Cathod gas stream

Besides the reaction involving H2 and O2 to produce H2O, the equation shows a transfer of CO2 from the cathode gas stream to the anode gas stream, with 1 mole CO2 transferred along with two Faradays of charge or 2 gram moles of electrons. The reversible potential for an MCFC, taking into account the transfer of CO2, is given by the equation... 

Figure 7 Steady-state iR corrected Tafel plots of cathodic ORR performance of several binary Pt alloy electrocatalysts at 90 °C and 5-atm pressure. Performance for a Pt/C electrocatalyst is shown for comparison. The electrodes had 0.3mg/cm metal loading and the loading of the metal on carbon support was 20%. The humidifaction temperature for the anode and cathode gas streams were kept at 10 and 5°C above the cell temperature. 

Results High current density operations require smaller width channels and bipolar plate shoulders, higher porosity electrodes result from increasing electrode area under bipolar plate shoulder, relative humidity in anode gas stream is more important for FC performance than relative humidity in cathode gas stream... 

Figure 2.20 Hydrogen gas-air fuel cell performance of PAE-BP and Nafion 115at 120 °C with anode and cathode gas streams humidified to 80% RH. Reproduced with permission from Ref. [184],...

Figure 7.10 Adding carbon dioxide to the cathode gas stream need not add to the overall system complexity.

For the cathode gas stream mixture consisting of oxygen, nitrogen, and water vapor, the mass transport is given by the following three equations ... 

Water transports to or from the cathode surface to the cathode gas stream by convective mass transfer and is given as... 

Heat transfer from the cathode electrode surface to the cathode gas stream convection heat transfer ... 

Manufacture and Economics. Nitrogen tritiuoride can be formed from a wide variety of chemical reactions. Only two processes have been technically and economically feasible for large-scale production the electrolysis of molten ammonium acid fluoride and the direct fluorination of the ammonia in the presence of molten ammonium fluoride. In the electrolytic process, NF is produced at the anode and H2 is produced at the cathode. In a divided cell of 4 kA having nickel anodes, extensive dilution of the gas streams with N2 was used to prevent explosive reactions between NF and H2 (17). 

Another tool the interstates use to maintain their pipelines is a device known as an intelligent pig. Propelled through the pipeline with the gas stream, these devices, taking thousands of measurements with electronic sensors that can be analyzed later by computers, can inspect pipeline interior walls for corrosion or other defects and remove accumulated debris from a section of pipeline. Pipelines also use state-of-the-art coating and cathodic protection to battle corrosion. 

The results for a 55 amp load change are shown in Figures 9.10 and 9.11. Figure 9.10 shows the temperature histories for the cell, interconnect, anode exit gas and cathode exit gas. As can be seen the thermal conditions reach their new equilibrium by approximately / = 800 s, resulting in an exponential time constant of r = 266 s. The temperature change for the gas stream is about 150°C. A calculation of the thermal time constant based on the fully lumped model (Equation (9.28) shows... 

SOFC cathode air stream co2 + h2o Combustion of remaining fuel in SOFC anode exhaust gas... 

Anode exhaust gas SOFC containing unconverted fuel h2o + co2 h2 Combustion of SOFC anode off-gas with cathode air stream (SOFC-GT concept). Recycling of fuel or for PEM, and so on. 

Regardless of the specific type of fuel cell, gaseous fuels (usually hydrogen) and oxidants (usually ambient air) are continuously fed to the anode and the cathode, respectively. The gas streams of the reactants do not mix, since they are separated by the electrolyte. The electrochemical combustion of hydrogen, and the electrochemical reduction of oxygen, takes place at the surface of the electrodes, the porosities of which provide an extensive area for these reactions to be catalysed, as well as to facilitate the mass transport of the reactants/products to/from the electrolyte from/to the gas phase. 

Positive rays were first clearly described in 1886 by E. Goldstein. He obtained these rays by introducing a small quantity of gas in a Crookes tube containing a perforated cathode. Besides the usual cathode rays there formed, behind the perforated cathode, a stream of positively charged particles. Thomson realized that this stream was composed of nothing else but positively charged atoms of the gas, that is, of atoms which had lost electrons and had become ions. 

Water management is dealt with by Voss etal. (1993 1995). It is shown that the cell voltage-current characteristic can be greatly improved, and the achievable power density increased, with improved water management. The technique is to create a steeper cathode to anode water concentration profile through the cell. The water at the anode is removed by the fuel gas stream, as a result of inducing a pressure drop in the flow plate channel, which can be optimised for best performance. 

Lim and Winnick [110] examined removal of H2S from a simulated hot coal-gas stream fed to the cathode while elemental sulfur gas was evolved at the anode. This process was performed in a cell that was similar in construction to a molten carbonate fuel cell (Fig. 23). The electrolyte was a mixture of Na2S and Li2S retained in a porous inert matrix material (MgO). The cathodic reaction involved the two-electron reduction of hydrogen sulfide to hydrogen (information on the equilibrium potential for H2S reduction can be obtained from [111] ... 

Weaver and Winnick [111] studied the performance of a nickel/nickel sulfide cathode for the electrochemical removal of hydrogen sulfide gas from a gas stream. At 650 °C, the porous nickel cathode was converted in situ to Ni3+ S2 by the H2S in the feed gas stream. The exact composition of the nickel sulfide was found to be a function of the H2S/H2 ratio in the gas stream. A current density of 150 mA/cm was attained at an iR free cathodic overpotential of 300 mV. A maximum H2S removal of 40% was reported. The low removal percentage was due to mass transport limitations of the reactant gas to the electrode. 

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