Macroporous carbon as support for PtRu catalysts

A high surface macroporous porous carbon (MPC) has been obtained by SiO₂ nanoparticles template and further used as support for PtRu catalysts. MPC supported PtRu materials show an enhanced activity for methanol electrooxidation when compared with commercial catalysts. This observation is discussed in terms of reactant accessibility to active sites. The improved diffusion through the porous matrix influences not only methanol feeding, but also removal of reaction subproducts, as clearly shown by differential electrochemical mass spectrometry (DEMS).     

PtIr alloy nanowire assembly on carbon cloth as advanced anode catalysts for methanol oxidation

The interconnecred PtIr alloy nanowires were uniformly deposited on carbon cloth via One-step wet chemistry method, which diameter is averaged to be 5 nm with a length of 50–200 nm. The carbon cloth supported PtIr nanowire assembly (PtIr NA/CC) shows a larger electrochemical active surface area (ECSA) due to its 3D nanostructure and a high CO-resistance as a result from the synergistic effect of PtIr alloy. The PtIr NA/CC exhibits an extremely high mass activity and a reliable long-term stability toward methanol oxidation reaction (MOR). The superior catalytic performance on MOR can match and even surpass those best Pt-based nanowires reported recently in the literature.     

Electrochemical impedance studies on carbon supported PtRuNi and PtRu anode catalysts in acid medium for direct methanol fuel cell

The anodic Pt–Ru–Ni/C and the Pt–Ru/C catalysts for potential application in direct methanol fuel cell (DMFC) were prepared by chemical reduction method. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements were carried out by using a glassy carbon working electrode covered with the catalyst powder in a solution of 0.5 mol L⁻¹ CH₃OH and 0.5 mol L⁻¹ H₂SO₄ at 25 °C. EIS information discloses that the methanol electrooxidation on the Pt–Ru–Ni/C catalyst at various potentials shows different impedance behaviors. The mechanism and the rate-determining step of methanol electrooxidation are changed with increasing potential. Its rate-determining steps are the methanol dehydrogenation and the oxidation reaction of adsorbed intermediate CO_ads and OH_ads in low (400–500 mV) and high (600–800 mV) potentials, respectively. The catalytic activity of the Pt–Ru–Ni/C catalyst is higher for methanol electrooxidation than that of the Pt–Ru/C catalyst. Its tolerance performance to CO formed as one of the intermediates of methanol dehydrogenation is also better than that of the Pt–Ru/C catalyst.     

Improving the performance of PtRu/C catalysts for methanol oxidation by sensitization and activation treatment

PtRu/C anode electrocatalysts for direct methanol fuel cells (DMFCs) have been prepared by electroless deposition with the pretreatment of Sn²⁺/Sn⁴⁺ sensitization and Pd activation. The as-prepared catalysts were composed of well dispersed PtRu alloy nanoparticles with relatively homogeneous size distribution, which were characterized by instrumental analyses, such as XRD, TEM, HRTEM and EDX. Electrochemical measurements demonstrated that the PtRu/C catalysts obtained with sensitizing and activating pretreatment exhibited an enhanced peak current density of 34% for methanol electrooxidation as compared to that synthesized without pretreatment.     

PtRu/C catalysts synthesized by a two-stage polyol reduction process for methanol oxidation reaction

Highly dispersed Ru/C catalysts are prepared using high viscosity glycerol as a reducing agent and are treated in H₂ atmosphere to ensure stability. A Pt^∧Ru/C catalyst is prepared by an ethylene glycol process based on the pre-formed Ru/C. The catalyst is tested for methanol oxidation reaction at room temperature and is compared with the activity of the as-prepared PtRu/C alloyed catalyst (prepared by co-reduction of Pt and Ru precursors) and commercial PtRu/C from E-TEK. The catalysts are extensively characterized by Transmission electron microscope (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Electrochemical measurements by cyclic voltammetry (CV) showed consistently high catalytic activities and improved CO resistance for the Pt^∧Ru/C catalyst.     

MWCNT-supported PtRu catalysts for the electrooxidation of methanol: Effect of the functionalized support

Functionalized carbonaceous materials have been investigated as supports of PtRu nanoparticles for the electrooxidation of methanol, using such conventional electrochemical methods as cyclic voltammetry and chronoamperommetry and by measurements in a CH₃OH/O₂-fed single cell. Further, to understand the effect of oxygen-containing groups on the supports in the methanol oxidation reaction (MOR), a kinetic study of the catalyst that has the best behavior in this process has been performed. The study at different temperatures of PtRu nanoparticles supported in multiwall carbon nanotubes (MWCNTs) with a high amounts of functional groups—PtRuCNT-ST—show that there was low CO poisoning during the MOR on this catalyst. The low apparent energy on PtRuCNT-ST in the MOR was attributed to CO diffusion or to the dissociative adsorption of methanol. Both factors had a beneficial effect on the oxygen-containing groups on MWCNTs, facilitating oxidation of the carbonaceous intermediates to CO₂ or HCOOH. These findings have been confirmed by studies in a single cell feeding with CH₃OH/O₂, demonstrating that PtRuCNT-ST is the best-performing anodic electrode.     

Carbon nanotube-supported Pt-Alloyed metal anode catalysts for methanol and ethanol oxidation

To improve the electrocatalytic activity of alcohol oxidation, functionalized carbon nanotubes (CNTs) decorated with various compositions of metal alloy catalyst nanoparticles (Pt_xM_y, where M = Au and Pd; x and y = 1–3) have been prepared via reduction. The CNTs were treated with an nitric acid solution to promote the oxygen-containing functional groups and further load the metal nanoparticles. X-ray diffraction (XRD) scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to probe the formation of catalyst microstructure morphologies. A uniform dispersion of the spherical metal particles with diameters of 2–6 nm was acquired. The catalytic properties of the catalyst for oxidation were thoroughly studied by electrochemical methods that involved in the cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). To maximize the electrocatalytic performance and minimize the metal integration of the loaded CNTs, various compositions of active catalysts with large active surface areas are expected to increase the activity of the enhanced catalysts for alcohol oxidation. Most of the prepared bimetallic catalysts have better alcohol oxidation kinetics than commercial PtRu/C. Among the prepared catalysts, the PtAu/CNTs and PtPd/CNTs catalysts with high electrochemically active surface area (ECSA) show excellent activities for alcohol oxidation resulting in their low onset potentials, small charge transfer resistances and high peak current densities and I_f/I_b ratios, stability, and better tolerance to CO for alcohol oxidation. The integration of Pt and different metal species with different stoichiometric ratios in the CNTs support affects the electrochemical active surface area achieved in the catalytic oxidation reactions.     

Stability and durability of PtRu catalysts supported on carbon nanofibers for direct methanol fuel cells

The chemical stability and durability of PtRu catalysts supported on carbon nanofibers (CNFs) for the anode electrode of a direct methanol fuel cell (DMFC) are investigated by Pt and Ru dissolution tests in sulfuric acid and long-term performance tests of a single cell discharging at a constant current density of 150 mA cm⁻² for approximately 2000 h. A CNF with a herringbone-type structure, which is characterized by the alignment of graphene symmetrically angled to the fiber axis, was selected as the catalyst support because it has an edge-rich surface and a high surface area. In the metal dissolution test, the PtRu/CNF catalysts showed 1.5–2 times lower Ru leaching than a tested commercial catalyst (supported on activated carbon). The results of long-term performance tests also prove the higher durability of the anode catalyst compared with the commercial catalyst, when the anode polarization is compared before and after operation for 2000 h. Some analytical measurements, including X-ray diffraction, energy dispersive spectroscopy, and transmission electron microscopy were conducted to study the degradation of the catalyst activity.     

Platinum supported catalysts for carbon monoxide preferential oxidation: Study of support influence

The aim of this work is to study the influence of the addition of different oxides to an alumina support, on surface acidity and platinum reducibility in platinum-based catalysts, as well as their effect on the activity and selectivity in CO preferential oxidation, in presence of hydrogen. A correlation between surface acidity and acid strength of surface sites and metal reducibility was obtained, being Pt-support interaction a function of the acid sites concentration under a particular temperature range. In platinum supported on alumina catalysts, CO oxidation follows a Langmuir-Hinshelwood mechanism, where O₂ and CO compete in the adsorption on the same type of active sites. It is noteworthy that the addition of La₂O₃ modifies the reaction mechanism. In this case, CO is not only adsorbed on the Pt active sites but also on La₂O₃, forming bridge bonded carbonates which leads to high reactivity at low temperatures. An increase on temperature produces CO desorption from Pt surface sites and favours oxygen adsorption producing CO₂. CO oxidation with surface hydroxyl groups was activated producing simultaneously CO₂ and H₂.     

Kinetics of methanol electrooxidation on Pt/C and PtRu/C catalysts

This paper analyzes the performance of platinum and platinum:ruthenium carbon-supported catalysts modified by the application of in-situ cathodic polarizations towards the methanol oxidation reaction. These new electrodes are characterized by electrochemical techniques together with transmission electron microscopy images to envisage the dispersion of the catalyst. We measure methanol electrooxidation current transients, fitting the results with a general kinetic equation for a mixed mass and charge transfer processes for adsorbed reactant species. The kinetic equation also helps to predict the exponent of the chronoamperometric decay as directly related to the fractal dimension of the catalyst surface and to discuss the possible processes involved in the electrocatalytic reaction.     

Improvement of methanol electro-oxidation activity of PtRu/C and PtNiCr/C catalysts by anodic treatment

The effect of an anodic treatment on the methanol oxidation activity of PtRu/C (50:50 at.%) and PtNiCr/C (Pt:Ni:Cr = 28:36:36 at.%) catalysts was investigated for various potential limits of 0.9, 1.1, 1.3 and 1.4 V (vs. reference hydrogen electrode, RHE). NaBH₄ reduced catalysts were further reduced at 900 °C for 5 min in an argon balanced hydrogen flow stream. Improved alloying was obtained by the hydrogen reduction procedure as confirmed by X-ray diffraction results. In the PtRu/C catalyst, a decrease of irreversible Ru (hydrous) oxide formation was observed when the anodic treatment was performed at 1.1 V (vs. RHE) or higher potentials. In chronoamperometry testing performed for 60 min at 0.6 V (vs. RHE), the highest activity of the PtRu/C catalyst was observed when anodic treatment was performed at 1.3 V (vs. RHE). The current density increased from 1.71 to 4.06 A g_cat.⁻¹ after the anodic treatment. In the PtNiCr/C catalyst, dissolution of Ni and Cr was observed when potentials ≥1.3 V (vs. RHE) were applied during the anodic treatment. In MOR activity tests, the current density of the PtNiCr/C catalyst dramatically increased by more than 13.5 times (from 0.182 to 2.47 A g_cat.⁻¹) when an anodic treatment was performed at 1.4 V. On an A g_{noble metal}⁻¹ basis, the current density of PtNiCr-1.4V is slightly higher than the best anodically treated PtRu-1.3V catalyst, suggesting the PtNiCr catalyst is a promising candidate to replace the PtRu catalysts.     

Electro-deposition on carbon black and carbon nanotubes of Pt nanostructured catalysts for methanol oxidation

An electrochemical method for the Pt nanoparticles deposition on porous and high surface carbon substrates (carbon black and carbon nanotubes), as an alternative way to prepare gas diffusion electrodes for polymer electrolyte fuel cells (PEFCs), is herein described. Pt nanoparticles well distributed and localized on the electrode surface were obtained by using an electric field. The electro-catalysts were prepared by single and multiple pulse galvanostatic polarizations in 1 M sulphuric acid + 5 mM exachloroplatinic acid solution. Chemical analysis, cyclic voltammetry and field emission gun scanning electron microscopy were used to determine the electrochemical features of Pt deposits and the influence of electro-deposition method on their nano-morphology. Electro-catalytic performances were studied by investigating the methanol oxidation reaction and the results are presented in form of surface specific activity and mass specific activity to take into account the electrochemical real surface and Pt loading. A comparison with commercial E-TEK Pt/C catalysts, prepared by traditional chemical reduction and heat treatment in hydrogen, shows that the electrodeposited catalyst presents higher activity at lower Pt loading.     

Recent progress of anode catalysts and their support materials for methanol electrooxidation reaction

This review paper summarizes the recent progress of anode catalysts for methanol oxidation reaction (MOR) in direct methanol fuel cells (DMFCs). The electrocatalytic activities of the noble and noble-free catalysts in different electrolyte media are compared and discussed. Noble-free catalysts exhibit high activity in alkaline medium, whereas Pt-based catalysts are the most active MOR catalysts in acidic medium. The types of catalyst support materials for DMFC anodes are also discussed and further divided into carbonaceous and non-carbonaceous materials. The ion and electron transport through the support materials and their effects on the overall performance are elaborated. Lastly, this paper highlights the major challenges in achieving the optimum DMFC performance from the aspect of tailoring the properties of MOR electrocatalysts to pave its way for commercialisation.     

Influence of carbon support properties on the electrocatalytic activity of PtRuCu nanoparticles for methanol and ethanol oxidation

This work set out to explore the influence of kind and surface condition of carbon supports on the electrocatalytic activity of trimetallic PtRuCu alloy nanoparticles. The structure, composition, particle size and catalyst loading were determined by XRD, EDX, XPS, TEM and ICP-AES analysis. XRD studies revealed that support physical characteristics and surface conditions have an important influence in lattice strain, while XPS pointed out that a strong electronic interaction exists between the particles and the carbon support. Electrochemical experiments showed that the activated carbon black supported PtRuCu catalyst exhibits the best performance for methanol and ethanol oxidation and the lowest poisoning rate. The superior catalytic activity of this electrode can be rationalized in terms of metal-support interaction, Pt utilization efficiency and electrical conductivity of the carbon support. Furthermore, the as-prepared electrode exhibits 13 and 7 times higher activity towards methanol and ethanol oxidation when compared with a PtRu/C commercial catalyst.     

A comparative study of tungsten-modified PtRu electrocatalysts for methanol oxidation

The carbon supported PtRu nanocatalyst is modified by two kinds of tungsten compounds, i.e., tungsten oxide (WO_x) and phosphotungstic acid (H₃PW₁₂O₄₀, PW₁₂), respectively, and the catalytic performances of the modified catalysts for methanol oxidation are evaluated. The results show that tungsten oxide and phosphotungstic acid exhibit different promoting effects on the catalytic performance of the PtRu nanocatalyst for methanol oxidation. The WO_x-modified PtRu nanocatalyst has a considerably high catalytic activity, which is attributed to the uniform distribution of PtRu nanoparticles on the carbon support and the strong metal-support interaction (SMSI) between the hypo-d-tungsten and the hyper-d-platinum. The PW₁₂-modified PtRu nanocatalyst has a good poison resistance, which is ascribed to the protective effect of the self-assembled PW₁₂ layer on the catalyst surface.     

Highly efficient carbon hybrid supported catalysts using nano-architecture as anode catalysts for direct methanol fuel cells

PtCo based nanoparticles in alloy structure were synthesized using the microwave-assisted reduction method. These nanoparticles were deposited on different carbon supporting materials. Here, these supporting materials such as rGO (reduced graphene oxide), rGO-VC (vulcan carbon) and AC-VC (activated carbon-vulcan carbon) were used and the methanol oxidation reaction (MOR) activity of single carbon support and hybrid carbon support material in the presence of PtCo nanoparticles were investigated at the same molar concentration. The average particle size of the PtCo nanoparticles detected in the TEM analysis was found to be 3.55 ± 0.64 nm. The MOR activity of the PtCo@rGO, PtCo@rGO-VC and PtCo@AC-VC catalysts was determined, where the anodic peak current of PtCo@AC-VC was determined as 73 mA/cm². It has been observed that PtCo nanoparticles with carbon hybrid support structures are more advantageous than single support structures due to the synergistic effect between carbon support structures and providing a larger surface area. Compared to previous studies, the MOR activity of PtCo@AC-VC is quite high. It can be stated that PtCo@AC-VC has comparable catalytic activity compared to the commercial available anode catalyst.     

Novel synthesis of PtRu/multi-walled carbon nanotube catalyst via a microwave-assisted imidazolium ionic liquid method for methanol oxidation

A facile and fast microwave-assisted ionic liquid method has been developed to prepare PtRu nanoparticles onto multi-walled carbon nanotubes (MWCNTs). This novel method has some advantages, such as the high electrocatalytic activity of the catalysts for the methanol oxidation, simple preparation procedures, and recycle of the ionic liquids. Transmission electron micrograph shows that PtRu nanoparticles with diameter of 2-5 nm are uniformly deposited along the length of the MWCNTs (PtRu/MWCNTs). The structure and nature of the resulting PtRu/MWCNT catalysts are also characterized by X-ray diffraction. Electrochemical measurements show that the electrocatalytic oxidation of methanol shows very high catalytic efficiency compared with commercial E-TEK Pt/C (20 wt%Pt) catalysts, which is crucial for anode electrocatalysis in direct methanol fuel cells.     

Catalytic activity,stability and impedance behavior of PtRu/C,PtPd/C and PtSn/C bimetallic catalysts toward methanol and formic acid oxidation

PtRu, PtPd and PtSn with weight ratios of (2:1) on carbon black (Vulcan XC-72) supported bimetallic catalysts were prepared by using microwave method via chemically reduction of H₂PtCl₆·6H₂O, RuCl₃, PdCl₂ and SnCl₂·2H₂O precursors with ethylene glycol (EG). These prepared catalysts were systematically investigated and obtained results were compared with commercial Pt black, PtRu black catalysts and with each other. The catalysts were characterized with XRD, ICP-MS, EDS and TEM. The electrocatalytic activities, stability and impedance of the catalysts were investigated in sulfuric acid/methanol and sulfuric acid/formic acid mixtures using electrochemical measurements. The results showed that PtSn/C catalyst showed comparable activity and durability with commercial Pt/C catalyst toward methanol oxidation. The synthesized PtRu/C catalyst was found to completely oxidize methanol and it showed more catalytic activity than commercial PtRu catalyst. Bimetallic PtPd/C catalyst gave better activity than both commercial Pt black and synthesized Pt/C catalyst for oxidation of formic acid. Higher electrochemical active surface areas were obtained with supported bimetallic catalysts.     

The stability of a PtRu/C electrocatalyst at anode potentials in a direct methanol fuel cell

Potential-scan tests were conducted to evaluate the stability of a PtRu/C electrocatalyst at anode potentials in a direct methanol fuel cell (DMFC). The results show that, under normal operating conditions, the anode potential in a DMFC is benign for the PtRu/C electrocatalyst. But in the case of deep discharge or short circuit, the anode potential value may exceed 0.6 V versus DHE, which is harmful to the PtRu/C electrocatalyst. The dissolution of catalyst components results in an enhanced ohmic resistance and a lowered catalytic activity for methanol electro-oxidation.     

Enhanced electrocatalytic activity of carbon-supported MnOx/Ru catalysts for methanol oxidation in fuel cells

This investigation reports the possible use of carbon-supported manganese octahedral molecular sieves (OMS-2) for the electrooxidation of methanol. The effect of combining these materials with a commercially available 5%Ru-carbon sample is examined. The activity of the OMS-2 materials is evaluated with respect to other forms of manganese oxides such as pyrolusite and nsutite. The OMS-2 materials show a synergistic interaction with the 5%Ru-C as well as the pyrolusite materials that enhances their electrochemical activities effectively. These OMS-2 materials are not only cost-effective but also very electrochemically active.