine accurately the H content in Pd particles, we propose a technique based on analysis of charge disbalance at anodic and cathodic scans of a cyclic voltammogram, and also address the contribution of adsorbed H. To illustrate the possibilities and limitations of this technique, we present the voltametric study of thin electrodeposited Pd layers on glassy carbon and of a carbon-supported Pd catalyst.

Designing electrocatalysts with optimal activity and selectivity relies on a thorough understanding of the surface structure under reaction conditions. In this study, experimental and computational approaches are combined to elucidate reconstruction processes on low-index Pd surfaces during H-insertion following proton electroreduction. While electrochemical scanning tunneling microscopy clearly reveals pronounced surface roughening and morphological changes on Pd(111), Pd(110), and Pd(100) surfaces during cyclic voltammetry, a complementary analysis using inductively coupled plasma mass spectrometry excludes Pd dissolution as the primary cause of the observed restructuring. Large-scale molecular dynamics simulations further show that these surface alterations are related to the creation and propagation of structural defects as well as phase transformations that take place during hydride formation.