Electrocatalysts For Formic Acid Oxidation Research Articles

Copper-enriched palladium-copper alloy nanoparticles for effective electrochemical formic acid oxidation

In this work, Pd-Cu alloy nanoparticles (NPs) with different atomic ratios are prepared on functionalized carbon nanotubes (CNTs) and applied as electrocatalysts for formic acid oxidation. The Cu-enriched Pd-Cu alloy NPs exhibit improved electrocatalytic activity and stability. Functionalized carbon supports are applied as substrates to tune the nanoscale morphologies of the obtained bimetallic phases under appropriate calcination and hydrogenation treatments. Spill-over effect aids a reduction of a high weight loading of Cu in its metallic phase, in turn, these Cu atoms integrate into Pd lattice and isolate Pd neighbouring atoms. Surface analyses show that a certain amount of the isolated Pd remains on the surfaces of Pd-Cu alloy NPs, which is responsible for the enhanced electrocatalytic performance.

Controlled Growth of Pt–Au Alloy Nanowires and Their Performance for Formic Acid Electrooxidation

Pt–Au alloy nanowires have been controllably electrodeposited on microelectrodes by applying an alternating current and were used as the electrocatalyst for formic acid oxidation. The frequency and voltage of the alternating current and the electrolyte composition were adjusted to precisely control the morphologies, alloying structures and composition. The characteristics of Pt–Au alloy nanowires were analyzed by scanning electron microscopy, X-ray diffraction and transmission electron spectroscopy. Electrocatalytic performance of formic acid oxidation at Pt–Au alloy nanowires electrode was investigated by cyclic voltammetry and chronoamperometry. The results showed that the Pt–Au alloy nanowires possessed highly-crystalline morphologies, the controllable bimetallic composition and single-phase alloy structures, which mainly grow in the crystal orientation. The electrocatalytic activity of formic acid oxidation strongly depended on the bimetallic Pt/Au composition. The Pt35Au65 alloy nanowires displayed superior electrocatalytic performance and high stability toward the electrooxidation of formic acid in acidic solution, owing to the ensemble effect of the Pt and Au components. These findings provided insights into the design of the Pt–Au bimetallic nanomaterials as electrocatalysts for formic acid oxidation.

Pd–Cu alloy with hierarchical network structure as enhanced electrocatalysts for formic acid oxidation

Pd–Cu alloy with hierarchical porous network structure is prepared via a facile one-pot hydrothermal reaction, by using a mixed solvent of ethylene glycol and water as the reaction media, and the block copolymer Pluronic P123 as the structure-directing agent. The Pd–Cu alloy networks are constructed by hierarchically assembled nanorods as building blocks. The structure, porosity, surface chemical state and electrochemical properties of as-prepared Pd–Cu alloy are characterized and analyzed. Owing to the superior hierarchical porous network structure, the Pt–Cu alloy catalysts present remarkably enhanced catalytic performance toward formic acid oxidation, in comparison with the commercial Pd black.

A highly active Pd-P nanoparticle electrocatalyst for enhanced formic acid oxidation synthesized via stepwise electroless deposition.

A highly active Pd-P nanoparticle electrocatalyst for formic acid oxidation was synthesized using NaH2PO2 as the reducing agent. The Pd-P nanoparticles were amorphous and exhibited higher specific and mass activity values compared to commercial Pd/C electrocatalyts and reported literature values. Furthermore, the Pd-P nanoparticles were found to be more durable than Pd/C electrocatalyts.

Three-dimensional highly branched Pd3Cu alloy multipods as enhanced electrocatalysts for formic acid oxidation

Pd3Cu alloy multipods with three-dimensional highly branched morphology were synthesized, which presents enhanced catalytic performance toward formic acid oxidation.

3D Graphene Hollow Nanospheres@Palladium‐Networks as an Efficient Electrocatalyst for Formic Acid Oxidation

Graphene has served widely as a support material for noble metal nanoparticle electrocatalysts in fuel cells. During the synthesis of electrocatalysts, however, the intense stacking and folding of graphene nanosheets decreases the utilization and activity of electrocatalysts, owing to the following aspects: i) the noble metal wrapped by the winding graphene cannot be fully utilized; ii) the structural destruction of graphene decreases the specific surface area and increases electrical resistance; and iii) the hydrophobicity and wrinkles of graphene greatly increase the mass transfer resistance of fuel molecules and electrolytes. In this work, 3D graphene oxide hollow nanospheres are designed to minimize wrinkles, maximize specific surface area, and realize the regular clipping of 2D graphene oxide. The 3D‐reduced graphene oxide hollow nanosphere supported Pd‐network nanohybrids (3D‐RGO/Pd‐NWs) are then obtained using 3D graphene oxide hollow nanospheres as a reaction precursor. The skeleton of 3D‐RGO not only acts as an exclusive inner conducting shell to promote electron and ion kinetics but is also crucial for enhancing the permeation of fuel molecules and electrolytes. Therefore, 3D‐RGO/Pd‐NWs exhibit enhanced electrocatalytic activity and durability for the formic oxidation reaction in an acidic medium compared to 2D graphene supported Pd nanoparticles and commercial Pd/C electrocatalysts.

Preparation of Nanoporous Pd by Dealloying Al-Pd Slice and Its Electrocatalysts for Formic Acid Oxidation

AlPd alloy slices with a thickness of 0.5 mm were taken as precursors during the fabrication of nanoporous palladium (np-Pd) using chemical dealloying in NaOH solution or electrochemical dealloying in NaCl solution. Scanning electron microscope photos and x-ray diffraction patterns demonstrate a full dealloying of Al out of the precursors and the formation of nP-Pd which is characterized by a three-dimensional, bicontinuous, ligament-channel structure with nanoscale length scales. Electrochemical measurements were performed to evaluate the electrocatalytic activity and structure stability of np-Pd towards formic acid oxidation and it showed a good structure stability.

Characterization of Au and Bimetallic PtAu Nanoparticles on PDDA-Graphene Sheets as Electrocatalysts for Formic Acid Oxidation.

Nanocomposite materials of the Au nanoparticles (Au/PDDA-G) and the bimetallic PtAu nanoparticles on poly-(diallyldimethylammonium chloride) (PDDA)-modified graphene sheets (PtAu/PDDA-G) were prepared with hydrothermal method at 90 °C for 24 h. The composite materials Au/PDDA-G and PtAu/PDDA-G were evaluated by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) for exploring the structural characterization for the electrochemical catalysis. According to TEM results, the diameter of Au and bimetallic PtAu nanoparticles is about 20–50 and 5–10 nm, respectively. X-ray diffraction (XRD) results indicate that both of PtAu and Au nanoparticles exhibit the crystalline plane of (111), (200), (210), and (311). Furthermore, XRD data also show the 2°–3° difference between pristine graphene sheets and the PDDA-modified graphene sheets. For the catalytic activity tests of Au/PDDA-G and PtAu/PDDA-G, the mixture of 0.5 M aqueous H2SO4 and 0.5 M aqueous formic acid was used as model to evaluate the electrochemical characterizations. The catalytic activities of the novel bimetallic PtAu/graphene electrocatalyst would be anticipated to be superior to the previous electrocatalyst of the cubic Pt/graphene.

Nitrogen-doped carbon-TiO2 composite as support of Pd electrocatalyst for formic acid oxidation

We report Pd nanoparticles supported on a composite consisting of oxide TiO2 and nitrogen-doped carbon for formic acid oxidation (FAO). The nitrogen-doped carbon-TiO2 (NCx-TiO2) composite support was prepared by a simple polymerization-pyrolysis process using commercial TiO2 nanoparticles (P25). Surface analysis showed that elements of Ti, C, O, and N were present on the composite surface, on which nitrogen existed in both pyridinic and quaternary forms. Pd nanoparticles with a mean size of ca. 4 nm were uniformly deposited on the composite via a polyol process. Electrochemical characterizations showed that the NCx-TiO2-supported Pd particles (Pd/NCx-TiO2) exhibited an electrocatalytic activity towards FAO that almost doubled that of the carbon black-supported Pd particles (Pd/C) with much enhanced electrocatalytic stability. The better performance of the composite supported Pd was attributed to a possible electronic structure modification in the metallic Pd particles and bifunctional effect produced by the NCx-TiO2 composite.

Structurally ordered Pt–Zn/C series nanoparticles as efficient anode catalysts for formic acid electrooxidation

Structurally ordered Pt3Zn and PtZn nanoparticles with ultrasmall particle sizes were obtained and exhibited enhanced catalytic activity toward HCOOH electrooxidation.

Towards improving the catalytic activity and stability of platinum-based anodes in direct formic acid fuel cells

The current investigation presents a novel catalyst for formic acid electro-oxidation (FAO); the essential anodic reaction in direct formic acid fuel cells (DFAFCs). The catalyst is developed by a sequential electrodeposition method for Pt (PtNPs), Au (AuNPs) and nickel oxide (nano-NiOx) nanoparticles onto the surface of a glassy carbon (GC) electrode. The objective of this modification was solely dedicated to the improvement of the electrode's catalytic activity by overcoming the CO poisoning, which is usually responsible for the deterioration of the catalytic performance of DFAFCs. The deposition sequence of the catalyst ingredients (PtNPs, AuNPs, and nano-NiOx) was adjusted to optimize the electrocatalytic activity and stability of the catalyst towards FAO. Interestingly, the highest catalytic activity and stability towards FAO was obtained at the NiOx/Au/Pt/GC electrode in which PtNPs were directly deposited onto the GC electrode followed by AuNPs then nano-NiOx. The discussion is oriented to adopt the role of the ternary catalyst ingredients in the catalytic enhancement.

CN x -modified montmorillonite as support to immobilize Pd and its enhanced electrocatalytic activity for formic acid oxidation

Nature clay, i.e., montmorillonite (MMT), can be used as support materials of anode electrocatalyst in the direct formic acid fuel cell. The nitrogen-containing composite support (MMT-CN x ) was prepared via carbonizing MMT which was covered by polyaniline. Pd/MMT-CN x and Pd/C catalysts were prepared as formic acid oxidation catalysts using an improved liquid reduction method. The composite, structure, surface properties, and electrical conductivity of the supports and catalysts were studied by energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electrochemical impedance spectroscopy (EIS). The results showed that well-dispersed Pd nanoparticles with a narrow size distribution of 3.5–5.5 nm could be easily prepared on the MMT-CN x . Larger electrochemical specific area (ECSA) was obtained for Pd/MMT-CN x than Pd/C according to CO-stripping voltammetry. Cyclic voltammetry (CV) and chronoamperometry (CA) measurements showed better catalytic activity and stability of the Pd/MMT-CN x catalyst than the conventional Pd/C catalyst for formic acid electrooxidation. Larger ECSA and doped nitrogen in the support of the Pd/MMT-CN x catalyst may be the main reason of higher activity and better stability for formic acid oxidation compared with the Pd/C catalyst. The results offered potential application of composite support (MMT-CN x ) for the catalyst of the direct formic acid fuel cell.

CeO2 Nanotubes Supported Pd Electrocatalysts for Formic Acid Oxidation

CeO2 nanotubes with well-defined hollow interiors are employed as support material for Pd electrocatalysts towards formic acid oxidation (FAO). Pd nanoparticles are deposited both on the outer surfaces and inside interiors of CeO2 nanotubes. The as-prepared Pd catalysts possess a large electrochemical surface area (ESA) and exhibit improved electrocatalytic performance towards FAO in comparison with the Vulcan XC-72 carbon black and the commercial CeO2 powder supported Pd catalysts.

Impurities Contributing to Catalysis: Enhanced Electro-Oxidation of Formic Acid at Pt/GC Electrodes in the Presence of Vinyl Acetate

Here we demonstrate a remarkable enhancement of the direct formic acid electro-oxidation (FAO) to CO2 (dehydrogenation pathway, Ipd) at Pt nanoparticle-modified GC (nano-Pt/GC) electrodes, in the presence of minute amount (∼ppm) of vinyl acetate (VA), while suppressing the dehydration pathway (producing the poisoning intermediate CO, Ipind). An excellent electrocatalytic activity of the nano-Pt/GC catalyst for FAO was found in the presence of VA (a possible contaminant) as revealed by comparing the intensity of the corresponding two oxidation peaks Ipd and Ipind observed respectively at 0.25 and 0.75 V vs Ag/AgCl/KCl(sat.). The degree of enhancement of Ipd depends on the surface coverage (θ) of VA at Pt nanoparticles. VA is believed to adsorb and consequently interrupt the surface contiguity of the Pt active sites favorable for CO poisoning. XPS measurements revealed a change in the electronic properties of Pt in the presence of VA in such a way that favors the charge transfer during the FAO and/or impedes/weakens the adsorption of the poisoning CO. Interestingly, VA (in ppm concentration) improves the electrode’s stability during FAO and also its catalytic tolerance against poisoning with chloride ions. Several indices were developed to measure the catalytic activity of the electrode in the absence and presence of VA, and several techniques as FE-SEM, XRD, EDX, and XPS were employed in the revelation of the electrode’s morphology, crystal structure, composition, and binding energy.

Enhanced catalytic performance of Pd catalyst for formic acid electrooxidation in ionic liquid aqueous solution

A protic ionic liquid (IL), n-butylammonium nitrate (N4NO3), is prepared and employed as the electrolyte for formic acid electrooxidation reaction (FAOR) on Pd catalysts. The oxidation peak potential of FAOR in the IL solution shows about a 200 mV negative shift as compared with those in traditional H2SO4/HClO4 electrolytes, suggesting that FAOR can be more easily carried out on Pd catalysts in IL media. The catalytic properties of Pd toward FAOR are not only dependent on the concentration of IL, as a consequence of the varied electronic conductivity of the IL solution, but also on the high potential limit of the cyclic voltammograms. When the Pd catalyst is cycled up to 1.0 V (vs. SCE), which induces a significant oxidation of Pd, it shows ca. 4.0 times higher activity than that not subjected to the Pd oxidation (up to 0.6 V). The Pd oxides, which are more easily formed in IL solution than in traditional H2SO4/HClO4 electrolytes, may play a crucial role in increasing the catalytic activities of Pd toward FAOR. Our work would shed new light on the mechanism of FAOR and highlight the potential applications of IL as green and environment-friendly electrolytes in fuel cells and other technologies.

Pd Nanoparticles Supported on PDDA-Functionalized Ti4O7 as an Effective Catalyst for Formic Acid Electrooxidation

Pd catalysts supported on carbon black and Ti4O7 were prepared and used as electrocatalysts for formic acid electrooxidation. The structure and morphology were characterized by XRD and TEM. CV results show that Pd/Ti4O7 possesses a higher catalytic activity than Pd/C. XPS analyzes suggest that the higher content of metallic Pd caused by Ti4O7 contributes to the better catalytic performance. Based on the good electrocatalytic performance of Pd/Ti4O7, Pd catalyst supported on PDDA-functionalized Ti4O7 was prepared and exhibited a better catalytic activity. The improvement results from the further increase of metallic Pd content due to the presence of PDDA. (C) 2014 The Electrochemical Society. All rights reserved.

Enhanced electrocatalytic activity and stability of platinum, gold, and nickel oxide nanoparticles-based ternary catalyst for formic acid electro-oxidation

The global interest to realize and commercialize the direct formic acid fuel cells has motivated the development of efficient and stable anodes for the formic acid (FA) electro-oxidation (FAO). In this investigation, a ternary catalyst composed of Pt nanoparticles (PtNPs), Au nanoparticles (AuNPs) and nickel oxide nanoparticles (nano-NiOx), all were sequentially electrodeposited onto the surface of a glassy carbon (GC) electrode, was recommended for this reaction. The surface morphology investigation revealed the deposition of grain-shaped PtNPs (25 nm average particle size), and flower-shaped nanospheres (less than 60 nm average particle size) of AuNPs and nano-NiOx. Interestingly, the ternary modified NiOx-Au-Pt/GC electrode has shown an outstanding electrocatalytic activity towards the direct FAO, concurrently with a complete suppression for the indirect route. It further exhibited excellent stability that extended for 7 h of continuous electrolysis. While PtNPs furnished a suitable base for FA adsorption, AuNPs played a significant role to interrupt the contiguity of the Pt surface sites, which is necessary for CO poisoning. On the other hand, nano-NiOx acted as a catalytic mediator facilitating the charge transfer of FAO and the oxidative removal of CO at a lower potential.

In-situ electrochemical extended X-ray absorption fine structure spectroscopy study on the reactivation of Pd electrocatalyst in formic acid oxidation

Palladium (Pd) has been considered as an excellent option to replace platinum-based electrocatalysts in formic acid oxidation owing to its superb catalytic activity to Pt and cheaper material price. However, unstable catalytic activity of Pd is the most critical obstacle in the development of Pd-based electrocatalysts for formic acid oxidation, and the fundamental understanding on Pd deactivation is still incomplete. In this study, the activity of deactivated Pd in a formic acid oxidation was recovered to 93% by applying a cathodic bias potential of -0.2V vs. RHE. Based on in-situ electrochemical extended X-ray absorption fine structure spectroscopy analysis we show that cathodic polarization of Pd/C electrode could remove the adsorption of poisoning species by increasing bond length of Pd-Pd and further discuss on the origin of reactivation mechanism of Pd.

WO3 modification effects on Pt–Pd/WO3-OMC electrocatalysts for formic acid oxidation

This manuscript presents an experimental investigation of the promotional effects of WO3 on Pt/Pd/WO3-OMC electrocatalysts for oxidation of formic acid. Cyclic voltametry of Pd/WO 3-OMC exhibits 15% higher anodic current activity than that of Pd/OMC. The peak potential is also shifted more than 151mV in the negative direction. In the bimetallic catalyst samples, the addition of a small amount of Pt improves the performance of PdPt/WO3-OMC significantly. The atomic Pd/Pt ratio of 2, displays the best current density (56.8mA/cm2), which is 1.2, 1.65 and 5.2 times higher than that of Pd/WO3-OMC, Pd1Pt1/WO3-OMC and Pd1Pt2/WO3-OMC, respectively. It also shows activity over an extended duration without any indication of CO poisoning effects. N2 adsorption/desorption analysis shows that WO3 modification enhances the surface characteristics of OMC with the pore size being slightly decreased from 3.84nm to3.28nm. Scanning electron microscopy, x-ray diffraction, transmission electron microscopy analyses reveal that the presence of WO3 enhances the uniform dispersion of active metal(s) on the support surface which is primarily believed to be responsible for superior activity/stability of the Pd2Pt1/WO3-OMC.

Novel palladium flower-like nanostructured networks for electrocatalytic oxidation of formic acid

Novel Pd flower-like nanostructured networks are synthesized via a simple CO-assisted reduction. The morphology and size of the Pd nanostructures are found to strongly depend on the temperature and solvent during the synthesis process. Such Pd flower-like nanostructured networks exhibit a much enhanced activity of about 3 times of that on conventional Pd nanoparticles towards the electrocatalytic oxidation of formic acid. The specific activity of formic acid oxidation on Pd nanostructures is also greatly improved, indicating that the formation of flower-like nanostructured networks is beneficial for the electrooxidation of formic acid. Thus, it could be served as highly active catalyst for formic acid electrooxidation although the stability needs to be greatly improved.