Pd Alloy Research Articles

Hydrogen generation of single alloy Pd/Pt quantum dots over Co3O4 nanoparticles via the hydrolysis of sodium borohydride at room temperature

To satisfy global energy demands and decrease the level of atmospheric greenhouse gases, alternative clean energy sources are required. Hydrogen is one of the most promising clean energy sources due to its high chemical energy density and near-zero greenhouse gas emissions. A single alloyed phase of Pd/Pt nanoclusters as quantum dots (QDs) was prepared and loaded over Co3O4 nanoparticles with a low loading percentage (1 wt.%) for hydrogen generation from the hydrolysis of NaBH4 at room temperature. L-glutathione (SG) was used as a capping ligand. It was found that the single alloy catalyst (Pd0.5–Pt0.5)n(SG)m/Co3O4 caused a significant enhancement in hydrogen generation in comparison to the monometallic clusters (Pdn(SG)m and Ptn(SG)m). Moreover, the Pd/Pt alloy showed a positive synergistic effect compared to the physical mixture of Pd and Pt clusters (1:1) over Co3O4. The QDs alloy and monometallic Pd and Pt clusters exhibited well-dispersed particle size in ~ 1 nm. The (Pd0.5–Pt0.5)n(SG)m)/Co3O4 catalyst offers a high hydrogen generation rate (HGR) of 8333 mL min− 1 g− 1 at room temperature. The synergistic effect of Pd and Pt atoms in the nanoclusters alloy is the key point beyond this high activity, plus the prepared clusters' unique atomic packing structure and electronic properties. The effect of the NaBH4 concentration, catalyst amount, and reaction temperature (25–60 °C) were investigated, where HGR reaches 50 L min− 1 g− 1 at 60 °C under the same reaction conditions. The prepared catalysts were analyzed by UV–Vis, TGA, HR-TEM, XRD, and N2 adsorption/desorption techniques. The charge state of the Pd and Pt in monometallic and alloy nanoclusters is zero, as confirmed by X-ray photoelectron spectroscopy analysis. The catalysts showed high recyclability efficiency for at least five cycles due to the high leaching resistance of the alloy nanoclusters within the Co3O4 host. The prepared catalysts are highly efficient for energy-based applications.

Design of a Metal/Oxide/Carbon Interface for Highly Active and Selective Electrocatalysis.

Sustainable energy-conversion and chemical-production require catalysts with high activity, durability, and product-selectivity. Metal/oxide hybrid structure has been intensively investigated to achieve promising catalytic performance, especially in neutral or alkaline electrocatalysis where water dissociation is promoted near the oxide surface for (de)protonation of intermediates. Although catalytic promise of the hybrid structure is demonstrated, it is still challenging to precisely modulate metal/oxide interfacial interactions on the nanoscale. Herein, we report an effective strategy to construct rich metal/oxide nano-interfaces on conductive carbon supports in a surfactant-free and self-terminated way. When compared to the physically mixed Pd/CeO2 system, a much higher degree of interface formation was identified with largely improved hydrogen oxidation reaction (HOR) kinetics. The benefits of the rich metal-CeO2 interface were further generalized to Pd alloys for optimized adsorption energy, where the Pd3Ni/CeO2/C catalyst shows superior performance with HOR selectivity against CO poisoning and shows long-term stability. We believe this work highlights the importance of controlling the interfacial junctions of the electrocatalyst in simultaneously achieving enhanced activity, selectivity, and stability.

Palladium nanosheets bunches for stable and high-concentration hydrogen sensing at room temperature

Pure palladium (Pd) and Pd alloy for hydrogen (H2) sensing is widely studied for detecting the high-concentration H2 leakage (e.g., 4–30 v/v%), such as in those applications of aerospace crafts and hydrogen-driven vehicles, which may suffer from the saturation of adsorbing H2, leading to instability at room temperature. To address the above issue, the ultrathin Pd nanosheets bunches (NSTs-BCHs) have been developed for the stable detection of high-concentration H2 at room temperature. With a wet-chemical synthesis, the CO released from the thermal decomposition of metal-carbonyl compounds assists in forming Pd-based NSTs-BCHs (2–5 nm thick). The Pd-based NSTs-BCHs without dopants show unstable and saturated response towards H2 with a concentration>3 v/v%. Comparatively, the ones with W dopants display excellent sensing stability towards a wide concentration range of 100 ppm − 30 v/v% H2. Theoretically, the large specific surface and the W dopants in Pd-based NSTs-BCHs are believed to contribute to stable detection of high-concentration H2, which may be applied to other sensing materials for high-concentration gas detection.

Enhancing the Chemo-Enzymatic One-Pot Oxidation of Cyclohexane via In Situ H2O2 Production over Supported Pd-Based Catalysts

The combination of an evolved unspecific peroxygenase (UPO), from Agrocybe aegerita (PaDa-I variant) and bimetallic Pd-based catalysts, is demonstrated to be highly effective for the one-pot oxidative valorization of cyclohexane to cyclohexanol and cyclohexanone (collectively KA oil), via the in situ formation of H2O2 from the elements. The alloying of Pd with Zn in particular is found to significantly enhance catalytic performance compared to bimetallic PdAu or monometallic Pd analogues. The improved activity of the PdZn/TiO2/PaDa-I system is attributed to the facile formation of PdZn alloys and the resulting electronic modification of Pd, which results in an inhibition of competitive chemo-catalyzed H2O2 degradation reactions and the total suppression of the overoxidation of cyclohexanol. By comparison, the large population of Pd-only clusters present in both the PdAu and monometallic Pd catalysts is considered to be responsible for the promotion of further oxidation products and the unselective conversion of H2O2 to H2O, which hampers overall process efficiency. Notably, given the susceptibility of the enzyme to deactivation at moderate H2O2 concentrations, the continual supply of low levels of the oxidant via in situ production represents a highly attractive alternative to the continuous addition of preformed H2O2 or co-enzyme-based systems.

Magnetism of Co-rich clusters embedded in nanoporous Pd prepared by electrochemical dealloying — Influence of thermal annealing

Nanoporous palladium samples containing superparamagnetic Co-rich clusters were prepared by electrochemical dealloying and the magnetic properties were subsequently varied by thermal annealing at different temperatures. It is shown that in this way porous magnetic nanomaterials exhibiting various magnetic characteristics can be obtained. The as-dealloyed, unannealed sample is ferromagnetic at 4.2 K and superparamagnetic at 300 K, with a blocking temperature TB of 100 K. The observed general decrease of the magnetization with increased annealing temperature is explained by the redistribution of Co from the Co-rich superparamagnetic clusters into the Pd matrix, leading to a shrinkage of the clusters and the formation of a diluted Co–Pd alloy phase. As a consequence of the smaller magnetic cluster size a down-shift of TB occurs for annealing temperatures of 373 K and 573 K. After annealing at 773 K the stronger dissolution of Co from the clusters into the Pd-matrix reduces TB further down to 35 K. Additionally, a second blocked magnetic phase with much higher TB emerges, which leads to ferromagnetic behavior at room temperature. The occurrence of this phase is attributed to the formation of larger magnetic entities consisting of Co-rich clusters lying close together and a Co–Pd alloy phase with relatively high Co concentration in between these clusters. After high temperature annealing at 973 K a weakly ferromagnetic phase is obtained at 4.2 K and at 300 K, which can be explained by the nearly completed dissolution of the Co in the Pd matrix.

Hydroxyapatite supported PdxIn100-x as a novel electrocatalyst for high-efficiency glucose electrooxidation

Fuel cells are a very good candidate to provide energy conversion with green technology. Glucose is used as a fuel in fuel cells since it is easily available and has a high energy density. Herein, hydroxyapatite (HAp) was synthesized by precipitation method, and the sodium borohydride (NaBH4) reduction method was used to fabricate HAp supported PdIn (PdIn/HAp) alloy anode catalysts at varying atomic molar ratios for glucose electrooxidation. Structural, crystallographic, and morphological properties of the PdIn/HAps were determined with X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET) analysis, transmission electron microscopy (TEM), and inductively coupled plasma mass spectrometry (ICP-MS). Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and chronoamperometry (CA) were employed for the electrocatalytic activity and stability of PdIn/Haps toward glucose electrooxidation. The results show that HAp has a boosting effect for PdIn alloy towards glucose electrooxidation. Pd80In20/HAp showed 2.6 times higher electrocatalytic activity than Pd/HAp, and it is the most active and stable catalyst in this study with a specific activity of 5.64 mA/cm2.

Investigation of perpendicular magnetic anisotropy in Pd/Co2FeSi/MgO structures with evaluations of magnetic property, crystal structure, and elemental mapping

The authors investigated origins of perpendicular magnetic anisotropy (PMA) in a multilayer of full-Heusler Co2FeSi (CFS) alloys, MgO, and Pd. The CFS thickness dependence of the magnetic properties indicated that the bulk magnetic anisotropy of the CFS layers also contributed to the PMA even in the samples where the CFS thickness tCFS was 10 nm. The anisotropy constant was drastically increased at tCFS = 1.8 nm, and 0.7 nm. The crystal structure analysis indicated that CFS layers had the tensile strain for out-of-plane when the thickness was thicker than 1.8 nm, which can induce the bulk magnetic anisotropy via the magnetostrictive effect. The elemental mapping by a scanning transmission electron microscope revealed that approximately 2 nm thick Pd existed at the CFS/MgO interface. The authors considered the whole CFS layers could contain Pd when the thickness of CFS was less than 2 nm. This Pd might cause the bulk anisotropy of the samples with the CFS thickness below 2 nm since some Pd alloys and Pd/Co and Pd/Fe multilayers have large bulk magnetic anisotropy.

Dilute Limit Alloy Pd–Cu Bimetallic Catalysts Prepared by Simultaneous Strong Electrostatic Adsorption: A Combined Infrared Spectroscopic and Density Functional Theory Investigation

Dilute Limit Alloy Pd–Cu Bimetallic Catalysts Prepared by Simultaneous Strong Electrostatic Adsorption: A Combined Infrared Spectroscopic and Density Functional Theory Investigation

Active site and adsorption behavior engineering of subsize PdNi nanoparticles for boosting electrocatalytic hydrodechlorination of 4-chlorophenol

Developing an efficient strategy to engineer the removal efficiency of catalysts for electrocatalytic hydrodechlorination (ECH) of acute toxic chlorophenols is of considerable importance but remains challenging. We report herein an efficient strategy to modulate the active site and adsorption behaviors of PdNi alloy nanoparticles (NPs) anchored on oxygen/nitrogen-doped porous carbon nanosheets (PdNi/NPCNs) through nanopore trapping. The competitive adsorption of PdCl42- and Ni2+ ions and subsequent reduction belowrmodynamic reduction temperature ensure the formation of highly dispersed subsize PdNi alloy NPs on the surface of NPCNs. More significantly, alloying of Pd with Ni not only provides abundant surface-active sites but also adjusts the adsorption behaviors of intermediates over PdNi/NPCNs because of the strong electronic interaction between the two metals, thereby considerably boosting the ECH performance for 4-chlorophenol (4-CP) removal. The complete removal of 4-CP (100 mg L−1) is achieved at 7.5 mA within 180 min, superior to that of monometallic Pd/NPCNs and many previous electrodes reported thus far. The catalyst also exhibits boosted stability toward the ECH of 4-CP with five successive recycling runs. This study provides an effective strategy to fabricate high-performance electrocatalysts for ECH reaction, which shows great promise in potential applications.

Optimizing Oxygen and Intermediate HOO* Adsorption of Cu–Pd Alloy Cocatalyst for Boosting Photocatalytic H2O2 Production of BiVO4

AbstractThe modification of Pd cocatalysts is considered to be an effective strategy to improve H2O2 production of photocatalysts because it can accelerate the reaction rate of O2 reduction. However, the strong adsorption between O2 molecules and Pd atoms is not conducive to the formation of intermediate HOO* and leads to the further reduction of H2O2 to H2O, thus limiting the improvement of H2O2 production. To solve the issue, in this work, Cu–Pd alloy cocatalysts are selectively modified on the electron‐rich facets of BiVO4 via facile photoinduced deposition and subsequent galvanic displacement. DFT calculations indicate that the incorporation of Cu atoms to Pd atoms weakens the oxygen adsorption energy and HOO* binding energy on Pd atom surfaces, thus increasing the activity and selectivity of O2 reduction to H2O2. Further experimental results show that the optimized Cu‐Pd/BiVO4(5:1) photocatalyst exhibits markedly boosted activity for H2O2 production (2189 µmol L‐1), which is 3.2‐fold higher than that of BiVO4 with modification of 0.3 wt% Pd cocatalyst (675 µmol L‐1). Additionally, the incorporation of metal Cu enables the economic utilization of Pd atoms and reduces the expense of the Pd cocatalyst.

Porous Pd-Sn Alloy Nanotube-Based Chemiresistor for Highly Stable and Sensitive H2 Detection.

While H2 is indispensable as a green fuel source, it is highly flammable and explosive. Because it is difficult to detect due to its lack of odor and color, a solution for proper monitoring of H2 leakage is essential to ensure safe handling. To this end, we have successfully fabricated hollow Pd-Sn alloy nanotubes (NTs) with a Brunauer-Emmett-Teller surface area of 223.0 m2/g through electrospinning and a subsequent etching method, which is the first demonstration of synthesizing Pd-based hollow alloy nanofibers with ultrafine grain sizes. We found that the alloying of Pd with Sn could effectively prevent degradation of the sensing performance upon the α-β phase transition during hydrogen detection. Besides, the highly porous structure with smaller nanograins offered more exposed active sites and higher gas accessibility to bulk materials. The resultant Pd-Sn NTs exhibited excellent sensitivity toward H2 (0.00005-3%). Notably, the limit of detection of 0.0001% is an outstanding achievement on H2 sensing among state-of-the-art H2 sensors. Moreover, when exposed to a high concentration of H2 (3%), Pd-Sn NTs showed excellent cycling stability with a standard deviation of 0.07% and a sensitivity of 9.27%. These obtained sensing results indicate that Pd-Sn NTs can be used as a highly sensitive and stable H2 gas sensor at room temperature (25 °C).

Influence of the composition and morphology of PdNiFe/C nanocatalysts toward ethanol oxidation

We investigate the electrocatalytic activity of Pd, NiFe@Pd, and PdxNiyFez catalysts toward ethanol oxidation in alkaline media using electrochemical and spectroelectrochemical measurements. The addition of Ni-Fe to Pd (both alloy and core–shell) enhances their activity and stability toward ethanol oxidation, mainly for those with 30at.% of Ni + Fe. In situ FTIR data reveals that Ni and Fe favor the formation of acetate and acetic acid at lower potentials due to their oxophilic character, while the core–shell catalyst produces these intermediates at the lowest potentials. Our study highlights the synergetic role of composition and core–shell morphology in their catalytic activity.

Pd Alloy Nanosheet Inks for Inkjet‐Printable H2 Sensors on Paper

Abstract2D palladium nanostructures enable sensitive room‐temperature detection of H2. However, they can be limited by stability and fabrication costs. Stability may be improved by alloying Pd with other metals, while cost could be reduced by using paper as a substrate. An ultra‐low‐cost sensor using Pd alloy (PdMoY) nanosheets (NS) on paper is reported. The 2D Pd alloy nanosheets are prepared by a solution‐phase route, drop cast onto paper (≈1 × 1 cm) with silver contacts drawn on it, and dried. The same material is deposited on an interdigitated electrode (IDE). Both sensors are tested for response to hydrogen in air. The resistance of the paper‐based sensor decreased by ≈18.7% in 1% H2, which is about 40 times the response of the IDE‐based sensor. Its H2 limit of detection (1 ppm) is also lower than that of the IDE‐based sensor (5 ppm). Compared to pristine Pd NS, PdMoY NS are more stable to repeated H2 pulses without any signs of buckling or cracks. The nanosheets are also deposited by inkjet printing to produce functional sensors, providing a simple route to manufacturing of ultra‐low‐cost gas sensors for use in fuel‐cell vehicles and related infrastructure.

A modified elastic constant calculation method for triclinic-like special quasi-random structures: Application to Pd-M (M = Cu, Ag) solid solutions

The mechanical properties of Palladium alloys need to be calculated using first principles due to high experiment cost. For FCC disordered Pd alloys, special quasi-random structure (SQS) is usually used for modeling at first and the calculation of mechanical properties usually begins with elastic constants. However, SQS supercells are often triclinic-like and show lower symmetry than origin FCC structure, which would lead to the elements of elastic matrix calculated by DFT aren’t equal to elastic constants. To solve this problem, a strain operation method is put forward by linear transformation, LSQS′=SDL, to modify energy-strain method. Taking Pd-M (M = Cu, Ag) random alloys as an application case, the elastic properties of Pd-Cu and Pd-Ag alloys with 5 at% concentration gradient are calculated. The calculation results are similar to experiment data and other DFT works, which indicate that the preceding formula is valid. Electron structure analysis shows that Pd valence electrons are the main contributors to metallic bonds.

In-situ synthesis of nickel/palladium bimetal/ZnIn2S4 Schottky heterojunction for efficient photocatalytic hydrogen evolution

Coupling with bimetallic nanoparticles (NPs) has been considered as a promising strategy to enhance photocatalytic hydrogen evolution (PHE) efficiency of semiconductor photocatalysts and simultaneously minimize the use of expensive noble metals. Herein, we firstly synthesized spherical-like ZnIn2S4 (ZIS) by a solvothermal method, and then combined with nickel/palladium (denoted as NiPd) bimetallic NPs to form NiPd bimetal/ZIS Schottky heterojunction. The chemical states of NiPd NPs were confirmed in the form of NiPd bimetal rather than Ni–Pd alloy. The detailed characterization results demonstrated that the deposition of NiPd bimetal played a major role in increasing light harvesting capacity, accelerating charge carrier (electrons and holes) separation and facilitating photogenerated electrons transfer, leading to the boosted PHE performance in NiPd-ZIS photocatalysts. By adjusting Ni:Pd molar ratio in NixPdy-ZIS photocatalysts, the desired sample of Ni3Pd7-ZIS exhibited the highest PHE efficiency (106.6 µmol/h) and apparent quantum yield (AQY) value of 40.22% at 400 nm under visible light as compared to ZIS, Ni-ZIS and Pd-ZIS. The multiple techniques were performed to deeply investigate the photogenerated charge carrier separation, transfer and recombination. The possible mechanism over Ni3Pd7-ZIS sample for boosting PHE performance was presented based on characterization results. On the whole, this work would provide some insights into the development of cost-effective and high-efficiency bimetallic cocatalyst-based photocatalysts.

Potential- and Time-Dependent Dynamic Nature of an Oxide-Derived PdIn Nanocatalyst during Electrochemical CO2 Reduction.

Electrochemical reduction of CO2 into valuable fuels and chemicals is a promising route of replacing fossil fuels by reducing CO2 emissions and minimizing its adverse effects on the climate. Tremendous efforts have been carried out for designing efficient catalyst materials to selectively produce the desired product in high yield from CO2 by the electrochemical process. In this work, a strategy is reported to enhance the electrochemical CO2 reduction reaction (ECO2RR) by constructing an interface between a metal-based alloy (PdIn) nanoparticle and an oxide (In2O3), which was synthesized by a facile solution method. The oxide-derived PdIn surface has shown excellent eCO2RR activity and enhanced CO selectivity with a Faradaic efficiency (FE) of 92.13% at -0.9 V (vs RHE). On the other hand, surface PdO formation due to charge transfer on the bare PdIn alloy reduces the CO2RR activity. With the support of in situ (EXAFS and IR) and ex situ (XPS, Raman) spectroscopic techniques, the optimum presence of the Pd-In-O interface has been identified as a crucial parameter for enhancing eCO2RR toward CO in a reducing atmosphere. The influence of eCO2RR duration is reported to affect the overall performance by switching the product selectivity from H2 (from water reduction) to CO (from eCO2RR) on the oxide-derived alloy surface. This work also succeeded in the multifold enhancement of the current density by employing the gas diffusion electrode (GDE) and optimizing its process parameters in a flow cell configuration.

Cooperative electrocatalytic effect of Pd and Ce alloys nanoparticles in PdCe@CNWs electrode for oxygen evolution reaction (OER)

Electrocatalytic water oxidation is an ecofriendly and intelligent approach for oxygen evolution from water because it requires only water and electrical potential/energy as inputs. However, the oxygen evolution reaction (OER) is the most challenging multi-electron and proton transfer reaction during water electrolysis for hydrogen production. The electrocatalyst is the critical component that controls the efficiency of oxygen evolution. Therefore, it is essential to explore efficient and durable electrocatalysts that must have significant efficiency compared to the benchmark catalyst (i.e., RuO2) for OER. Herein, self-supported carbon nanowires (CNWs) decorated with bimetallic palladium-cerium PdCe alloys nanoparticles (NPs) were synthesized through an electrospinning-thermal carbonation approach to overcome the kinetic barriers and deliver decent alkaline OER activity. As a result, the PdCe/CNWs requires a low overpotential of ∼360 and ∼450 mV vs. RHE to deliver the current density of 10 and 50 mA/cm2 with low Tafel slope (62 mV/dec) for OER, which is even comparable to the benchmark, RuO2 (360 mV and 73 mV/ dec). Notably, only a slight increase (∼ 10 %) in overpotential was observed after 10,000 cycles indicating high electrocatalyst stability. The high stability and improved OER performance of the PdCe/CNWs electrode can be explained by the cooperative catalytic influence between Pd, Ce, and C species.

The Direct Synthesis of Hydrogen Peroxide Over Supported Pd-Based Catalysts: An Investigation into the Role of the Support and Secondary Metal Modifiers

AbstractThe direct synthesis of H2O2 from molecular H2 and O2 over Pd-based catalysts, prepared via an industrially relevant, excess chloride co-impregnation procedure is investigated. Initial studies into the well-established PdAu system demonstrated the key role of Pd: Au ratio on catalytic activity, under conditions that have previously been found to be optimal for H2O2 formation. Further investigations using the optimal Pd: Au ratio identified the role of the catalyst support in controlling particle size and Pd oxidation state and thus catalytic performance. Subsequently, with an aim to replace Au with cheaper alternatives, the alloying of Pd with more abundant secondary metals is explored. Graphical Abstract

Achieving excellent cycle stability in Zr–Nb–Co–Ni based hydrogen isotope storage alloys by controllable phase transformation reaction

Hydrogen isotope (deuterium and tritium) as a special form of hydrogen energy, its storage in an efficient and safe way has been paid more and more attention by researchers in recent years. ZrCo alloy is regarding as the one and only promising material for large-scale storage of hydrogen isotope. However, poor cycle life and inferior capacity retention restrict its engineering application. Herein, we propose a co-substitution strategy of Nb (for Zr) and Ni (for Co) in ZrCo alloy to overcome the defects. Significantly, Zr0.8Nb0.2Co0.8Ni0.2 alloy exhibits ultralong cycle life (97.6% retention) and remarkable capacity (2.42 H (f. u.)) in 100 cycles, which far exceeds all existing hydrogen isotope storage alloys (Pd, U and other ZrCo-based alloys). These outstanding performances are entirely revealed from two aspects: stable homogeneous structural phase transformation process of parent structure (Zr0.8Nb0.2Co0.8Ni0.2H0.3-B33 ↔ Zr0.8Nb0.2Co0.8Ni0.2H2.8-B33″) and ordered migration mechanism of H atom (layered and linear de-/intercalation). Our attractive insights into the ultralong cycle life of ZrCo-based alloys through homogeneous structural phase transformation will serve as a pioneer on cycle optimization in the field of hydrogen storage materials.

Formation of Short-Range Atomic Order in Cu–Pd Alloys with a Low Palladium Content: Resistometric Study

Formation of Short-Range Atomic Order in Cu–Pd Alloys with a Low Palladium Content: Resistometric Study