Activity For Formic Acid Oxidation Research Articles

Mechanistic studies of formic acid oxidation at polycarbazole supported Pt nanoparticles

Mechanistic aspects of the promotion of formic acid oxidation at Pt nanoparticles supported on a thin layer of polycarbazole (PCZ) have been investigated by voltammetry and X-ray photoelectron spectroscopy (XPS). The Pt nanoparticles were drop coated onto a glassy carbon (GC) electrode coated with a ca. 9nm layer of electrochemically deposited polycarbazole. After 500s of formic acid oxidation at 0V vs. SCE, the current at a GC/PCZ/Pt electrode was 25 times higher than at a GC/Pt electrode. Voltammetry in formic acid free H2SO4 following potentiostatic oxidation of formic acid revealed that there was less accumulation of adsorbed intermediates for the polycarbazole supported Pt nanoparticles than for those deposited directly onto the glassy carbon with, 50% more Pt sites remaining available for the GC/PCZ/Pt electrode relative to the GC/Pt electrode. Independent CO stripping experiments revealed only slight differences, while Cu underpotential deposition surprisingly resulted in the deposition of a ca. two-fold excess of Cu on the polycarbazole supported particles. This observation was supported by XPS which also revealed a second Cu signal at a higher binding energy, suggesting electron donation into the conjugated π system of the polymer. Such an interaction of Pt with the polycarbazole may be responsible for its higher activity for formic acid oxidation.

Pd and PdCo alloy nanoparticles supported on polypropylenimine dendrimer-grafted graphene: A highly efficient anodic catalyst for direct formic acid fuel cells

For the first time, Pd and PdCo alloy nanoparticles supported on polypropylenimine dendrimer-grafted graphene (Pd and PdCo/PPI-g-G) are prepared and characterized with Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The electrocatalytic activity of Pd and PdCo/PPI-g-G are investigated in terms of formic acid electrooxidation in H2SO4 aqueous solution. The PdCo/PPI-g-G shows much higher formic acid oxidation activities in comparison with Pd/PPI-g-G, and it is more resistant to the surface poisoning. This improved electrocatalytic performance may be due to the fine dispersion of PdCo alloy nanoparticles and bi-functional effect. The kinetic parameters such as charge transfer coefficient and the diffusion coefficient of formic acid are estimated under the quasi steady-state conditions.

Electrochemical-reduced graphene oxide-modified carbon fiber as Pt–Au nanoparticle support and its high efficient electrocatalytic activity for formic acid oxidation

A simple electrochemical approach is developed to prepare reduced graphene oxide (RGO)-wrapped carbon fiber (CF) as a novel support for Pt–Au nanocatalysts. The obtained composite electrodes have been characterized by scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDX), thermal gravimetric analysis (TGA), and electrochemical methods. SEM images reveal that the Pt–Au nanoparticles deposited on RGO-wrapped CF (RGO/CF) electrode display smaller particle size and more uniform dispersion than those on the bare CF electrode. Cyclic voltammetry, linear sweep voltammetry, chronoamperometry, chronopotentiometry, Tafel plots, and electrochemical impedance spectroscopy (EIS) analyses demonstrate that the introduced RGO on CF electrode surface is beneficial to the dispersion of Pt–Au nanoparticles, as a consequence, to the enhancement of the electrocatalytic activity and the antipoisoning ability of Pt–Au towards formic acid electrooxidation.

A High-Performance Bimetallic Pd-Cu Nanoparticles Membrane on Glassy Carbon Electrode for Formic Acid Oxidation

The Palladium-copper nanoparticles (PdCu NPs) have been prepared by potentiostatic electrodeposition from a mixture electrolyte of H2PdCl4 and CuSO4,then placed the electrode in sulfuric acid using cyclic voltammetry sweep a few laps to fabricate the PdCu NPs/glass carbon electrode (Pd-Cu/GCE). The modified electrode electrochemical properties of a preliminary study found that this modified electrode has good stability and electrochemical activity, experiments show that formic aicd has good voltammetric response of the electrode. The electrical activity of the formic acid in the Pd/GCE is lower than that in the Pd-Cu/GCE, this is due to the synergistic effect of the bimetal. When the Cu content is increased gradually in H2PdCl4 and CuSO4 a mixed solution, the formic acid oxidation peak currentlower, because Cu has no electrocatalytic activity for formic acid oxidation.

Hydrothermal synthesis of titanium-supported nanoporous palladium–copper electrocatalysts for formic acid oxidation and oxygen reduction reaction

Nanoporous Pd and binary Pd-Cu particles were prepared by a hydrothermal method using ethylene glycol as a reduction agent and they were directly immobilized on Ti substrates named as Ti-supported Pd-based catalysts. Their electrocatalytic activity for formic acid oxidation and oxygen reduction reaction (ORR) in alkaline media was examined by voltammetric techniques. Among the as-prepared catalysts, nanoPd81Cu19/Ti catalyst presents the highest current density of 39.8 mA/cm2 at −0.5 V or 66.4 mA/cm2 at −0.3 V for formic acid oxidation. The onset potential of ORR on the nanoPd81Cu19/Ti catalyst presents an about 70 mV positive shift compared to that on the nanoPd/Ti, and the current density of ORR at −0.3 V is 2.12 mA/cm2, which is 3.7 times larger than that on the nanoPd/Ti.

Au/Pd core-shell nanoparticles with varied hollow Au cores for enhanced formic acid oxidation

A facile method has been developed to synthesize Au/Pd core-shell nanoparticles via galvanic replacement of Cu by Pd on hollow Au nanospheres. The unique nanoparticles were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, ultraviolet–visible spectroscopy, and electrochemical measurements. When the concentration of the Au solution was decreased, grain size of the polycrystalline hollow Au nanospheres was reduced, and the structures became highly porous. After the Pd shell formed on these Au nanospheres, the morphology and structure of the Au/Pd nanoparticles varied and hence significantly affected the catalytic properties. The Au/Pd nanoparticles synthesized with reduced Au concentrations showed higher formic acid oxidation activity (0.93 mA cm-2 at 0.3 V) than the commercial Pd black (0.85 mA cm-2 at 0.3 V), suggesting a promising candidate as fuel cell catalysts. In addition, the Au/Pd nanoparticles displayed lower CO-stripping potential, improved stability, and higher durability compared to the Pd black due to their unique core-shell structures tuned by Au core morphologies.

Atomically Dispersed Platinum on Gold Nano-Octahedra with High Catalytic Activity on Formic Acid Oxidation

Platinum was epitaxially deposited on gold octahedral nanocrystals using an electrochemical method. The coverage of platinum on the gold surface was finely controlled from fully covered multiple overlayers (5 monolayers; denoted as ML) to atomically dispersed submonolayer (0.05 ML). Catalytic activity for formic acid oxidation increased significantly (0.52 A/mgPt for 5 ML to 62.6 A/mgPt for 0.05 ML) with decreasing coverage. This high activity resulted from the control of the reaction pathway toward direct oxidation producing no surface-poisoning species, induced by the absence of platinum ensembles and the bifunctional effect from neighboring Pt–Au sites. The distribution of atomically dispersed platinum was further confirmed by no activity for methanol oxidation, which necessitates platinum ensembles. This result exemplifies that a rational design of the catalyst nanostructure can lead to contrasting activities with the same catalyst, unprecedentedly high activity for formic acid oxidation vs no activit...

Bismuth decoration of electrodeposited platinum thin films with a preferential (100) orientation

ABSTRACTPreferentially {100} oriented and polycrystalline platinum electrodes were prepared by potentiostatic electrodeposition. The surface of the electrodes was characterized by deconvolution of the hydrogen desorption region. The catalytic activity for formic acid oxidation was determined by cyclic voltammetry and chronoamperometry. The results indicate that although the maximum current observed in cyclic voltammogram does not increase, the long term performances as measured by chronoamperometry dramatically increase up to 33 times with increased Bi coverage despite the loss of electroactive Pt surface area.

Synthesis of carbon-supported PdSn–SnO2 nanoparticles with different degrees of interfacial contact and enhanced catalytic activities for formic acid oxidation

The conjunction of the PdSn alloy and SnO2 is of interest for improving catalytic activity in formic acid oxidation (FAO). Here, we report the synthesis of PdSn-SnO2 nanoparticles and a study of their catalytic FAO activity. Different degrees of interfacial contact between SnO2 and PdSn were obtained using two different stabilizers (sodium citrate and EDTA) during the reduction process in catalyst preparation. Compared to the PdSn alloy, PdSn-SnO2 supported on carbon black showed enhanced FAO catalytic activity due to the presence of SnO2 species. It was also found that interfacial contact between the PdSn alloy and the SnO2 phase has an impact on the activity towards CO oxidation and FAO.

Electrocatalytic activity of well-defined and homogeneous cubic-shaped Pd nanoparticles

Well-ordered, homogenous cube-shaped highly ordered Pd, without other geometries, was obtained by chemical reduction in aqueous media by employing ascorbic acid, polyvinylpyrrolidone and sodium bromide as the reducing agent, surfactant and additive, respectively. The X-ray diffraction (XRD) patterns exhibited a face-centred cubic structure with an average crystallite size of 11.5 nm. Transmission electron microscopy (TEM) images showed a homogeneous distribution of cubic Pd nanoparticles (namely Pd nanocubes) with a preferential (200) crystallographic plane and a particle size of approximately 10.6 ± 1.2 nm. The electrocatalytic activity of the Pd nanocubes was evaluated in terms of the current density attributed to the oxidation reaction of the following three common fuels: methanol, ethanol and formic acid. The results obtained showed that the current density achieved with the Pd nanocube electrocatalyst is 4, 3 and 3.5 (12, 10 and 8.7 mA mg−1 cm−2, respectively) times higher than that reached with commercial Pd at similar oxidation potential values. Furthermore, the Pd nanocube catalyst exhibited higher catalytic activity for formic acid oxidation than that reported for Pd-based materials. The oxygen reduction reaction using the Pd nanocubes in basic media was also tested.

Carbon-supported AuPd bimetallic nanoparticles synthesized by high-energy electron beam irradiation for direct formic acid fuel cell

Nanoparticle catalysts of carbon-supported Pd (Pd/C) and carbon-supported AuPd (AuPd/C) for the direct formic acid fuel cell (DFAFC) anode were synthesized by the reduction of precursor ions in an aqueous solution irradiated with a high-energy electron beam. We obtained three kinds of nanoparticle catalysts: (1) Pd/C, (2) AuPd/C of the core–shell structure, and (3) AuPd/C of the alloy structure. The structures of AuPd nanoparticles were controlled by the addition of citric acid as a chelate agent, and sodium hydroxide as a pH controller. The structures of nanoparticle catalysts were characterized using transmission electron microscopy, inductively coupled plasma atomic emission spectrometry, the techniques of X-ray diffraction and X-ray absorption fine structure. The catalytic activity of the formic acid oxidation was evaluated using linear sweep voltammetry. The oxidation current value of AuPd/C was higher than that of Pd/C. This indicated that the addition of Au to Pd/C improved the oxidation activity of the DFAFC anode. In addition, the AuPd/C of the alloy structure had higher oxidation activity than the AuPd/C of the core–shell structure. The control of the AuPd mixing state was effective in enhancing the formic acid oxidation activity.

Control Over the Branched Structures of Platinum Nanocrystals for Electrocatalytic Applications

Structural control of branched nanocrystals allows tuning two parameters that are critical to their catalytic activity--the surface-to-volume ratio, and the number of atomic steps, ledges, and kinks on surface. In this work, we have developed a simple synthetic system that allows tailoring the numbers of branches in Pt nanocrystals by tuning the concentration of additional HCl. In the synthesis, HCl plays triple functions in tuning branched structures via oxidative etching: (i) the crystallinity of seeds and nanocrystals; (ii) the number of {111} or {100} faces provided for growth sites; (iii) the supply kinetics of freshly formed Pt atoms in solution. As a result, tunable Pt branched structures--tripods, tetrapods, hexapods, and octopods with identical chemical environment--can be rationally synthesized in a single system by simply altering the etching strength. The controllability in branched structures enables to reveal that their electrocatalytic performance can be optimized by constructing complex structures. Among various branched structures, Pt octopods exhibit particularly high activity in formic acid oxidation as compared with their counterparts and commercial Pt/C catalysts. It is anticipated that this work will open a door to design more complex nanostructures and to achieve specific functions for various applications.

Fabrication of Pd/TiO2-multiwall carbon nanotubes catalyst and investigation of its electrocatalytic activity for formic acid oxidation

In this study, a novel Pd/TiO2-MWNTs catalyst is synthesized by a unique chemical method. The pretreated TiO2 nanoparticles are applied as support materials between Pd nanoparticles and functional multiwall carbon nanotubes (MWNTs) template. The morphology and physicochemical properties of the catalysts are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). It is observed that the functional MWNTs are partially covered by TiO2 nanoparticles, and that the metallic Pd nanoparticles are homogeneously deposited onto the TiO2 nanoparticles with smaller sizes compared with those of Pd/MWNTs. The electrocatalytic activity of the Pd/TiO2-MWNTs is investigated by cyclic voltammetry and chronoamperometry measurements in 0.5 M H2SO4 and 1 M HCOOH acidic solution, respectively. Results indicate that the introduction of pretreated TiO2 into the nanocomposite highly improves its electrocatalytic activity, durability, and stability. Thus, the Pd/TiO2-MWNTs catalyst is expected to be an effective electrode material for formic acid oxidation.

Additive-Free Fabrication of Spherical Hollow Palladium/Copper Alloyed Nanostructures for Fuel Cell Application

Herein, through tuning the surface energy difference of the major crystal planes by alloying, hollow palladium/copper alloyed nanostructures are successfully prepared through a one-pot template-free strategy. Compared with the solid PdCu alloyed nanoparticles, the hollow PdCu alloyed nanostructures exhibit the increased accessible electrochemical active surface area and the enhanced electrocatalytic activity for formic acid oxidation. It is concluded that the as-prepared hollow PdCu alloyed nanostructures would be a potential candidate as an anode electrocatalyst in direct formic acid fuel cell. More importantly, the strategy developed in this study might be expanded to fabricate other metal alloyed hollow nanostructures.

New insights into enhanced electrocatalytic performance of carbon supported Pd–Cu catalyst for formic acid oxidation

The direct formic acid fuel cell (DFAFC) has two major shortcomings that limit its lifespan and performance: (i) the poor electrocatalytic stability of the carbon supported Pd (Pd/C) catalyst and (ii) rapid decomposition of formic acid over the Pd/C catalyst. To solve the problems, the carbon-supported Pd–Cu (Pd–Cu/C) catalysts with different atomic ratios of Pd and Cu are successfully prepared with a simple impregnation–reduction method. It is reported for the first time that the electrocatalytic performances of the Pd–Cu/C catalysts for formic acid oxidation are related to the decomposition rate of formic acid over the Pd–Cu/C catalysts. When the content of Cu in the Pd–Cu/C catalysts is gradually increased, the decomposition rate of formic acid over the Pd–Cu/C catalysts is correspondingly decreased, leading to the decrease in the production of poisoned CO. Therefore, the electrocatalytic performances of the Pd–Cu/C catalysts for formic acid oxidation are much better than that of the Pd/C catalyst. However, when the content of Cu in the Pd–Cu/C catalyst is too high, the electrocatalytic performance of the Pd–Cu/C catalyst would be decreased because Cu has no electrocatalytic activity for formic acid oxidation. Based on the above reasons, among all Pd–Cu/C catalysts prepared, the electrocatalytic performance of the Pd–Cu/C catalyst with 3:1 atomic ratio of Pd and Cu for formic acid oxidation is best.

Synthesis of hollow and nanoporous gold/platinum alloy nanoparticles and their electrocatalytic activity for formic acid oxidation

In this work, hollow Au/Pt alloy nanoparticles (NPs) with porous surfaces were synthesized in a two-step procedure. In the first step, tri-component Ag/Au/Pt alloy NPs were synthesized through the galvanic replacement reaction between Ag NPs and aqueous solutions containing a mixture of HAuCl4 and H2PtCl4. In the second step, the Ag component was selectively dealloyed with nitric acid (HNO3), resulting in hollow di-component Au/Pt alloy NPs with a porous surface morphology. The atomic ratio of Au to Pt in the NPs was easily tunable by controlling the molar ratio of the precursor solution (HAuCl4 and H2PtCl6). Hollow, porous Au/Pt alloy NPs showed enhanced catalytic activity toward formic acid electrooxidation compared to the analogous pure Pt NPs. This improved activity can be attributable to the suppression of CO poisoning via the “ensemble” effect.

Palladium nanocrystals enclosed by {100} and {111} facets in controlled proportions and their catalytic activities for formic acid oxidation

This article reports a seed-mediated approach to polyhedral nanocrystals of Pd with controlled sizes, shapes, and different proportions of {100} to {111} facets on the surface. The success of this synthesis relies on the use of Pd nanocubes with different sizes as the seeds and the use of formaldehyde as a relatively mild reducing agent. By controlling the ratio of Pd precursor to the seed, we obtained uniform polyhedrons such as truncated cubes, cuboctahedrons, truncated octahedrons, and octahedrons in a purity approaching 100%. The sizes of these polyhedrons were determined by the edge length of the cubic seeds. Since these Pd polyhedrons were characterized by different proportions of {111} to {100} facets, they could serve as model catalysts to uncover the correlation between the surface structure and the catalytic performance for formic acid oxidation. Our measurements indicate that Pd nanocubes exhibited the highest maximum current density in the forward anodic scan, but the peak position was also located at a potential higher than those of the other polyhedrons. When both the current density and the operation potential are taken into consideration, Pd nanocubes with slight truncation at the corners become the best choice of catalyst for formic acid oxidation. Our study also revealed that the size of Pd polyhedrons had essentially no effect on the activity for formic acid oxidation.

Mesoporous vanadium nitride as a high performance catalyst support for formic acid electrooxidation

Mesoporous vanadium nitride (VN) with high surface area and good electrical conductivity was prepared by a solid-solid phase separation method from a Zn containing vanadium oxide, Zn(3)V(2)O(8). The VN supported Pd catalyst exhibited significant catalytic activity for formic acid oxidation.

Butylphenyl-functionalized Pt nanoparticles as CO-resistant electrocatalysts for formic acid oxidation

Butylphenyl-functionalized Pt nanoparticles (Pt-BP) with an average core diameter of 2.93 ± 0.49 nm were synthesized by the co-reduction of butylphenyl diazonium salt and H(2)PtCl(4). Cyclic voltammetric studies of the Pt-BP nanoparticles showed a much less pronounced hysteresis between the oxidation currents of formic acid in the forward and reverse scans, as compared to that on naked Pt surfaces. Electrochemical in situ FTIR studies confirmed that no adsorbed CO, a poisoning intermediate, was generated on the Pt-BP nanoparticle surface. These results suggest that functionalization of the Pt nanoparticles by butylphenyl fragments effectively blocked the CO poisoning pathway, most probably through third-body effects, and hence led to an apparent improvement of the electrocatalytic activity in formic acid oxidation.

Pt–Au core/shell nanorods: preparation and applications as electrocatalysts for fuel cells

Carbon-supported Pt–Au nanorods with a core/shell structure and excellent oxygen reduction (ORR) activities have been prepared. The Pt shell nanorods exhibit high CO oxidation activity, while the PtAu shell nanorods benefits formic acid oxidation (FAO). The 1-D morphology of the nanorods enhances the electrochemical activity of ORR, FAO and CO oxidation.