Graphene-supported Pd Nanoparticles Research Articles

Fundamental Mechanisms of Reversible Dehydrogenation of Formate on N-Doped Graphene-Supported Pd Nanoparticles

Reversible formate (HCOO–) dehydrogenation and bicarbonate (HCO3–) hydrogenation would be desirable for the utilization and storage of hydrogen (H2) as an effective energy carrier. Carbon-supported Pd-based nanoparticles demonstrated enormous competitive advantages for these reactions. However, the fundamental mechanisms underlying these reversible reactions have not yet been elucidated. Herein, we report the reaction pathways for reversible reactions on a Pd-based catalyst using density functional theory (DFT) calculations and propose key factors for improving the reaction efficiency. As the first essential step, the difficulty in the conventional DFT modeling, that is simulation of an anion environment caused by HCOO–, was overcome by designing two-sided Pd12 nanoclusters supported on graphene (Pd12NC-G) with extra electrons. Using Pd12NC-G, we demonstrated that the key factor determining the potential limiting steps for the reversible reaction was desorption of hydrogen in HCOO– dehydrogenation (1.24 e...

Graphene-templated synthesis of palladium nanoplates as novel electrocatalyst for direct methanol fuel cell

The shape-controlled synthesis of Pd nanocrystals supported on the surface of graphene is of great importance in designing an electrocatalyst for direct methanol fuel cells. This work demonstrates the synthesis and characterization of a novel Pd nanoplate structure templated by graphene (PdNPts/G). The combined use of Poly Vingl Pyrrolidone and a graphene template is critical to successfully obtaining novel palladium nanoplates via a one-step reduction strategy using ascorbic acid as a soft reductant. In particular, owing to the presence of a high surface area to mass ratio of Pd nanoplates with dominant active {1 1 0} crystal facets and the enhanced electron transfer of graphene, the as-prepared PdNPts/G shows superior electrocatalytic activity along with satisfactory stability and greater tolerance over both the commercial Vulcan XC-72 and graphene supported Pd nanoparticles (abbr. PdNPs/V and PdNPs/G, respectively) for methanol electro-oxidation.

Fabrication of Graphene-Supported Palladium Nanoparticles-Decorated Zinc Oxide Nanorods for Potential Application

We report the facile synthesis of graphene-supported palladium (Pd) nanoparticles anchored zinc oxide nanorods (Pd-ZnO/G) by the sol-gel method. X-ray diffraction (XRD) pattern confirmed the hexagonal wurtzite crystal structure (with P63mc phase) of Pd-ZnO/G nanorods similar to ZnO structure. X-ray diffraction results showed that graphene-supported Pd nanoparticles anchored on ZnO nanorods increases the average crystallite size of ZnO nanorods. Field emission scanning electron microscopy (FESEM) revealed the successful anchoring of Pd nanoparticles on the surface of ZnO/G nanorods. X-ray spectroscopy (XPS) was used to obtain the different oxidation state and surface compositional details of nanorods. Energy dispersive spectroscopy analysis confirmed the presence of palladium, carbon, and oxygen in Pd-ZnO/G structure. The optical absorption measurement indicates that after graphene and palladium doping, it shifted towards the low wavelength region for Pd-ZnO/G structure and high wavelength region in the case of ZnO/G nanostructure. Magnetic measurement showed that the saturation magnetization of Pd nanoparticles anchored nanorods increased when compared with that of ZnO/G and ZnO nanorods.

Design of a Solid-State Electrochemical Methane Sensor Based on Laser-Induced Graphene for Deployment in the Natural Gas Distribution Network

Methane is the primary component of natural gas. As a result of mining and defects in the distribution network, methane emissions occur throughout the oil and gas industry. This corresponds to the largest anthropogenic source of the potent greenhouse gas and leads to a significant loss in revenue for the oil and gas industries: 60% of methane loss is due to fugitive release, out of which a major percentage is due to transmission lines (pipelines)[1]. However, these leaks are currently challenging to identify or detect due to the expansive nature of the distribution network using the currently available optical and combustion-based sensors. The development of inexpensive, low-power electrochemical sensors could provide a cost-effective means to carry out distributed sensing over the entire network. While high temperature, solid-state electrochemical methane sensors (> 500°C) have been developed using Yttria stabilized zirconia as a solid-state electrolyte,[2] the requirement of high temperature makes them impractical for use. More recently, non-volatile ionic liquids (ILs) have gained traction for use in gas sensor design; In particular, room temperature ILs (RTILs) have found increasing use since they circumvent the extreme process conditions required for certain oxidation pathways of the methane analyte.[3] Unlike many solid-state electrolyte systems, RTILs do not suffer from ionic contact loss with cycling, and do not require significant pre-processing to integrate into the sensor design. While promising results have been demonstrated using RTILs, previous designs have run into challenges with slow diffusion of gases through the fully dense liquid films formed or have been carried out by sparging the gases through the ionic liquid.[3] To address these challenges we explore the use of a porous, easy to process, pseudo-solid-state electrolyte comprised of a 1-ethyl-3-methylimidazolium tetrafluoroborate /polyvinylidene fluoride. The sensor electrodes are based on laser-induced graphene which can be rapidly patterned into flexible/conformable KaptonTM substrates using a commercially available CO2 laser technology.[4] Such lasers are inexpensive and commonly used in industry for high throughput cutting and etching. A method to decorate the high surface area interdigitated electrodes written into the KaptonTM with Pd nanoparticles was developed enabling minimal Pd content but high sensitivity. The porous nature of pseudo solid-state electrolyte in contact with the graphene-supported Pd nanoparticles enables fast gas diffusion and leads to a sensitivity to methane. As shown in Figure 1, on subjecting the sensor to dilute methane samples, the sensors can easily detect ppm and potentially ppb concentrations in air when a cell voltage of 0.6V is applied across the decorated electrodes. We analyze the performance as a function of potential using impedance spectroscopy and potentiostatic measurements under various conditions of temperature and interfering gases. The ease of processing, low cost and sensitivity make the system promising for future use in distributed sensing networks.

Heteropolyacid-Mediated Self-Assembly of Heteropolyacid-Modified Pristine Graphene Supported Pd Nanoflowers for Superior Catalytic Performance toward Formic Acid Oxidation

The in situ growth of Pd nanoflowers on pristine graphene is achieved using phosphomolybdic acid (HPMo) to mediate self-assembly. The HPMo serves simultaneously as a linker, stabilizer, and structure-directing agent, and the nanoflowers are formed by kinetically controlled growth. When the resulting material, Pd nanoflowers on HPMo-modified graphene (HPMo-G) support, is used to catalyze the formic acid oxidation reaction (FAOR), much higher catalytic activity and durability are found than with HPMo-G supported Pd nanospheres, graphene supported Pd nanoparticles, and commercial Pd/C catalysts. The catalytic activity for Pd nanoflowers on HPMo-G is also among the highest reported for Pd-based catalysts. The superior electrocatalytic performance is attributed to the unique nanoflower shape, a promotion by the HPMo mediator, and the excellent support properties of pristine graphene. The use of HPMo to mediate self-assembly of metals on graphene can be extended to fabricate other hybrid nanostructures promisin...

Graphene-Supported Pd Nanoclusters Probed by Carbon Monoxide Adsorption

The adsorption of CO on graphene-supported Pd nanoparticles was studied in situ with high-resolution synchrotron-based X-ray photoelectron spectroscopy. At 150 K, CO adsorbs mainly in bridge and 3-fold-hollow sites. The nanoparticles are considered as a mixture of low-index facets. The variation of the amount of deposited Pd revealed identical CO adsorption behavior for all investigated cases, confirming a similar average cluster size over a wide range of Pd coverages. The desorption characteristics were studied with temperature-programmed XPS. The observed desorption maxima at 230 and 430 K are in good agreement with temperature-programmed desorption data on stepped Pd single crystals. At 500 K, CO is completely desorbed from the Pd clusters. The adsorption and desorption of CO are found to be not fully reversible as the Pd particles undergo restructuring upon heating.

Graphene-Supported Pd Nanoparticles Composites Synthesized in Ionic Liquid Microemulsion

Pd/graphene composites were successfully prepared in H2O/TX-100/[BMIM]PF6 microemulsion in which ions were reduced in situ by TX-100 and graphene oxide was reduced by hydrazine hydrate. In the confinement region of the microemulsion, ultrafine Pd nanoparticles (NPs) supported on graphene composites were successfully prepared. The as-prepared composite materials of Pd NPs and graphene were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction. It is demonstrated that the size distribution of Pd NPs is narrow, with an average size of 4 nm. The Pd/graphene composites were tested as electrocatalysts for application in fuel cells. Cyclic voltammetry and chronoamperometry measurements show good electrocatalytic performance of the composite materials for oxidation of ethanol in alkaline medium.

Graphene-supported small-sized palladium nanoparticles made by facile photochemical approaches

To achieve small-sized and well-dispersed palladium (Pd) nanoparticles, we make use of effective photochemical approaches to synthesis of clean Pd nanoparticles on the surface of graphene at room temperature. By modulating the photochemical reaction conditions, the size and dispersion of graphene–Pd composites can be well controlled, where PdCl42− and graphene oxide (GO) are the reaction precursors, Hantzsch 1,4-dihydropyridine (HEH) is used as an electron donor and an amine-type ligand to stabilize small Pd nanoparticles on the surface of graphene. As a result, the easy and effective photochemical approaches to the graphene–Pd composites with well-dispersed, small-sized Pd nanoparticles and highly conductive reduced GO, are established. Good to excellent yields have also been achieved with the graphene-supported Pd nanoparticles catalysts for the Suzuki coupling reaction.

Palladium nanoparticle catalysts synthesis on graphene in sodium dodecyl sulfate for oxygen reduction reaction

We prepare large areas of graphene on carbon paper from graphite powder and anionic surfactant, assisted electrochemical exfoliation as previous work. Using a four-point probe technique, we found the conductivity of graphene on carbon paper to be 66 mS cm−1, which is approximately 1.2 and 1.65 times better than that of graphite coated carbon paper and carbon paper. Then palladium is electro-reduced onto the carbon paper based electrodes (with or without graphene) in absence or presence of different concentrations of sodium dodecyl sulfate (SDS), that are used in oxygen reduction reaction (ORR) for direct methanol fuel cells. The electrochemically reduced Pd is carefully characterized by scanning electron microscopy (SEM). Their electrochemical properties are investigated with cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance spectroscopy. Particularly, SEM images show that the size of the nanoparticles decreases from 1000 to 70 nm as SDS concentration increases from 0 to 14 mM. The catalytic activities of graphene-supported Pd nanoparticles and Pd–carbon paper electro-catalysts for ORR are 112 and 2 Ag−1 Pd, which can reveal the particular properties of the exfoliated graphene supports and SDS media.

Graphene-supported Pd nanoparticles: microwave-assisted synthesis and as microwave-active selective hydrogenation catalysts

Facile synthesis of graphene-supported Pd nanoparticles (NPs) with an average size of 5 nm (Pd/G) was achieved by a microwave-assisted reduction approach; the obtained Pd/G can be very effectively coupled to the microwave field, making it a high-performance catalyst (with turnover frequency (TOF) of 158 465 h−1) for microwave-assisted selective hydrogenation of isophorone at low temperatures.