Palladium nanoparticles supported by three-dimensional freestanding electrodes for high-performance methanol electro-oxidation

Palladium (Pd) nanoparticles (NPs) prepared by gas phase cluster deposition demonstrated excellent electrocatalytic activity. Herein, a series of Pd NPs modified freestanding electrodes with a super clean surface and easy repeating process for methanol oxidation reaction is reported. Pd NPs with different coverage were deposited on Ni foams and three-dimensional graphene-Ni foams, respectively. Owning to the special three-dimensional structure of Ni foam, the Pd NPs-Ni foam composite exhibited remarkable activity and unusually long-term stability for methanol electro-oxidation. The introduced three-dimensional graphene prepared by conventional chemical vapour deposition improved the electrocatalytic performance. The results can be attributed to the Pd NPs with high electrochemical activity and unique properties for three-dimensional supports.     

Electrocatalytic properties of monometallic and bimetallic nanoparticles-incorporated polypyrrole films for electro-oxidation of methanol

Oxidative electrochemical polymerization of pyrrole at indium-doped tin oxide (ITO) is accomplished from a neat monomer solution with a supporting electrolyte (0.3 M n-tetrabutyl ammonium tetrafluoroborate) by multiple-scan cyclic voltammetry. Polypyrrole (Ppy) films containing nanometer-sized platinum and Pt/Pd bimetallic particles are electro-synthesized on ITO glass plates by voltammetric cycling between −0.1 and +1 V (versus Ag/AgCl/3 M NaCl). The electrocatalytic oxidation of methanol on the nanoparticle-modified polypyrrole films is studied by means of electrochemical techniques. The modified electrode exhibits significant eletrocatalytic activity for methanol oxidation. The enhanced electrocatalytic activities may be due to the uniform dispersion of nanoparticles in the polypyrrole film and a synergistic effect of the highly-dispersed metal particles so that the polypyrrole film reduces electrode poisoning by adsorbed CO species. The monometallic (Pt) and bimetallic (Pt/Pd) nanoparticles are uniformly dispersed in polypyrrole matrixes, as confirmed by scanning electron microscopic and atomic force microscopic analysis. Energy dispersive X-ray analysis is used to characterize the composition of metal present in the nanoparticle-modified electrodes.     

Pd‐Ni/Cd loaded PPy/Ti composite electrode: Synthesis,characterization, and application for hydrogen storage

A wide compositional range of Pd‐Ni/Cd on polypyrrole (PPy)‐modified Ti plates (Pd‐Ni/Cd/PPy/Ti) was fabricated via electrochemical deposition. The hydrogen absorption properties of the prepared Pd‐Ni/Cd/PPy/Ti electrodes were evaluated using cyclic voltammetry and chronoamperometry in acidic media. The optimal Pd₃₆‐Ni₇/Cd₅₇/PPy/Ti electrode achieved a hydrogen storage capacity of 331.3 mC cm^?2 mg^?1 and an H/Pd ratio of 0.77. The enhancement of the hydrogen storage was attributed to a synergistic effect between the Pd‐Ni/Cd catalysts. The surface morphology, crystallinity, and chemical composition of the Pd‐Ni/Cd/PPy/Ti electrode were characterized using scanning electron microscope (SEM), X‐ray diffraction (XRD), and X‐ray photoelectron spectroscopy (XPS), respectively. Hydrogen spillover occurred on the trimetallic catalysts, and secondary hydrogen spillover occurred on the PPy/Ti support. The enhanced hydrogen sorption capacity was due to both the synergistic effect of the trimetallic catalysts and the assistance of PPy, making Pd‐Ni/Cd/PPy/Ti a promising hydrogen storage material.     

Investigation of the effect of carbonaceous supports on the activity and stability of supported palladium catalysts for methanol electro-oxidation reaction

In this study, nitrogen doped graphene (NG) and multi-walled carbon nanotubes (MWCNT) were used as supporting materials for palladium active phase to investigate their performance in direct methanol fuel cells (DMFCs). The facile and low temperature solvothermal method was used for the synthesis of NG. Palladium nanoparticles were deposited on the surface of NG and MWCNT by a modified polyol reduction method. The morphologies and microstructures of the prepared catalysts were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. Also, cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy were carried out to evaluate the electrocatalytic activity and the durability of the obtained catalysts towards methanol oxidation reaction. Pd/NG catalyst had a better activity and durability of methanol electrocatalytic oxidation rather than Pd/MWCNT catalyst, which is related to good dispersion of Pd nanoparticles on the surface of nitrogen doped graphene and the physicochemical characteristics of NG.     

Effect of over-oxidation treatment of Pt–Co/polypyrrole-carbon nanotube catalysts on methanol oxidation

Bimetallic Pt–Co nanoparticles were co-deposited on polypyrrole (PPy)-multiwalled carbon nanotube (MWCNT) composite by formaldehyde reduction route to develop an anode catalyst for direct methanol fuel cells (DMFCs). PPy-MWCNT support was prepared by in situ polymerization of pyrrole on MWCNT. The electrochemical activity of this catalyst towards methanol oxidation and the important influencing factors have been investigated. The Pt–Co/PPy-MWCNT composite via over-oxidation treatment shows higher catalytic activity and potential application value for DMFCs.     

Enhancement of anodic oxidation of formic acid on Pd–Fe bimetallic nanoparticles by thermal treatment

The surface composition and catalytic properties of Pd–Fe bimetallic catalysts with identical bulk composition can be continuously tuned by treatment at different temperatures. The activity of these catalysts in formic acid oxidation was related to the treatment temperature. The thermal treatment temperatures ranged from 400 to 600 °C. The Pd–Fe nanoparticles are characterized by an array of analytical techniques including TEM (transmission electron microscopy), XRD (X-ray diffraction), ICP (inductively coupled plasma) and HS-LEIS (low energy ion scattering spectroscopy). The electrocatalytic activity is examined using cyclic voltammetric and chronoamperometric measurements. The Pd–Fe/C catalyst with 500 °C shows the highest electrocatalytic activity for formic acid oxidation, with a current activity 3 times higher than that of before treated Pd–Fe/C catalyst, 5.6 times higher than that of commercial Pt/C catalyst. The migration of Pd to the surface on the nanoparticle catalysts as well as the electrochemical active surface area of the PdFe–H catalysts was shown to play a major role in enhancing the electrocatalytic activity for catalyst. These findings provided important insights into the correlation between the electrocatalytic activity and the treatment temperature of the nanoengineered bimetallic catalysts.     

Electrocatalytic activity of Pd–Au nanoalloys during methanol oxidation reaction

Methanol fuel cells are very promising power source due to its high efficiency and low emissions of pollutants but their commercialization is hindered by development of the effective catalysts. Bimetallic nanostructured catalysts have been used to increase the effectiveness of methanol electrooxidation. Their high electrocatalytic activity can be accounted largely by the difference in electronegativity of two metals (e.g. Pd and Au), that resulting in gradual Au^δ+→Au^δ– transition with the increase in Pd content. Therefore, gold-enriched bimetallic Pd-Au_nano were recommended as catalysts for oxidation processes since they are characterized by the presence of Au^δ+ on their surface. Deposition of Pd, Au and Pd–Au nanoparticles (~50–350 nm) were carried out in dimethyl sulfoxide by pulsed mode of electrolysis directly on electrode surface. Cyclic voltammetry was the main method to study catalytic properties of the modified electrode in the anode oxidation process of methanol. It was found that oxidation rate on the electrode surface modified by bimetallic Pd–Au nanoparticles is ~1.5 times higher as compared to that in the case of electrodes modified by Pd or Au monometallic nanoparticles individually. In order to find highly active, selective, and stable catalysts for methanol electrocatalytic oxidation reaction additional studies are needed to understand the role of electrode surface charge and local OH⁻ ions concentration from alkali solution.     

Heteroatom doped 3D graphene aerogel supported catalysts for formic acid and methanol oxidation

In this study, nitrogen (N) and boron (B) heteroatom doped graphene aerogel support materials have been employed for the dispersion of platinum (Pt) nanoparticles to improve their electrocatalytic activities for formic acid and methanol oxidation. Pt nanoparticles dispersed on the heteroatom doped graphene aerogel (GA) support materials by a microwave heating method. The as-prepared catalysts were characterized by a variety of means such as SEM, EDS, ICP-MS, TEM, XRD, BET and XPS. The electrocatalytic activities, stability and impedance of the synthesized catalysts were investigated for formic acid and methanol oxidation using electrochemical measurements. The 3D graphene aerogels have higher capacitive currents than the Vulcan XC-72 in the double layer region. The results of electrochemical chronoamperometry tests reveal that Pt/BGA shows the best stability for methanol oxidation and also exhibited superior electrocatalytic activity towards the oxidation of methanol in cyclic voltammetry. In addition to, heteroatom doped GA supported catalysts higher activity compared to the Vulcan XC-72 supported catalyst for formic acid oxidation.     

One-step synthesis in deep eutectic solvents of PtV alloy nanonetworks on carbon nanotubes with enhanced methanol electrooxidation performance

We report a simple one-step chemical reduction strategy in deep eutectic solvents (DESs) for the fabrication of a PtV alloy nanonetwork (ANN)/multiwalled carbon nanotube (MWCNT) nanohybrid, which exhibits excellent electrocatalytic performance in both activity and stability for the methanol oxidation reaction (MOR). The as-synthesized nanohybrid was characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy, confirming the formation of a porous nanonetwork structure composed of smaller PtV alloy nanoparticles (~3.8 nm) and the presence of strong electronic transfer interactions between Pt and alloyed V. The electrochemical properties of catalysts for the MOR were evaluated by using cyclic voltammetry and chronoamperometry techniques. The electrocatalytic activity, durability and CO tolerance ability of PtV ANNs/MWCNTs toward the MOR are found to be considerably higher than those of the Pt/MWCNT and commercial Pt/C catalysts. This investigation of the effect of several reaction parameters (e.g., scan rate and methanol concentration) indicates that the electrocatalytic oxidation of methanol on PtV ANNs/MWCNTs is a diffusion-controlled electrochemical process. The performance enhancement mechanism of MOR on the PtV ANN/MWCNT catalyst is analyzed based on the structure and electrochemical studies.     

Hydrazine electrooxidation on a composite catalyst consisting of nickel and palladium

A carbon nanotubes (CNTs) supported composite catalyst consisting of Pd and Ni (Pd-Ni/CNT) is synthesized by a chemical method. The electrocatalytic activities of Pd/CNT, Ni/CNT and Pd-Ni/CNT toward the hydrazine oxidation reaction (HOR) are evaluated by linear sweep voltammetry, electrochemical impedance spectroscopy and polarization measurement. The composite catalyst demonstrates higher electrocatalytic activity than its single-constituent catalysts due to the synergy between Ni and Pd. The Pd addition in the composite catalyst prevents oxidation of Ni so that the Pd-Ni/CNT electrode exhibits smaller reaction resistance to the HOR than the Ni/CNT and Pd/CNT electrodes.     

Modification of palladium surfaces by bismuth adatoms or clusters: Effect on electrochemical activity and selectivity towards polyol electrooxidation

The syntheses of Bi-modified Pd catalysts with a controlled size distribution are presented as well as the characterizations of their structures and of their surfaces. Effects of the modification either of non-supported Pd nanospheres by spontaneous deposition of Bi or of carbon-supported Pd-based nanomaterials by decoration with bismuth clusters on the electrocatalytic activity towards glycerol electrooxidation were evaluated and compared in alkaline medium. The method of bismuth deposition has a dramatic effect on the activity of the palladium based catalysts: spontaneous deposition of Bi on non-supported Pd nanoparticles leads to relatively low activity enhancement, whereas decoration of carbon-supported Pd nanoparticles by Bi₂O₃ and Bi(OH)₃ clusters leads to very high activity increase at low overpotentials. In situ infrared spectroscopy indicated that the modification of Pd by Bi did not affect the selectivity of glycerol oxidation, whereas in the case of Pt containing catalyst, a dramatic change in selectivity occurred at low potentials.     

High efficient electrocatalytic oxidation of methanol on Pt/polyindoles composite catalysts

Novel composite catalysts have been fabricated by the electrodeposition of Pt onto the glassy carbon electrode (GC) modified respectively with polyindole (PIn) and poly(5-methoxyindole) (PMI) and used for the electrooxidation of methanol in acid solution of 0.5 M H₂SO₄ containing 1.0 M methanol. As-formed composite catalysts are characterized by SEM, XRD and the electrochemical methods. The results of the catalytic activity for methanol oxidation show that the two composite catalysts exhibit higher catalytic activity and stronger poisoning-tolerance than Pt/polypyrrole/GC (Pt/PPy/GC) and Pt/GC. Electrochemical impedance spectroscopy indicates that the methanol electrooxidation on the composite catalysts at various potentials shows different impedance behaviors. At the same time, the charge-transfer resistance for electrooxidation of methanol on Pt/PIn/GC and Pt/PMI/GC is smaller than those on Pt/PPy/GC and Pt/GC. The present study shows a promising choice of Pt/PIn and Pt/PMI as composite catalysts for methanol electrooxidation.     

Pd nanoparticles assembled on Ni- and N-doped carbon nanotubes towards superior electrochemical activity

Metal-based catalysts within single-atom to 1–2 nm size range are attracting considerable attention recent years. Carbon-based materials with their excellent electro- and photo-chemical properties are ideal candidates as supporting substrate for constructing of metal catalyst. Here we report a palladium (less than 5 nm in average diameter) deposited Ni carbon nanotubes (CNTs) with Ni metal nanoparticles (NPs) to be around single atom to 1–2 nm on average. Mono-dispersed Pd NPs are homogeneously immobilized on both synthesized Ni- and N-doped CNTs and N-doped commercial made CNTs using poly(diallyldimethyl ammonium) chloride (PDDA) as the key bonding components. Enhanced electrocatalytic activity is observed in measurements including hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and methanol oxidation reaction (MOR), with some of the samples having higher HER (under acidic condition) and OER (under basic condition) activity comparing with the commercial Pd/C (40 wt%) sample. The result provides a forward-looking strategy for fabricating efficient and low-cost catalysts.     

Synthesis, characterization, and electrocatalytic properties of a polypyrrole-composited Pd/C catalyst

Polypyrrole composition over carbon-supported palladium nanoparticles (Pd-PPy/C) is successfully performed as electrocatalysts for acid-based fuel cell. This approach demonstrates that PPy modification on a Pd surface remarkably suppresses the deactivation of Pd under acidic conditions. We attempted to determine the influence of PPy on the Pd surface with respect to stability. For this purpose, a potential cycling test and inductively coupled plasma mass spectrometry (ICP-MS) analysis are applied to this system to investigate how PPy affects Pd surface area loss by dissolution and particle growth/agglomeration. The electronic structure of the catalysts is also analyzed with X-ray absorption-near-edge spectroscopy (XANES) and X-ray photoelectron spectroscopy (XPS). The increase in stability upon PPy modification of Pd nanoparticles can be interpreted as a result of the redox properties of PPy polymer itself because the electronic interaction of Pd and PPy doesn’t reveal a shifting of the d-band center (?_d). Consequently, our work may suggest that conjugated polymer-composited metal catalysts are good potential candidate in the development of efficient electrocatalysts because of the possibility of electrochemical role of the conjugated polymer.     

Preparation of Pd/ZnO/Ni hierarchical porous array film with enhanced electrocatalytic activity for methanol oxidation

In this study, we successfully synthesized a Pd/ZnO/Ni hierarchical porous array-film catalyst by electrodeposition and magnetron sputtering with the assistance of the monodisperse colloidal sphere template. Structural characterisation indicated that a layer of Pd nanoparticles was uniformly grown on the ZnO/Ni ordered bowl-like micro/nano array film. Electrochemical measurements in alkaline solution demonstrated that the as-grown array film had outstanding electrocatalytic activity for methanol oxidation. The specific activity of the Pd/ZnO/Ni porous array film was up to 130.1 mA cm⁻². The corresponding mass activity (812.7 mA mg⁻¹) was 6 times higher than that of commercial Pd/C catalyst (134.8 mA mg⁻¹), and the stability was also much better than the commercial one. These excellent electrochemical properties can be attributed to the unique hierarchical porous structure, which offers a high specific surface area for the methanol reaction, and ZnO intermediate layer, which effectively removes the poisoning species from the Pd sites through the strong oxidative hydroxyl radicals.     

Performance and carbon deposition over Pd nanoparticle catalyst promoted Ni/GDC anode of SOFCs in methane,methanol and ethanol fuels

The electrochemical performance and carbon deposition on palladium catalyst promoted Ni/Gd_0.1C_0.9O_1.95 (Ni/GDC) anode in methane and alcohol fuels like methanol and ethanol are investigated at open circuit potential and under dc bias using electrochemical impedance spectroscopy technique. Presence of Pd nanoparticle catalyst significantly promotes the electrocatalytic activity of Ni/GDC for the electrooxidation reaction in methane and in particularly in methanol and ethanol fuels. For instance, in the case of methanol oxidation reaction, there is clear separation of the impedance arcs at high and low frequencies and activation energy for the reaction is reduced by ∼33% on a 0.15 mg cm⁻² PdO impregnated or infiltrated Ni/GDC anode. The transitional impedance response study when the inlet gas is switched from hydrogen to methane or alcohol fuels indicates that the oxidation reaction in methane and alcohol fuels is most likely dominated by adsorption, dissociation and diffusion steps of the reaction. Carbon deposition is also observed on Pd-infiltrated Ni/GDC in methanol and ethanol, but different from that observed in methane, there is no filament carbon fibers formation on the Pd-impregnated Ni/GDC surface in methanol fuel.     

Enhanced methanol electrooxidation by electroactivated Pd/Ni(OH)2/N-rGO catalyst

Direct methanol fuel cells, in which electrocatalytic oxidation of methanol takes place, are one of the most promising technologies for facilitating the shift to renewable energy sources. However, they still suffer from high-catalyst-prices, as well as sluggish kinetics of methanol oxidation reaction (MOR). Therefore, herein, palladium/Nickel(II) hydroxide/nitrogen doped reduced graphene oxide (Pd/Ni(OH)2/N-rGO) hybrid was fabricated via facile two-step solution method and utilized as electrocatalyst for MOR. The in-situ electrochemical activation pre-treatment was proposed to engineer a highly active electrocatalyst. The Pd/Ni(OH)2/N-rGO, which had distinctive structural features along with robust synergistic effects, outperformed the commercial Pd electrocatalyst in terms of catalytic activity towards MOR, with elevated anodic peak current density values. The in-situ electrochemical activation pre-treatment lead to 3.3, 3.0, and 2.0-fold increase in activity of Pd/Ni(OH)2/N-rGO, Pd/N-rGO, and Pd/C, respectively. This research lays the door for a unique technique to manufacture high-performance, low-cost electrocatalysts that might be used in fuel cell technology instead of existing Pd electrocatalysts.     

A UPD-spontaneous redox approach to the preparation of monolayer palladium on reduced graphene oxide-supported gold nanoparticles for ethanol electrooxidation in alkaline media

Monolayer Pd on electrochemical-reduced graphene oxide supported Au nanoparticles (m-Pd–Au/ERG) was designed by a simple and effective route, which produces electrocatalyst with a considerably low Pd loading and good electrocatalytic performance for ethanol oxidation. The as-prepared m-Pd–Au/ERG nanocompostie was characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results show that high-density m-Pd–Au nanoparticles are dispersed on the surface of ERG uniformly. The electrochemical activities of the as-prepared nanocomposites toward ethanol oxidation in alkaline media were investigated by using cyclic voltammetry and chronoamperometric technique. The results demonstrate that the m-Pd–Au/ERG catalyst shows much higher electrocatalytic activity, stronger tolerance to CO than the m-Pd–Au and b-Pd–Au/ERG catalysts for ethanol oxidation.     

Different interesting enhanced influence from polyaniline and poly(o-toluidine) on electrocatalytic activities of Pt on them toward electrooxidation of methanol

Polyaniline (PANI) and poly(o-toluidine) (POT) with various film thickness were electropolymerized using potentiostatic method at the surface of GC electrode. The two conducting polymers were characterized by CV, in situ UV–vis spectroscopy and electrochemical impedance spectroscopy. Two composite catalysts (Pt/PANI/GC and Pt/POT/GC) with various film growth charge have been fabricated by the electro deposition of Pt on the PANI/GC and POT/GC at ?0.1 V. then they were used for the electrooxidation of methanol in 0.5 M H₂SO₄ containing 1.0 M methanol. The properties of both the polymers change with the increase of film growth charge. As-formed composite catalysts were characterized by SEM and the electrochemical methods. The Pt nanoparticles deposited at ?0.1 V exhibit thorns morphology and good dispersion on the POT with the film growth charge of 4.5 mC. The electrocatalytic activity for methanol oxidation of Pt/POT/GC is higher than Pt/PANI/GC for all the film charge, and they both exhibit the largest electrocatalytic activity at film charge of 4.5 mC. The present study shows that Pt/POT/GC would be a promising choice for methanol electrooxidation in comparison with Pt/PANI/GC.     

Pt–Ru nanoparticles anchored on poly(brilliant cresyl blue) as a new polymeric support: Application as an efficient electrocatalyst in methanol oxidation reaction

The glassy carbon electrode is modified by poly(brilliant cresyl blue) (PBCB) to be applied as a new green and efficient platform for Pt and Pt–Ru alloy nanoparticles deposition. Surface composition, morphology and catalytic activity of these modified electrodes towards methanol oxidation are assessed by applying X-ray diffraction, field emission scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy techniques. The X-ray diffraction patterns reveal that the highly crystalline Pt and Pt–Ru alloy and RuO₂ nanoparticles with low crystallinity are deposited on the PBCB modified glassy carbon electrodes. The microscopic images indicate smaller size and better distribution of deposited nanoparticles on the surface of PBCB modified electrodes. Cyclic voltammetry and electrochemical impedance spectroscopy results reveal that PBCB supported Pt and Pt–Ru nanoparticles have better electrocatalytic performance and durability towards methanol oxidation rather than the unsupported nanoparticles. From the obtained results it can be concluded that the presence of PBCB not only improves the stability of nanoparticles on the surface, but also leads to the formation of smaller size and more uniform distribution of nanoparticles on the surface, which, in turn, cause the nanoparticles to provide a higher accessible surface area and more active centers for the oxidation of methanol. The results will be valuable in extending the applications of this polymer in surface modification steps and in developing promising catalyst supports to be applied in direct methanol fuel cells.