Silica-sol-templated mesoporous carbon as catalyst support for polymer electrolyte membrane fuel cell applications

Mesoporous carbon (MC) samples having especially high specific surface area, pore size, and pore volume (e.g. pore volume in excess of 4 cm³ g⁻¹) were prepared and their suitability as Pt catalyst supports in polymer electrolyte membrane fuel cells was examined. Pt particles on the MC support were slightly larger than those on commercial samples of Pt on carbon black, and they showed a greater tendency to agglomerate on the MC support than on carbon black. Ex situ cyclic voltammetry gave values for electrochemically active surface area that were about half that for a commercial Pt-on-carbon black sample. Preliminary attempts to prepare thin-film electrodes from Pt/MC samples with a Nafion binder using conventional ink formulations failed, probably because much of the Nafion electrolyte was taken up inside support pores and was not available to bind the support particles together. An alternate approach involving painting of catalyst inks directly onto gas diffusion layers was used to prepare membrane electrode assemblies (MEAs) from Pt/MC samples, which were tested using single-cell test hardware. Performance of these Pt/MC sample MEAs was compared with that prepared by decal transfer method with commercially obtained Vulcan XC-72R supported Pt catalyst. The reasons for the lower performance of Pt/MC were discussed.     

Monodispersed hard carbon spherules as a catalyst support for the electrooxidation of methanol

Hard carbon spherules (HCS) were used as support of Pt nanoparticles as electrocatalyst for direct methanol fuel cells (DMFCs). Scanning electron microscopy (SEM) images show that the size of the Pt particles on HCS by reduction of K₂PtCl₆ with ethylene glycol is 4-5 nm. High-resolution transmission electron microscopy (HRTEM) study reveals that the Pt particles on the HCS surface have faceted crystalline structures. The size and aggregation of the Pt particles depend on the surface properties of the carbon support and the medium of the reduction reaction. Cyclic voltammetry and galvanostatic polarization experiments show that the Pt/HCS catalyst exhibits a higher catalytic activity in the electrooxidation of methanol than either the Pt/MCMB or the commercial Pt/Vulcan XC-72 catalyst does.     

竹制活性炭作为催化剂载体的研究

利用SEM、N₂-物理吸附和联碱滴定法等表征手段系统比较了竹质活性炭和普通竹炭与其他材质活性炭在物化性能方面的异同,同时利用CO-化学吸附考察了这些材料作为催化剂载体对负载钯催化剂金属钯分散度的影响。实验结果表明,竹质活性炭在比表面积、孔结构、灰分含量和表面基团等物化性能方面都已具备作为催化剂载体的条件,显示出成为新催化剂载体的潜力。     

Facile synthesis of bimodal porous silica and multimodal porous carbon as an anode catalyst support in proton exchange membrane fuel cell

A simple and easy sol-gel approach has been developed to directly synthesize in situ three-dimensionally interconnected uniform ordered bimodal porous silica (BPS) incorporating both the macroporosity and mesoporosity in the lattice without extra synthesis process performed in previous work. Multimodal porous carbon (MPC) was fabricated through the inverse replication of the BPS. The unique structural characteristics such as well-developed 3-D interconnected ordered macropore framework with open mesopores embedded in the macropore walls, large surface area (1120 m² g⁻¹) and mesopore volume (1.95 cm³ g⁻¹) make MPC very attractive as an anode catalyst support in polymer exchange membrane fuel cell. The MPC-supported Pt-Ru alloy catalyst has demonstrated much higher power density toward hydrogen oxidation than the commercial carbon black Vulcan XC-72-supported ones.     

Hollow core/mesoporous shell carbon capsule as an unique cathode catalyst support in direct methanol fuel cell

Hollow core mesoporous shell (HCMS) carbon has been explored for the first time as a cathode catalyst support in direct methanol fuel cells (DMFCs). The HCMS carbon consisting of discrete spherical particles possesses unique structural characteristics including large specific surface area and mesoporous volume and well-developed interconnected void structure, which are highly desired for a cathode catalyst support in low temperature fuel cells. Significant enhancement in the electrocatalytic activity toward oxygen reduction reaction has been achieved by the HCMS carbon-supported Pt nanoparticles compared with carbon black Vulcan XC-72-supported ones in the DMFC. In addition, much higher power was delivered by the Pt/HCMS catalysts (i.e., corresponding to an enhancement of ca. 91–128% in power density compared with that of Pt/Vulcan), suggesting that HCMS carbon is a unique cathode catalyst support in direct methanol fuel cell.     

Functional mesoporous carbon built from the 1,10-phenanthroline building block: A new class of catalyst support

A simple synthesis of a high surface area catalyst support composed of a nanoporous carbon architecture built from a 1,10-phenanthroline precursor is described.     

Role of active sites in the steam activation of high unburned carbon fly ashes

Previous studies on carbon gasification have not included high unburned carbon content fly ashes, and therefore it remains unclear why not all fly ash carbon samples are equally suitable for activation. The concentration of active sites is well known to influence carbon gasification reactions. Therefore, the objective of this work was to investigate the effect of the concentration of active sites on the behavior of fly ash carbon samples upon steam activation. Six fly ash carbons were selected to produce activated carbons using steam at 850 °C. The concentration of active sites was determined by non-dispersive infrared analysis (NDIR), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). XRD analyses were also conducted to determine the crystallite size. It was observed that the concentration of active sites played a more significant effect on the surface areas of activated carbons in the carbon burn-off zone of >60%. Statistical analysis was used to relate the surface areas of activated carbon variances with carbon burn-off levels.     

A study of the characteristics of activated carbons produced by steam and carbon dioxide activation of waste tyre rubber

This paper presents a study into the effect of different activation conditions on the porosity and adsorption characteristics of carbon adsorbents produced from waste tyre rubber. For the purpose of this work, three carbon series were produced using different activation temperatures (between 925 and 1100 °C) and oxidising agents (steam or carbon dioxide). Carbons produced to different degrees of burn off were characterised using gas (nitrogen) and liquid phase (phenol, methylene blue and Procion Red H-E2B) adsorption. Total micropore volumes and BET surface areas increased almost linearly with the degree of activation to 0.554 ml/g and 1070 m²/g, respectively, while the development of external surface area was particularly rapid at degrees of activation above 50 wt% burn off. Steam was observed to generate a narrower but more extensive microporosity than carbon dioxide. However, carbon dioxide produced carbons of slightly larger external surface areas. Activation at higher temperatures resulted in pores of slightly larger dimensions, although this was only evident in highly activated samples. Porosity characteristics were reflected in the capacity of the carbons to adsorb species of different molecular size from solution. In this respect, steam-activated carbons presented greater capacities for the adsorption of smaller molecular size compounds (phenol), while carbon dioxide-activated carbons adsorbed larger textile dyes more effectively.     

Graphitic spherical carbon as a support for a PtRu-alloy catalyst in the methanol electro-oxidation

Spherical carbons were prepared using sucrose as a carbon precursor via hydrothermal method for use as supports for PtRu-alloy catalysts in the methanol electro-oxidation. Spherical carbon particles with an average diameter of 1μm (SC-1) were prepared under static condition (without stirring), while spherical carbon materials with a diameter of 500–600 nm (SC-2) were obtained under dynamic condition (with stirring). A graphitic spherical carbon material (SC-g) was successfully prepared by the addition of Fe salt under dynamic condition. It was revealed that the catalytic action of Fe species during the hydrothermal process was essential for the formation of a graphitic structure of SC-g. The surface areas were found to be 112, 383, and 252 m²/g for SC-1, SC-2, and SC-g, respectively. PtRu nanoparticles were then supported on the spherical carbons by a NaBH₄-reduction method for use in the methanol electro-oxidation. The average metal particle sizes were 3.5, 2.6, and 2.7 nm for PtRu/SC-1, PtRu/SC-2, and PtRu/SC-g, respectively. The PtRu/SC-1 and PtRu/SC-2 showed a lower catalytic performance in the methanol electro-oxidation than the PtRu/Vulcan. However, the PtRu/SC-g exhibited a higher catalytic performance than the PtRu/Vulcan. It is believed that the high graphitic nature of SC-g was responsible for the enhanced catalytic performance of PtRu/SC-g.     

Fabrication and characterization of La-added MgFe2O4 as catalyst support for CO oxidation

Fe-containing oxides can serve as excellent supports for precious metal catalysts. Therefore, we investigated the catalytic properties of noble metals supported on Fe-containing mixed oxides. MgFe₂O₄ and La-added MgFe₂O₄ (La-MgFe₂O₄) were prepared via complexation with malic acid and characterized by X-ray diffraction, N₂ adsorption–desorption, and Fe K-edge X-ray fine structure analysis. MgFe₂O₄ calcined at 400–800 °C has a spinel structure and is porous. The addition of La to MgFe₂O₄ increased the local structural disorder around Fe, suppressed grain growth, affected the pore size, and increased the specific surface area. In addition, a Pd-loaded La-MgFe₂O₄ catalyst was prepared and found to exhibit higher activity for CO oxidation than a representative Pd/γ-Al₂O₃ catalyst. Further, temperature-programmed reduction studies revealed that the reactivity of the surface lattice oxygen of La-MgFe₂O₄ was enhanced by the Pd loading. Further, diffuse reflectance Fourier transform infrared spectroscopy studies showed that the surface lattice oxygen reacted with CO to form CO₂.     

Activity and long-term stability of PEDOT as Pt catalyst support for the DMFC anode

The feasibility of using poly(3,4-ethylenedioxythiophene) (PEDOT) as Pt catalyst support for direct methanol fuel cell (DMFC) anodes was investigated. Measurements with freshly prepared Pt-PEDOT/C electrodes showed poor activity for methanol oxidation in a half-cell and a DMFC. A substantial enhancement in that activity was evident after either electrochemical over-oxidation of PEDOT or long-time storage of the Pt-PEDOT/C gas diffusion electrode (GDE) in air. Both procedures led to a reorganization and increase in porosity of the reaction layer, which obviously contributed to better methanol accessibility to Pt catalyst active centres. The effects of electrochemical activation and long-time storage in air on the morphology and elementary composition of the Pt-PEDOT layer were investigated by means of Hg porosimetry and SEM/EDAX. It was found that the increase in porosity was due to degradation of PEDOT characterized by a significant depletion of sulphur and oxygen in the conducting polymer matrix.     

Effect of steam and carbon dioxide pretreatments on methane decomposition and carbon gasification over doped-ceria supported nickel catalyst

Effects of steam (H₂O) and carbon dioxide (CO₂) pretreatments on methane (CH₄) decomposition and carbon gasification over doped-ceria supported nickel catalysts have been studied from 400 to 500 °C. The doped ceria employed were gadolinia-doped ceria and samaria-doped ceria. Results indicate that a drastic increase of both H₂O and CO₂ dissociation activities occurs as the temperature increases from 450 to 500 °C. The formation of the surface hydroxyl species during H₂O treatment inhibits the followed CH₄ decomposition. CO but no CO₂ was formed during CH₄ reaction after H₂O treatment. Carbon deposition during CH₄ decomposition is quite large but can be removed via gasification with afterward CO₂ treatment. However, some of the deposited carbon species is in a form which can not be removed with CO₂ treatment but can be removed with O₂ treatment. And, higher values of the oxygen-ion conductivity and the density of the surface oxygen vacancies lead to higher activities for all dissociation and decomposition reactions.     

Effect of heat treatment of activated carbon supports on the loading and activity of Pt catalyst

The study has been done on the effect of heat treatment of activated carbon at 1573-1773 K on its structural and electronic properties as a catalyst support. The X-ray diffraction result indicated that a partly graphitized structure was formed when the activated carbon was heated to a high temperature (1673 K). From the X-ray photoelectron spectroscopy result, it was found that Pt⁰ concentration was increased, but PtO and PtO₂ concentrations were decreased with an increase in the heat treatment temperature. From the van Dam’s model applied to this result, it might be concluded that more “π-sites” are created as the heat treatment temperature becomes higher. From the CO-chemisorption result, the highest loading was observed in case of Pt/AC1673 sample. This improved loading ability could be explained by the special interaction of the graphitic planes (π-sites) with the metal particles. Based on the catalytic activity, CO-chemisorption and XPS results, it is concluded that the well-loaded Pt⁰ species mainly contribute to the catalytic activity. Moreover, it was found that different degrees of graphitization of heat treated activated carbon could cause different surface Pt⁰ and improve the resistance of carbon support against gasification under air oxidation.     

Pore structure of activated carbons prepared by carbon dioxide and steam activation at different temperatures from extracted rockrose

The influence of the activation temperature on the pore structure of granular activated carbons prepared from rockrose (Cistus ladaniferus L.), extracted previously into petroleum ether, is comparatively studied. The preparation was carried out by pyrolysis of a char in nitrogen and its subsequent activation by carbon dioxide and steam (flow of water controlled to generate the same mol number per minute of water as well as carbon dioxide/nitrogen) at 700-950°C to 40% burn-off. The techniques applied to study the pore structure were: pycnometry (mercury, helium), adsorption (carbon dioxide, 298 K; nitrogen, 77 K), mercury porosimetry and scanning electron microscopy. The preparation by steam activation, especially at 700°C, yields activated carbons showing a total pore volume larger than those prepared by carbon dioxide activation. The pore structures present the greatest differences when the activations are carried out between 700 and 850°C and closer at higher temperatures. At high temperatures, the decrease of differences in pore development caused by carbon dioxide or steam is attributed to an external burn-off. The micropore structure of each activated carbon is mainly formed by wide micropores. At the lowest activation temperatures, especially at 700°C, steam develops the mesoporosity much more than carbon dioxide. At 950°C, a similar reduction of pore volume in the macropore range occurs.     

Expanded graphite applied in the catalytic process as a catalyst support

An amorphous NiB supported on expanded graphite (EG) catalyst was prepared as an example to show the superior characteristics of EG as a novel carbon support material. EG and the prepared catalysts were characterized by mercury porosimetry, inductively coupled plasma spectrometer (ICP), scanning electronic microscopy (SEM), transmission electron microscope (TEM) and selected area electron diffraction (SAED). The catalytic activities of prepared catalysts were investigated by the hydrogenation of sulfolene to sulfalone and the selective hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CA). We showed that the prepared Ni-B/EG catalyst exhibited very high catalytic activity.