Effect of MEA fabrication techniques on the cell performance of Pt–Pd/C electrocatalyst for oxygen reduction in PEM fuel cell

The effect of three different membrane electrode assembly (MEA) fabrication techniques, catalyst-coated substrate by direct spray (CCS) and catalyst-coated membrane by direct spray (CCM-DS) or decal transfer (CCM-DT), on the performance of oxygen reduction in a proton exchange membrane (PEM) fuel cell was carried out under identical conditions of Pt–Pd/C electrocatalyst loading. The results indicated that the fabrication technique had only a very slight effect on the ohmic resistance of the PEM fuel cell but it significantly affected the charge transfer resistance and open circuit voltage (OCV). The cells prepared by the CCM method, and particularly by decal transfer, exhibited a significantly higher OCV but a lower ohmic and charge transfer resistance compared with the other investigated fabrication techniques. By using cyclic voltammetry with H₂ adsorption, it was found that the electrochemical active area of the electrocatalyst prepared by CCM-DT was higher than those prepared by CCS and CCM-DS by around 1.76- and 1.05-fold, respectively. Under a H₂/O₂ system at 0.6 V, the cells with MEA made by CCM-DT provided the highest cell performance of around 350 mA/cm², significantly greater than those prepared by the CCS and CCM-DS (149 and 42 mA/cm², respectively).     

Pt promotional effects on Pd–Pt alloy catalysts for hydrogen peroxide synthesis directly from hydrogen and oxygen

H₂O₂ synthesis directly from H₂ and O₂ over supported Pd–Pt alloy catalysts was carried out using a semibatch reactor under ambient conditions. As compared to pure Pd, the performance of Pd–Pt catalysts was enhanced significantly. The promotional role of Pt was studied systematically by using in situ diffuse reflectance infrared Fourier transform spectroscopy of CO adsorption (DRIFTS), quantitative powder X-ray diffraction (XRD), X-rays photoelectron spectroscopy (XPS), and temperature-programmed desorption of H₂/O₂ (H₂/O₂-TPD). The spectra of DRIFT, XPS, and XRD demonstrate the formation of Pd–Pt alloy particles, which surfaces are enriched by Pt accompanying with possible electron transfer from Pd to Pt. The addition of Pt into Pd phase was proposed to impact on reactants adsorption, stabilization of intermediates such as OOH and OH radicals, and the formation and decomposition of H₂O₂.     

An efficient reduction route for the production of Pd–Pt nanoparticles anchored on graphene nanosheets for use as durable oxygen reduction electrocatalysts

Pt and Pd–Pt nanoparticles were anchored on reduced graphene oxide (RGO) with the aid of poly(diallyldimethylammonium chloride) (PDDA), where Pt and Pd ions were first attached to PDDA-functionalized graphene oxide sheets and the encased metal ions and graphene oxide were then reduced simultaneously by ethylene glycol. As supported by transmission electron microscopy, metal nanoparticles, of small particle size even at a high metal loading, were chemically attached to PDDA–RGO. X-ray diffraction indicates that the as-prepared Pd–Pt nanoparticles have a single-phase fcc structure and are principally alloys of Pd and Pt. Among the RGO-supported Pt and Pd–Pt catalysts, Pt nanoparticles anchored on PDDA–RGO exhibit the highest activity for the oxygen reduction reaction (ORR), and the ORR activity of the Pd–Pt alloy electrocatalysts increases with Pt content. All the catalysts demonstrate an enhanced ORR durability when PDDA is present; strongly suggesting that PDDA plays a crucial role in the dispersion and stabilization of the metal nanoparticles on RGO. The ORR activities of the Pd–Pt catalysts remain enhanced even after accelerated durability testing. The formation of a Pt-rich shell, as confirmed by X-ray photoelectron spectroscopy and CO stripping voltammetry, may account for the increased activity.     

An electrocatalyst for detection of glucose in human blood: synergy in Pd–AuNPs/GOx/C surfaces

Glucose oxidase (GOx)-based amperometric enzyme electrodes have been the target of substantial research. In this study, new amperometric biosensor for determination of glucose was developed. GOx enzyme was immobilized at bovine serum albumin via entrapment method. For this reason, the optimum conditions of Pd–Au NPs/GOx/C-modified glassy carbon electrode were determined. The electron is directly transferred from glucose to the electrode via the active site of the enzyme. The absence of mediators is the main advantage of such third-generation biosensors. The resulting materials were characterized employing scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction. In addition, the effects of glucose concentration, scan rate, temperature, electroactive interference, stability, reusability of the biosensors were discussed. The applicability to blood analysis was also evaluated. The biosensor has a limit of detection for the determination of glucose 0.0014?mM.     

Fabrication of Ag/WO3 nanobars for Baeyer–Villiger oxidation using hydrogen peroxide

We report the preparation of Ag/WO₃ nanobars, mediated by cationic surfactant CTAB through hydrothermal route. XRD revealed the formation of metallic Ag supported on monoclinic WO₃ phase and TEM diagram showed the formation of bar-like structure, where supported Ag nanoparticles are in the range between 2 and 7 nm. The catalyst exhibited high activity for selective oxidation of cyclohexanone to caprolactone with H₂O₂. A cyclohexanone conversion of 97% with 99% caprolactone selectivity was achieved over this catalyst at 80 °C temperature. Moreover, the catalyst did not show any significant activity loss even after 5 reuses and proved its efficiency in the oxidation of other cycloalkanones also.     

Green synthesized Au–Ag bimetallic nanoparticles modified electrodes for the amperometric detection of hydrogen peroxide

Simple and eco-friendly electro deposition method was employed for the fabrication of Au–Ag bimetallic nanoparticles modified glassy carbon electrode. Nano Au–Ag film modified glassy carbon electrode surface morphology has been examined using atomic force microscopy. Electrodeposited Au–Ag bimetallic nanoparticles were found in the average size range of 15–50 nm. The electrochemical investigations of nano Au–Ag/1-butyl-3-methylimidazolium tetrafluoroborate-nafion film have been carried out using cyclic voltammetry and electrochemical impedance spectroscopy. The nano Au–Ag/1-butyl-3-methylimidazolium tetrafluoroborate-nafion film modified glassy carbon electrode holds the good electrochemical behavior and stability in pH 7.0 phosphate buffer solutions. The nano Au–Ag/1-butyl-3-methylimidazolium tetrafluoroborate-nafion modified glassy carbon electrode was successfully employed for the detection of H₂O₂ in the linear range of 1–250 μM in lab samples, and 1 × 10⁻³–2 × 10⁻² M in real samples, respectively.     

Novel Pd–Au/TiO2 catalyst for the selective catalytic reduction of NOx by H2

Novel Pd–Au/TiO₂ catalyst exhibited high catalytic activity with a wide temperature window for the selective catalytic reduction of NO_x by H₂ in the presence of oxygen. The synergetic effect between Pd and Au contributes to the formation of Pd⁰ and Pd–Au alloy, thus promoting the NO_x reduction to proceed.     

Carbon nano-tube supported Pt–Pd as methanol-resistant oxygen reduction electrocatalyts for enhancing catalytic activity in DMFCs

This work tries to study the problem of methanol crossover through the polymer electrolyte in direct methanol fuel cells (DMFCs) by developing new cathode electrocatalysts. For this purpose, a series of gas diffusion electrodes (GDEs) were prepared by using single-walled carbon nanotubes (SWCNTs) supported Pt–Pd (Pt–Pd/SWCNT) with different Pd contents at the fixed metal loading of 50 wt%, as bimetallic electrocatalysts, in the catalyst layer. Pt–Pd/SWCNT was prepared by depositing the Pt and Pd nanoparticles on a SWCNTs support. The elemental compositions of bimetallic catalysts were characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES) system. The performances of the GDEs in the methanol oxidation reaction (MOR) and in the oxygen reduction reaction with/without the effect of methanol oxidation reaction were investigated by means of electrochemical techniques: cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS). The results indicated that GDEs with Pt–Pd/SWCNT possess excellent electrocatalytic properties for oxygen reduction reaction in the presence of methanol, which can originate from the presence of Pd atoms and from the composition effect.     

Modulation of the textures and chemical nature of C–SiC as the support of Pd for liquid phase hydrogenation

A C–SiC composite with a thin layer of carbon surrounding the SiC substrate has been produced by the reaction of SiC with CCl₄. The pore structures, graphitization levels and the chemical compositions can be finely modulated by the synthesis temperature, and atmosphere. A higher synthesis temperature accelerates the chlorination rate, increases the thickness of carbon layers and enhances their graphitization. Mesopores can be generated in C–SiC composites in comparison to predominant micropores in commercial activated carbon (AC), particularly in the presence of reactive atmosphere such as CO₂ and NH₃. Furthermore, with cofeeding of NH₃ with CCl₄, N heteroatoms can be incorporated into the carbon layer and the N content varies in a range of 4.7–9.5 at.%, depending on the synthesis conditions. Both increased fraction of mesopores and their sizes, as well as N doping facilitate significantly hydrogenation of 4-carboxybenzaldehyde. The activity of Pd catalyst supported on N-doped C–SiC is five times that on commercially used AC under the same conditions.     

Yolk–shell structured iron carbide/N-doped carbon composite as highly efficient and stable oxygen reduction reaction electrocatalyst

We report a simple route to synthesize iron carbide/carbon yolk–shell composite via a facile two-step process including polymerization of pyrrole using Fe₃O₄ as a sacrificial template to form a Fe₃O₄/polypyrrole composite, followed by annealing at high temperature in N₂ atmosphere. The yolk–shell composite, with iron carbide (Fe_2.5C) embedded in nitrogen-doped carbon layers, shows impressively high catalytic activity and stability for oxygen reduction reaction in alkaline solution. Both the pyridinic-N and graphic-N in the shell of Fe₃O₄–PPy-700, together with the Fe_2.5C confined in carbon layers are believed to be the active sites for the ORR.     

Characterization of methanol-tolerant Pd–WO3 and Pd–SnO2 electrocatalysts for the oxygen reduction reaction in direct methanol fuel cells

Palladium (Pd) catalysts containing nanosized metal oxides, tungsten oxide (WO₃) and tin oxide (SnO₂), supported on carbon black (Pd–MO_x/C) were synthesized, and the effect of the metal oxide on the oxygen reduction reaction (ORR) in a direct methanol fuel cell (DMFC) was investigated. The SEM images showed that the Pd nanoparticles were highly dispersed on the carbon black, and the metal oxide particles were also distributed well. Pd/C and Pd–WO₃/C catalysts as cathode materials for the ORR in DMFCs showed activity similar to or better than that of Pt/C, whereas Pd–SnO₂/C showed no improvement in catalytic activity.     

Promotional effect of Ni–Co/ordered mesoporous carbon as non-noble hybrid electrocatalyst for methanol electro-oxidation

Journal of Applied Electrochemistry - The development of a ternary hybrid catalytic system, inclusive of Ni species/Co species/ordered mesoporous carbon (catalyst/co-catalyst/support) and its...     

Effect of praseodymium oxide and cerium–praseodymium mixed oxide in the Pt electrocatalyst performance for the oxygen reduction reaction in PAFCs

The effect of praseodymium oxide and cerium–praseodymium mixed oxide in the Pt electrocatalyst performance for oxygen reduction reaction (ORR) in Phosphoric Acid Fuel Cells (PAFCs) has been studied. Three electrocatalysts (Pt/C, PtPrO _x /C and PtCe_0.9Pr_0.1O _y /C, where x and y are ≤2) have been prepared and tested by cyclic voltammetry (CV) and long term chronoamperometry (CA) experiments. The fresh and tested electrocatalysts have been characterized by X-ray diffraction (XRD) and Transmission Electron Microscopy–Energy Dispersion Spectroscopy (TEM–EDS). The Pr and Ce–Pr oxides improved Pt dispersion in the fresh electrocatalysts with regard to the Pt-only catalyst, and the PtPrO _x /C and PtCe_0.9Pr_0.1O _y /C electrocatalysts presented a slightly improved catalytic activity towards ORR in comparison to the reference Pt/C electrocatalyst. The activity decay during the long term CA tests was slower for PtPrO _x /C and PtCe_0.9Pr_0.1O _y /C than for Pt/C. Although the Pr and Ce–Pr oxides were dissolved during the CA measurements, the Pt sintering was prevented.     

Fabrication of a novel ZnO–CoO/rGO nanocomposite for nonenzymatic detection of glucose and hydrogen peroxide

Herein, a novel nanocomposite of binary ZnO–CoO nanoparticles loaded on the graphene nanosheets (ZnO–CoO/rGO) has been successfully constructed via a facile, economical and two–step process. The obtained ZnO–CoO/rGO hybrids with high electrical conductivity and abundant active sites, could be modified on a glassy carbon electrode to detect glucose and H₂O₂ multi–functionally. The fabricated biosensor exhibits wide linear range for glucose (10 μM to 11.205 mM) and H₂O₂ (25 μM to 11.1 mM), and their corresponding sensitivity are 168.7 μA mM^?1 cm^?2 and 183.3 μA mM^?1 cm^?2. The limits of detection are 1.3 μM and 0.44 μM for the oxidation of glucose and the reduction of H₂O₂, respectively. Furthermore, remarkable selectivity, long–term stability and outstanding reproducibility of the non–enzyme biosensor prove that ZnO–CoO/rGO hybrids are the promising candidate in practical applications.     

Dependences of the Oxygen Reduction Reaction Activity of Pd–Co/C and Pd–Ni/C Alloy Electrocatalysts on the Nanoparticle Size and Lattice Constant

Carbon-supported Pd-based binary alloy electrocatalysts (Pd–Co and Pd–Ni) with different particle sizes for polymer electrolyte fuel cells were prepared by a NaBH₄ reduction method and investigated to examine effects of the size and lattice constant of the Pd alloy nanoparticles on the oxygen reduction reaction (ORR) activity. The particle size and lattice constant were controlled in the wide ranges 4.2–12.1 and 0.3802–0.3948 nm, respectively by heating the catalysts in specific atmospheres. The alloy structures were characterized by X-ray diffraction, transmission electron microscopy and X-ray absorption fine structure. The electrochemical tests of the Pd–Co/C and Pd–Ni/C catalysts were performed by cyclic voltammetry and rotating disk electrode in 0.1 M HClO₄. Nearly linear relationship between the lattice constant and nanoparticle size was observed with the Pd–Co and Pd–Ni nanoparticles. The nanoparticle sizes and lattice constants of the Pd–Co/C and Pd–Ni/C electrocatalysts, which influence the Pd d-band center, showed positive and inverse relations with the ORR specific activities, respectively. The mass activities of the Pd–Co/C and Pd–Ni/C electrocatalysts showed an increasing trend with the lattice expansion.     

IrO2–SnO2 mixtures as electrocatalysts for the oxygen reduction reaction in alkaline media

In this work, SnO₂ + IrO₂ mixed oxides are studied as electrocatalysts for the oxygen reduction reaction (ORR) in alkaline media by means of voltammetric techniques under controlled mass transfer conditions thanks to the use of rotating (ring) disk electrodes (RDE/RRDE). The oxides, prepared by sol–gel methodology, are supported on the disk electrodes using a thin layer of anionic exchange polymer as gluing agent. The amount of deposited polymer was optimized to avoid any limitation due to the diffusion of reactant/products across the film thickness. The mixed oxides were prepared at the following mole fractions of IrO₂: $ x_{{{\text{IrO}}_{ 2} }} $  = 0.15, 0.31, 0.55, 0.73, and 1. The role of composition was studied in terms of the reaction pathways and the relevant fraction of H₂O₂ production, together with the potentials of the onset of ORR. The fraction of sites able to give proton/hydroxyl and electron transfers is also determined and discussed. The results point to the best performance of low-Ir containing mixtures and to their low sensitivity to the presence of methanol, a key feature in the case of crossover in alkaline direct alcohol fuel cells.     

Pd Nanoparticles Stabilized on the Cross-Linked Melamine-Based SBA-15 as a Catalyst for the Mizoroki–Heck Reaction

Catalysis Letters - Mesoporous SBA-15 silicate with a high surface area was prepared by a hydrothermal method, successively modified by organic melamine ligands and then used for deposition of Pd...     

A porous metal–organic framework as active catalyst for multiple C–N/C–C bond formation reactions

A 3D porous metal–organic framework {[Cu(4-tba)₂](solvent)}_n (1⋅S) is assembled via 4-(1H-1,2,4-triazol-1-yl)benzoic acid (Htba) and Cu(II) nodes, which shows the [2 + 2] roto-translational interpenetrating network. Interestingly, 1 displays high CO₂ adsorption selectivity over CH₄/H₂/O₂/Ar/N₂ gases, and acts an efficient catalyst precursor in some C–N/C–C bond formation reactions, including Chan–Lam coupling reaction of phenylboronic acid with imidazole, Suzuki–Miyoura coupling reaction of phenylboronic acids with aryl halides, and Heck coupling reaction of styrene with aryl halides.     

Electro-oxidation of ethanol on PtSn/CeO2–C electrocatalyst

PtSn/CeO₂–C electrocatalyst was prepared in a single step by an alcohol-reduction process using ethylene glycol as solvent and reducing agent and CeO₂ (15 wt%) and Vulcan XC72 (85 wt%) as supports. The performance for ethanol oxidation was investigated by cyclic voltammetry and in situ FTIR spectroscopy. The electrocatalytic activity of the PtSn/CeO₂–C electrocatalyst was higher than that of the PtSn/C electrocatalyst. FTIR studies for ethanol oxidation on PtSn/C electrocatalyst showed that acetaldehyde and acetic acid were the principal products formed, while on PtSn/CeO₂–C electrocatalyst the principal products formed were CO₂ and acetic acid.