Kinetics and mechanism of oxygen electroreduction in alkaline solutions on xc-72r carbon black modified by products of pyrolysis of cobalt 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin

Cathodic oxygen reduction on XC-72R carbon black modified by products of pyrolysis of cobalt 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin (CoTMPP) (XC-72M) was studied. When XC-72R carbon black is modified, new active centers (ACs) are formed on the surface of the carbon support, on which the direct reaction to OH^- occurs, as shown using the rotating ring-disk electrode technique. The process of oxygen reduction on nonmodified carbon black occurs via the serial path. At low polarizations, the dependence of potential on pH corresponds to the slope of ??30 mV both for the carbon material and modified carbon black. This value is close to the coefficient in the Nernst equation for H₂/HO ₂ ^? . The slow stage of oxygen reduction is the transfer of the first or second electron to the adsorbed molecule. Herewith, the difference in the kinetics and mechanism of oxygen reduction on XC-72R and XC-72M is related to a stronger adsorption interaction of oxygen and ACs on XC-72M. The {ie1113-1} value in the pH range of 12?C14.6 is ?15 to ?20 mV both for XC-72R and XC-72M. In the case of the second halfwave potential on XC-72R, it is ?50 to ?60 mV. The observed effects are explained by a change in the surface state of catalysts at an increase in adsorption of OH^? ions at an increase in pH.     

Comparative characteristics of cathodes with different catalytic systems in hydrogen–oxygen and hydrogen–air fuel cells with proton-conducting polymer electrolyte

The characteristics of low-temperature hydrogen–oxygen (air) fuel cell (FC) with cathodes based on the 50 wt % PtCoCr/C and 40 wt % Pt/CNT catalysts synthesized on XC72 carbon black and carbon nanotubes (CNT) are compared with the characteristics of commercial monoplatinum systems 9100 60 wt % Pt/C and 13100 70% Pt/C HiSPEC. It is shown that the synthesized catalysts exhibit a high mass activity, which is not lower than that of commercial Pt/C catalysts, a high selectivity with respect to the oxygen reduction to water, and a significantly higher stability. The characteristics of PtCoCr/C and Pt/CNT were confirmed by testing in the hydrogen—oxygen FCs. However, when air was used at the cathode, especially in the absence of excessive pressure, a voltage of FC with the cathode based on PtCoCr/XC72 is lower as compared with the commercial systems. Probably, this is associated with the transport limitations in the structure of trimetallic catalyst synthesized on XC72 carbon black due to the absence of mesopores. This drawback was eliminated to a large extent by raising the volume of mesopores as a result of application of mixed support (XC72 + CNT) and the use of only CNT for the synthesis of the monoplatinum catalyst. However, this did not eliminate another drawback, namely, a low platinum utilization coefficient in the cathode active layer as compared with that measured under the model conditions in the 0.5 M Н₂SO₄ solution. Therefore, further research is required to improve the structure of the catalytic systems, which are synthesized both on carbon black and nanotubes, while maintaining their high stability and selectivity.     

Activity, stability and degradation of multi walled carbon nanotube (MWCNT) supported Pt fuel cell electrocatalysts

Understanding and improving durability of fuel cell catalysts are currently one of the major goals in fuel cell research. Here, we present a comparative stability study of multi walled carbon nanotube (MWCNT) and conventional carbon supported platinum nanoparticle electrocatalysts for the oxygen reduction reaction (ORR). The aim of this study was to obtain insight into the mechanisms controlling degradation, in particular the role of nanoparticle coarsening and support corrosion effects. A MWCNT-supported 20 wt.% Pt catalyst and a Vulcan XC 72R-supported 20 wt.% Pt catalyst with a BET surface area of around 150 m(2) g(-1) and with a comparable Pt mean particle size were subjected to electrode potential cycling in a "lifetime" stability regime (voltage cycles between 0.5 to 1.0 V vs. RHE) and a "start-up" stability regime (cycles between 0.5 to 1.5 V vs. RHE). Before, during and after potential cycling, the ORR activity and structural/morphological (XRD, TEM) characteristics were recorded and analyzed. Our results did not indicate any activity benefit of MWCNT support for the kinetic rate of ORR. In the "lifetime" regime, the MWCNT supported Pt catalyst showed clearly smaller electrochemically active surface area (ECSA) and mass activity losses compared to the Vulcan XC 72R supported Pt catalyst. In the "start-up" regime, Pt on MWCNT exhibited a reduced relative ECSA loss compared to Pt on Vulcan XC 72R. We directly imaged the trace of a migrating platinum particle inside a MWCNT suggesting enhanced adhesion between Pt atoms and the graphene tube walls. Our data suggests that the ECSA loss differences between the two catalysts are not controlled by particle growth. We rather conclude that over the time scale of our stability tests (10,000 potential cycles and beyond), the macroscopic ECSA loss is primarily controlled by carbon corrosion associated with Pt particle detachment and loss of electrical contact.     

Structural and electrocatalytic features of Pt/C catalysts fabricated in supercritical carbon dioxide

Pt/carbon black samples fabricated from dimethyl (1,5-cyclooctadiene) platinum(II) in supercritical CO₂ are characterized in relation to possible applications in methanol fuel cell. The problem of precise material characterization is addressed in frames of X-ray diffractometry, transmission electron microscopy, and electrochemical techniques of the true surface area determination. The catalysts with Pt loading of 20–40 wt.% consist of nm-size particles, with the lattice defectiveness dependent on the fabrication mode. To check the effect of support, various types of carbon blacks (Vulcan XC72R and acetylene black AC-1) are used. In contrast to commercial HiSpec catalysts, no pronounced increase of particle size with Pt loading is found. Specific steady-state activity towards methanol oxidation appears to be essentially higher than for commercial catalysts, mostly because the self-poisoning effects are less pronounced. As for poisoning of Pt with organic species (resulting from the ligand of precursor), its effects are demonstrated to be minor after CO or methanol adsorption accompanied by desorption of contaminating by-product.     

Supercritical,Freezing and Thermal Drying Process of Resorcinol‐Formaldehyde Polymer based Nano‐carbons and their Highly Loaded PtRu Anode Electrocatalyst for DMFC

The capillary condensation is affected by micropore and nanopore of catalyst layer on fuel cell. Due to limitation of sluggish mass transport and electrocatalytic activity, to retain the pore skeleton of carbon and metal nanoparticles are very significant for enhanced utilizations of pore structure in electrochemical reaction. Besides, thickness of electrocatalyst layer is very crucial due to one of the factor affected by cell performance of direct methanol fuel cell. Highly loaded four Pt?Ru anode catalysts supported on resorcinol‐formaldehyde (RF) polymer based on meso‐porous carbons (80 wt.% Pt?Ru/carbon cryogel, 80 wt.% Pt?Ru/carbon xerogel and 80 wt.% Pt?Ru/carbon aerogel) and conventional carbon (80 wt.% Pt?Ru/Vulcan XC‐72) were prepared by colloidal method for direct methanol fuel cell. These catalysts were characterized by X‐Ray diffraction (XRD), High resolution transmission electron microscopy (HR‐TEM) and X‐ray photoemission (XPS). The results of CO stripping voltammetry, cyclic voltammetry (CV) and single cell test performed on DMFC show that Pt?Ru/carbon cryogel and Pt?Ru/carbon aerogel exhibits better performances in comparison to Pt?Ru/carbon xerogel and Pt?Ru/Vulcan XC‐72. It is thus considered that particle size, oxidation state of metal and electrochemical active surface area of these catalysts are important role in electrocatalytic activity in DMFC.     

Oxygen electroreduction at catalysts PtM (M = Co,Ni, or Cr)

Bimetallic catalysts PtM (M = Co, Ni, or Cr) are synthesized. They exceed purely platinum commercial catalyst E-TEK (20 wt % Pt) in its mass activity (mA/mg_Pt) and specific activity (mA/c_Pt²) in the oxygen reduction reaction. According to XRD data, the high-temperature synthesis involving metal N₄-complexes, chloroplatinic acid, and XC72 carbon black as precursors, yields alloys (or solid solutions) of the metals. The higher activity of the bimetallic catalyst PtCo/C is likely to be caused by the practically entire formation of solid solutions (Pt₃Co and PtCo), unlike PtNi and PtCr where nickel and chromium exist also as oxides that decorate the electrode surface and partly block active centers. It is shown that the mechanism of the oxygen reduction reaction at the synthesized catalysts is similar to that of oxygen reduction at the purely platinum catalyst. The slow stage in the process is transfer of the 1st electron; at potentials more positive than 0.6 V the reaction mainly yields water. The higher electrocatalytic activity of the bimetallic systems is caused by the alloy formation, which leads to changes in the bond length between platinum atoms. The achieving of the optimal bond length, as a result of the alloy formation, provides appropriate conditions for dissociative adsorption of oxygen molecules; the surface coverage with oxygen-containing particles adsorbed from water (which block active centers for O₂ adsorption) decreased. The increase in the activity may also be caused by the formation of the “core-shell” structures whose surface is enriched with platinum whose surface properties are changed under the ligand action of the core formed by the metal alloy     

The role of carbon support morphology in the formation of catalytic layer of solid-polymer fuel cell

The Pt/C catalysts with similar morphology of active catalytic phase (platinum nanoparticles), which were deposited on the supports with different types of carbon structures (Vulkan XC-72 carbon black, Taunit carbon tubes, and Timrex HSAG-300 carbon support with graphite structure), were fabricated by the method of electrochemical dispersion. The effect of the carbon structure type on the electrocatalytic properties of Pt/C catalysts was studied in their operation in the three-electrode cell and in-service in the membrane-electrode assembly of air-hydrogen solid-polymer fuel cell. The Pt/C catalyst based on the Vulkan XC-72 carbon support showed the best performance. The anisotropic shape of Taunit carbon nanotubes and the microstructure of Timrex HSAG-300 carbon support do not allow us to form a catalytic layer with a large active platinum surface area and a structure, which provides an effective ionic transport and mass exchange near the platinum surface.     

Novel electroactive surface functionality from the coupling of an aryl diamine to carbon black

The reaction of 1,2-diaminoanthraquinone with Vulcan XC72 carbon in 4 M HCl produces two distinct surface bound anthraquinone species, with formal potentials of ca. ?0.03 and ?0.19 V vs. SCE. The more positive couple is very stable to electrochemical cycling and has been assigned to the expected benzimidazole linkage. The other wave, which decays over hours of cycling is thought to be due to an amine linkage. This type of linkage also appears to be formed spontaneously when 1,2-diaminoanthraquinone is adsorbed onto Vulcan XC72 from methanol.     

Impact of the Pt catalyst on the oxygen electroreduction reaction kinetics on various carbon supports

Micro- and mesoporous carbide-derived carbons synthesized from molybdenum and tungsten carbides were used as porous supports for a platinum catalyst. Synthesized materials were compared with commercial Vulcan XC72R conducting furnace black. The scanning electron microscopy, X-ray diffraction, Raman spectroscopy, high-resolution transmission electron microscopy, and low-temperature N₂ adsorption methods were applied to characterize the structure of catalysts prepared. The kinetics of oxygen electroreduction in 0.5 M H₂SO₄ solution was studied using cyclic voltammetry and rotating disk electrode methods. The synthesized carbide-derived carbons exhibited high specific surface area and narrow pore size distribution. The platinum catalyst was deposited onto the surface of a carbon support in the form of nanoparticles or agglomerates of nanoparticles. Comparison of carbide-derived carbons and Vulcan XC72R as a support showed that the catalysts prepared using carbide-derived carbons are more active towards oxygen electroreduction. It was shown that the structure of the carbon support has a great influence on the activity of the catalyst towards oxygen electroreduction.     

Effect of supports on activity and stability of Pt–Pd catalysts for oxygen reduction reaction in proton exchange membrane fuel cells

The platinum–palladium alloy (Pt–Pd) catalysts were prepared on various supports including Vulcan XC72, Hicon Black (HB), multiwalled carbon nanotubes (MWCNTs), and titanium dioxide (TiO₂) by a combined approach of impregnation and seeding using NaBH₄ reduction at low temperature. Their oxygen reduction reaction (ORR) activities in single proton exchange membrane fuel cell (PEMFC) under a H₂/O₂ environment and their stability in an acid electrolyte (0.5 M H₂SO₄) were tested and compared with the Vulcan XC72-supported Pt (Pt/C) catalysts. The presence of the Pd metal as well as different types of supports affected the ORR activity in H₂/O₂ environment and stability in the acid electrolyte. Overall, the HB-supported Pt–Pd (Pt–Pd/HB) catalysts provided the highest current density at 0.6 V under a H₂/O₂ environment, while the MWCNT-supported Pt–Pd (Pt–Pd/MWCNT) catalyst provided the best stability in an acid electrolyte.     

Pig Bone Derived Hierarchical Porous Carbon‐Supported Platinum Nanoparticles with Superior Electrocatalytic Activity Towards Oxygen Reduction Reaction

Hierarchical porous carbon (HPC) with nitrogen doped three dimension open macropore structure was prepared from pig bone, and applied for the support material for platinum nanoparticle (Pt NP) electrocatalyst. Compared with carbon black supported Pt NP electrocatalysts, the Pt/HPC exhibited larger electrochemical active surface area and enhanced catalytic properties for the oxygen reduction reaction (ORR) in terms of on‐set potential, current density, mass activity and stability. The superior catalytic activity is mainly attributed to the high surface area, hierarchical porous structures and the nitrogen‐doped surface properties of the HPC, indicating it is a promising support material for the ORR electrocatalysts.     

大孔碳载Ir催化剂对氧还原的电催化性能和抗甲酸能力

本文用X射线能量色散谱(EDS)、X射线衍射(XRD)谱、拉曼光谱和电化学等技术研究了直接甲酸燃料电池(DFAFC)中Vulcan XC-72炭黑载Ir(Ir/XC)和大孔炭载(Ir/MC)催化剂对氧还原的电催化性能和抗甲酸的能力。发现Ir/MC催化剂对氧还原的电催化性能要优于Ir/XC催化剂,氧起始还原电位比在Ir/XC催化剂上正移0.1V,极限电流密度比在Ir/XC催化剂上大30％左右。由于Ir/MC和Ir/XC催化剂的Ir粒子平均粒径和相对结晶度相似,因此,这只能归结于MC有大的孔径和孔率及高的石墨化程度。另外2种催化剂都有很好的抗甲酸能力。因此MC是一种比XC更好的催化剂的炭载体。     

Bioelectrocatalytic Reduction of Oxygen in the Presence of Laccase Adsorbed on Carbon Electrodes

The kinetics of electroreduction of molecular oxygen on isotropic pyrocarbon with adsorbed laccase or a laccase–Nafion composite is studied. Kinetic parameters thus obtained are compared with those determined previously for electrodes of carbon black with adsorbed laccase. The closeness of kinetic parameters of the reaction of bioelectrocatalytic reduction of oxygen by laccase adsorbed on smooth (pyrocarbon) and disperse (carbon black) carbon materials led to a refined reaction mechanism. The slow stage of the reaction of bioelectrocatalytic reduction of oxygen is a synchronous transfer of two first electrons onto the oxygen molecule, similar to the mechanism of enzymatic catalysis by laccase.     

Pt/Pd/C catalysts with ultra low platinum content for oxygen reduction reaction

The activity of Pt/Pd/C ETEK catalysts of the core-shell type with an ultralow content of platinum (0.5–15 μg cm^?2) based on a commercial palladium catalyst is shown to exceed the activity of commercial Pt/C ETEK catalysts in the oxygen reduction reaction. The activity sharply increases with the decrease in the platinum content down to values corresponding to monolayer and submonolayer of platinum on palladium. This dependence wasn’t observed for the same amounts of platinum deposited on the carbon support Vulcan XC-72. This makes it possible to conclude that the most probable factor responsible for the high catalytic activity of Pt/Pd/C ETEK is the effect of palladium on the electronic properties of platinum rather than the effect of structural modification of the platinum deposit induced by the decrease in the platinum amount deposited on a foreign metal or a carbon support.     

Effect of metal loading and carbon support microstructure on the dispersion of Pt/C catalysts prepared viaadsorption of chloroplatinic acid

Summary Adsorption of<span lang=EN-US style='mso-ansi-language:EN-US'>H₂PtCl₆onto a carbon support followed by reduction of the adsorbed platinum species with H₂at 250°C leads to<span lang=EN-GB style='mso-ansi-language:EN-GB'>Pt/C catalysts, which show universal volcano-like dependence of platinum dispersion on the metal loading in the range from 0.01 to 0.55mmol (Pt)/m²(S_BET)<span lang=EN-GB style='mso-ansi-language:EN-GB'>when highly disordered carbons, namely, active carbons and carbon blacks, are used as supports. The maximal dispersion D(CO/Pt) = 0.8 is attained at<span lang=EN-US style='mso-ansi-language:EN-US'>0.18mmol (Pt)/m² (S_BET). With<span lang=EN-GB style='mso-ansi-language:EN-GB'>other factors being equal, the dispersion of platinum supported on carbons with a more regular crystal structure, especially Sibunit-type supports, proves to be the highest and independent of the metal loading.The differences between the two groups of carbon supports are explained by the differences in the state of the adsorbed platinum precursors.     

Electrochemical and physical characterization of Pt–Ru alloy catalyst deposited onto microporous–mesoporous carbon support derived from Mo2C at 600 °C

The electrochemical reduction of oxygen on binary Pt–Ru alloy deposited onto microporous–mesoporous carbon support was studied in 0.5 M H₂SO₄ solution using cyclic voltammetry, rotating disk electrode (RDE), and impedance method. The microporous–mesoporous carbon support C(Mo₂C) with specific surface area of 1,990 m²?g^?1 was prepared from Mo₂C at 600 °C using the chlorination method. Analysis of X-ray diffraction, photoelectron spectroscopy, and high-resolution transmission electron microscopy data confirms that the Pt–Ru alloy has been formed and the atomic fraction of Ru in the alloy was ～0.5. High cathodic oxygen reduction current densities (?160 A?m^?2 at 3,000 rev?min^?1) have been measured by the RDE method. The O₂ diffusion constant (1.9?±?0.3?×?10^?5?cm²?s^?1) and the number of electrons transferred per electroreduction of one O₂ molecule (～4), calculated from the Levich and Koutecky–Levich plots, are in agreement with literature data. Similarly to the Ru/RuO₂ system in H₂SO₄ aqueous solution, nearly capacitive behavior was observed from impedance data at very low ac frequencies, explained by slow electrical double-layer formation limited by the adsorption of reaction intermediates and products into microporous–mesoporous Pt–Ru–C(Mo₂C) catalyst. All results obtained for C(Mo₂C) and Pt–Ru–C(Mo₂C) electrodes have been compared with corresponding data for commercial carbon VULCAN® XC72 (C(Vulcan)) and Pt–Ru–C(Vulcan) electrodes processed and measured in the same experimental conditions. Higher activity for C(Mo₂C) and Pt–Ru–C(Mo₂C) has been demonstrated.     

Electroreduction of Oxygen and Electrooxidation of Methanol at Carbon and Single Wall Carbon Nanotube Supported Platinum Electrodes

The present research aimed at investigating the electrocatalytic properties and the electrochemical deposition of Pt nanoparticles on carbon powder, carbon nanotube and preparation of carbon and single wall carbon nanotube supported platinum electrodes. The Pt nanoparticles were synthesized by electroreduction of hexachloroplatinic acid in aqueous solution at ?200 mV. Electrocatalytic properties of the modified electrodes for oxygen reduction were investigated by cyclic voltammetry in O₂ saturated solution containing 0.1 M HClO₄. Methanol electrooxidation at the modified surfaces in 0.5 M HCLO₄ was studied by cyclic voltammetry. The corresponding results showed that the Pt/SWCNT/GC electrode exhibits more improved catalytical activity than the Pt/C/GC electrode.     

高分散的介孔碳载Pt纳米粒子的制备及其对乙二醇的电催化氧化性能

以二氧化硅溶胶为硬模板,嵌段聚合物F127为软模板,通过双模板法合成了高介孔比例、窄孔径分布的介孔碳(MC).进而经乙二醇还原法制备了高分散的MC载铂催化剂(Pt/MC).采用循环伏安、计时电流、线性扫描伏安和电化学阻抗谱法研究了硫酸溶液中乙二醇在Pt/MC催化剂电极上的电化学氧化行为.实验结果表明,Pt/MC催化剂对乙二醇的电催化氧化性能显著高于商业化炭黑XC72R载Pt(Pt/XC72R)催化剂.电化学阻抗谱分析进一步揭示,乙二醇在Pt/MC催化剂电极上的电氧化反应具有较低的电荷传递电阻.Pt/MC催化剂高的电催化活性可以归结于MC大的孔径和均一的介孔结构对电子传输和传质的促进作用.     

Carbon Corrosion in Proton-Exchange Membrane Fuel Cells: Spectrometric Evidence for Pt-Catalysed Decarboxylation at Anode-Relevant Potentials

The carbon oxidation reaction (COR) is a critical issue in proton-exchange membrane fuel cells (PEMFCs), as carbon in various forms is the most used electrocatalyst support material. The COR is thermodynamically possible above the C/CO₂ standard potential, but its rate becomes significantly important only at high overpotential (e. g. PEMFC cathode potential). Herein, using on-line differential electrochemical mass spectrometry, we show that oxygen-containing carbon surface groups present on high-surface aera carbon, Vulcan XC72 or reinforced graphite are oxidized at PEMFC anode-relevant potential (E=0.1 V vs. the reversible hydrogen electrode, RHE), but not at E=0.4 V vs. RHE. We rationalized our findings by considering a Pt-catalysed decarboxylation mechanism in which Pt nanoparticles provide adsorbed hydrogen species to the oxygen-containing carbon surface groups, eventually leading to evolution of carbon dioxide and carbon monoxide. These results shed fundamental light on an unexpected degradation mechanism and facilitate the understanding of the long-term stability of PEMFC anode nanocatalysts.     

Stabilization of high-performance oxygen reduction reaction pt electrocatalyst supported on reduced graphene oxide/carbon black composite

Oxygen reduction reaction (ORR) catalyst supported by hybrid composite materials is prepared by well-mixing carbon black (CB) with Pt-loaded reduced graphene oxide (RGO). With the insertion of CB particles between RGO sheets, stacking of RGO can be effectively prevented, promoting diffusion of oxygen molecules through the RGO sheets and enhancing the ORR electrocatalytic activity. The accelerated durability test (ADT) demonstrates that the hybrid supporting material can dramatically enhance the durability of the catalyst and retain the electrochemical surface area (ECSA) of Pt: the final ECSA of the Pt nanocrystal on the hybrid support after 20?000 ADT cycles is retained at >95%, much higher than the commercially available catalyst. We suggest that the unique 2D profile of the RGO functions as a barrier, preventing leaching of Pt into the electrolyte, and the CB in the vicinity acts as active sites to recapture/renucleate the dissolved Pt species. We furthermore demonstrate that the working mechanism can be applied to the commercial Pt/C product to greatly enhance its durability.