Bimetallic Anode Research Articles

Synergistic effects of Ni 1− xCo x-YSZ and Ni 1− xCu x-YSZ alloyed cermet SOFC anodes for oxidation of hydrogen and methane fuels containing H 2S

Preparation and performance of bimetallic Ni (1− x) Co x -YSZ and Ni (1− x) Cu x -YSZ anodes were tested to overcome common deficiencies of carbon and sulfur poisoning in SOFCs. Ni 1− x Co x O-YSZ and Ni (1− x) Cu x O-YSZ precursors were synthesized via co-precipitation of their respective chlorides. Single cell solid oxide fuel cells of these bimetallic anodes were tested in H 2, CH 4, and H 2S/CH 4 fuel mixtures. Addition of Cu 2+ into the NiO lattice resulted in large metal particle sizes and decreased SOFC performance. Addition of Co 2+ into the NiO lattice to form Ni 0.92Co 0.08O-YSZ anode precursor produced a cermet with a large BET surface area and active metal surface area, thus increasing the rate of hydrogen oxidation for this sample. The performance of both bimetallics was found to quickly degrade in dry CH 4 due to carbon deposition and lifting of the anode from the electrolyte. However, Ni 0.69Co 0.31-YSZ showed superior activity in a 10% (v/v) H 2S/CH 4 fuel mixture, surpassing performance with H 2 fuel, thereby demonstrating the exciting prospect of using sulfidated Ni (1− x) Co x -YSZ as SOFC anodes in sulfur containing methane streams. The active anode becomes a sulfidated alloy (Ni-Co-S) under operating conditions. This anode showed enhanced performance, which surpassed those of sulfidated Ni and Co anodes, thereby suggesting a synergistic behaviour in the Ni-Co-S anode.

Investigation of various ionomer-coated carbon supports for direct methanol fuel cell applications

High-performance fuel cell electrodes require architectures that offer appropriate electrochemical and nanoscopic catalytic reaction zones. In this direction, ionomer (perfluoro sulfonic acid)-coated carbon supports were prepared by adopting a simple and cheap synthetic strategy to offer both electronic and protonic contacts to the catalyst particulates. Pt–Ru bimetallic anode catalysts were prepared on these modified carbon supports by a colloidal method. The role of surface area of carbon supports and the influence of ionomer content in them towards the catalytic activities of Pt–Ru catalysts has been probed by using three kinds of carbon black powders with different physical properties. Their electrocatalytic efficiencies toward methanol oxidation were scrutinized via half-cell measurements in cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. Catalysts particulates dispersed on carbon supports coated with ionomer exhibited better performance than those on the plain carbon supports, owing to the reduced micropores and increased interfacial area between catalyst particles and ionomer. Plain and modified carbon (MC) supports were characterized by using FTIR, BET-PSD and TEM techniques. Physico-chemical characterizations of supported catalyst systems were done by using XRD and TEM.

Recent progress in SOFC anodes for direct utilization of hydrocarbons

There would be significant advantages to having anodes for solid oxide fuel cells (SOFCs) that were capable of directly utilizing hydrocarbon fuels. Because conventional Ni-based anodes catalyze the formation of carbon fibers, new anode compositions are required for this application, but most of the materials that have been proposed exhibit either limited thermal stability or poor electrochemical activity. In this paper, we will describe two strategies for the development of new anodes with improved performance. The first strategy involves the use of bimetallic compositions with layered microstructures. In the bimetallic anodes, one metal is used for thermal stability while the other provides the required carbon tolerance. The second strategy involves separating the anode into two layers: a thin functional layer for electrocatalysis and a thicker conduction layer for current collection. With this approach, the functional layer can be optimized for catalytic activity and, if it is thin enough, requires minimal conductivity. Examples are shown for each of these approaches and possible future directions are outlined.

Ni–Fe bimetallic anode as an active anode for intermediate temperature SOFC using LaGaO 3 based electrolyte film

Effects of additives to Ni anode were studied and it was found that the anodic overpotential can be suppressed by addition of Fe. La 0.9Sr 0.1Ga 0.8Mg 0.2O 3 (LSGM) film was deposited on the dense anode substrate consisting of NiO(Fe 3O 4)–Sm doped CeO 2. After in-situ reduction of NiO and Fe 3O 4 in the dense substrate, the substrate turned to be porous, however, change in size was not large by mixing with SDC. As a result, LSGM dense film with few micrometer thickness was successfully obtained on the porous Ni based anode substrate. By optimizing the thickness of the LSGM film and application of SDC interlayer, the high power density of SOFC single cell using LSGM/SDC bi-layer film as electrolyte at decreased temperature was fabricated and the electrical power generating property was measured as a function of temperature. The high maximum power density could be achieved to a value of 2 W/cm 2 at 873 K. Even at 673 K, the maximum power density of ca. 80 mW/cm 2 is exhibited and this high power density was a result of the low electrolyte resistance and the small anodic overpotential of Ni–Fe bimetallic anode.

High oxide ion conductivity in Fe and Mg doped LaGaO 3 as the electrolyte of solid oxide fuel cells

La(Sr)Ga(Fe,Mg)O 3 exhibited the high oxide ion conductivity and the electrical power generating property of SOFC single cell using La 0.7Sr 0.3Ga 0.7Fe 0.2Mg 0.1O 3-δ (LSGFM) electrolyte was investigated in this study. The transport number of oxide ion is almost 0.8 in LSGFM and so open circuit potential (OCV) is as low as 0.8 V. OCV was strongly affected by anode materials and the highest OCV was achieved on Ni–Fe bimetallic anode. The extremely high power density was achieved by using LSGFM for electrolyte of SOFC. The maximum power densities of the cells can be elevated by coating with oxide ion conductor film at anode side. The maximum power density increased in the following order for coating film: LSGM > SDC > YSZ. The maximum power density of 197 and 100 mW/cm 2 can be achieved at 873 and 773 K, respectively, when LSGM film deposited on the anode side of LSGFM. Therefore, LSGFM can be used as electrolyte of SOFC operating at intermediate temperature.

Novel Bimetallic Anodes for Direct Utilization of Hydrocarbon Fuels

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Cu-Co Bimetallic Anodes for Direct Utilization of Methane in SOFCs

Cu-Co bimetallic mixtures with ceria and YSZ have been investigated as solid oxide fuel cell (SOFC) anodes. While pure Co is unstable in dry CH 4 at 1073 K due to severe carbon formation, Cu-Co mixtures with even 90 wt % Co showed only small amounts of carbon following exposure to dry CH 4 for 2 h at 1073 K. Cells based on Cu-Co mixtures showed improved performance in both H 2 and CH 4 compared to cells prepared with only Cu. Finally, a cell with a 50:50 ratio of Cu and Co was shown to be stable for 500 h in humidified (3 mol % H 2 O) CH 4 at 1073 K.

Novel Bimetallic Anodes for Direct Utilization of Hydrocarbon Fuels

Cu-Ni and Cu-Co bimetallic mixtures with ceria and YSZ have been investigated as SOFC anodes. While all Cu-Ni alloys were found to form carbon upon exposure to dry CH 4 at 1073 K, carbon formation was completely suppressed on Cu-Co composites, apparently due to Cu coatings over the Co phase. Fuel cells based on Cu-Co mixtures showed improved power densities in H 2 , CH 4 , and n-butane compared to cells prepared with only Cu, suggesting that there is some Co at the surface of the bimetallic particles that is providing enhanced catalytic activity. While a cell with a 50:50 ratio of Cu and Co was shown to be stable for 500 h in humidified (3 mol% H 2 O) CH 4 at 1073 K, Cu-Co cells exhibited periodic spikes in the power densities when operating on n-butane at 973 K.

Improvement in Anodic Activity of Ni By Fe Addition for Intermediate Temperature SOFC Using LaGaO3 Electrolyte

Effects of various additives to Ni anode on SOFC using La 0.9 Sr 0.1 Ga 0.8 Mg 2 O 3 based oxide electrolyte were investigated in this study for increasing the surface activity. Among the examined additives, it was found that the addition of small amount of Fe is highly effective for increasing the anodic activity. When 5 wt% Fe was added to Ni anode, the anodic overpotential was as small as 34 mV at 873 K, 0.1 A/cm 2 , which is almost half of pure Ni anode. Since the estimated activation energy for anodic reaction decreased, addition of Fe to Ni seems to be effective for increasing the activity of Ni for anodic reaction. XRD measurement after power generation measurement suggests that added Fe formed alloy with Ni. Addition of third element to Ni-Fe bimetallic anode was also studied and it was found that addition of small amount of Pt is effective for further increasing the activity of Ni anode. Consequently, this study reveals that Ni-Fe-Pt is highly active for anodic reaction of SOFCs at decreased temperatures.

Oxidation of H2 and CO in a fuel cell with a Platinum-tin Anode

This report describes the construction and evaluation of a fuel cell with a bi-metallic anode of Pt-Sn supported on carbon, as catalysts for oxidation of pure hydrogen, pure CO and a 2% CO in H2 mixture. Both, cathode and anode were made with a structure composed by a diffusive layer and a catalytic layer. The diffusive layer was made with a carbon cloth while the catalytic layer contained the platinum and tin supported on carbon. To test the performance of the catalytic mixture, a proton exchange membrane fuel cell (PEMFC) was developed with an original design for the gas distribution plates. The reactants were feed to ambient temperature and 3 psig in the anode side, while 5 psig pure oxygen was used in the cathode. The anode catalytic load was 0.57 mg/cm2 of platinum and 0.08 mg/cm2 of tin. The catalytic load in cathode was 0.85 mg/cm2 of pure platinum. It was found that this catalytic mixture is tolerant to CO presence.

Preparation of Pt–Ru bimetallic anodes by galvanostatic pulse electrodeposition: characterization and application to the direct methanol fuel cell

The electrodeposition of platinum and ruthenium was carried out on carbon electrodes to prepare methanol anodes with different Pt/Ru atomic ratios using a galvanostatic pulse technique. Characterizations by XRD, TEM, EDX and atomic absorption spectroscopy indicated that most of the electrocatalytic anodes consisted of 2 mg cm−2 of Pt–Ru alloy particles with the desired composition and with particle sizes ranging from 5 to 8 nm. Electrochemical tests in a single DMFC show that these electrodes are very active for methanol oxidation and that the best Pt/Ru atomic ratio in the temperature range used (50–110 °C) is 80:20. The influence of the relaxation time t off was also studied and it appeared that a low t off led to smaller particle sizes and higher performances in terms of current density and power density.