Carbonate fuel cell Stack performance

Yoshiba, F., Ono, N., Izaki, Y., Watanabe, T., and Abe, T. (1998) Numerical analyses of the internal conditions of a molten carbonate fuel cell stack comparison of stack performances for various gas flow types. J. Power Sources, 71 (1-2), 328 336. Yoshiba, F., Abe, T., and Watanabe, T. (2000) Numerical analysis of molten carbonate fuel cell stack performance diagnosis of internal conditions using cell voltage profiles, f. Power Sources, 87 (1-2), 21-27. 

Fig. 17 Full-area carbonate fuel cell stack performance Progression of performance improvements has been validated.

Fig. 23. (a) Experimental IR-free overpotentials in MCFC-based separator. Cell performance 0.25% C02 Feed. All curves calculated [32] (b) C02 production scheme using molten carbonate fuel cell stack. 

D. Rastler, EPRI, G. Devore, Destec Engineering, R. Castle, Haldor Topsoe, C. Chi, ERC, "Demonstration of a Carbonate Fuel Cell Stack on Coal-Derived Gas," in Fuel Cell Seminar. "Effects of Coal-Derived Trace Species on the Performance of Molten Carbonate Fuel Cells," Topical Report prepared by Energy Research Corporation for US DOE/METC, DOE/MC/25009-T26, October, 1991. 

M. Farooque, "Development of Internal Reforming Carbonate Fuel Cell Stack Technology," Performed under Contract No. DE-AC21-87MC23274, DOE/MC/23374-2941, October 1990. M. Farooque, et al., "Comparative Assessment of Coal-Fueled Carbonate Fuel Cell and Competing TQdaao o Q%," presented at the 25th lECEC, Vol. 3, pp. 193-200, 1990. 

Hirata, H. and Hori, M. (1996) Gas-flow uniformity and cell performance in a molten carbonate fuel cell stack, Journal of Power Sources 63, 115-120. 

Rajalashmi N, Jayanth T T, Dhathathreyan K S (2003), Effect of carbon dioxide and ammonia on polymer electrolyte membrane fuel cell stack performance , Fuel Cells, 3, 177-180. 

Watanabe, T., and Abe, T. (1998) Numerical analyses of the internal conditions of a molten carbonate fuel cell stack comparison of stack performances for various gas flow types. J. Power Sources, 71 (1-2), 328-336. 

M. Farooque, "Development of Internal Reforming Carbonate Fuel Cell Stack Technology," Performed under Contract No. DE-AC21-87MC23274, DOE/MC/23374-2941, October 1990. 

The transient response of DMFC is inherently slower and consequently the performance is worse than that of the hydrogen fuel cell, since the electrochemical oxidation kinetics of methanol are inherently slower due to intermediates formed during methanol oxidation [3]. Since the methanol solution should penetrate a diffusion layer toward the anode catalyst layer for oxidation, it is inevitable for the DMFC to experience the hi mass transport resistance. The carbon dioxide produced as the result of the oxidation reaction of methanol could also partly block the narrow flow path to be more difScult for the methanol to diflhise toward the catalyst. All these resistances and limitations can alter the cell characteristics and the power output when the cell is operated under variable load conditions. Especially when the DMFC stack is considered, the fluid dynamics inside the fuel cell stack is more complicated and so the transient stack performance could be more dependent of the variable load conditions. 

Another important parameter that has to be taken into account when choosing the appropriate diffusion layer is the overall cost of the material. In the last few years, a number of cost analysis studies have been performed in order to determine fuel cell system costs now and in the future, depending on the power output, size of the system, and number of xmits. Carlson et al. [1] reported that in 2005 the manufacturing costs of diffusion layers (for both anode and cathode sides) corresponded to 5% of the total cost for an 80 kW direct hydrogen fuel cell stack (assuming 500,000 units) used in the automotive sector. The total value for the DLs was US 18.40 m-, which included two carbon cloths (E-TEK GDL LT 1200-W) with 27 wt% P ILE, an MPL with PTFE, and Cabot carbon black. Capital, manufacturing, tooling, and labor costs were included in the total. 

In another report, James and Kalinoski [4] performed an estimation of the costs for a direct hydrogen fuel cell system used in automotive applications. The assumed system consisted of an 80 kW system with four fuel cell stacks, each with 93 active cells this represents around 400 MEAs (i.e., 800 DLs) per system. The study was performed assuming that the DL material used for both the anode and cathode sides would be carbon fiber paper with an MPL. In fact, the cost estimate was based on SGL Carbon prices for its DLs with an approximate CEP value of around US 12 m for 500,000 systems per year. Based on this report, the overall value of the DLs (with MPL) is around US 42.98 per kilowatt (for current technology and 1,000 systems per year) and 3.27 per kilowatt (for 2015 technology and 500,000 systems per year). Figure 4.2 shows the cost component distribution for this 80 kW fuel cell system. In conclusion, the diffusion layer materials used for fuel cells not only have to comply with all the technical requirements that different fuel cell systems require, but also have to be cost effective. 

The proper design of fuel reformer systems must pay careful attention to the minimization of carbon monoxide before the processed fuel stream enters the fuel cell stack. Many reformer systems use a secondary preferential oxidation reactor that selectively oxidizes the carbon monoxide present in reformate streams. In most transportation applications the steam reformer and the selective oxidation reactors do not operate under steady state conditions large transients may occur which produce relatively large amounts of carbon monoxide. It is highly desirable to have a low-cost real-time carbon monoxide measurement system that provides feedback control to the fuel processing system in order to protect the PEM fuel cells from performance degrading concentrations of carbon monoxide. 

Rajalakshmi, N., T.T.Jayanth, and K.S.Dhathathreyan. 2004. Effect of Carbon Dioxide and Ammonia on Polymer Electrolyte Membrane Euel Cell Stack Performance. Fuel Cells 3(4) 177-180. 

Even if the reformate is purified by catalytic carbon monoxide clean-up to well below 50 ppm carbon monoxide and if other impurities are reduced to the ppb level, performance losses are to be expected when running a fuel cell with reformate. A 7% lower power production was observed by Shi et al. [31] when mnning a 2 kW PEM fuel cell stack with reformate produced from liquid hydrocarbons. 

Durability is the capability of a PEM fuel cell stack to resist permanent change in performance over time. A durability failure may not cause catastrophic failure in the fuel cell. However, this mode of failure will decrease the performance of the fuel cell. It also can involve irreversible failures, such as electrochemical surface area reduction, carbon corrosion, etc., and losses mainly related to ageing [12]. 

HR should not be as efficient as DIR, however t it allows a more stable cell performance. Since the external reformer is physically separated from the fuel cell stack it can be operated at different pressures and temperatures if necessary. This is of particular importance because in this way it is possible to eliminate the problem of carbon deposition via fuel decomposition that deactivates the anode [13,133,168,169]. 

The membrane electrode assembly (MEA) is the heart of a fuel cell stack and most likely to ultimately dictate stack life. Recent studies have shown that a considerable part of the cell performance loss is due to the degradation of the catalyst layer, in addition to membrane degradation. The catalyst layer in PEMFCs typically contains platinum/platinum alloy nanoparticles distributed on a catalyst support to enhance the reaction rate, to reach a maximum utilization ratio and to decrease the cost of fuel cells. The carbon-supported Pt nanoparticle (Pt/C) catalysts are the most popular for PEMFCs. Catalyst support corrosion and Pt dissolution/aggregation are considered as the major contributions to the degradation... 

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