Cathodes cost/performance

In summary, the RDE results indicate that ORR kinetics obtained on Pd/C and Ag/C catalysts were comparable to that on Pt/C, with reactions primarily through a 4e ORR pathway but with 50-100 mV larger overpotentials. However, Pd oxidization at fuel cell cathode working potentials can be a hindrance for its practical application in AEMFCs. Balancing cost, performance, and durability, Ag/C catalysts have been identified by several research groups as the preferred cathode catalysts to replace Pt/C for AEMFC applications. The performance of Ag/C catalysts as compared with Pt/C catalysts in AEMFCs is presented here. 

Adsorptive cathodic stripping voltammetry has an advantage over graphite furnace atomic absorption spectrometry in that the metal preconcentration is performed in situ, hence reducing analysis time and risk of contamination. Additional advantages are low cost of instrumentation and maintenance, and the possibility to use adapted instrumentation for online and shipboard monitoring. 

A number of technical and cost issues facing polymer electrolyte fuel cells at the present stage of development have been recognized by managers and researchers (6, 27, 28, 29). These issues concern the cell membrane, cathode performance, and cell heating limits. 

For recycling to improve the performance of an MCFC network, it must provide benefits that outweigh its inherent disadvantages. If carbon dioxide is not separated from the anode-anode recycle, the concentration of carbon dioxide in the anode is increased. This reduces the Nemst potential. The Nemst potential is similarly reduced by the anode-cathode recycle if steam is not condensed out, since recycled steam dilutes reactant concentrations in the oxidant. In addition, part of the power generated by the network is consumed by the equipment necessary to circulate the recycle streams. Such circulation equipment, along with the additional ducting required by recycling, also increases the capital cost of the MCFC network. 

General Motors has assessed the required activity of a catalyst that costs less compared to the current state-of-the-art Pt activity based on these con-straints. i Assuming that the catalyst layer thickness could be increased to MOO pm from the currently used 10 pm, GM has calculated that the minimum volume activity (i.e., Acm ) for a cathode catalyst that costs less should be at least 10% of the current Pt activity. In reality, this seems rather generous, given the recent trend to reduce catalyst layer thicknesses to optimize high-current performances. The DoE has developed a series of volume activity targets for nonprecious metal catalysts, with the 10% of Pt activity target (300 Acm 3 at 0.8 V, H2/O2) necessary by 2015. 

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. 

---