Nanostructured Palladium Research Articles

Studies on Porous Nanostructured Palladium–Cobalt–Silica as Heterogeneous Catalysts for Oxygen Evolution Reaction

Studies on Porous Nanostructured Palladium–Cobalt–Silica as Heterogeneous Catalysts for Oxygen Evolution Reaction

Surfactant-free synthesis of nanostructured palladium materials under mild conditions and their highly catalytic selective hydrogenation

Nanostructured palladium (Pd) materials are highly efficient noble metal catalysts in various fields, but developing a simple and mild strategy to prepare Pd nanomaterials with high activity and selectivity still remains a big challenge. In this study, uniform-sized Pd popcorn-like nanospheres (PNSs) were successfully synthesized by the slow reduction of Pd(OAc)2 in anhydrous methanol under ambient conditions in the dark without any surfactant, additional reductant and support. The obtained Pd PNSs have rough surface with the average diameter of approximately 140 nm, and are composed of many smaller PNSs with the average size of about 12 nm. Pd PNSs have excellent catalytic performance in the hydrogenation of 4-nitrobenzaldehyde to 4-aminobenzaldehyde under mild conditions. Specifically, using the as-prepared Pd PNSs as catalyst, the 98 % conversion of 4-nitrobenzaldehyde and 98 % selectivity to 4-aminobenzaldehyde can be achieved within 1.5 h at 35°C under atmospheric pressure. After three recycling, the Pd PNSs can still maintain highly catalytic activity and selectivity. The very simple strategy developed here will be a valuable supplement to the methodology for the surfactant-free fabrication of other surface-active metallic nanomaterials for advanced applications.

Steel slag as low-cost catalyst for artificial photosynthesis to convert CO2 and water into hydrogen and methanol

Photoreduction of CO2 with sunlight to produce solar fuels, also named artificial photosynthesis, is considered one of the most attractive strategies to face the challenge of reducing greenhouse gases and achieving climate neutrality. Following an approach in line with the principles of the circular economy, the low-cost catalytic system (1) based on an industrial by-product such as steel slag was assessed, which was properly modified with nanostructured palladium on its surface in order to make it capable of promoting the conversion of CO2 into methanol and hydrogen through a two-stage process of photoreduction and thermal conversion having formic acid as the intermediate. Notably, for the first time in the literature steel slag is used as photoreduction catalyst.

Structural, morphological and catalytic characteristics of nanostructured palladium catalysts

A new method for the highly active palladium catalyst synthesis on the surface of a Pd-23%Ag film has been developed to increase the material activity with respect to reactions involving hydrogen. Comparison of the electrochemical experiments data of classical palladium black and a new developed nanocatalyst demonstrated a significant increase in catalytic activity in the methanol oxidation reaction (up to 17.09 μA cm−2) for electrodes modified with the latter catalyst. The reason for that is an increase in the number of localized potentially more active surface regions due to the creation of a larger number of active sites in comparison with spherical particles. Estimation of resistance to CO poisoning showed high efficiency of nanocatalysts. Chronoamperometric experiment established the long-term stability and activity of the developed catalyst and confirmed the possibility of its practical use.

Design of nanostructured palladium catalyst supported by chitosan/Co3O4 microspheres and investigation of its catalytic behavior against synthesis of benzonitriles

Designing of eco-friendly, low cost, and thermally stable stabilizing/supporting agents are always desired for production of catalyst systems which provide good catalytic performance in organic reactions. In this study, a novel, green, and efficient stabilizer containing chitosan/Co3O4 microspheres (CS/Co3O4) was developed. Palladium nanoparticles (Pd NPs) were then successfully immobilized on CS/Co3O4 as a heterogeneous nanocatalyst (Pd NPs/CS/Co3O4). Characterization of the designed materials were performed by FT-IR, TEM, FE-SEM, XRD, and EDS and it was determined that Pd NPs formed as approximately 20 nm. Catalytic behavior of Pd NPs/CS/Co3O4 was investigated in the production of different substituted benzonitriles via aryl halide cyanation. Catalytic studies indicate that electron-rich or poor aromatic halides were smoothly cyanated with good reaction yields by Pd NPs/CS/Co3O4 nanocatalyst by using K4[Fe(CN)6] as the cyanating agent. Moreover, it was found that Pd NPs/CS/Co3O4 nanocatalyst provided not only good reaction yields and but also good recovery/reusability for six times in the aryl halide cyanations. This paper displays that Pd NPs/CS/Co3O4 nanocatalyst has a great catalytic and recycling potential for aryl halide cyanations.

Synergistic influence of mesoporous spinel nickel ferrite on the electrocatalytic activity of nano-structured palladium.

Structure and surface area are critical factors for catalysts in fuel cells. Hence, a spinel nickel ferrite mesoporous (SNFM) is prepared via the solution combustion technique, an efficient and one-step synthesis. Dynamic X-ray analysis has clarified the structural properties of SNFM. The grain size of SNFM is determined to be ∼11.6 nm. The specific surface area (87.69 m2. g−1) of SNFM is obtained via the Brunauer–Emmett–Teller method. The Barrett–Joyner–Halenda pore size distributions revealed that the size of the mesopores in as-synthesized SNFM mainly falls in the size range of 2–16 nm. Scanning electron microscopy studies showed the regularities involved during porous-structure formation. SNFM is employed as the support for nano-structured palladium (PdNS). Field emission scanning electron microscope studies of PdNS-SNFM showed the deposition of PdNS in cavities and on/in the pores of SNFM. The electrochemical surface area obtained for PdNS-SNFM is about 27 times larger than that of PdNS via cyclic voltammetry. The electrochemical studies are utilized to study the features and catalytic performance of PdNS-SNFM in the electro-oxidation of diverse small organic fuels, whereas the electrooxidation of diethylene glycol is reported for first-time.

Acetol as a high-performance molecule for oxidation in alkaline direct liquid fuel cell

This work describes acetol as fuel for electrochemical oxidation in direct alkaline liquid fuel cells, in addition to electrochemical studies for acetol oxidation reactions (AOR) in alkaline medium, catalyzed by nanostructured palladium electrocatalysts supported on carbon (Pd/C). The AOR’s were evaluated by cyclic voltammetry and chronoamperometry and the results were similar those described in the literature for oxidation of small organic molecules, revealing evident oxidation peaks and chronoamperometric currents. Experiments were performed in an alkaline direct liquid fuel cell (ADLFC), using acetol as fuel and electrocatalysts of the Pd/C type as anode. The results in ADLFC showed high values of open circuit potential (OCP), obtaining 1341.3 mV, considerably higher than the results reported in the literature for ethanol oxidation, in addition to a promising power density, in the maximum result of 31.55 mW cm−2, presenting acetol as a high-performance molecule for oxidation in the ADLFC.

Development and evaluation of nanostructured palladium thin film prepared by dealloying using dilute citric acid for hydrogen gas sensing application

The safe application of H2 gas requires a high-performance H2 gas sensing system. An attractive H2 gas sensor for industrial application which has H2 gas selectivity, high sensitivity, high response, high durability, small size, and low cost has not been developed yet. Durability is one of the most important problems in H2 gas sensors using Pd. This study focused on electric resistivity changes in metallic Pd with hydrogen gas absorption. Nanostructured palladium (NSPd) films for a hydrogen gas sensing material were fabricated by a dealloying method using dilute citric acid. Fabricated NSPd films exhibited a nanoscaled network structure or aggregated particle structure, a linear electric resistance change with hydrogen gas concentration, and high sensitivity compared to flat pure Pd films. Therefore, NSPd film is useful for hydrogen gas sensing applications and has both high sensitivity and low usage of the noble metal. Furthermore, we also revealed a degradation mechanism of pure Pd film due to repeated H2 gas exposure, and this phenomenon did not appear in the NSPd film. NSPd also showed a higher durability with repeated H2 gas exposure compared to pure Pd film. We concluded that NSPd is suitable for use as a practical H2 gas sensor due to its cost effectiveness and high sensing ability.

Hydrogen permeability of surface-modified Pd-Ag membranes at low temperatures

Hydrogen-permeable membranes of the Pd77% Ag33% alloy were obtained. Membranes were modified with a catalytically active coating, which consist of a crystalline nanostructured palladium black. Membranes were obtained by magnetron sputtering using mosaic targets. The surface modification with a catalytically active coating was performed by electrochemical deposition from an aqueous solution of H2PdCl4. The low-temperature kinetic characteristics of the hydrogen permeability of metallic Pd77% Ag23% membranes with a modifying coating of crystallized palladium black were analysed. During the analysis of the obtained experimental data about the kinetic characteristics of the obtained membranes, it was revealed that the surface effects are the limiting stage of hydrogen transport through palladium membranes at low temperatures. It was experimentally confirmed that the high specific surface of the synthesized catalysts causes the acceleration of the kinetic characteristics of hydrogen transport. The possibility of intensifying the processes of hydrogen transport through metallic membranes by creating active centers of chemisorption and dissociation on their surface is shown.

Rational strain engineering in delafossite oxides for highly efficient hydrogen evolution catalysis in acidic media

The rational design of hydrogen evolution reaction (HER) electrocatalysts which are competitive with platinum is an outstanding challenge to make power-to-gas technologies economically viable. Here, we introduce the delafossites PdCrO$_2$, PdCoO$_2$ and PtCoO$_2$ as a new family of electrocatalysts for the HER in acidic media. We show that in PdCoO$_2$ the inherently strained Pd metal sublattice acts as a pseudomorphic template for the growth of a strained (by +2.3%) Pd rich capping layer under reductive conditions. The surface modification continuously improves the electrocatalytic activity by simultaneously increasing the exchange current density j$_0$ from 2 to 5 mA/cm$^2_{geo}$ and by reducing the Tafel slope down to 38 mV/decade, leading to overpotentials $\eta_{10}$ < 15 mV for 10 mA/cm$^2_{geo}$, superior to bulk platinum. The greatly improved activity is attributed to the in-situ stabilization of a $\beta$-palladium hydride phase with drastically enhanced surface catalytic properties with respect to pure or nanostructured palladium. These findings illustrate how operando induced electrodissolution can be used as a top-down design concept for rational surface and property engineering through the strain-stabilized formation of catalytically active phases.

Recent Advances in Palladium Nanoparticles-Based Hydrogen Sensors for Leak Detection.

Along with the development of hydrogen as a sustainable energy carrier, it is imperative to develop very rapid and sensitive hydrogen leaks sensors due to the highly explosive and flammable character of this gas. For this purpose, palladium-based materials are being widely investigated by research teams because of the high affinity between this metal and hydrogen. Furthermore, nanostructured palladium may provide improved sensing performances compared to the use of bulk palladium. This arises from a higher effective surface available for interaction of palladium with the hydrogen gas molecules. Several works taking advantage of palladium nanostructures properties for hydrogen sensing applications have been published. This paper reviews the recent advances reported in the literature in this scope. The electrical and optical detection techniques, most common ones, are investigated and less common techniques such as gasochromic and surface wave acoustic sensors are also addressed. Here, the sensor performances are mostly evaluated by considering their response time and limit of detection.

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.

Electrochemical Promotion of Nanostructured Palladium Catalyst for Complete Methane Oxidation

Electrochemical promotion of catalysis (EPOC) was investigated for methane complete oxidation over palladium nano-structured catalysts deposited on yttria-stabilized zirconia (YSZ) solid electrolyte. The catalytic rate was evaluated at different temperatures (400, 425 and 450 °C), reactant ratios and polarization values. The electrophobic behavior of the catalyst, i.e., reaction rate increase upon anodic polarization was observed for all temperatures and gas compositions with an apparent Faradaic efficiency as high as 3000 (a current application as low as 1 μA) and maximum rate enhancement ratio up to 2.7. Temperature increase resulted in higher enhancement ratios under closed-circuit conditions. Electrochemical promotion experiments showed persistent behavior, where the catalyst remained in the promoted state upon current or potential interruption for a long period of time. An increase in the polarization time resulted in a longer-lasting persistent promotion (p-EPOC) and required more time for the reaction rate to reach its initial open-circuit value. This was attributed to continuous promotion by the stored oxygen in palladium oxide, which was formed during the anodic polarization in agreement with p-EPOC mechanism reported earlier.

Deposition and morphological evolution of nanostructured palladium during potential cycling: a liquid-cell TEM study.

In order to gain better control over the functionality of Pd nanostructures used in several CO2-mitigating electrochemical energy conversion systems, it is imperative to underpin different nanoscale phenomena influencing their structural durability. Hitherto, such analyses have been carried out before/after an electrochemical treatment, but not during the entire process. Here, we demonstrate monitoring of morphological evolution in Pd nanostructures over the entire course of electrochemical treatment using a liquid-cell transmission electron microscope (TEM) set-up. Our findings reveal new insights into nanoparticle growth, dissolution, detachment, and aggregation that are relevant for the development of functional Pd nanomaterials.

Three-Dimensional Nanostructured Palladium with Single Diamond Architecture for Enhanced Catalytic Activity

Fuel cells are a key new green technology that have applications in both transport and portable power generation. Carbon-supported platinum (Pt) is used as an anode and cathode electrocatalyst in low-temperature fuel cells fueled with hydrogen or low-molecular-weight alcohols. The cost of Pt and the limited world supply are significant barriers to the widespread use of these types of fuel cells. Comparatively, palladium has a 3 times higher abundance in the Earth's crust. Here, a facile, low-temperature, and scalable synthetic route toward three-dimensional nanostructured palladium (Pd) employing electrochemical templating from inverse lyotropic lipid phases is presented. The obtained single diamond morphology Pd nanostructures exhibited excellent catalytic activity and stability toward methanol, ethanol, and glycerol oxidation compared to commercial Pd black, and the nanostructure was verified by small-angle X-ray scattering, scanning tunneling electron microscopy, and cyclic voltammetry.

Facile synthesis, characterization and antibacterial activity of nanostructured palladium loaded silicon carbide

In this work, noble metal (Palladium) loaded silicon carbide (SiC) nanoparticles have been successfully synthesized using a single step synthetic route and its antibacterial action against gram-negative (E. coli) and gram-positive (S. aureus) bacteria have been investigated. The structural and morphological characterizations of pure SiC and Palladium (Pd) loaded SiC nanoparticles were carried out by x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FE-SEM), Energy dispersive x-ray spectroscopy (EDX), Elemental mapping and Transmission electron microscopy (TEM). The characterizations results offer substantial proof that the SiC surface was successfully decorated by Pd. Furthermore the EDS analysis reveals that the product contained Pd as well as W and O, thus reaffirming the production of Pd loaded SiC nanoparticles. The MICs and MBCs values examined by standard agar dilution methods show that MICs and MBCs values of pure SiC were > 16 and > 32 mg/ml, respectively against E. coli and S. aureus, whereas Pd loaded SiC nanoparticles exhibited MIC and MBC value of 4 mg/ml and 8 mg/ml, respectively. The morphological and structural alterations caused by SiC and Pd loaded SiC nanoparticles on E. coli and S. aureus cells were further investigated by SEM analysis. A noteworthy improvement in antibacterial performance was observed, when E. coli and S. aureus cells were exposed to Palladium (Pd) nanoparticles (NPs) loaded silicon carbide (SiC). The results obtained show a significant impact by loading Pd on SiC in the deactivation of microorganisms in vitro.

Active sites contribution from nanostructured interface of palladium and cerium oxide with enhanced catalytic performance for alcohols oxidation in alkaline solution

Nanostructured interface is significant for the electrocatalysis process. Here we comparatively studied the electrooxidation of alcohols catalyzed by nanostructured palladium or palladium–cerium oxide. Two kinds of active sites were observed in palladium–cerium oxide system, attributing to the co-action of Pd–cerium oxide interface and Pd sites alone, by CO stripping technique, a structure-sensitive process generally employed to probe the active sites. Active sites resulting from the nanostructured interfacial contact of Pd and cerium oxide were confirmed by high resolution transmission electron microscopy and electrochemical CO stripping approaches. Electrochemical measurements of cyclic voltammetry and chronometry results demonstrated that Pd–cerium oxide catalysts exhibited much higher catalytic performances for alcohols oxidation than Pd alone in terms of activity, stability and anti-poisoning ability. The improved performance was probably attributed to the nanostructured active interface in which the catalytic ability from each component can be maximized through the synergistic action of bi-functional mechanism and electronic effect. The calculated catalytic efficiency of such active sites was many times higher than that of the Pd active sites alone. The present work showed the significance of valid nanostructured interface design and fabrication in the advanced catalysis system.

Functionality of Surface Acoustic Wave (SAW) transducer for palladium–platinum-based hydrogen sensor

The nanostructured palladium–platinum (PdPt) catalyst and the Surface Acoustic Wave device offers functional possibilities for developing an innovative hydrogen sensor. Since the catalysis between hydrogen and oxygen in ambient air releases heat, an electrical signal correlated with hydrogen concentration can be obtained by transferring PdPt heat over the SAW delay path. This scheme of detection has never been performed up to now and special attention is given in this article to prove its feasibility. In this purpose, we report an alternative SAW model that incorporates representations for interdigital transducers and delay path, and can reproduce changes in temperature. This model can be used to design an optimized temperature-sensitive SAW taking into account the effects of temperature over the delay path. We report as well the choice of the phase signal for temperature variation measurements (phase as a function of temperature) of a SAW made of LiNb03 128° YX (128°, rot Y cut, X prop.). We consider that an optimized SAW device can detect the slight PdPt temperature increase.

Influence of spontaneous decomposition on the electrochemical formic acid oxidation on a nanostructured palladium electrode

The formic acid electrooxidation reaction was studied in a flow cell in 1M HCOOH–0.5M H2SO4 solution on a palladium film electrode. The evaluation of the open circuit potential (OCP) decay demonstrated that the spontaneous dehydrogenation of formic acid is quickly verified, leading to hydrogen adsorption and absorption. Moreover, the absence of carbon containing adsorbed species was verified by the application of voltammetric stripping after OCP and chronoamperometry. The results obtained demonstrate that the electrocatalytic oxidation of formic acid on Pd takes place through the spontaneous HCOOH dissociative adsorption with CO2 evolution and the adsorbed hydrogen electrooxidation.

Magnetic Core–Shell Nanostructured Palladium Catalysts for Green Oxidation of Benzyl Alcohol

Multifunctional catalysts are highly attractive for green oxidation process integrating excellent conversion and selectivity with high separability and recyclability. In this regards, a facile method is developed to fabricate yolk–shell microspheres consisting of Fe3O4 cores, mesoporous CeO2 shells and loaded Pd nanoparticles. Microspheres with 2.6 % Pd loading exemplify excellent catalytic activity for solvent-free, selective oxidation of benzyl alcohol to benzaldehyde by molecular oxygen at 373 K and atmospheric pressure, resulting in 80.5 % conversion of benzyl alcohol with 94.8 % selectivity for benzaldehyde. The catalyst can be magnetically separated and recycled without significant loss of catalytic efficiency even after seven catalytic runs.