We value your privacy
We report here an electrochemical method for precise and accurate quantification of hydrogen absorption in palladium materials. We demonstrate that conventional chronocoulometry over-reports adsorbed hydrogen due to charge from the accompanying hydrogen oxidation reaction (HOR). We designed and built a bespoke electrochemical flow cell that mitigates the concurrent HOR reaction and consequently provides improved accuracy and reproducibility relative to other existing electrochemical techniques. The efficacy of this technique is demonstrated experimentally for a series of palladium sample types: a 100 nm electron-beam deposited thin film, a 20 μm electrodeposited palladium film, a casting of 21 nm edge-length cubic nanoparticles, and a casting of 27 nm edge-length octahedral nanoparticles. We contend that this method is the most effective for measuring hydrogen uptake in different palladium samples.
Do you want to read the rest of this article?
... We note that faster hydrogen absorption was previously reported for octahedral palladium samples relative to cubes 18 , but these studies compared samples with different surface-to-bulk atom ratios, unlike our investigation ( Supplementary Fig. 2). To study how particle shape affects hydrogen loading, the hydrogen concentration per palladium atom (H:Pd) was determined by coulometry 19 using a custom-built electrochemical flow cell 20 . The hydrogen loading values were measured to be higher for the samples with exclusively (111) surfaces and lower for samples with (100)-rich surfaces ( Supplementary Fig. 11). ...
The 1989 claim of ‘cold fusion’ was publicly heralded as the future of clean energy generation. However, subsequent failures to reproduce the effect heightened scepticism of this claim in the academic community, and effectively led to the disqualification of the subject from further study. Motivated by the possibility that such judgement might have been premature, we embarked on a multi-institution programme to re-evaluate cold fusion to a high standard of scientific rigour. Here we describe our efforts, which have yet to yield any evidence of such an effect. Nonetheless, a by-product of our investigations has been to provide new insights into highly hydrided metals and low-energy nuclear reactions, and we contend that there remains much interesting science to be done in this underexplored parameter space.
Link to full article: https://rdcu.be/bEAsT
Metal hydrides often display dramatic changes in optical properties upon hydrogenation. These shifts make them prime candidates for many tunable optical devices, such as optical hydrogen sensors and switchable mirrors. While some of these metals, such as palladium, have been well studied, many other promising materials have only been characterized over a limited optical range and lack direct in situ measurements of hydrogen loading, limiting their potential applications. Further, there have been no systematic studies that allow for a clear comparison between these metals. In this work, we present such a systematic study of the dynamically tunable optical properties of Pd, Mg, Zr, Ti, and V throughout hydrogenation with a wavelength range of 250 - 1690 nm. These measurements were performed in an environmental chamber, which combines mass measurements via a quartz crystal microbalance with ellipsometric measurements in up to 7 bar of hydrogen gas, allowing us to determine the optical properties during hydrogen loading. In addition, we demonstrate a further tunability of the optical properties of titanium and its hydride by altering annealing conditions, and we investigate the optical and gravimetric hysteresis that occurs during hydrogenation cycling of palladium. Finally, we demonstrate several nanoscale optical and plasmonic structures based on these dynamic properties. We show structures that, upon hydrogenation, demonstrate five orders of magnitude change in reflectivity, resonance shifts of >200 nm, and relative transmission switching of >3000%, suggesting a wide range of applications.
High pressure x-ray diffraction of PdHx and PdDx demonstrate that these materials remain in a face-centered cubic (fcc, Fm3 ̅m) structure to these pressures at room temperature. The volumes indicate stoichiometric compositions under pressure with x = 1 for both materials. No indications of phase transitions were observed up to the highest pressures reached in the experiments. A third-order Birch-Murnaghan equation of state used to fit the pressure-volume data gives V0 = 10.73 (±0.03) cm³/mol, K0 = 147 (±11) GPa, and K0' = 4.7 (±0.5), whereas a Vinet fit gives V0 = 10.74 (±0.03) cm³/mol, K0 = 143 (±11) GPa, and K0' = 5.1 (±0.5), for both PdHx and PdDx. The results are used to obtain the pressure dependence of the effective volume of H and D atoms in PdHx and PdDx to megabar pressure for comparison with other hydrides, with implications for superconductivity in this class of materials.
Defects such as dislocations and grain boundaries often control the properties of polycrystalline materials. In nanocrystalline materials, investigating this structure-function relationship while preserving the sample remains challenging because of the short length scales and buried interfaces involved. Here we use Bragg coherent diffractive imaging to investigate the role of structural inhomogeneity on the hydriding phase transformation dynamics of individual Pd grains in polycrystalline films in three-dimensional detail. In contrast to previous reports on nanoparticles, we observe no evidence of a hydrogen-rich surface layer and consequently no size dependence in the hydriding phase transformation pressure over a 125-325 nm size range. We do observe interesting grain boundary dynamics, including reversible rotations of grain lattices while the material remains in the hydrogen-poor phase. The mobility of the grain boundaries, combined with the lack of a hydrogen-rich surface layer, suggests that the grain boundaries are acting as fast diffusion sites for the hydrogen atoms. Such hydrogen-enhanced plasticity in the hydrogen-poor phase provides insight into the switch from the size-dependent behavior of single crystal nanoparticles to the lower transformation pressures of polycrystalline materials and may play a role in hydrogen embrittlement.
The electrochemical carbon dioxide reduction reaction (CO2RR) to simultaneously produce carbon monoxide (CO) and hydrogen (H2) has been achieved on carbon supported palladium (Pd/C) nanoparticles in an aqueous electrolyte. The synthesis gas product has a CO to H2 ratio between 0.5 and 1, which is in the desirable range for thermochemical synthesis of methanol and Fischer–Tropsch reactions using existing industrial processes. In situ X-ray absorption spectroscopy in both near-edge (XANES) and extended regions (EXAFS) and in situ X-ray diffraction show that Pd has transformed into β-phase palladium hydride (β-PdH) during the CO2RR. Density functional theory (DFT) calculations demonstrate that the binding energies of both adsorbed CO and H are significantly weakened on PdH than on Pd surfaces, and that these energies are potential descriptors to facilitate the search for more efficient electrocatalysts for syngas production through the CO2RR.