Palladium Thin Films Research Articles

Palladium thin films on microfiber filtration paper as flexible substrate and its hydrogen gas sensing mechanism

Cost-effective, simple and flexible hydrogen gas sensors operating at room temperature were demonstrated based on DC magnetron sputtered palladium thin films. The main idea is to use commercial microfiber filtration paper as a cheap, fibrous and flexible substrate for palladium. With this objective, Pd thin films with 21, 38 and 54 nm thicknesses were deposited and characterized by grazing incident X-ray diffraction (GIXRD) and scanning electron microscope (SEM). The gas sensing behavior was tested by hydrogen gas in the concentration rang of 0.5–10%. GIXRD showed a PdX/Pd phase and SEM revealed existing of many structural nanocracks. An activation process was needed where sensors were heated up to 110 °C in the presence of 10% H2. Then a desirable hydrogen sensitivity with good stability based on hydrogen induced lattice expansion (HILE) effect in which conductance increases was observed. However, for low Pd thicknesses (21 and 38 nm) and at below 4% H2, an inverse effect was observed in which the conductance decreased instead of increasing. For all samples the response time is incremental in the range of 0.5–4% and declining for 4–10%. Moreover, the deposited Pd sensors operate well when they are bent inward or outward. The governed physical mechanism was expressed and discussed.

Formic Acid Oxidation on Pd Thin Film Coated Au Nanocrystals

Cubic, octahedral, and rhombic dodecahedral gold nanocrystals enclosed by {100}, {111}, and {110} facets, respectively, were prepared by a seed-mediated growth method at the room temperature. Palladium thin films were coated on these Au nanocrystals by a redox replacement approach to explore their catalytic activities. It is revealed that formic acid and carbon monoxide oxidation in 0.1 M HClO4 on Au nanocrystals coated with one monolayer (ML) of Pd are facet-dependent and resemble those obtained from corresponding Pd single crystals and Pd films deposited on bulk Au single crystals, suggesting epitaxial growth of Pd overlayers on the Au nanocrystal surfaces. As the Pd film thickness increased, formic acid oxidation current density decreased and the CO oxidation potential moved to more negative. The catalytic activity remained largely unchanged after 3–5 MLs of Pd deposition. The specific adsorption of (bi)sulfate was shown to hinder the formic acid oxidation and the effect decreased with the increasing Pd film thickness. These observations were explained in the framework of the d-band theory. This study highlights the feasibility of engineering high-performance catalysts through deposition of catalytically active metal thin films on facet-controlled inert nanocrystals.

Probing the Effect of Surface Strain on CO Binding to Pd Thin Films

We report measurements to investigate the effects of mechanical strain on the binding energy of carbon monoxide (CO) on the (111) surface of a 16 nm thin film of palladium (Pd) grown on rutile titanium dioxide (r-TiO2). The lattice mismatch between Pd and the r-TiO2 leads to a tensile mechanical in-plane stress in the Pd layer of approximately 0.38 GPa. We observe an increase of (40 ± 10) kJ mol–1 in the CO binding energy for the 16 nm sample compared to a bulk Pd(111) crystal, which is in qualitative agreement with expectations based on the d-band model.

Palladium microfiber network as a platform for hydrogen sensing applications

In this study, we developed a hydrogen sensor based on a palladium microfiber network on a paper substrate. A 60-nm pure palladium film was deposited on photocopy paper using a vacuum evaporation technique. The photocopy paper was employed as the sensor substrate because of its low cost and the simple and rapid fabrication process. The texture of the microfiber network on the paper greatly increased the surface area to volume ratio for the palladium thin film, which is crucial for rapid response sensors. The experimental results showed that the hydrogen sensor exhibited a rapid response and linear gas response characteristics at room temperature and pressure. The gas response of the paper–substrate sensor was much higher compared with the glass substrate.

Annealing effects on elemental composition and morphological properties of Pd thin films grown on crystalline silicon substrate

Silicon (Si) has been the most widely used semiconductor for decades, playing an important role in the field of electronics, energy conversion and energy storage. Because of their unique morphological energy band characteristics, Si nanostructures exhibit superior performance in many applications in comparison with their bulk counterparts. In this study, the effects of thermal annealing on elemental composition and morphological properties of palladium metal thin films grown on c-Si substrates were investigated. Palladium (Pd) thin films of different thicknesses were deposited on Si (1 0 0) with and without native oxide layers by electron beam evaporation and annealed in vacuum at 600 °C for two hours. Scanning electron microscopy (SEM) studies have shown that the surface morphology showed an effective dewetting in individual droplets and islands which further coalesce into bigger islands. Rutherford backscattering spectrometry (RBS) and electrical measurements analyses revealed the diffusion of the Si substrate into the Pd layer during annealing. This contribution will discuss the effects of the metal layer thickness as well as the native oxide on the metal thin films.

Single-Step Fabrication of Nanostructured Palladium Thin Films via Aerosol-Assisted Chemical Vapor Deposition (AACVD) for the Electrochemical Detection of Hydrazine

Aerosol-assisted chemical vapor deposition (AACVD) is successfully implemented for the fabrication of nanostructured palladium (Pd) thin films on FTO substrate. The Pd films are produced using a commercially available precursor palladium acetylacetonate (Pd(C5H7O2)2) under the flow of N2 gas without incorporating hydrogen gas or any other reducing agent. This synthetic strategy can effectively confront the previous problems related with conventional CVD approach while depositing palladium thin films such as reduced volatility and thermal instability of precursors. The palladium thin films were characterized by powder X-ray diffraction (pXRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) analysis. Hydrazine is a colorless and flammable chemical routinely used in rocket fuel, agro-chemicals, textile dyes, and as corrosion inhibitors in various industries. However, hydrazine is a toxic and highly carcinogenic chemical. The newly fabricated palladium nanostructured films were tested for electrochemical sensing of hydrazine in this study. A highly stable and reproducible amperometric response for hydrazine oxidation was obtained with a superior limit of detection (LOD) of 10 nM, and limit of quantification (LOQ) of 33 nM while the sensitivity value calculated was 2.94 μA μM−1 cm−2. A linear concentration range of 1–325 μM was achieved by chronoamperometry.

Fabrication of Nanostructured Pd Thin Films Using Aerosol-Assisted Chemical Vapor Deposition for the Nonenzymatic Electrochemical Detection of H2O2

An improved and facile aerosol-assisted chemical vapor deposition (AACVD) process for the production of palladium thin film on indium tin oxide (PdNP-ITO) electrodes was described and applied for the electrochemical detection of hydrogen peroxide (H2O2). The detailed characterization of the films by X-ray diffraction (XRD), scanning electron microscopy/energy-dispersive X-ray (SEM/EDX) spectroscopy, and X-ray photoelectron spectroscopy (XPS) analysis proved the high crystallinity and phase purity of the nanosized metallic palladium films without the evolution of any elemental impurities from the precursor compound. The as-prepared electrodes were used for nonenzymatic amperometric H2O2 detection via electrochemical reduction. The LOD was 40.8 nM with a high sensitivity of 760.84 μA/(μM cm2). From the experimental scan rate variation analysis, the reduction of H2O2 on the PdNP-ITO electrode surface was determined to be adsorption controlled. For this process of adsorption, we calculated the number of elect...

Fabrication and Morphological Control of a Palladium Film with a Three-Dimensional Nano-Network Structure as a Hydrogen Gas Sensing Material using Organic Acid Chelation

ABSTRACTNano-porous palladium (Pd) thin films could potentially be applied to hydrogen gas sensing materials with high sensitivity and selectivity. In our previous study, a nano-porous Pd film was fabricated with a three-dimensional network structure from an AlPd mother alloy film by a dealloying method using the chelating ability of an organic acid. This process was simple and environmentally friendly because it only required organic acid in a ppm concentration, and did not exhaust a strong acid waste solution, including heavy metal ions. This method was modified to improve the Pd purity of the dealloyed specimen, reaction rate, and morphology control. In this study, the existence of a composition undulation pattern was shown in the AlPd mother alloy film, and its effects on the morphology of the dealloyed specimen were evaluated. Furthermore, this pattern could be controlled by N2 gas addition to the Ar sputtering gas during the preparation of the AlPd mother alloy film.

Selective Detection of Dopamine at the AACVD Synthesized Palladium Nanoparticles and Understanding the Sensing Mechanism through Electrochemical and Computational Study

In this work, a selective dopamine (DA) sensor has been constructed based on thin film (TF) palladium nanoparticles (PdNPs) fabricated over indium tin oxide (ITO) (TFPdNP_ITO) by aerosol assisted chemical vapor deposition (AACVD) method. The TFPdNP_ITO electrodes were characterized with SEM, XRD, EDX, XPS, cyclic voltammetry (CV), tafel plot analysis, and electrochemical impedance spectroscopy (EIS). We performed geometry optimization of metallic planes, and Monte Carlo Search (MCS) computational simulations of DA, and interfering species to understand the effects of PdNPs on the selective DA detection at the atomic level. The total energy, and bind energy calculations from geometry optimizations showed that DA had the most negative energy value, and was most likely to interact with the TF of PdNPs. The adsorption locator module also predicted similar results through MCSs. A possible reaction mechanism for the DA oxidation at the TFPdNP_ITO was predicted based on the experimental and computational findings. The amperometry analysis showed linear range, sensitivity, and LOD of 1.77 μM – 543 μM, 0.009 μA/μM, and 0.13 ± 0.06 μM, respectively. The TFPdNP_ITO sensor was further tested for stability, and reproducibility. Commercial dopamine hydrochloride injection (DAHI) was used for the real sample analysis using both DPV, and amperometry techniques.

Delamination of palladium thin film on polymer substrate due to hydrogen absorption

Delamination of palladium thin film on polymer substrate due to hydrogen absorption

Growth of Palladium Thin Film Deposited on Stainless Steel Current Electrodes by Wet Chemical Method for Actived Carbon Supercapacitor and Their Electrochemical Properties

Growth of Palladium Thin Film Deposited on Stainless Steel Current Electrodes by Wet Chemical Method for Actived Carbon Supercapacitor and Their Electrochemical Properties

Effect of hydriding induced defects on the small-scale plasticity mechanisms in nanocrystalline palladium thin films

Nanoindentation tests performed on nanocrystalline palladium films subjected to hydriding/dehydriding cycles demonstrate a significant softening when compared to the as-received material. The origin of this softening is unraveled by combining in situ TEM nanomechanical testing with automated crystal orientation mapping in TEM and high resolution TEM. The softening is attributed to the presence of a high density of stacking faults and of Shockley partial dislocations after hydrogen loading. The hydrogen induced defects affect the elementary plasticity mechanisms and the mechanical response by acting as preferential sites for twinning/detwinning during deformation. These results are analyzed and compared to previous experimental and simulation works in the literature. This study provides new insights into the effect of hydrogen on the atomistic deformation and cracking mechanisms as well as on the mechanical properties of nanocrystalline thin films and membranes.

Accurate Coulometric Quantification of Hydrogen Absorption in Palladium Nanoparticles and Thin Films

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.

Room-temperature optical detection of hydrogen gas using palladium nano-islands

Palladium thin films of different thicknesses have been processed by oxidation and subsequent reduction in hydrogen atmosphere. Hydrogen optical sensing properties of as-deposited (Pd) and processed (r-Pd) samples have been experimentally tested with a H2 concentration of 5% and 1%, discovering that the reduced films show improved performances in term of response/recovery time. As reveled by SEM images, the oxidation/reduction process modifies the surface appearance, which assumes a nano-islands structured morphology. The porosity of the processed films may explain the reduction of the response/recovery time, while the larger effective sensing surface in thinner samples justifies the responsivity performances.

Palladium nanostructure incorporated cupric oxide thin film with strong optical absorption, compatible charge collection and low recombination loss for low cost solar cell applications

Cupric oxide (CuO) is one of the most promising and low-cost materials for solar cell application, but its power conversion efficiency is limited by discrepancy between short carrier diffusion length and optical absorption length, low charge collection efficiency, and high recombination rate. We present a novel optical absorbing CuO film to simultaneously address all of these issues by combining thin films of palladium (Pd) nanoparticles-incorporated CuO (CuO:Pd), nitrogen-doped CuO (CuO:N), and nitrogen-doped cuprous oxide (Cu2O:N). Incorporation of Pd nanoparticles significantly increases photo-generated charge collection efficiency and enhances optical absorption over the wide range of solar spectrum. Graded refractive index and step distribution of carrier concentration of Cu2O:N/CuO:N thin films reduce optical reflectance and build high potential into optical absorbing thin film. The Cu2O:N/CuO:N/CuO:Pd/CuO thin film increases charge collection efficiency and reduces recombination rates. Using this design, record high short circuit current density (Jsc) and efficiency (η) of around 28.5 mA cm−2 and 8.3 are achieved, respectively, for heterojunction solar cell using Cu2O:N/CuO:N/CuO:Pd/CuO thin film on titanium (Ti) passivated n-type silicon (Si) substrate (p-(Cu2O:N/CuO:N/CuO:Pd/CuO)/Ti/n-Si). Jsc and η for p-(Cu2O:N/CuO:N/CuO:Pd/CuO)/Ti/n-Si solar cell are around 14 and 40 times higher than the control p-CuO/n-Si solar cell, respectively. This work provides a novel approach to achieve high efficiency CuO-based thin film solar cells.

Optical investigation of palladium(II) phthalocyanine including an aromatic group

Peripherally β-naphthoxy unit substituted palladium(II) phthalocyanine was synthesized from corresponding phthalonitrile compounds. The palladium (II) phthalocyanine was characterized with ultraviolet–visible spectroscopy (UV-Vis), fourier transform- infrared spectroscopy (FT-IR), mass and elemental analyses techniques. Thin films of palladium (II) phthalocyanine were prepared using different organic solvents by spin coating technique. Transmittance and absorbance spectra of the thin films were studied in the wavelength range of 200–1000 nm. Optical band gaps of palladium (II) phthalocyanine thin films were also calculated.

Unexpected Behavior of the Hydrogen Oxidation Reaction on Palladium in Alkaline Solution: A Feasible Kinetic Explanation

The hydrogen oxidation reaction was studied on a thin film palladium electrode supported on a gold substrate in alkaline solution. The hydrogen absorption process was analyzed by open circuit potential transient and the current - overpotential dependences were obtained by chronoamperometry at different rotation rates in a solution saturated with hydrogen. The results obtained show an unexpected profile at low overpotentials, where current decreases as rotation rate increases. A kinetic mechanism was proposed to interpret this behavior and the corresponding equations were derived. They were used to correlate the results, with a good agreement between the experimental and fitted curves.

Imaging the Hydrogen Absorption Dynamics of Individual Grains in Polycrystalline Palladium Thin Films in 3D.

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 single- and polycrystalline 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.

X-ray diffraction study on a (111)-textured palladium thin film under hydrogen loading and unloading: film structure evolution and its mechanism

The incorporation of hydrogen normally results in degradation when applied to metals. In this diffraction study, however, improvement of the film structure, such as in-plane grain growth, lattice defect removal and texture enhancement, was observed in a (111)-textured palladium thin film during hydrogen loading and unloading cycles. Accordingly, diffraction stress analysis was performed to investigate the evolution mechanism. It was found that the formation of the β phase during the α-to-β phase transformation occurred at the same in-plane stress present in the α phase, andvice versa. This suggests that the cyclic α–β grain boundary motion during the transformation occurred mainly along the in-plane direction, contributing to the film structure evolution.

Antibacterial Efficacy of Sacrifical Anode Thin Films Combining Silver with Platinum Group Elements within a Bacteria‐Containing Human Plasma Clot

Silver (Ag) dots arrays (64 and 400 dots per mm2) are fabricated on a continuous platinum (Pt), palladium (Pd), or iridium (Ir) thin film (sacrifical anode systems for Ag) and for comparison on titanium (Ti) film (non‐sacrifical anode system for Ag) by sputter deposition and photolithographic patterning. The samples are embedded within a tissue‐like plasma clot matrix containing Staphylococcus aureus (S. aureus), cultivated for 24 h. Bacterial growth is analyzed by fluorescence microscopy. Among platinum group sacrifical anode elements and a dense Ag sample, only the high Ag ion releasing Ag–Ir system is able to inhibit the bacterial growth within the adjacent plasma clot matrix. This study demonstrates that the antibacterial efficiency of Ag coatings is reduced under tissue‐like conditions. However, the new sacrificial anode based Ag–Ir system can overcome this limitation.