Nanoscale Pd Research Articles

An exceptional amorphous nanoscale Pd/carbon cloth composite electrode for energy-saving oxalic acid electrolysis coupled with hydrogen production

In this paper, we report a carbon cloth/amorphous nanoscale Pd (CC/AN Pd) composite electrode and realizes the modifier-free composite of low-cost intractable carbon support and low-loading Pd metal by designing a mild and facile oxidation-ion exchange-reduction (OIR) route. This CC/AN Pd composite electrode presents high activity, robust, cost-effective, modifier-free, micro-nano porous and low Pd loading characteristics compared with the traditional Pd/C electrode. This composite electrode shows superior oxalic acid (OA) oxidization reaction (OOR) catalysis performance, outperforming all the as-reported OOR catalysts especially at high current density. Moreover, on the basis of catalysis performance and the cost of Pd loading amount, this CC/AN Pd composite electrode shows superior hydrogen evolution reaction (HER) catalysis performance with high cost-effective characteristic, surpassing all the as-reported HER catalytic electrodes. Importantly, this composite electrode was used as HER and OOR electrodes to assemble an oxalic acid electrolytic cell (OAEC), which drives 10 mA/cm2 and 100 mA/cm2 current density at only 1.09 V and 1.52 V voltage, respectively, and obtains up to 95.2% average faraday efficiency for 50 mA/cm2 oxalic acid electrolysis. Notable, this CC/AN Pd composite electrode-based OAEC has better energy-saving and stability advantage compared with the commercial CC/Pd–C-based OAEC especially for high current density OA electrolysis. This work opens new avenues to the design of novel composite electrode materials and enables new opportunities in green energy or environmental catalysis areas.

Efficient and Recyclable Heterogeneous Catalyst Based on PdNPs Stabilized on a Green-Synthesized Graphene-like Nanomaterial: Effect of Surface Functionalization.

This work reports for the first time a straightforward and efficient approach to covalent surface functionalization of a sustainable graphene-like nanomaterial with abundant carboxylic acid groups. This approach results in an efficient and robust chelatant platform for anchoring highly dispersed ultrasmall palladium particles with excellent catalytic activity in the reduction of both cationic (methylene blue, MB) and anionic (eosin-Y, Eo-Y) toxic organic dyes. The large-specific-surface-area (SBET = 266.94 m2/g) graphene-like nanomaterial (GHN) was prepared through a green and cost-effective pyrolysis process from saccharose using layered bentonite clay as a template. To introduce a high density of carboxylic acid functions, GHN was first doubly functionalized by successive grafting reaction using two different strategies: (i) in the first case, GHN was first grafted by (3-glycidyloxypropyl) trimethoxysilane (GPTMS) and then bifunctionalized by chemical grafting of tris(4-hydroxyphenyl)methane triglycidyl ether (TGE). In the second case, the grafting order of the two molecules has been reversed. GHN-GPTMS-TGE provided the highest number of grafted reactive epoxy groups, and it was selected for further functionalization with carboxylic acid functions via a ring-opening reaction through a two-step hydrolysis (H2SO4)/oxidation (KMnO4) approach. The GHN nanomaterial bearing carboxylic acid groups was then treated with sodium hydroxide to produce a deprotonated carboxylic acid-rich platform. Finally, due to a high density of accessible chelatant carboxylic acid groups, GHN-COO- binds strongly a great amount of Pd2+ ions to form stable complexes which after reduction by NaBH4 leads to highly dispersed, densely anchored, and uniformly distributed nanoscale Pd particles (d ∼ 4.5 nm) on the surface of the functionalized GHN. The GHN-COO-@PdNPs nanohybrid proved to be highly efficient for dye reduction by NaBH4 in aqueous solution at room temperature. Moreover, because of the high stability of the as-prepared graphene-like supported PdNPs, it exhibited very good reusability and could be recycled up to eight times without any significant loss in activity.

Development of Atomic Hydrogen-Mediated Electrocatalytic Filtration System for Peroxymonosulfate Activation Towards Ultrafast Degradation of Emerging Organic Contaminants

The peroxymonosulfate (PMS) activation by atomic H* is thermodynamically favorable. Herein, we rationally designed a novel H*-mediated electrocatalytic filtration system for PMS activation system to achieve highly efficient degradation of emerging organic contaminants. The key to this system was an electroactive carbon nanotube (CNT) filter functionalized with nanoscale Pd. A complete degradation of 0.04 mM sulfamethoxazole could be achieved just by passing through the filter once (τ < 2 sec). The experimental analysis and DFT studies verified that H* was the key component triggering the generation of reactive oxygen species by PMS activation. The flow-through configuration significantly outperformed the conventional batch reactor due to the enhanced mass transport by convection. The observed efficacy could be maintained in complex matrices as well as for the degrading of diverse persistent contaminants. The mechanistic studies suggested that both radical and non-radical pathways contributed collectively to the ultrafast degradation of organic contaminants.

Nanoscale Pd Supported on Layered Co(OH)2 as Efficient Catalysts for Solvent‐Free Oxidation of Benzyl Alcohol

AbstractIn this work, two‐dimensional (2D) Co(OH)2 nanosheets, with large surface areas and wrinkles are obtained, and used to support Pd nanoparticles (NPs) by simple impregnation method as an efficient catalyst for the oxidation of benzyl alcohol under solvent‐free conditions. The resulting 1 wt.% Pd/Co(OH)2 catalyst exhibits a high turnover frequency value of 57999 h−1. The catalysts were characterized by SEM, TEM, AFM, XRD, BET, XPS and CO‐pulse chemisorption. The results of characterizations reveal that the Pd NPs are highly dispersed on the Co(OH)2 nanosheets. The abundant hydroxyl groups on the surface of Co(OH)2 nanosheets promote the reduction of Pd species, resulting in a higher proportion of Pd0 than that of Pd/AC catalyst, which further facilitates the catalytic performances.

Synthesis and characterization of a supported Pd complex on volcanic pumice laminates textured by cellulose for facilitating Suzuki-Miyaura cross-coupling reactions.

Herein, a novel high-performance heterogeneous catalytic system made of volcanic pumice magnetic particles (VPMP), cellulose (CLS) natural polymeric texture, and palladium nanoparticles (Pd NPs) is presented. The introduced VPMP@CLS-Pd composite has been designed based on the principles of green chemistry, and suitably applied in the Suzuki–Miyaura cross-coupling reactions, as an efficient heterogeneous catalytic system. Concisely, the inherent magnetic property of VPMP (30 emu g−1) provides a great possibility for separation of the catalyst particles from the reaction mixture with great ease. In addition, high heterogeneity and high structural stability are obtained by this composition resulting in remarkable recyclability (ten times successive use). As the main catalytic sites, palladium nanoparticles (Pd NPs) are finely distributed onto the VPMP@CLS structure. To catalyze the Suzuki–Miyaura cross-coupling reactions producing biphenyl pharmaceutical derivatives, the present Pd NPs were reduced from chemical state Pd2+ to Pd0. In this regard, a plausible mechanism is submitted in the context as well. As the main result of the performed analytical methods (including FT-IR, EDX, VSM, TGA, FESEM, TEM, BTE, and XPS), it is shown that the spherical-shaped nanoscale Pd particles have been well distributed onto the surfaces of the porous laminate-shaped VPMP. However, the novel designed VPMP@CLS-Pd catalyst is used for facilitating the synthetic reactions of biphenyls, and high reaction yields (∼98%) are obtained in a short reaction time (10 min) by using a small amount of catalytic system (0.01 g), under mild conditions (room temperature).

Strain-Induced Corrosion Kinetics at Nanoscale Revealed in Liquid: Enabling Control of Corrosion Dynamics of Electrocatalysis

SummaryCorrosion at the nanoscale is vital for the stability of nanoparticles. Understanding the corrosion mechanism can offer insights on how to design more stable nanoparticles during electrocatalysis, such as oxygen reduction reaction (ORR). Here, using a liquid cell (LC) transmission electron microscopy (TEM) technique, we study the corrosion process of palladium@platinum (Pd@Pt) core-shell octahedra at real time. The results revealed that the nanoscale corrosion kinetics was determined synergistically by both the quasi-static factor, local strain, and dynamic factor, local curvature. Specifically, in locations with tensile strain and high local curvature, the etching process is much faster than other places. Density functional theory (DFT) calculation suggested that the dissolution potential of the nanoscale Pd nanocrystal is decreased by the increasement of the strain and meanwhile the calculation indicated that the nanoscale surface Pd atoms trended to be corroded more easily under tensile strain than that under compressive strain. Through the investigation of the nanoscale corrosion mechanisms above, we subsequently designed and synthesized a nanoparticle with smaller strain, which showed higher durability both in in-situ liquid cell and ex-situ ORR stability test.

Nanoscale Pd catalysts decorated WO3–SnO2 heterojunction nanotubes for highly sensitive and selective acetone sensing

In this study, we report on the construction of multiple heterojunctions by functionalization of WO3–SnO2 n–n junction nanotubes (NTs) with nanoscale Pd catalysts for highly sensitive and selective acetone sensing. WO3–SnO2 n–n junction NTs with various W/Sn molar ratios were fabricated via an electrospinning technique. Pd decoration of WO3–SnO2 NTs was further developed by a chemical deposition method. As a result, the enhancement of sensing selectivity and sensitivity to acetone and reduction of operating temperature were simultaneously achieved. The enhanced sensing characteristics of Pd@WO3–SnO2 NTs were mainly ascribed to the formation of multiple heterojunctions (WO3–SnO2 n–n junctions, PdO–SnO2 and PdO–WO3 p–n junctions) and chemical sensitization effect of Pd nanocatalysts. The present results demonstrate that porous WO3–SnO2 heterojunction NTs decorated with nanoscale Pd catalysts have a good potential for sensitive and selective detection of acetone.

Pd/MXene(Ti3C2Tx)/reduced graphene oxide hybrid catalyst for methanol electrooxidation

A key challenge in developing direct methanol fuel cells is the fabrication of electrocatalysts with high activity and long durability. Herein, we report a performance enhanced electrocatalyst of nanoscale Pd on MXene (Ti3C2Tx) and reduced graphene oxide (rGO). The mass activity of Pd/Ti3C2Tx-rGO (1: 1) hybrid toward methanol oxidation reaction is 753 mA mg−1, which is 1.7 times than that of Pd/C (446 mA mg−1). Additionally, the current density of Pd/Ti3C2Tx-rGO (1:1) catalyst contains 212 mAmg−1 which is nine times higher than that of Pd/C (23 mA mg−1) after 7200 s. The Pd/Ti3C2Tx-rGO (1:1) catalyst exhibits excellent cycling stability and long-term life. These remarkable catalytic performances are attributed to the role of Ti3C2Tx and rGO in enhancing the catalytic activity surface area and rapid mass/charge transfer due to the synergistic effect between Pd and Ti3C2Tx/rGO.

Efficient anchoring of nanoscale Pd on three-dimensional carbon hybrid as highly active and stable catalyst for electro-oxidation of formic acid

The commercialization of fuel cells requires the design and development of novel effective electrocatalysts. Thus, considerable efforts have been directed at the synthesis of supported electrocatalyst particles with an optimum size of <6 nm and controlled shape/size. To date, although most studies have focused on the exploitation of supports facilitating charge/mass transfer and capable of inhibiting catalyst sintering/detachment during the catalytic process, comprehensive and straightforward investigation of the anchoring effect and the stabilization mechanism of complex hybrid supports with tunable electronic properties and tuned morphologies remain challenging. Herein, we prepare nanoscale Pd supported by a three-dimensional hybrid of boron-doped graphene with carbon nitride (Pd/BG-CN). The results show that the mass (2215 mA mg−1) and specific (31.7 mA cm−2) activities of Pd/BG-CN for formic acid oxidation are 2.8- and 2.5-fold higher than those of commercial Pd/C, respectively. This enhanced activity was ascribed to the electronic effect of the BG-CN substrate and the high content of surface metallic Pd0 (55.2 at%). Moreover, identical-location transmission electron microscopy imaging show that the stabilization of Pd particles on BG-CN and the strong anchoring effect of this support reduced the extent of active Pd detachment, whereas the weakening of metal–carbon support interactions in commercial Pd/C resulted in remarkable performance degradation. Theoretical calculations of the intrinsic stabilization mechanism of Pd/BG-CN reveal that BG-CN could efficiently trap Pd atoms, which could accumulate and form Pd clusters at trapping (nucleation) sites.

Effective immobilization of nanoscale Pd on a carbon hybrid for enhanced electrocatalytic performances: stabilization mechanism investigations.

The grand challenge inhibiting the use of electrocatalysts is the degradation of active species which results in poor durability and long-term performances. Studying the origin of active metal particle stabilization mechanisms by using supports and the immobilization-induced changes of active particles is of significant importance. This study describes the preparation of Pd nanoparticles supported by carbon hybrid NPG-CN, revealing that the mass and specific activities (1987 A g-1 Pd and 28.7 A m-2) of this catalyst for formic acid oxidation significantly exceed those of commercial Pd/C, and excellent stability and enhanced CO-poisoning tolerance properties are obtained. The origin of this behavior is probed by surface analytical techniques and identical-location transmission electron microscopy (IL-TEM), and the enhanced activity of Pd/NPG-CN is ascribed to the electronic effect of the substrate, the high content of surface metallic Pd0, and the reduced extent of active Pd leaching and physical ripening during the FOA process compared with commercial Pd/C. In addition, theoretical calculations demonstrate that NPG-CN can efficiently trap Pd atoms, which accumulate and form Pd clusters at trapping (nucleation) sites.

Construction of Pd-M (M = Ni, Ag, Cu) alloy surfaces for catalytic applications

The fabrication of ultrathin alloy shells as heterogeneous catalysts to increase the utilization efficiency and enhance the catalytic activity of metal atoms has been recognized as an effective method for the construction of efficient metal nanocatalysts, particularly noble-metal nanocatalysts. In this study, we demonstrate the successful formation of Pd-M (M = Ni, Ag, Cu) alloy shells with a tunable thickness on preformed nanoscale Pd seeds. The success of this synthesis mainly relies on the combination of the slow reduction of “M” ions and the subsequent diffusion of M ad-atoms into the surface lattice of Pd seeds. The composition of the Pd-M alloy shell is easily tuned by changing the type and amount of the added precursor, and the shell thickness is manipulated according to the reaction time. More significantly, the surface structure of these alloy shells is maintained after the reaction, implying that any desired surface structure of Pd-M alloy shells can be prepared by using the appropriate starting materials. Further catalytic evaluation of the hydrogenation of chloronitrobenzenes shows that these alloy surfaces exhibit significantly improved selectivity compared to the Pd seeds. The Pd-Ni alloy surfaces exhibit much better catalytic selectivity (as high as > 99%) than Pd catalysts.

Influence of nanoscale distribution of Pd particles in the mesopores of MCM-41 on the catalytic performance of Pd/MCM-41

Two different nanoscale Pd particle distributions in MCM-41, i.e. in the mesopores and on the external surface, were obtained by using a siliceous MCM-41 and a silylated MCM-41 (S-MCM-41) as the starting support materials, respectively. The electron density of Pd in Pd/S-MCM-41 was lower than that in Pd/MCM-41. Pd/S-MCM-41 exhibited much better selective hydrogenation performance but a lower hydrogenolysis activity than Pd/MCM-41. These differences are related to the different Pd particle distributions in MCM-41 and S-MCM-41, demonstrating that the performance of noble metal catalysts is tunable by simply controlling the nanoscale metal particle distribution in the pores.

Metal-Organic Framework Templated Catalysts: Dual Sensitization of PdO-ZnO Composite on Hollow SnO2 Nanotubes for Selective Acetone Sensors.

Metal-organic framework (MOF)-derived synergistic catalysts were easily functionalized on hollow SnO2 nanotubes (NTs) via electrospinning and subsequent calcination. Nanoscale Pd NPs (∼2 nm) loaded Zn-based zeolite imidazole framework (Pd@ZIF-8, ∼80 nm) was used as a new catalyst-loading platform for the effective functionalization of a PdO@ZnO complex catalyst onto the thin wall of one-dimensional metal oxide NTs. The well-dispersed nanoscale PdO catalysts (3-4 nm) and multiheterojunctions (PdO/ZnO and ZnO/SnO2) on hollow structures are essential for the development of high-performance gas sensors. As a result, the PdO@ZnO dual catalysts-loaded hollow SnO2 NTs (PdO@ZnO-SnO2 NTs) exhibited high acetone response (Rair/Rgas = 5.06 at 400 °C @ 1 ppm), superior acetone selectivity against other interfering gases, and fast response (20 s) and recovery (64 s) time under highly humid atmosphere (95% RH). In this work, the advantages of hollow SnO2 NT structures with high surface area and open porosity were clearly demonstrated by the comparison to SnO2 nanofibers (NFs). Moreover, the sensor arrays composed of SnO2 NFs, SnO2 NTs, PdO@ZnO-SnO2 NFs, and PdO@ZnO-SnO2 NTs successfully identified the patterns of the exhaled breath of normal people and simulated diabetics by using a principal component analysis.

Metal-Organic Framework Templated Synthesis of Ultrasmall Catalyst Loaded ZnO/ZnCo2O4 Hollow Spheres for Enhanced Gas Sensing Properties

To achieve the rational design of nanostructures for superior gas sensors, the ultrasmall nanoparticles (NPs) loaded on ternary metal oxide (TMO) hollow spheres (HS) were synthesized by using the polystyrene (PS) sphere template and bimetallic metal-organic framework (BM-MOFs) mold. The zinc and cobalt based zeolite imidazole frameworks (BM-ZIFs) encapsulating ultrasmall Pd NPs (2–3 nm) were assembled on PS spheres at room temperature. After calcination at 450 °C, these nanoscale Pd particles were effectively infiltrated on the surface of ZnO/ZnCo2O4 HSs. In addition, the heterojunctions of Pd-ZnO, Pd-ZnCo2O4, and ZnO-ZnCo2O4 were formed on each phase. The synthesized Pd-ZnO/ZnCo2O4 HSs exhibited extremely high selectivity toward acetone gas with notable sensitivity (S = 69% to 5 ppm at 250 °C). The results demonstrate that MOF driven ultrasmall catalyst loaded TMO HSs were highly effective platform for high performance chemical gas sensors.

Nanoscale PdO Catalyst Functionalized Co3O4 Hollow Nanocages Using MOF Templates for Selective Detection of Acetone Molecules in Exhaled Breath

The increase of surface area and the functionalization of catalyst are crucial to development of high-performance semiconductor metal oxide (SMO) based chemiresistive gas sensors. Herein, nanoscale catalyst loaded Co3O4 hollow nanocages (HNCs) by using metal-organic framework (MOF) templates have been developed as a new sensing platform. Nanoscale Pd nanoparticles (NPs) were easily loaded on the cavity of Co based zeolite imidazole framework (ZIF-67). The porous structure of ZIF-67 can restrict the size of Pd NPs (2-3 nm) and separate Pd NPs from each other. Subsequently, the calcination of Pd loaded ZIF-67 produced the catalytic PdO NPs functionalized Co3O4 HNCs (PdO-Co3O4 HNCs). The ultrasmall PdO NPs (3-4 nm) are well-distributed in the wall of Co3O4 HNCs, the unique structure of which can provide high surface area and high catalytic activity. As a result, the PdO-Co3O4 HNCs exhibited improved acetone sensing response (Rgas/Rair = 2.51-5 ppm) compared to PdO-Co3O4 powders (Rgas/Rair = 1.98), Co3O4 HNCs (Rgas/Rair = 1.96), and Co3O4 powders (Rgas/Rair = 1.45). In addition, the PdO-Co3O4 HNCs showed high acetone selectivity against other interfering gases. Moreover, the sensor array clearly distinguished simulated exhaled breath of diabetics from healthy people's breath. These results confirmed the novel synthesis of MOF templated nanoscale catalyst loaded SMO HNCs for high performance gas sensors.

Nanoscale Pd supported on 3D porous carbon for enhanced selective oxidation of benzyl alcohol

A 3D porous carbon framework (PCF) supporting palladium nanoparticles (Pd/PCF) was synthesized by a simple and economical method and used for catalyzing benzyl alcohol oxidation.

Efforts for long-term protection of palladium hydrodechlorination catalysts

Nano-sized palladium (Pd) catalysts are known for their high intrinsic hydrodechlorination (HDC) activity towards many chlorinated water pollutants, converting them into non-harmful compounds. Optimization of catalyst protection by embedding various types of Pd catalysts (Pd on oxidic supports and in-situ generated Pd clusters) into poly(dimethylsiloxane) (PDMS) layers was studied together with their use in HDC reactions. The catalyst performance in standard batch and long-term experimental set-ups was used to better understand and optimize the Pd-PDMS system. The phenomenon of polymer deterioration by entrapped HDC-generated HCl is studied for various systems and found to be the main reason for limited life times of Pd-PDMS systems.Pd-PDMS composites were found to provide long-term protection from ionic catalyst poisons. This gain in prolonged catalyst protection goes along with an inevitable decrease in specific catalyst activity which is unhesitantly accepted for the benefit of a longer-lasting catalytic activity. However, when comparing the relative loss of the specific Pd activity due to embedding, it is found to be much lower for initially less active catalyst particles (e.g. a factor of 2 for Pd/Al2O3) compared to about two orders of magnitude for the highly active nanoscale Pd particles. It could be shown that embedded catalysts in continuously operated long-term set-ups have enhanced resistance and longevity compared to those tested in repeated batch-type reaction cycles. PDMS-embedded Pd/Al2O3 maintains its full initial activity up to turnover numbers of >750 (for trichloroethene as probe substance), whereas the catalyst system loses more than 50% of its initial activity for a comparable catalyst utilization (TON≈750) operated in batch cycles.

Novel Pd-catalyzed electroless Au deposition method using a sulfite solution

A novel method is reported for the electroless deposition of Au using nanoscale Pd catalysts in a sulfite solution. A uniform and high quality Au film was generated.

Continuous and Collective Grain Rotation in Nanoscale Thin Films during Silicidation.

Texture evolution is an important issue in materials and nanosciences. Understanding it is fundamental for controlling the final orientation, which infine controls the desired properties of nanodevices. Here, we reveal the formation of a peculiar texture during the silicidation of nanoscale Pd thin films. We demonstrate that the crystallographic relationship observed between the silicide and the Si(001) substrate, named gyroaxy, evolves continuously and collectively during silicidation. This continuous rotation of the nanosized grains over a wide angular range is proposed to be associated with a diffusional mechanism.

Pd/Ni Synergestic Activity for Hydrogen Oxidation Reaction in Alkaline Conditions

The investigation of hydrogen oxidation reaction (HOR) in alkaline conditions has been the subject of a wide interest in the past few years with the rise of alkaline membrane fuel cells (AMFCs). In particular, the quest for the lowest content of platinum group metals (PGMs) in the HOR catalyst is ongoing. In this article, we propose the use of a nanoscale Pd layer partially covering a Ni film to provide the most efficient use of the PGM in the HOR catalyst. The Pd/Ni electrodes were prepared by spontaneous and electrolytic deposition of Pd onto smooth polycrystalline Ni surfaces with different surface compositions. The electrodes were characterized by cyclic voltammetry and atomic force microscopy. Electrocatalytic activity in HOR of the Pd/Ni electrodes was measured in alkaline solution by rotating disc electrode method. In the manuscript, we demonstrate that a Pd coverage as low as 1.5% vs. Ni coverage is sufficient to provide a high current density compared to pure Ni. The current density linearly increases with the Pd coverage up to a Pd coverage of 17%; upon further increase in the Pd coverage, the current density reaches a plateau, i.e. the diffusion limit for the HOR process. The comparison with Pd supported on carbon shows the clear benefit for the bimetallic catalyst.