Methane electrolytic generation

Fuel cells such as the one shown on Fig. 3.4a convert H2 to H20 and produce electrical power with no intermediate combustion cycle. Thus their thermodynamic efficiency compares favorably with thermal power generation which is limited by Carnot-type constraints. One important advantage of solid electrolyte fuel cells is that, due to their high operating temperature (typically 700° to 1100°C), they offer the possibility of "internal reforming" which permits the use of fuels such as methane without a separate external reformer.33 36... 

The extent to which anode polarization affects the catalytic properties of the Ni surface for the methane-steam reforming reaction via NEMCA is of considerable practical interest. In a recent investigation62 a 70 wt% Ni-YSZ cermet was used at temperatures 800° to 900°C with low steam to methane ratios, i.e., 0.2 to 0.35. At 900°C the anode characteristics were i<>=0.2 mA/cm2, Oa=2 and ac=1.5. Under these conditions spontaneously generated currents were of the order of 60 mA/cm2 and catalyst overpotentials were as high as 250 mV. It was found that the rate of CH4 consumption due to the reforming reaction increases with increasing catalyst potential, i.e., the reaction exhibits overall electrophobic NEMCA behaviour with a 0.13. Measured A and p values were of the order of 12 and 2 respectively.62 These results show that NEMCA can play an important role in anode performance even when the anode-solid electrolyte interface is non-polarizable (high Io values) as is the case in fuel cell applications. 

Experiments have been carried out to mimic the reactions of model systems for coenzyme F430 that is involved in the terminal step in the biosynthesis of methane, and that is able to dechlorinate CCI4 successively to CHCI3 and CH2CI2 (Krone et al. 1989). Nickel(I) isobacteriochlorin anion was generated electrolytically and used to examine the reactions with alkyl halides in dimethylformamide (Helvenston and Castro 1992). The three classes of reaction were the same as those observed with Fe(II) deuteroporphyrin IX that have already been noted. 

The work on the electrochemical generation of a solution of ceric sulphate from slurry of cerous sulphate in 1-2 M sulphuric acid was abandoned by BCR due to difficulties encountered in handling slurried reactants. A 6kW pilot reactor operated at 50 °C using a Ti plate anode and a tungsten wire cathode (electrolyte velocity about 2ms 1) produced 0.5 M Ce(S04)2 on the anode with a current efficiency of 60%. The usefulness of Ce(IV) has been limited by the counter anions [131,132], Problems include instability to oxidation, reactivity with organic substrates and low solubility. Grace found that use of cerium salts of methane sulfonate avoids the above problems. Walsh has summarized the process history, Scheme 6 [133],... 

A p-type silicon (p-Si) electrode modified with copper particles (particulate-Cu/p-Si) was applied to photoelectrochemical (PEC) reduction of carbon dioxide (CO2) in acetonitrile electrolyte solutions with and without 3.0 M HjO. The particulate-Cu/p-Si electrode generated high photovoltages of 0.50 to 0.75 V, and produced methane, ethylene, etc., under addition of 3.0 M HjO, similar to a Cu metal electrode, indicating that the particulate-Cu/p-Si electrode acted as an efficient electrode for the PEC reduction of CO2 in non-aqueous solutions. 

Barz, D.P. Tragner, U.K. Schmidt, V.M. Koschowitz, M. Thermodynamics of hydrogen generation from methane for domestic polymer electrolyte fuel cell systems. Fuel Cells 2004, 3 (4), 199-207. 

One breakthrough in SC-SOFCs was accomplished by Hibino et al. [4]. An SC-SOFC was operated using yttria-stabilized zirconia (YSZ), Ni and Lao.8Sro.2Mn03 (LSM) as the electrolyte, and anode and cathode, respectively. When the fuel cell was supplied with a methane-air mixture (methane/oxygen mole ratio = 2 1) at 950 °C, it generated an open-circuit voltage (OCV) of 795 mV and a peak power density of 121 mW cm. Half-cell measurements were carried out for these electrodes. Partial oxidation... 

In 2009, Wei et al. reported a star-shaped stack comprised of four Ni-YSZIYSZILSM cells [21], This stack generated an OCV of approximately 3.5 V and a peak power output of 421 mW in a methane-air mixture feed at 700 °C. They concluded that the symmetric design can ensure the identical operation of each cell. On the other hand, as described in the previous section, SC-SOFCs allows for a coplanar electrode arrangement, where the two electrodes reside on the same surface of the electrolyte. Also in 2009, Kuhn et al. fabricated cells with one, two, three, four, five and ten pairs of electrodes with a width of 260 pm, thickness of 17 pm, and interelectrode gap of 114 pm [22]. The OCV roughly increased with increasing number of the electrode lines, although the maximum OCV value was as low as 0.8 V. 

PC is also a very useful solvent of LIBs because of its superior ionic conductivity over a wide temperature range. However, despite the close structural similarity between EC and PC, PC cannot form as effective SEI films as EC does, for LIBs that employ graphite as negative electrodes. " To enable to use PC in these batteries, there have been a lot of efforts focusing on the identification of proper additives and/or co-solvents for PC-based electrolytes, which would help to generate an efficient SEI layer. The typical liquid additives include chloroethylene carbonate (CEC), other halogen-substituted carbonates, a variety of unsaturated carbonates such as vinylpropylene carbonate and vinylene carbonate, and ethylene/propylene sulfite (ES/PS). The most common co-solvents are DMC, DEC, EMC, y-butyrolactone (y-BL), dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), dimethyl amide (DMA), 1,2-dimethoxy-ethane (DME) and 1,2-dimethoxy-methane (DMM). To explore the role of these additives and co-solvents, it is necessary to understand their structures and some properties that may affect the SEI formation on graphite anodes. 

Three strategies for direct conversion of hydrocarbon fuels are possible. The first strategy utilizes conventional Ni-cermet anodes but modifies the operating conditions of the fuel cell [50]. For methane at intermediate temperatures, the rate of carbon deposition may be slow enough so that oxygen anions electrochemically driven through the electrolyte and steam generated by oxidation of methane will remove carbon as it is deposited. 

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