Pd-Ni Alloys Research Articles

Dilute Pd-Ni Alloy through Low-temperature Pyrolysis for Enhanced Electrocatalytic Hydrogen Oxidation.

Designing highly active and cost-effective electrocatalysts for the alkaline hydrogen oxidation reaction (HOR) is critical for advancing anion-exchange membrane fuel cells (AEMFCs). While dilute metal alloys have demonstrated substantial potential in enhancing alkaline HOR performance, there has been limited exploration in terms of rational design, controllable synthesis, and mechanism study. Herein, we developed a series of dilute Pd-Ni alloys, denoted as x% Pd-Ni, based on a trace-Pd decorated Ni-based coordination polymer through a facile low-temperature pyrolysis approach. The x% Pd-Ni alloys exhibit efficient electrocatalytic activity for HOR in alkaline media. Notably, the optimal 0.5 % Pd-Ni catalyst demonstrates high intrinsic activity with an exchange current density of 0.055 mA cm-2, surpassing that of many other alkaline HOR catalysts. The mechanism study reveals that the strong synergy between Pd single atoms (SAs)/Pd dimer and Ni substrate can modulate the binding strength of proton (H)/hydroxyl (OH), thereby significantly reducing the activation energy barrier of a decisive reaction step. This work offers new insights into designing advanced dilute metal or single-atom-alloys (SAAs) for alkaline HOR and potentially other energy conversion processes.

Surface segregation on Ag@MNi (M = Pd, Pt, Rh, and Ru) core–shell nanocrystals for enhancing the oxygen reduction performance

Synthesis of cost-effective electrocatalysts for oxygen reduction reaction (ORR) has received wide attention due to their sluggish kinetics, which limits the development and application of fuel cell technique. In this work, we report a versatile synthetic approach to prepare a series of small-sized Ag@MNi (M = Pd, Pt, Rh, Ru) nanocrystals with core–shell structures by a simple solvothermal method. According to characterization analysis, surface segregation of Pd was proved in the outermost layer with the Pd-rich shell layer, which can regulate the adsorption energy of *OH. Electrochemical results show that the onset potential and half-wave potential of Ag@PdNi nanocrystals (Ag@PdNi NCs) are 1.005 and 0.913 V vs. RHE (reversible hydrogen electrode), respectively, with a Tafel slope of 55.31 mV dec-1 and strong ORR catalytic durability, which is similar to Ag@MNi (M = Pt, Rh, Ru) NCs and slightly higher than that of PdAg alloy nanoparticles (PdAg alloy NPs), PdNi alloy nanoparticles (PdNi alloy NPs), commercial Pd black and even commercial Pt/C, in alkaline medium. Density Functional (DFT) calculations show that the presence of Agcore effectively promotes the segregation of Pd atoms to the outer shell surface, where Ni provides better segregated substitution sites for Pd, which significantly improves the ORR activity and durability due to the electronic synergistic effect between Agcore nuclei and Pdshell can reduce the adsorption strength of OHads.

INFLUENCE OF Ni CONTENT OF ELECTRODEPOSITED Pd-Ni ALLOY COATINGS ON THEIR ELECTROCATALYTIC ACTIVITY IN ALKALINE MEDIUM

The influence of the Ni content (1.4 - 9.0 wt. %) in electrodeposited Pd-Ni alloy coatings on the rate of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in an alkaline media was investigated. Electrocatalytic activity of the electrodeposited layers towards methanol oxidation reaction (MOR) was also studied. The composition and surface morphology of the samples were characterized by energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). The crystal structure of the Pd-Ni alloys was examined by X-ray diffraction (XRD). Electrochemical experiments were performed by cyclic voltammetry (CV). The presence of concentration ranges with respect to the Ni content is shown, wherein the electrocatalytic activity of the Pd-Ni alloy towards HER, OER and MOR is higher than that of pure Pd.

MgAl hydrotalcite supported ultrafine PdNi bimetallic catalyst for the dehydrogenation of dodecahydro-N-ethylcarbazole

Liquid organic hydrogen storage is a promising way of storing hydrogen. The development of efficient and low-cost dehydrogenation catalysts is still required to advance the commercialization of N-ethylcarbazole/dodecahydro-N-ethylcarbazole (NEC/H12-NEC) hydrogen storage and transport system.In this paper, PdNi bimetallic catalyst (Pd3Ni1/LDHs) supported on MgAl hydrotalcite was prepared by NaBH4 and ultrasound-assisted stepwise reduction. Ultrasonic cavitation could excite the hydroxyl hydrogen of hydrotalcite in the form of hydrogen radicals to reduce PdCl42− to Pd nanoparticles (NPs), and also promoted the formation of PdNi alloys as well as the dispersion of NPs. In the Pd3Ni1/LDHs catalyst, the average particle size of NPs was 1.98 nm, suggesting an excellent dispersion of Pd, Ni, and PdNi NPs. The electronic effects of Ni and Pd significantly improved the catalytic efficiency of Pd3Ni1/LDHs in H12-NEC dehydrogenation, resulting in a hydrogen release rate of 98.4 % after 6 h at 180 °C, surpassing that of Pd/LDHs. It can be considered that the dehydrogenation performance of Pd3Ni1/LDHs for H12-NEC is related to the alloy phase, electronic structure and NPs size.

Calculation of Surface Binding Energy in NixPdy Alloys Using Density Functional Theory

In the study, surface binding energies for pure Ni and Pd metals were calculated using density functional theory. The values obtained were 5.32 eV and 4.65 eV, respectively, which represents good accuracy for ab initio calculations. The work also included calculations of surface binding energy for different configurations of NiPd alloys with nickel and palladium concentrations of 66%, 50%, and 33%. Calculations were performed for each type of lattice for both Ni and Pd surface binding energies. Several types of lattices were simulated, and it was found that the average surface binding energies for Ni and Pd are: 5.02 eV and 4.36 eV respectively in the alloy with a Ni concentration of 50%; 4.89 eV and 4.22 eV respectively in the alloy with a Ni concentration of 66%; 5.12 eV and 4.40 eV respectively in the alloy with a Ni concentration of 33%.

Charge-controlled compositional/microstructural regulations and electrochemical actuation performance of bulk nanoporous Ni-Pd alloys

Charge-controlled compositional/microstructural regulations and electrochemical actuation performance of bulk nanoporous Ni-Pd alloys

Influence of the Pd Oxidation State in PdNi Thin Films on Surface Acoustic Wave Hydrogen Sensing Performance.

PdNi alloy thin films demonstrate exceptional hydrogen sensing performance and exhibit significant potential for application in surface acoustic wave (SAW) hydrogen sensors. However, the long-term stability of SAW H2 sensors utilizing PdNi films as catalysts experiences a substantial decrease during operation. In this paper, X-ray photoelectron spectroscopy (XPS) is employed to investigate the failure mechanisms of PdNi thin films under operational conditions. The XPS analysis reveals that the formation of PdO species on PdNi thin films plays a crucial role in the failure of hydrogen sensing. Additionally, density functional theory (DFT) calculations indicate that hydrogen atoms encounter a diffusion energy barrier during the penetration process from the PdNiOx surface to the subsurface region. The identification of PdNi film failure mechanisms through XPS and DFT offers valuable insights into the development of gas sensors with enhanced long-term stability. Guided by these mechanisms, we propose a method to restore the hydrogen sensing response time and magnitude to a certain extent by reducing the partially oxidized surface of the PdNi alloy under a hydrogen atmosphere at 70 °C, thereby restoring Pd to its metallic state with zero valence.

New Design PdNi Heterogeneous Nanocatalysts for the Direct Synthesis of Hydrogen Peroxide

Hydrogen peroxide (H2O2) is a widely used chemical as an eco-friendly oxidizing agent, with water being the only byproduct of oxidation in applications like bleaching pulp and paper, making electronic semiconductors, chemical and detergent synthesis, and wastewater treatment. The direct synthesis approach is preferred to provide the environmentally friendly production of H2O2 for market requirements. Bimetallic PdNi nanocatalysts were chosen for this study because of their catalytic activity and the structural characteristics of the material system. First, for the development of order-structured bimetallic PdNi nanocatalysts based on mesoporous carbon template after hydrogen-assisted heat treatment at 750∘C. The transformation of the disordered structure into ordered intermetallically structured PdNi alloys with higher alloying extents was confirmed by X-ray absorption spectroscopy (XAS) and high-resolution transition electron microscopy (HR-TEM). Then, to improve the oxygen oxidation reaction, two-electron pathway selectivity was used by TiO2-C as a support-ordered structure material to facilitate strong metal-support interactions. XAS and X-ray photoelectron spectra (XPS) techniques show more clear evidence of metal-support interactions with electron transfer from defects in the TiO2-C support to the ordered alloyed PdNi nanocatalysts, resulting in record productivity and selectivity of H2O2 production at ambient conditions. The results demonstrated in this study will enlighten a reliable design of new heterogeneous nanocatalysts with ordered structure. Electron transfer between hybrid support and active sites can clarify the catalytic behavior and prompt further research during the direct synthesis of hydrogen peroxide.
 Keywords: hydrogen peroxide, direct synthesis, heterogeneous nanocatalysts PdNi, TiO2-C

In Situ Creation of Surface Defects on Pd@NiPd with Core-shell Hierarchical Structure Toward Boosting Electrocatalytic Activity.

A deep insight into surface structural evolution of the catalyst is a challenging issue to reveal the structure-activity relationship. In this contribution, based on a surface alloying strategy, the dual-functional Pd@NiPd catalyst with a unique core-shell hierarchical structure is developed through selective crystal growth, surface cocrystallization, directional self-assembly, and reduction process. The surface defects are created in situ on the outer NiPd alloy layer in the electrochemical redox processes, which endow the Pd@NiPd catalyst with excellent electrocatalytic activity of hydrogen generation reaction (HER) and oxygen generation reaction (OER) in alkaline media. The optimal Pd@NiPd-2 catalyst requires an overpotential of only 18 mV that is far lower than Pt/C benchmark (43 mV) at the current density of 10 mA cm-2 for the HER, and 210 mV that is far lower than RuO2 benchmark (430 mV) at 50 mA cm-2 for the OER. Density functional theory (DFT) calculations reveal that the outstanding electrocatalytic activity is originated from the creation of surface defect structure that induces a significant reduction in the adsorption and dissociation energy barriers of H2O molecules in the HER and a decrease in the conversion energy from O* to OOH* that resulted from the synergy of two adjacent Pd sites by forming O-bridge. This work affords a typical paradigm for exploiting efficient catalysts and investigating the dependence of electrocatalytic activity on the surface structural evolution.

Fabrication of thin(∼2 μm) pure Ni and Pd–Ni alloy composite membranes by the organic-inorganic activation method for hydrogen separation

In this study, we have reported a new strategy to prepare metal/ceramic membranes that can be used as an alternative to conventional high-cost palladium membranes. For the first time, a uniform Ni layer was deposited using the organic-inorganic activation method via the ELP technique. Although, alloying Pd–Ni resulted in a defect-free thin membrane layer (2 μm). The H2 permeation flux of the composite membrane was 1.43 × 10−2 mol m−2 s−1 at 450 °C and TMP of 100 kPa with infinite H2/N2 selectivity. Stage cut effect as a function of transmembrane pressure (TMP) was assessed in binary mixtures at 450 °C. The prepared composite membrane indicated perfect long-time permeance stability for 145 h at 450 °C and TMP of 100–300 kPa. The results showed that solution-diffusion is the dominant mechanism in the hydrogen transport through the composite membranes.

Crowding-Out Effect in Synergistic C–C Coupling on PdNi Alloy Nanoparticles Studied by Surface-Enhanced Raman Spectroscopy

Crowding-Out Effect in Synergistic C–C Coupling on PdNi Alloy Nanoparticles Studied by Surface-Enhanced Raman Spectroscopy

PdNi alloys with surface segregation of Pd@hydrophilic N, O doped carbons toward hydrogen production with high current densities

A series of catalysts, which consist of PdNi alloy cores and N, O co-doped carbon (NOC) shells, are developed by pyrolysis of metal–organic framework (PdNi) for hydrogen production with high current densities. The bulk or surface Pd compositions (Pd/(Pd + Ni) molar ratios) of PdNi alloys can be well controlled by the fed ones. Meanwhile, some structural features that are favorable to HER activity, especially to achieving high HER current densities under low overpotentials, are further adjusted by the Pd compositions, including d-band center (εd) of PdNi alloy affected by surface segregation of Pd, hydrophilicity of NOC shell, and charge transfer and mass diffusion efficiency of an entire catalyst. When the bulk Pd/(Pd + Ni) molar ratio is ∼ 0.21, Pd0.21Ni0.79@NOC has a moderate εd, the highest hydrophilicity, the highest charge transfer and mass diffusion efficiency, and finally the highest electric double-layer capacitance (or electrochemical active surface area). Accordingly, it affords the optimal apparent or specific activity for hydrogen production with high current densities under low overpotentials in 0.5 M H2SO4, including a low apparent η1000 of ∼ 240 mV or specific η2500(BET) of ∼ 240.9 mV, and a high current density of ∼ 1590 mA cm−2 at only ∼ 242 mV.

Oxidation of Formaldehyde on PdNi Nanowires Synthesized in Superfluid Helium

The possibility of using a boron-doped diamond electrode with a net structure of PdNi alloy nanowires deposited on its surface by laser ablation in superfluid helium as a formaldehyde sensor is considered. High sensitivity of such an electrode to trace amounts of formaldehyde was shown.

PdNi biatomic clusters from metallene unlock record-low onset dehydrogenation temperature for bulk-MgH2.

Hydrogen storage has long been a priority on the renewable energy research agenda. Due to its high volumetric and gravimetric hydrogen density, MgH2 is a desirable candidate for solid-state hydrogen storage. However, its practical use is constrained by high thermal stability and sluggish kinetics. Here, we report PdNi bilayer metallenes as catalysts for hydrogen storage of bulk-MgH2 near ambient temperature. Unprecedented 422 K beginning dehydrogenation temperature and up to 6.36wt.% reliable hydrogen storage capacity were achieved. Fast hydrogen desorption was also provided by the system (5.49wt.% in 1h, 523 K). The in-situ generated PdNi alloy clusters with suitable d-band centers were identified as the main active sites during the de/re-hydrogenation process by AC-TEM and theoretical simulations, while other active species including Pd/Ni pure phase clusters and Pd/Ni single atoms obtained via metallene ball milling, also enhance reaction. These findings present fundamental insights into active species identification and rational design of highly efficient hydrogen storage materials. This article is protected by copyright. All rights reserved.

N-doped carbon-stabilized PdNiCu nanoparticles derived from PdNi@Cu-ZIF-8 as highly active and durable electrocatalyst for boosting ethanol oxidation

Controlling the component, tailoring the size and designing the carbon supporting materials are three promising strategies to improve electrocatalytic activity. Herein, a monatomic Cu carrier (CuCN) with larger specific surface area was used to anchor PdNi alloy nanoparticles by a facile one-step reduction method. Physical characterization revealed that the PdNi nanoparticles in the synthesized material possess good dispersion, which is mainly attributed to the high specific surface area of CuCN-900.Electrochemicalresults revealed that CuCN supported PdNi nanoparticles (Pd1Ni1/CuCN-900) nanohybrids had superior durability and catalytic activity for ethanoloxidation (EOR) compared with that of other PdxNiy/CuCN and commercial Pd/C. Rotating disk electrode (RDE) results further demonstrated that Pd1Ni1/CuCN-900 has a faster kinetic process of EOR than commercial Pd/C. DFT calculation implies that OH adsorption is preferentially near the Ni atom, the OH species on Ni1Pd1 surface play an important role in the process of EOR. This is of great research implications for finding new carbon carriers and regulating catalyst components to improve the catalytic efficiency of PdNi catalysts.

PANI-SnO2 nanorods decorated with Pdx-Niy nanoparticles for improved electrooxidation of methanol with extended durability

This work shows that PANI-SnO2 nanorods with unique morphology and fine distribution of Pd-Ni alloy nanoparticles exhibit superior electrocatalytic performance toward methanol oxidation reaction (MOR). The amount of Ni content in Pdx-Niy/PANI-SnO2 nanorods plays a key role in Pd utilization. Ni in Pdx-Niy/PANI-SnO2 catalyst significantly reduces the CO adsorption on the active catalyst surface and enhances the electrode kinetics. The Pd3Ni1/PANI-SnO2 composite exhibits high mass activity (1861.9 mA mg−1) with extended stability even after 10000 cycles (∼90% retention) compared to other PdxNiy counterparts, Pd/PANI-SnO2, and commercial Pd/C catalysts. Interestingly, adding Ni along with SnO2 improves the electronic effect of Pd metal, significantly enhancing its catalyst activity and stability. Based on the results, we hope the present work brings an innovative approach to constructing efficient and cost-effective electrocatalysts for electrooxidation methanol in an alkaline medium.

Potential reversible reactions over PdNix alloy catalysts: Hydrogen evolution from formic acid and formic acid formation by CO2 reduction reaction

A novel approach is required to achieve effective CO2 utilization. This study demonstrates a new approach for the reversible reaction in the CO2-HCOOH cycle, that is, FA decomposition and CO2 reduction, under ambient pressure using Pd-based alloy catalysts. First, Pd-based alloys (Pd-M; M = Co, Ni, and Zn) were screened for FA decomposition; the PdNi alloy showed superior catalytic activity compared to Pd and the other alloys. Second, Pd3Ni, PdNi, and PdNi3 were prepared to understand the composition-dependent activity of the PdNix series. DFT calculations provided insight into why the PdNix alloys show higher catalytic activities for FA decomposition than Pd. Finally, the electrochemical CO2 reduction reaction was investigated, and the PdNix alloy catalysts showed superior selectivity for FA formation compared to Pd catalysts. Thus, this study provides a novel strategy for CO2 utilization using bimetallic Pd-Ni heterogeneous catalysts.

Improved hydrogen gas sensing performance of Pd–Ni alloy thin films

Improved hydrogen gas sensing performance of Pd–Ni alloy thin films

Sphere-like PdNi Alloy: Unveiling the Twin Functional Properties toward Oxygen Reduction and Temperature-Dependent Methanol Oxidation for Alkaline Direct Methanol Fuel Cells

The development of high-performance bifunctional palladium-based (Pd) alloys for the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) is a great challenge in direct methanol fuel cells. The incorporation of an oxophilic atom into the Pd atom is an effective strategy to enhance the electrocatalytic activity of the catalysts. Herein a sphere-like PdNi alloy (sPdNiA) was developed via a simple hydrazine-assisted reduction method to overcome the kinetic drawbacks of palladium and delivers superior ORR/MOR performance. The successful alloy formation, the induced strain effect in the electronic structure, and structural characteristics of the sPdNiA were confirmed through XRD, XPS, and HR-TEM studies. As a result, for ORR, the sPdNiA exhibits a positive halfwave potential (E1/2) of ∼0.854 V (vs RHE) compared to the pure Pd (0.833 V vs RHE) nanoparticles. For MOR, the sPdNiA presents the low onset potential and high mass activity of 518 mA mgPd–1 in 1.0 M KOH electrolyte. Furthermore, the temperature-dependent MOR and 3D Bode plot investigations reveal a five-fold higher mass activity at elevated temperature (60 °C) with a lower activation energy (Ea). For the first time, the direct methanol fuel cell is fabricated utilizing sPdNiA as a bifunctional electrode, exhibited a higher peak power density (Pmax) of 34 mW cm–2, whereas 22 mW cm–2 was obtained for Pd Np-based fuel cells. Incorporating oxophilic atom (Ni) not only improves the performance of Pd but significantly reduces the cost of the catalyst material by lowering the Pd content.

Selective catalytic hydrodeoxygenation of vanillin to 2-Methoxy-4-methyl phenol and 4-Methyl cyclohexanol over Pd/CuFe2O4 and PdNi/CuFe2O4 catalysts

The development of a sustainable catalytic process for the hydrodeoxygenation of lignin model compounds to renewable fuels and chemicals is essential to meet the requirement of a fossil-fuel-free modern society. Herein a Pd/CuFe2O4 and bimetallic PdNi/CuFe2O4 catalysts were developed for the hydrodeoxygenation of vanillin to 2-methoxy-4-methylphenol (MMP) and 4-methyl cyclohexanol (4-MC), respectively. The Pd/CuFe2O4 provided selective catalytic transfer hydrodeoxygenation of vanillin to MMP with isopropanol (IPA). The synergistic participation of Pd NPs and CuFe2O4 (1Pd/CuFe2O4) afforded 99.4% vanillin conversion and 99.2% MMP selectivity at 150 °C. The acidity of the catalyst facilitated the efficient adsorption of vanillin and IPA, and the high dispersion of Pd NPs lowered the hydrogen abstraction barrier of IPA to facilitate the transformation. Then Ni was incorporated into Pd/CuFe2O4 to produce 4-methyl cyclohexanol from vanillin. The interfacial interaction between Pd and Ni over CuFe2O4 (1Pd7Ni/CuFe2O4) provided 95.8% 4-methyl cyclohexanol (4-MC) in H2 (20 bar) at 180 °C. The acidity of the catalyst, formation of Pd-Ni alloys, and efficient adsorption of vanillin and MMP were responsible for the high activity of the catalyst towards 4-methyl cyclohexanol (4-MC) production. Density functional theory (DFT) calculations were also performed to elucidate the reaction mechanism for vanillin transformation to MMP and 4-MC on the Pd/CuFe2O4 and bimetallic PdNi/CuFe2O4 catalysts.