Stability For Formic Acid Oxidation Research Articles

Improving the electrochemical oxidation of formic acid by tuning the electronic properties of Pd-based bimetallic nanoparticles

Pd-based bimetallic nanoparticles have superior electrochemical activity and stability for formic acid oxidation (FAO) than pure Pd. Previous DFT-based calculations show that the catalytic properties of the Pd surface could be altered by modifying its electronic properties. However, only a few experimental studies investigate how the electronic properties of Pd are modified by introducing various metals and how the resulting electronic perturbation affects its electrochemical activity and stability for FAO. Here, we demonstrate a correlation between electrochemistry and electronic properties for Pd-M bimetallic nanoparticles (M = Ru, Pt, Cu, Au, and Ag). The volcano shape relationship obtained between activity and d-band center values suggests that the electronic effects play a major role in modifying the surface electrochemical properties of Pd-M bimetallic nanoparticles for FAO. Among all the bimetallic catalysts investigated in this study, Pd-Pt/C and Pd-Cu/C with d-band center values of 2.58 eV and 2.85 eV, respectively, demonstrate the highest activities and Pd-Cu/C exhibits the highest stability for FAO.

Facile fabrication of stable PdCu clusters uniformly decorated on graphene as an efficient electrocatalyst for formic acid oxidation

Small-sized nanocrystals uniformly distributed on suitable supports are promising as active electrocatalysts due to their unique electronic structure and high accessible surface area. Herein, we report the synthesis of graphene supported PdCu nanoclusters with a uniform size of 2.3 nm via a facile one-pot solvothermal method. This nanohybrid exhibits much higher inherent catalytic activity and stability for formic acid oxidation in comparison to graphene supported Pd clusters and commercial Pd/C. The PdCu nanoclusters can maintain their original size and dispersity on graphene even after 200 CV cycles. This work offers an efficient low Pd-loading catalyst for formic acid oxidation, and the synthetic approach is of significance to preparing uniform metal-based clusters decorated on supports with superior catalytic properties for fuel cells and sensors.

Cu3PdN nanocrystals electrocatalyst for formic acid oxidation

We report a hot-injection method to fabricate monodispersed Cu3PdN nanoparticles (NPs). The crystal structure, morphology, and chemical composition of the as-synthesized Cu3PdN have been characterized by X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy. The as-developed Cu3PdN NPs electrocatalysts show improved activity and enhanced stability for formic acid oxidation compared with the corresponding Pd and Cu3Pd NPs.

Supportless, Bismuth-Modified Palladium Nanotubes with Improved Activity and Stability for Formic Acid Oxidation

Palladium nanotubes (PdNTs) were synthesized by templated vapor deposition and investigated for formic acid electrooxidation. Annealed PdNTs are 2.4 times more active (2.19 mA/cm2) than commercial carbon-supported palladium (0.91 mA/cm2) at 0.3 V vs RHE. Bismuth modification improved nanotube performance over 4 times (3.75 mA/cm2) vs Pd/C and nearly 2 times vs unmodified PdNTs. A surface Bi coverage of 80% results in optimal site-specific activity by drastically reducing surface-poisoning CO generation during formic acid electrooxidation. The Bi-modified PdNTs are exceptionally stable, maintaining 2 times the area-normalized current density as Pd/C after 24 h at 0.2 V vs RHE. We attribute the enhanced activity and stability of the nanotube catalysts to the presence of highly coordinated surfaces, mimicking a flat polycrystal while retaining high surface area geometry.

Synthesis and characterizations of palladium catalysts with high activity and stability for formic acid oxidation by hydrogen reduction in ethylene glycol at room temperature

In this work, a Pd/C catalyst with high activity as well as excellent stability has been prepared by hydrogen gas reduction of Pd(II) precursor in ethylene glycol solution with the assistance of appropriate amount of sodium citrate. Pd nanoparticles with an average particle size of 3.8 nm and excellent uniformity are obtained. The Pd/C catalyst synthesized in this work shows an electrochemical surface area of 68.6 m2 g−1 and displays activities of 819 A g−1. Strikingly, the Pd/C catalyst also exhibits excellent stability, which has been confirmed by its slow activity decay under repeated potential cycles as well as chronoamperometric test. The activity for Pd/C at the 300th and 500th cycle remains at 5.5 and 2.4 mA cm−2, respectively, which is 25% and 11% of its initial value, respectively. The oxidation currents at the Pd/C and Pd/C-Citrate (control) at 0 V decrease to 44% and 25% of their initial values. Transmission electron microscopy observations on the Pd/C catalyst after 1000 potential cycles reveal that, in addition to carbon support corrosion, Pd agglomeration together with more serious Pd dissolution occur at the same time, leading to a decrease of the electrocatalytic performance.

Insight into electrocatalytic stability of low loading Pt-Bi/GC and Pt/GC clusters in formic acid oxidation

Formic acid oxidation was examined on platinum-bismuth deposits on glassy carbon substrate prepared by two-step process, i.e., electrochemical deposition of Bi followed by electrochemical deposition of Pt as described in our previous article (J Electrochem Soc 161:H547–H554, 2014). Upon treatment of as-prepared clusters by slow anodic sweep, bimetallic structure consisting of Bi core occluded by Pt and Bi-oxide was obtained and exhibited significant activity and exceptional stability in HCOOH oxidation. In order to explain such electrocatalytic stability, in this work, the electrochemical properties of Pt@Bi/GC catalyst were investigated applying same protocols in supporting electrolyte with or without HCOOH and compared with Pt/GC. The protocols comprised potentiodynamic, quasi-steady-state, and chronoamperometric measurements combined with the surface characterization by COads stripping voltammetry. Application of potential cycling at Pt@Bi/GC electrode in supporting electrolyte containing HCOOH leads to minor change in surface morphology, mildly leaching of Bi from the electrode surface, and negligible decrease in activity. On the other hand, significant Bi dissolution and considerable decrease in activity are the effects of the same treatment without HCOOH. Contrary to Pt@Bi/GC, Pt/GC electrodes subjected to the same protocols exhibit completely opposite properties being more stabile during potential cycling without HCOOH than in the presence of this acid. Exceptional stability in formic acid oxidation of Pt@Bi/GC catalyst is thus most probably the result of the combination of predominant dehydrogenation path of the reaction, suppressed Bi leaching, and compensation of dissolved Bi from the core as its source due to which surface morphology endured minor changes.

Facile synthesis of PdNi nanowire networks supported on reduced graphene oxide with enhanced catalytic performance for formic acid oxidation

The as-prepared PdNi nanowire networks/RGO catalysts exhibited efficiently the electrocatalytic activity and stability for formic acid oxidation.

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.

Formic acid electrooxidation catalyzed by Pd/SmOx-C hybrid catalyst in fuel cells

Pd nanoparticles supported on Samarium oxide modified carbon (SmOx/C) hybrid support for the electrooxidation of formic acid is studied. The morphology, composition and electrocatalytic properties are investigated by physical characterization and electrochemical measurements. The results demonstrate that Pd/SmOx-C catalyst has excellent catalytic activity and stability for formic acid oxidation. The current density is about 1.32 times that of the Pd/C catalyst. The electronic effect and oxygen-containing species provided by SmOx accelerate the rate of formic acid electrooxidation. When integrated into the anode of a direct formic acid fuel cell, the maximum power density of 167mWcm−2 is obtained, which is about 1.4 times that of a commercial Pd/C catalyst.

Synthesis of Cu@Pd core-shell nanowires with enhanced activity and stability for formic acid oxidation

A core-shell Cu@Pd nanowire with enhanced activity and stability for formic acid oxidation (FAO) was prepared by decorating Pd shell on the surface of Cu nanowire. Detailed characterization (XRD, TEM and HAADF-STEM) results confirm that the prepared nanowires are of Cu@Pd core-shell structure with enlarged surface areas. The catalytic activity of Cu@Pd/C (2197.88mA/mg at 0.257V) toward FAO is about 4 times higher than that of the commercial Pd/C (547mA/mg at 0.257V). The enhanced activity of the catalyst may mainly result from the synergetic effect of Cu and Pd, which was confirmed by density-functional theory (DFT) calculations.

PdM nanoparticles (M = Ni, Co, Fe, Mn) with high activity and stability in formic acid oxidation synthesized by sonochemical reactions

Bimetallic alloy PdnM (n = 1 for M = Mn, Fe, and Co; n = 1, 2, and 3 for M = Ni) nanoparticles (NPs) are synthesized on carbon supports by sonochemical reactions of Pd(acac)2 (acac = acetylacetonate) with M(acac)2 (M = Ni, Co, Mn) or Fe(acac)3 in ethylene glycol. The NPs are characterized by powder X-ray diffractometry, transmission electron microscopy (TEM), and inductively coupled plasma-atomic emission spectroscopy to determine their crystal structures, particle sizes, morphology, and elemental compositions. Alloy formation of the NPs is proven by energy dispersive X-ray spectroscopy line profiles using scanning TEM. The electronic structures and the surface compositions of NPs are analyzed using X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy, respectively. PdnM NPs are applied as electrocatalysts for formic acid oxidation. The incorporation of M in Pd reduces the poisoning by surface hydroxyl groups. Activities based on the current densities are in the order of PdNi > PdFe > PdCo > PdMn. Within the PdnNi series, the activity is in the order of PdNi > Pd2Ni > Pd3Ni. The PdnM NP electrocatalysts show higher activity by a factor of 2–3.5 and improved durability than similarly prepared Pd NP electrocatalyst.

Preparation of Carbon Nanotubes Supported Pd-Au Catalyst and Their Electrocatalytic Activity for Formic Acid Oxidation

Naphthalen-1-ylmethylphosphonic acid was modified on multiwall carbon nanotube( MWCNT) by the π-π stacking interaction. Then,the Pd catalyst was supported on it. Furthermore,the MWCNT supported Pd-Au( Pd-Au/MWCNT) catalyst was facially prepared by the replacement reaction between Pd nanoparticles and HAuCl 4. Transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy measurements showed that non-alloyed Pd-Au nanoparticles were highly dispersed on the surface of MWCNT. Cyclic voltammetry and chronoamperometric measurements indicated that the Pd-Au/MWCNT catalyst exhibited better electrocatalytic activity and stability for formic acid oxidation than that of the Pd/MWCNT catalyst.

Multi-generation overgrowth induced synthesis of three-dimensional highly branched palladium tetrapods and their electrocatalytic activity for formic acid oxidation

Highly branched noble metal nanostructures are highly attractive for catalytic applications owing to their specific physical and chemical properties. In this work, three-dimensional highly branched palladium tetrapods (Pd-THBTs) have been constructed in the presence of polyvinylpyrrolidone (PVP) through one-step hydrothermal reduction of ethylenediamine-tetramethylene phosphonate-palladium(II) (EDTMP-Pd(II)) by formaldehyde. The morphology and structure of the Pd-THBTs were fully characterized and the growth mechanism was explored and discussed based on the experimental observation. The concave Pd tetrahedra grew into highly branched Pd tetrapods consisting of four nanothorn-like branches with tetrahedral dimensions through interesting multi-generation nanocrystal overgrowth. The electrocatalytic activities of the as-synthesized Pd-THBTs toward formic acid oxidation were also studied by cyclic voltammetry and chronoamperometry. The Pd-THBTs showed higher catalytic activity and stability for formic acid oxidation than the commercial Pd black.

Effects of additives on palladium nanocrystals supported on multiwalled carbon nanotubes and their electrocatalytic properties toward formic acid oxidation

Carbon nanotubes are believed to be powerful materials for constructing novel hybrid composites with desirable functionalities and applications in many fields. Therefore, a better understanding of the functionalization of multiwalled carbon nanotubes (MWCNTs) holds the key to a better performance of the hybrid properties. In this paper, with a series of aromatic bifunctional molecule additives, modified MWCNTs were used as composite supports for synthesizing nanostructured palladium catalysts for formic acid oxidation. The additives contain anthranilic acid, o-phenylenediamine, salicylic acid, catechol, and phthalic acid. The influence of the different bifunctional groups (such as –NH2, –OH, –COOH, and their mixed groups) on the morphologies, particle sizes, and electrical properties of Pd nanocrystals was intensively studied. Transmission electron microscopy measurement demonstrates that the palladium nanoparticles were well dispersed on the surface of MWCNTs with a relatively narrow particle size distribution in the presence of the additives. Cyclic voltammetry and chronoamperometry tests demonstrate that the functional groups of the additives play an important role in electrocatalytic activity and stability for formic acid oxidation, and the influence law of various functional groups on electrocatalytic activity and stability is also investigated in this paper. We hope it can provide certain theoretical guidance meaning and practical reference value in future studies.

High Activity and Stability of Pt2Bi Catalyst in Formic Acid Oxidation

Formic acid oxidation was studied on a new prepared Pt2Bi characterized by X-ray diffraction spectroscopy (phase composition), scanning tunneling microscopy (STM) (surface morphology), and COads stripping voltammetry (surface composition). Bulk composition of Pt2Bi revealed two phases—55% PtBi alloy and 45% Pt. Estimated contribution of pure Pt on the Pt2Bi surface (43.5%) determined by COads stripping voltammetry corresponds closely to bulk composition. Pt2Bi reveals high activity and stability in formic acid oxidation. High activity originates from the fact that formic acid oxidation proceeds completely through dehydrogenation path based on an ensemble effect. The high stability of Pt2Bi surface is induced by the suppression of Bi leaching as it was evidenced by insignificant changes of surface morphology and surface roughness shown by STM images before and after electrochemical treatment in formic acid containing solution. Pt2Bi is found to be powerful catalyst exhibiting up to two orders of magnitude larger current densities at 0.0 V and onset potential shifted for ∼0.2 V to more negative value relative to Pt under steady-state condition.

Carbon nanofiber supported bimetallic PdAu nanoparticles for formic acid electrooxidation

Carbon nanofiber (CNF) supported PdAu nanoparticles are synthesized with sodium citrate as the stabilizing agent and sodium borohydride as the reducing agent. High resolution transmission electron microscopy (HRTEM) characterization indicates that the synthesized PdAu particles are well dispersed on the CNF surface and X-ray diffraction (XRD) characterization indicates that the alloying degree of the synthesized PdAu nanoparticles can be improved by adding tetrahydrofuran to the synthesis solution. The results of electrochemical characterization indicate that the addition of Au can promote the electrocatalytic activity of Pd/C catalyst for formic acid oxidation and the CNF supported high-alloying PdAu catalyst possesses better electrocatalytic activity and stability for formic acid oxidation than either the CNF supported low-alloying PdAu catalyst or the CNF supported Pd catalyst.

Poisoning effect diminished on a novel PdHoOx/C catalyst for the electrooxidation of formic acid

A surprisingly high and stable current was observed after the peak current on the PdHoOx/C catalyst indicating the diminished poisoning effect. Moreover, the novel PdHoOx/C catalyst exhibited excellent catalytic activity and stability for formic acid oxidation due to the large electrochemical surface area and electronic effect.

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.

High activity of Pd–WO3/C catalyst as anodic catalyst for direct formic acid fuel cell

Pd nanoparticles supported on the WO3/C hybrid are prepared by a two-step procedure and the catalysts are studied for the electrooxidation of formic acid. For the purpose of comparison, phosphotungstic acid (PWA) and sodium tungstate are used as the precursor of WO3. Both the Pd–WO3/C catalysts have much higher catalytic activity for the electrooxidation of formic acid than the Pd/C catalyst. The Pd–WO3/C catalyst prepared from PWA shows the best catalytic activity and stability for formic acid oxidation; it also shows the maximum power density of approximately 7.6mWcm−2 when tested with a small single passive fuel cell. The increase of electrocatalytic activity and stability is ascribed to the interaction between the Pd and WO3, which promotes the oxidation of formic acid in the direct pathway. The precursors used for the preparation of the WO3/C hybrid support have a great effect on the performance of the Pd–WO3/C catalyst. The WO3/C hybrid support prepared from PWA is beneficial to the dispersion of Pd nanoparticles, and the catalyst has potential application for direct formic acid fuel cell.

Graphene Supported Pd Electrocatalysts for Formic Acid Oxidation

Highly loaded 80 wt.% Pd/graphene nanosheet (GNS) electrocatalysts were synthesized by colloidal method in order to alleviate the degradation rate of Pd catalysts in formic acid oxidation. Pd nanoparticles deposited on the GNS were well distributed on the surface more homogenously and average particle size of these metals is 4.6 ± 0.6 nm as compared to Pd/VC (5.0 ± 1 nm), which is verified by X-ray diffraction peak and high-resolution transmission electron microscope images. Electrochemical measurements conducted by cyclic voltammetry and chronoamperometry show that Pd/GNS catalysts exhibited significantly enhanced electrocatalytic activity and stability for formic acid oxidation compared to Pd/VC catalysts.