Electrocatalysts For Formic Acid Oxidation Research Articles

Graphene ribbon-supported Pd nanoparticles as highly durable, efficient electrocatalysts for formic acid oxidation

Graphene ribbon-supported Pd nanoparticles (Pd/GR) have been prepared by a simple, clean process in aqueous medium, involving only a Pd precursor and graphene ribbon (GR) as both a reducing agent and a catalyst support. A high density of Pd nanoparticles with a small average particle size (∼2.8±0.8nm) could be successfully deposited on graphene ribbons. The as-obtained Pd/GR electrocatalysts show increased electrochemical surface area and significantly enhanced catalytic activity for formic acid oxidation reaction (FAOR) compared to the conventional Pd/C electrocatalysts in terms of peak current density (1.4Amg−1 vs. 0.79Amg−1) and peak potential (−0.15V shift). Both the good dispersion and the relatively small particle size of the Pd nanoparticles on graphene ribbon and the synergetic effect between Pd and GR lead to high initial catalytic activity for FAOR. More importantly, a dramatic enhancement in durability is found with Pd/GR for FAOR due to the strong interaction between Pd and GR.

Efficient anchorage of highly dispersed and ultrafine palladium nanoparticles on the water-soluble phosphonate functionalized multiwall carbon nanotubes

A facile noncovalent approach is proposed to graft phosphonate groups onto the surface of the multiwall carbon nanotubes (MWCNTs) by π–π stacking interaction between naphthalen-1-ylmethylphosphonic acid (NYPA) and MWCNTs. Noncovalently attachment of phosphonate groups on the MWCNTs surface is confirmed by Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and zeta potential analysis. The water-soluble phosphonate functionalized MWCNTs are further deposited with Pd nanoparticles (Pd-NPs) as electrocatalyst for formic acid oxidation. The morphology and structure of Pd-MWCNTs nanocomposites are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and XPS measurements. It is observed that Pd-NPs are highly dispersed and effectively anchored on the side walls of the phosphonate functionalized MWCNTs. The Pd-MWCNTs nanocomposites exhibit better electrocatalytic activity and long-term stability for formic acid electrooxidation than the un-phosphonated counterpart.

Natural DNA-Modified Graphene/Pd Nanoparticles as Highly Active Catalyst for Formic Acid Electro-Oxidation and for the Suzuki Reaction

Natural DNA has been considered as a building block for developing novel functional materials. It is abundant, renewable, and biodegradable and has a well-defined structure and conformation with many unique features, which are difficult to find in other polymers. Herein, calf thymus DNA modified graphene/Pd nanoparticle (DNA-G-Pd) hybrid materials are constructed for the first time using DNA as a mediator, and the prepared DNA-G-Pd hybrid shows high catalytic activity for fuel cell formic acid electro-oxidation and for organic Suzuki reaction. The main advantages of using DNA are not only because the aromatic nucleobases in DNA can interact through π-π stacking with graphene basal surface but also because they can chelate Pd via dative bonding in such defined sites along the DNA lattice. Our results indicate that isolated, homogeneous, and ultrafine spherical Pd nanoparticles are densely in situ decorated on DNA-modified graphene surfaces with high stability and dispersibility. The prepared DNA-G-Pd hybrid has much greater activity and durability for formic acid electro-oxidation than the commercial Pd/C catalyst and polyvinylpyrrolidone-mediated graphene/Pd nanoparticle (PVP-G-Pd) hybrid used for direct formic acid fuel cells (DFAFCs). Besides, the DNA-G-Pd hybrid can also be an efficient and recyclable catalyst for the organic Suzuki reaction in aqueous solution under aerobic conditions without any preactivation. Since DNA can chelate various transition metal cations, this proof-of-concept protocol provides the possibility for the tailored design of other novel catalytic materials based on graphene with full exploitation of their properties.

Titanium compounds TiC–C and TiO2–C supported Pd catalysts for formic acid electrooxidation

In this work, Pd nanoparticles supported on TiC–C and TiO2–C as novel and efficient supports for formic acid electrooxidation are investigated. The Pd/TiC–C and Pd/TiO2–C catalysts have been synthesized by microwave-assisted polyol process. The Pd nanoparticles in the Pd/TiC–C and Pd/TiO2–C catalysts are found to disperse more uniformly and have smaller sizes on the TiC–C and TiO2–C supports than that on carbon support alone. The addition of titanium compounds (TiC and TiO2) significantly increases catalytic activity and stability of Pd for formic acid electrooxidation because of outstanding oxidation and acid corrosion resistance of titanium compounds (TiC and TiO2), and metal-support interaction between Pd nanoparticles and titanium compound (TiC or TiO2). The Pd/TiC–C catalyst displays the best performance among all the samples. The effect of TiC:C mass ratio on the catalytic activity is also investigated. It is found that the maximal catalytic activity and stability for formic acid electrooxidation is observed at the Pd/TiC–C catalyst with TiC:C mass ratio of 1:2.

Shape- and Composition-Sensitive Activity of Pt and PtAu Catalysts for Formic Acid Electrooxidation

In this work, we have probed the shape- and composition-dependent activities of Pt and PtAu catalysts for formic acid electrooxidation. Pt-based hollow nanostructures such as Pt hollow nanospheres (Pt HNSs), Pt nanotubes (Pt NTs), and PtAu alloy nanotubes (PtAu NTs) with controlled Pt:Au compositions are successfully prepared via a galvanic replacement process using sacrificial Ag templates. The physicochemical properties of these Pt and PtAu catalysts are confirmed by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy techniques. The electrochemical activities of these hollow structured catalysts are compared for formic acid oxidation by cyclic voltammetry and chronoamperometry methods. Relative to the commercial Pt black and Pt/C nanoparticle catalysts, the hollow nanostructured Pt materials (Pt HNS, Pt NT) exhibit enhanced catalytic activities due to structural effects. Moreover, the bimetallic PtAu NT series shows improved catalytic activities over the monometallic Pt catalysts due to compositional effects. The present study demonstrates that the catalytic activity and the extent of surface poisoning are strongly dependent on both the structural and compositional variations of the nanostructured electrocatalysts, as shown by a systemically prepared series of nanostructured catalysts for formic acid oxidation.

Formic acid electrooxidation over carbon-supported nanoparticles of non-stoichiometric palladium carbide

Catalytic performance of the 5 wt.% Pd/C and 5 wt.% PdC0.14/C catalysts for formic acid electrooxidation was compared under potentiodynamic (0.06–1.0 V vs. RHE, sweep rate 50 mV s−1) and potentiostatic (0.2 and 0.3 V vs. RHE) regimes in 0.5 M HCOOH + 0.1 M H2SO4 solution at 25 °C. The non-stoichiometric palladium carbide catalyst demonstrates superior catalytic performance and stability during HCOOH electrooxidation as compared to the unmodified Pd/C precursor. The observed phenomenon is explained in terms of modification of electronic and adsorption properties of palladium caused by the embedding of carbon atoms in the interstitial cites of the crystalline lattice of Pd nanoparticles.

Three-dimensional cubic ordered mesoporous carbon (CMK-8) as highly efficient stable Pd electro-catalyst support for formic acid oxidation

In this work, Pd nanoparticles were supported on two types of three-dimensional cubic highly ordered mesoporous carbon (CMK-8) by the sodium borohydride reduction method and the activity of the Pd/CMK-8 electro-catalysts towards formic acid oxidation was evaluated and compared with that of commercial Pd/C (E-TEK) catalyst. The catalysts were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), cyclic voltammetry, and chronoamperometry. Cyclic voltammetry revealed Pd/CMK-8 with larger pores as being the most electroactive with a mass specific activity (mAmgPd−1) of 486.4 that exceeded not only that of the Pd/C (E-TEK) (386.5mAmgPd−1) but also that of recently reported Pd/CNT (200mAmgPd−1), Pd/Graphene (210mAmgPd−1) and Pd/Vulcan XC 72 (193mAmgPd−1). As demonstrated with chronoamperometry, the larger pore Pd/CMK-8 also proved to be the most stable catalyst. This exceptional performance can be ascribed to the very high surface area and Ia3d symmetry that yields a relatively isotropic graphitized structure with a high conductivity. In addition, the open framework of the 3-D bicontinous channels and highly ordered mesopores allows for an advanced mass transfer characteristics. The results show that CMK-8 support would significantly improve the power output and stability of Pd-based electro-catalysts for formic acid oxidation.

Highly Active Pt3Pb and Core–Shell Pt3Pb–Pt Electrocatalysts for Formic Acid Oxidation

Formic acid is a promising chemical fuel for fuel cell applications. However, due to the dominance of the indirect reaction pathway and strong poisoning effects, the development of direct formic acid fuel cells has been impeded by the low activity of existing electrocatalysts at desirable operating voltage. We report the first synthesis of Pt(3)Pb nanocrystals through solution phase synthesis and show they are highly efficient formic acid oxidation electrocatalysts. The activity can be further improved by manipulating the Pt(3)Pb-Pt core-shell structure. Combined experimental and theoretical studies suggest that the high activity from Pt(3)Pb and the Pt-Pb core-shell nanocrystals results from the elimination of CO poisoning and decreased barriers for the dehydrogenation steps. Therefore, the Pt(3)Pb and Pt-Pb core-shell nanocrystals can improve the performance of direct formic acid fuel cells at desired operating voltage to enable their practical application.

Facile electrochemical codeposition of “clean” graphene–Pd nanocomposite as an anode catalyst for formic acid electrooxidation

Highly dispersed Pd nanoparticles (NPs) supported on graphene were successfully prepared by a one-step electrochemical codeposition approach. The as-obtained nanocomposite was very “clean” as a result of the reductant-free and surfactant-free synthesis process. The catalyst remarkably improved the electrocatalytic performance for formic acid oxidation (FAO). This facile and controllable method is of significance for the preparation of graphene–metal NPs with desirable catalytic performance.

Controllable synthesis of carbon nanofiber supported Pd catalyst for formic acid electrooxidation

Carbon nanofiber (CNF) supported Pd nanoparticles are synthesized with sodium citrate and sodium borohydride served as stabilizing agent and reducing agent, respectively. The size and distribution of the supported Pd nanoparticles are controlled by adjusting the pH value of the synthesis solution. Analyses of the obtained Pd/CNF catalysts indicate that the supported Pd nanoparticles become more uniform in size and the average particle size is decreased from 5.85 to 3.62 nm with pH value of the synthesis solution increasing from 3.2 to 6.0. However, the further increasing of the pH value to 6.5 leads to an increased particle size and the formation of PdO phase in the synthesized Pd/CNF catalyst. The Pd/CNF catalyst synthesized at the pH value of 6.0 exhibits superior catalytic activity and stability for formic acid electrooxidation due to its small particle size and uniform size distribution.

Electrocatalytic properties of PdCeOx/C anodic catalyst for formic acid electrooxidation

The PdCeOx/C catalyst was prepared and studied as anodic catalyst for formic acid electrooxidation. The morphology, composition and electrocatalytic properties were investigated by transmission electronmicroscopy, energy dispersive X-ray analysis, X-ray diffraction, X-ray photoelectron spectroscopy, the linear sweep voltammetry and chronoamperometry, respectively. The average particle size of Pd nanoparticles for PdCeOx/C catalyst was about 3.4 nm with a narrow size distribution. The electrochemical surface area (ESA) of PdCeOx/C catalyst was larger than the Pd/C catalyst. According to the Tafel plots, the presence of CeOx in the Pd/C catalyst can accelerate the rate of formic acid electrooxidation. The electrochemical measurements showed that the PdCeOx/C catalyst exhibited excellent catalytic activity and stability. For example, the peak current of PdCeOx/C catalyst for formic acid oxidation was about 1.67 times of the Pd/C catalyst and the stable current at 3600 s of PdCeOx/C catalyst was about 7 times of the Pd/C catalyst. The promotion effect should be attributed to the larger ESA, the electronic effect and more oxygen-containing species provided by the CeOx and this catalyst may be used as an effective catalyst for direct formic acid fuel cell.

Preparation of TiO2-Nanorods Supported Pd Catalyst and Its Electrocatalytic Oxidation on Formic Acid

TiO 2 nanorods (TiO2-R) and irregular TiO2 (TiO2-I) with anatase phase structure are synthesized by hydrothermal synthesis and inorganic sol gel method, respectively. Using as-prepared TiO2 as support, Pd/TiO2 catalysts are prepared by using sodium ethylenediamine tetracetate (EDTA) as complexing agent and NaBH4 as reductant. The studies of transmission electron microscopy (TEM) and X-ray diffraction (XRD) reveal that the average particle size of Pd/TiO2-R catalyst is very similar to that of Pd/TiO2-I catalyst. Cyclic voltammetry measurements show that the peak current of formic acid oxidation at Pd/TiO2-R catalyst increases by 70%. Chronoamperometric measurements indicate that the current density at the Pd/TiO2-R catalyst electrode at 3000 s is almost 16 times larger than that at the Pd/TiO2-I catalyst electrode. These electrochemical experiments show that the electrocatalytic activity and long-term operation stability of Pd/TiO2-R catalyst are much better than that of Pd/TiO2-I catalyst for formic acid oxidation in acidic media, indicating that TiO2 nanorods support material can effectively promote the electrocatalytic activity and sta- bility of Pd catalyst for formic acid electrooxidation. Likely, TiO2 nanorods possess good electronic conduc- tivity and abundant surface oxygen-containing groups, which improve the electrocatalytic activity and the anti-poisoned performance of Pd catalyst for the formic acid electrooxidation. Thus, TiO2 nanorods with

Preparation of Polypyrrole-Carbon Black Supported Pd Catalyst for Formic Acid Electrooxidation

Preparation of Polypyrrole-Carbon Black Supported Pd Catalyst for Formic Acid Electrooxidation

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.

Electrocatalytic reduction of carbon dioxide on platinum single crystal electrodes modified with adsorbed adatoms

Platinum single crystal electrodes, Pt(hkl), represent ideal materials where studying the effect of adatoms presence in surface sensitive reactions such as carbon dioxide reduction and formic acid oxidation. In particular, we study here if some of the platinum single crystal electrodes modified with adsorbed adatoms already reported as highly active electrocatalysts for formic acid oxidation can act as bifunctional electrocatalysts and present high activity for CO2 reduction as well. After testing 12 different modified platinum single crystal electrodes, we proved by cyclic voltammetry that only Bi–Pt(111), Te–Pt(111), and Sb–Pt(100) electrodes show a significant current increase in the presence of CO2 in neutral bicarbonate buffer solution. Thus, we demonstrate their behavior as active bifunctional electrocatalysts for carbon dioxide reduction and formic acid oxidation reactions. Moreover, we provide the voltammetric fingerprint for several Bi-, Se-, Te, and Sb–Pt(hkl) electrodes in both, acid and neutral aqueous solution.

Electrocatalytic properties of Pd/C catalyst for formic acid electrooxidation promoted by europium oxide

It is found that the electrocatalytic activity and stability of Pd/C nanocatalyst for formic acid electrooxidation are enhanced by the introduction of EuOx. The morphology, composition and electrocatalytic properties of the PdEuOx/C catalyst are investigated by the transmission electronmicroscopy, energy dispersive X-ray analysis, X-ray diffraction, the linear sweep voltammetry and chronoamperometry, respectively. The EDX results confirm the existence of EuOx in the PdEuOx/C catalysts. The XRD results indicate that the Pd is in the state of face-centered cubic phase structure. The linear sweeping voltammetry and chronoamperometry measurements show that the current of formic acid electrooxidation on the PdEuOx/C catalyst is ca. 2.5 times and 9 times as high as that of the home-made Pd/C catalyst, respectively; moreover, the performances are also much higher than the commercial Pd/C catalyst. The high performances can be attributed to the larger electrochemical surface area and the electronic effect of the EuOx in the PdEuOx/C catalyst.

Highly Active and Stable Carbon Supported PtBi Catalyst for Formic Acid Electrooxidation

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Nanostructured PdRu/C catalysts for formic acid oxidation

Pd and bimetallic PdRu nanoparticles supported on Vulcan XC-72 carbon prepared by the microwave-assisted polyol process are examined as electrocatalysts for the electrooxidation of formic acid. The catalysts are characterized by transmission electron microscopy and X-ray diffraction. The Pd and PdRu nanoparticles with sizes of <10 nm display the characteristic diffraction peaks of a Pd face-centered cubic (fcc) crystal structure. It is found that the addition of Ru to Pd/C can decrease the lattice parameter of Pd (fcc) crystal. The electrocatalytic activities of the catalysts are evaluated in sulfuric acid solution containing 1 M formic acid using linear sweeping voltammetry and chronoamperometry. The results show that Pd5Ru1/C displays the best electrocatalytic performance among all catalysts for formic acid electrooxidation.

Effect of pH Value and Temperatures on Performances of Pd/C Catalysts Prepared by Modified Polyol Process for Formic Acid Electrooxidation

AbstractThe highly active Pd/C catalysts for formic acid electrooxidation have been prepared by a modified polyol process at different pH values of reaction solutions and different reducing temperatures, respectively. Their physical properties have been characterised by energy dispersive analysis of X‐ray, X‐ray diffraction and transmission electron microscopy. Their electrochemical performances for formic acid electrooxidation have been tested by cyclic voltammetry and amperometric i–t curves. The results of physical characterisations show that all the Pd/C catalysts present an excellent face centered cubic crystalline structure. Their particle sizes are decreasing firstly and then increasing with the increasing of the pH values of reaction solutions. The reducing temperatures also markedly affect the Pd particle sizes. And their nanoparticles have narrow size distributions and are highly dispersed on the surface of carbon support, and Pd metal loading in Pd/C catalyst is similar to the theoretical value of 20 wt.%. The results of electrochemical measurements present that the Pd/C catalyst prepared by waterless polyol process at the pH value of 10 and the reducing temperature of 120 °C has the smallest particle size of about 5.6 nm, and exhibits the highest catalytic activity (1172.0 A · gPd&lt;?h‐2.85&gt;–1&lt;?h.8&gt;) and stability for formic acid electrooxidation.

Effect of deposition sequences on electrocatalytic properties of PtPd/C catalysts for formic acid electrooxidation

Abstract PtPd/C catalysts with different surface compositions (Pt + Pd, Pt–Pd and Pd–Pt) were synthesized with different deposition sequences, and characterized by electrochemical experiments and XPS measurements. The different catalytic characteristics for formic acid electrooxidation occurred on the three PtPd/C catalysts were preliminarily discussed according to the oxidation pathway. Due to the synergistic effect between Pt and Pd, especially for Pt + Pd, the catalytic stability for formic acid oxidation was greatly increased. The results are helpful in preparing of PtPd catalyst and understanding the oxidation mechanism for formic acid oxidation.