Electrodeposition of mesoscopic Pt-Ru on reticulated vitreous carbon from reverse emulsions and microemulsions: Application to methanol electro-oxidation

High surface area Pt-Ru (between 120 and 400 cm² mg⁻¹) meso-sized particles and mesoporous coatings were electrodeposited on reticulated vitreous carbon (RVC) three-dimensional electrodes using reverse emulsions and microemulsions. The organic phase of the colloidal media was composed of cyclohexane, Triton X-100 non-ionic surfactant and tetrabutylammonium perchlorate (for ionic conductivity) while the aqueous phase contained H₂PtCl₆ and RuCl₃ (or (NH₄)₂RuCl₆). For microemulsification to occur isopropanol was also added as co-surfactant. The catalytic activity for the electro-oxidation of methanol was assessed by cyclic voltammetry and chronopotentiometry in conjunction with surface area measurement by Cu underpotential deposition. The composition and morphology of the Pt-Ru deposit was analyzed by inductively coupled plasma atomic emission spectroscopy and scanning electron microscopy, respectively. The effects on the catalytic activity of the deposition current density, temperature, RVC pretreatment and plating bath composition are presented. It was found that the electrodeposition of Pt-Ru in reverse microemulsion yielded the highest specific surface area (400 cm² mg⁻¹) and catalytic activity toward CH₃OH electro-oxidation as shown, for example, by a 50-200 mV more negative anode potential determined by chronopotentiometry compared to a catalyst obtained by pure aqueous and emulsion electroplating.     

Pt-Ru electrodeposited on gold from chloride electrolytes

Voltammetric behavior of submicron-thick electrodeposited Pt-Ru on gold support is studied in sulfuric acid solution as a function of deposition potential and Pt:Ru ratio in chloride bath. In contrast to Pt-Ru, deposition of pure Ru is observed only at potentials of hydrogen evolution. The reason is found to be of kinetic nature, namely an inhibition of Ru deposition in presence of chloride. Chloride ions remain adsorbed on Ru at more negative potentials than on Pt and Au because of more negative ruthenium potential of zero free charge. Cu-UPD is applied to test the surface content of the oxidized Ru on pure Ru and various Pt-Ru surfaces. An enhancement of Ru oxohydroxides reduction in presence of Pt is observed. The electrocatalytic activity of Pt-Ru in respect to methanol oxidation correlates with the content of rechargeable surface Ru oxide. Ageing and ‘training’ of Pt-Ru electrodeposits under various modes is studied in order to determine the conditions of irreversible Ru oxidation. No manifestations of Ru dissolution from Pt-Ru electrodeposits in 0.5 M H₂SO₄ are found for anodic potential limits up to 1.1 V (RHE), in agreement with thermodynamic predictions. Electrodeposited Pt-Ru can be considered as a convenient model system for the study of Ru dissolution and crossover, as well as for determining the nature of the active surface species in the real composite catalysts for methanol oxidation.     

Pt-Ru catalysts prepared by high energy ball-milling for PEMFC and DMFC: Influence of the synthesis conditions

High energy ball-milling was used to prepare several unsupported Pt-Ru anode catalysts for PEM- and direct methanol fuel cells. Pt and Ru with a 50:50 nominal Pt/Ru ratio were ball-milled at various ball-to-powder weight ratios (from 4/1 to 12/1) and with various Pt:Ru:MgH₂ proportions (from 1:1:2 to 1:1:10), where MgH₂ is a leacheable dispersive agent. The presence of MgH₂ is necessary to obtain unsupported catalysts with a specific surface area of between 50 and 75 m² g⁻¹. The ball-milling parameters greatly affected the relative proportions of the three phases constituting the catalysts. These phases are: Pt(Ru) alloy nanocrystallites, unalloyed Ru crystallites and nanocrystallites. The best CO tolerant catalyst is obtained by using a 12/1 ball-to-powder ratio and a 1:1:8 Pt:Ru:MgH₂ proportion of dispersive agent. It is made of 57 at.% of a nanocrystalline (3 nm) Pt₈₀Ru₂₀ alloy, 42 at.% of a nanocrystalline (3 nm) Ru phase and 1 at.% of a crystalline (∼40 nm) Ru phase. This catalyst has the lowest Pt/Ru surface ratio (0.9), the highest content in nanocrystalline Ru, and the highest ratio of oxidized/metallic Ru (3.3). Both Pt-Ru alloy and nanocrystalline Ru participate to the CO tolerance. The best CO tolerant catalyst is, however, not the best catalyst in DMFC. The latter is obtained by using a 4/1 ball-to-powder ratio and a 1:1:6 Pt:Ru:MgH₂ proportion. Within the starting 50:50 Pt-Ru nominal atomic ratio, no specific correlation was found between catalyst performance in DMFC and atomic surface Pt/Ru ratio, nor nanocrystalline Ru content, nor oxidized/metallic Ru ratio. Performances of the best ball-milled catalysts are compared to those of commercial unsupported catalysts in PEMFC and DMFC.     

Effect of the structure of Pt-Ru/C particles on COad monolayer vibrational properties and electrooxidation kinetics

In this paper, we combined FTIR spectroscopy and CO_ad stripping voltammetry to investigate CO_ad adsorption and electrooxidation on Pt-Ru/C nanoparticles. The Pt:Ru elemental composition and the metal loading were determined by ICP-AES. The X-ray diffraction patterns of the Pt-Ru/C indicated formation of a Pt-Ru (fcc) alloy. HREM images revealed an increase in the fraction of agglomerated Pt-Ru/C particles with increasing the metal loading and showed that agglomerated Pt-Ru/C nanoparticles present structural defects such as twins or grain boundaries. In addition, isolated Pt-Ru/C nanoparticles have similar mean particle size (ca. 2.5 nm) and particle size distributions whatever the metal loading. Therefore, we could determine precisely the effect of particle agglomeration on the CO_ad vibrational properties and electrooxidation kinetics. FTIR measurements revealed a main CO_ad stretching band at ca. , which we ascribed to a-top CO_ad on Pt domains electronically modified by the presence of Ru. As the metal loading increased, the position of this band was blue shifted by ca. 5 cm⁻¹ and a shoulder around 2005 cm⁻¹ developed, which was ascribed to a-top CO_ad on Ru domains. The reason for this was suggested to be the increasing size of Ru domains on agglomerated Pt-Ru/C particles, which lifts dipole-dipole coupling and allows two vibrational features to be observed (CO_ad/Ru, CO_ad/Pt). This is evidence that FTIR spectroscopy can be used to probe small chemical fluctuations of the Pt-Ru/C surface. Finally, we comment on the CO_ad electrooxidation kinetics. We observed that CO_ad was converted more easily into CO₂ as the metal loading, i.e. the fraction of agglomerated Pt-Ru/C nanoparticles, increased.     

Electrochemical reduction of oxygen on thin-film Pt electrodes in acid solutions

The electrochemical reduction of oxygen on thin-film platinum electrodes in 0.1 M HClO₄ and 0.05 M H₂SO₄ solutions has been investigated using the rotating disk electrode (RDE) method. Thin films of Pt (0.25-20 nm thick) were prepared by vacuum evaporation onto glassy carbon substrate. The surface morphology of Pt films was examined by transmission electron microscopy (TEM). The specific activity of O₂ reduction was higher in HClO₄ and decreased with decreasing film thickness. In H₂SO₄, the specific activity was lower and appeared to be independent of the Pt loading. The values of Tafel slopes close to −120 mV dec⁻¹ in high current density range and −60 mV dec⁻¹ in low current density range were obtained for all electrodes in both solutions, indicating that the mechanism of O₂ reduction is the same for thin-film electrodes as for bulk Pt. The number of electrons transferred per O₂ molecule was close to four for all thin Pt films studied.     

Pt-WO3 supported on carbon nanotubes as possible anodes for direct methanol fuel cells

The carbon nanotube (CNT) synthesised by the template carbonisation of polypyrrole on alumina membrane has been used as the support for Pt-WO₃, Pt-Ru, and Pt. These materials have been used as the electrodes for methanol oxidation in acid medium in comparison with E-TEK 20 wt% Pt and Pt-Ru on Vulcan XC72R carbon. The higher electrochemical surface of the carbon nanotube (as evaluated by cyclic voltammetry) has been effectively used to disperse the catalytic particles. The morphology of the supported and unsupported CNT has been characterised by scanning electron micrograph and high-resolution transmission electron micrograph. The particle size of Pt, Pt-Ru, and Pt-WO₃ loaded CNT was found to be 1.2, 2, and 5 nm, respectively. The X-ray photoelectron spectra indicated that Pt and Ru are in the metallic state and W is in the +VI oxidation state. The electrochemical activity of the methanol oxidation electrode has been evaluated using cyclic voltammetry. The activity and stability (evaluated from chronoamperometric response) of the electrodes for methanol oxidation follows the order: GC/CNT-Pt-WO₃-Nafion>GC/E-TEK 20% Pt-Ru/Vulcan Carbon-Nafion>GC/CNT-Pt-Nafion>GC/E-TEK 20% Pt/Vulcan carbon-Nafion>Bulk Pt. The amount of nitrogen in the CNT plays an important role as observed by the increase in activity and stability of methanol oxidation with N₂ content, probably due to the hydrophilic nature of the CNT.     

Novel catalyst-support interaction for direct formic acid fuel cell anodes: Pd electrodeposition on surface-modified graphite felt

The electrodeposition of Pd on graphite felt (GF, thickness ~3 mm in uncompressed state) was studied and the resulting catalyst was compared with Pt-Ru/GF for the electro-oxidation of formic acid. A micellar solution composed of the non-ionic surfactant Triton X-102 and an aqueous phase containing PdCl₂ were utilized for the galvanostatic electrodeposition of Pd nanoparticles. The presence of the surfactant during electrodeposition coupled with pretreatment of the GF surface by a Shipley-type method (PdCl₂ + SnCl₂ solution) creating nucleation sites had a major impact on the Pd catalyst morphology and penetration throughout the electrode thickness, affecting, therefore, the electrocatalytic activity toward formic acid oxidation. It was found that large (~1,000 nm) Pd particles with smooth surface favored the indirect CO_ad pathway, while Pd nanoparticles (diameter <40 nm) with rough surface, formed with surfactant and pretreatment, were much more active leading to the direct non-CO_ad pathway. Due to pretreatment the GF surface has been modified and the effective catalytic system could be described as Pd/SnO₂–Pd(PdO)/GF with possible electronic interaction between support and catalyst. In direct formic acid fuel cell (DFAFC) experiments at 333 K and 1 M HCOOH, the peak power density using the Pd/GF anode reached 852 W m^?2 (57 g m^?2 Pd) compared to 392 W m^?2 (40 g m^?2 Pd) with a commercial Pd catalyst-coated membrane (CCM). The long-term stability of Pd-based anodes was poor and inferior to Pt–Ru (4:1 at. ratio) prepared and tested under identical conditions.     

Characteristics of solubilization and encapsulation of fullerene C60 in non-ionic Triton X-100 micelles

The solubilization and encapsulation of monomeric C₆₀ in Triton X-100 micelles were investigated. Characteristic hydrophobic interactions of the type π-π and CH-π between the Triton X-100 micelle and C₆₀ resulted in stable aqueous dispersions of C₆₀ in the micellar medium, as evidenced from UV-vis, fluorescence emission and micro-Raman spectroscopy. Cyclic voltammetry of C₆₀ encapsulated Triton X-100 in aqueous 5 mM LiClO₄ solution revealed a quasi-reversible one-electron reduction peak with E_1/2 = −0.61 V and a reversible reduction peak at E_1/2 = −1.11 V vs. Ag/AgCl reference electrode at a scan rate of 10 mV s⁻¹, a redox behaviour drifting substantially from that of pure C₆₀. An onset concentration of ∼0.025 mM for C₆₀ aggregation in the micellar core was substantiated from the characteristic absorption spectral broadening and quenching of pyrene fluorescence. The molar solubilization capacity of C₆₀ in aqueous Triton X-100 micellar solution was estimated spectrophotometrically to be 0.22.     

Distribution profile of water and suppression of methanol crossover in sulfonated polyimide electrolyte membrane for direct methanol fuel cells

We have developed novel cross-linked sulfonated polyimide (c-SPI) membrane as an electrolyte for direct methanol fuel cells (DMFCs). When the DMFC using the c-SPI membrane (thickness = 155 μm), Pt-Ru dispersed on carbon black (Pt-Ru/CB) anode and Pt/CB cathode with a Nafion^® ionomer was operated at 80 °C and 0.1 A cm⁻² with 1 M CH₃OH and oxygen (oxidant), the methanol crossover rate, j(CH₃OH), was suppressed to about 1/2 compared with that of the Nafion^® 117 membrane (thickness = 180 μm) with the same electrodes. It was found for both cells that the j(CH₃OH) was not so small as expected from the membrane thickness. In order to obtain a clue for the suppression of j(CH₃OH), the distribution profiles of water (containing CH₃OH) in thickness direction were investigated by measuring the specific resistances (ρ) between Pt probes inserted into the electrolyte membrane. Values of ρ at the anode side were low irrespective of the discharge current density, because such a part of the membrane was humidified thoroughly by liquid water (1 M CH₃OH) allowing free penetration of CH₃OH into the swollen polymer. In contrast, the values of ρ at the cathode side were high at the low current density due to drying of the membrane contacting with oxidant gas (O₂ or air) in low humidity. We have succeeded to suppress the j(CH₃OH) further (about 1/2 at 0.2 A cm⁻²) by using bilayer c-SPI, having a low ion exchanging (low swelling) barrier layer at the anode side without increasing the ohmic resistance, compared with that of the single c-SPI.     

Methanol oxidation at carbon supported Pt and Pt-Ru electrodes: an on line MS study using technical electrodes

Methanol oxidation at technical carbon based electrodes in 0.05 M H₂SO₄ has been investigated by cyclic voltammetry using online MS under the conditions of an acid methanol fuel cell (DMFC). 5% Pt on Norit BRX and 30% Pt/Ru (40/60) on Norit BRX were used as catalysts. It is shown that methanol oxidation at technical electrodes can be characterized by a combination of cyclic voltammetry and mass spectroscopy. The onset potentials and potential dependences of the methanol oxidation rate can be determined directly by monitoring the formation of CO₂. Onset potentials of 0.5V and 0.25 V/RHE have been measured for Pt and Pt-Ru catalysts, respectively. The onset of methanol oxidation can be shifted to even more cathodic potentials (0.2V) if the Pt-Ru electrode reduces oxygen simultaneously. Carbon monoxide gas was also purged into the methanol containing electroyte during measurement in order to investigate the catalyst performance under more adverse conditions. C¹³-labelled methanol was used to distinguish between CO₂. formed from methanol (m/e = 45) and CO-oxidation (m/e = 44). Without CO the use of C¹³-labelled methanol enabled a distinction between methanol oxidation and carbon corrosion. The methanol oxidation at the platinum catalyst is severely inhibited by the presence of CO, shifting its onset to 0.65 V/RHE. In contrast the performance of the Pt-Ru electrode is not seriously affected under these conditions. It is concluded that Pt-Ru is an excellent catalyst for a methanol anode in an acid methanol fuel cell (DMFC).     

Electrocatalytic properties of Pt/carbon composite nanofibers

Pt/carbon composite nanofibers were prepared by electrodepositing Pt nanoparticles directly onto electrospun carbon nanofibers. The morphology and size of Pt nanoparticles were controlled by the electrodeposition time. The resulting Pt/carbon composite nanofibers were characterized by running cyclic voltammograms in 0.20 M H₂SO₄ and 5.0 mM K₄[Fe(CN)₆] + 0.10 M KCl solutions. The electrocatalytic activities of Pt/carbon composite nanofibers were measured by the oxidation of methanol. Results show that Pt/carbon composite nanofibers possess the properties of high active surface area and fast electron transfer rate, which lead to a good performance towards the electrocatalytic oxidation of methanol. It is also found that the Pt/carbon nanofiber electrode with a Pt loading of 0.170 mg cm⁻² has the highest activity.     

电沉积制备Pt-Ru合金电极

采用电沉积法制备Pt-Ru合金电极.研究了电解液中Pt和Ru的浓度对电极表面组成形貌和电催化活性的影响.实验表明,优化电解液中Ru的浓度,可使电极表面形成分布均匀的纳米级Pt-Ru合金,并表现出良好的电催化性能.采用环境扫描电子显微镜表征电极的表面形貌;采用能谱仪测定Pt-Ru电极的表面组成;采用循环伏安法测量Pt-Ru电极的电化学性能.     

New mechanism of gas transport at the interface solid/liquid

It was recently shown that an abnormally fast transport of CO molecules takes place at the electrode/electrolyte interface of Pt and PtRu electrodes in H₂SO₄ and HClO₄ solutions. In the present paper, this phenomenon is tested for other gases, such as hydrogen and oxygen. The fast transport is also observed at the solid/electrolyte solution interface of other electrode materials and at the glass/electrolyte interface. Several experiments are shown, demonstrating that mass transfer takes place at a velocity, which is more than one order of magnitude higher than expected for usual diffusion conditions.Assuming radial mass transfer at the interface of a Pt disc, the activation energy, E_a = 23 kJ mol⁻¹, was calculated from Arrhenius plots. The same value was measured in H₂SO₄ and HClO₄ as supporting electrolytes. The mass transport parameter, Y, at 298 K was 4.8 × 10⁻³ cm² s⁻¹ and 2.9 × 10⁻³ cm² s⁻¹ in 0.5 M H₂SO₄ and 1 M HClO₄ respectively.     

Electrodeposited Pd-Co catalyst for direct methanol fuel cell electrodes: Preparation and characterization

Pd-Co alloy has been recently proposed as a catalyst for the cathode of direct methanol fuel cells with both excellent oxygen reduction activity and methanol tolerance, hence electrodeposition of this alloy is an attractive approach for synthesizing porous metal electrodes with high methanol tolerance in direct methanol fuel cells. In this study, we electrodeposited two types of Pd-Co films onto Au substrates by applying different current density (−10 or −200 mA cm⁻²); and then characterized them in terms of morphology, composition, crystal structure, and catalytic activity. Pd-Co deposited at −10 mA cm⁻² was smooth and possessed smaller particles (ca. 10 nm), while that at −200 mA cm⁻² was dendritic (or rough) and possessed larger particles (ca. 50 nm). Both the Pd-Co alloys were found to be almost the same structure, i.e. a solid solution of ca. Pd₇Co₃ with Pd-skin, and also confirmed to possess comparable activity in oxygen reduction to Pt (potential difference at 1.0 μA cm⁻² was 0.05 V). As for methanol tolerance, cell-voltage was not influenced by addition of 1 mol dm⁻³ methanol to the oxidant solution. Our approach provides fundamental technique for synthesizing Pd-Co porous metal electrodes by electrodeposition.     

Apparent electrocatalysis on 3D nanoporous platinum film electroplated from hexagonal lyotropic liquid crystalline phase of Triton X-100

Electrocatalytic effect of nanoporous interface between platinum (Pt) and electrolyte was investigated in terms of direct electrochemical oxidation of glucose. A Pt film with 3D nanopores was electroplated from the hexagonal (H₁) lyotropic liquid crystal (LLC) phase of t-octylphenoxypolyethoxyethanol (Triton X-100), a nonionic surfactant with a phenyl group in a hydrophobic tail. This Pt film, which was electroplated from H₁-LLC of Triton X-100 (ePt-H₁-TX100), comprised closely stacked crystalline (face centered cubic) nanoparticles (diameter, 4-7 nm) with 3D nanopores (width, 1-2 nm) developed among the particles. The ePt-H₁-TX100 showed high surface roughness and selective enhancement of a sluggish redox reaction, that is, kinetic-controlled reaction such as glucose oxidation. Nonenzymatic glucose sensing can be achieved by using discriminatively enhanced sensitivity to glucose over redox active interfering molecules.     

Effect of metals on silver electrodeposition: Application to the detection of cisplatin

In the present work, the influence of several metals (Co, Ru, Pd, Os, Pt, Cu, Pb), deposited on a carbon paste electrode, towards silver electrodeposition was tested. First, adequate conditions for the electrodeposition of metals on the electrode were found. Then, the cyclic voltammograms registered (silver deposition curves and analytical signals) showed that Co, Cu, Pt and Pd were able to accelerate silver electrodeposition. Finally, a valid methodology for the detection of cisplatin was established. It is based on the deposition of silver on a Pt (from cisplatin) modified electrode and the analytical signal corresponds to the anodic stripping of the deposited silver. A limit of detection of 3.2 × 10⁻⁹ mol dm⁻³ (1 ng cm⁻³) cisplatin was obtained.     

Anodic catalysts for polymer electrolyte fuel cells: the catalytic activity of Pt/C,Ru/C and Pt-Ru/C in oxidation of CO by O2

The catalytic activity for oxidation of CO by O₂ was investigated on commercial Pt/C, Pt-Ru/C (Pt/Ru atomic ratio = 20, 3, 1, 1/3) and Ru/C. All samples contained 20 wt.% metal. Assuming equal surface and bulk composition, the number of surface Pt and Ru atoms was calculated from the average size of the supported metal particle as determined by TEM. On Pt-Ru/C alloys, the turnover frequency per Ru atom, N_Ru/molecules s⁻¹ Ru-atom⁻¹, was independent of chemical composition. This finding suggests that the active site in these alloys is Ru. In the temperature range 300–400 K, the turnover frequency per active metal atom was 50–300 times higher on Pt-Ru/C than on Pt/C. The turnover frequency was 400 times higher on Ru/C than on Pt/C at 313 K and 90 times higher at 353 K. Addition of water vapor to the reactant mixture left the catalytic activity of Ru/C unchanged but slightly increased the activity of Pt/C. On both catalysts the activation energy and reaction orders were nearly the same as in dry atmosphere. Conversely, the addition of water markedly decreased the activation energy for Pt-Ru(1 : 1)/C alloy (from 19 to 11 kcal mol⁻¹). These findings suggest that fuel cells equipped with Pt-Ru/C anodes perform better than cells with Pt/C anodes. They do so because Ru effectively oxidizes the carbon monoxide present as an impurity in the H₂-reformed fuel.     

Effects of ozone treatment of carbon support on Pt-Ru/C catalysts performance for direct methanol fuel cell

This research is aimed to increase the activity and utilization of Pt-Ru alloy catalysts and thus to lower the catalyst loading in anodes for methanol electrooxidation. The Pt-Ru/C catalysts were prepared by chemical reduction. The support of Vulcan XC-72 carbon black was pretreated by ozone at different temperatures for different times. The specific surface area of the samples was evaluated by the standard BET method. The surface concentrations of oxygen were determined by XPS. The results showed that the surface concentrations of oxygen on the carbon were first decreased and then increased with pretreating times, and the specific surface area of the carbon was decreased with pretreating times at the same temperature. The specific surface area was increased with increasing temperature, and the surface concentration of oxygen was first decreased and then increased with increasing temperature for the same pretreating time. Pt-Ru/C catalysts supported by untreated and O₃ treated carbon black were characterized and tested for methanol electrooxidation. X-ray diffraction (XRD) was used to characterize the influence of carbon treated with ozone on Pt-Ru/C catalysts. It was found that the catalysts were composed only of f.c.c. Pt-Ru alloy particles without metallic Ru or Ru oxide. Cyclic voltammetry (CV) and Tafel curves were used for methanol electrooxidation on Pt-Ru/C catalysts in a solution of 0.5 mol/L CH₃OH and 0.5 mol/L H₂SO₄, showing that the catalytic activity of Pt-Ru/C catalysts supported by ozone treated carbon was higher than that by the untreated one. The ozone treatment time and temperature, which affect the performance of Pt-Ru/C catalysts, were discussed. Electrochemical measurements showed that the catalysts supported by the carbon after ozone treatment for 6 min at 140 °C had the best performance.     

In situ radiotracer and voltammetric study of the formation of surface adlayers in the course of Cr(VI) reduction on polycrystalline and (1 1 1) oriented platinum

This paper is focused on the in situ radiotracer and voltammetric studies of the induced HSO₄⁻/SO₄²⁻ adsorption at Pt(poly) and Pt(1 1 1) surfaces in 0.1 mol dm⁻³ HClO₄ solution in the course of Cr(VI) electroreduction. Besides this, the sorption behavior of HSO₄⁻/SO₄²⁻ ions on bare Pt(poly) and Pt(1 1 1) electrodes is compared and discussed. From the experimental results it can be stated that: (i) although the extent of bisulfate/sulfate adsorption is strongly dependent upon the crystallographic orientation of Pt surfaces, the maximum coverage on the Pt(1 1 1) does not exceed 0.2 monolayer; (ii) the Cr(VI) electroreduction on both poly- and (1 1 1) oriented platinum proceeds via a ce (chemical-electron-transfer) mechanism to yield Pt surfaces covered with intermediate surface adlayers containing Cr(VI) particles (and reduced Cr-containing adspecies) and ‘strongly bonded’ HSO₄⁻/SO₄²⁻ ions; (iii) while the coverage of platinum surfaces by the intermediate complexes formed in the course of Cr(VI) electroreduction at E > 0.20 V is basically independent of the crystallographic orientation of the Pt electrode, the onset for rapid Cr(VI) reduction is highly affected by the nature and crystallographic orientation of the electrode.     

CO tolerance and CO oxidation at Pt and Pt-Ru anode catalysts in fuel cell with polybenzimidazole-H3PO4 membrane

CO tolerance of H₂-air single cell with phosphoric acid doped polybenzidazole (PA-PBI) membrane was studied in the temperature range 140-180 °C using either dry or humidified fuel. Fuel composition was varied from neat hydrogen to 67% (vol.) H₂-33% CO mixtures. It was found that poisoning by CO of Pt/C and Pt-Ru/C hydrogen oxidation catalysts is mitigated by fuel humidification. Electrochemical hydrogen oxidation at Pt/C and Pt-Ru/C catalysts in the presence of up to 50% CO in dry or humidified H₂-CO mixtures was studied in a cell driven mode at 180 °C. High CO tolerance of Pt/C and Pt-Ru/C catalysts in FC with PA-PBI membrane at 180 °C can be ascribed to combined action of two factors—reduced energy of CO adsorption at high temperature and removal of adsorbed CO from the catalyst surface by oxidation. Rate of electrochemical CO oxidation at Pt/C and Pt-Ru/C catalysts was measured in a cell driven mode in the temperature range 120-180 °C. Electrochemical CO oxidation might proceed via one of the reaction paths—direct electrochemical CO oxidation and water-gas shift reaction at the catalyst surface followed by electrochemical hydrogen oxidation stage. Steady state CO oxidation at Pt-Ru/C catalyst was demonstrated using CO-air single cell with Pt-Ru/C anode. At 180 °C maximum CO-air single cell power density was 17 mW cm⁻² at cell voltage U = 0.18 V.