Catalyst gradient

Cho et al. [140] examined the performance of PEM fuel cells fabricated using different catalyst loadings (20, 40, and 60 wt% on a carbon support). The best performance—742 mA/cm at a cell voltage of 0.6 V— was achieved using 40 wt% Pt/C in both anode and cathode. Antonie et al. [28] studied the effect of catalyst gradients on CL performances using both experimental and modeling approaches. Optimal catalyst utilization could also be achieved when a preferential location of Pt nanoparticles was close to the PEM side ... 

Antoine, O., Bultel, Y, Ozil, P, and Durand, R. Catalyst gradient for cathode active layer of proton exchange membrane fuel cell. Electrochimica Acta 2000 45 4493 500. 

The distribution of contaminants within the porous layer again has to be considered separately for monolithic and pelleted catalysts. Gradients of the contaminant concentration in both cases can be very steep or relatively flat. Some inferences on the poison-carrying species can be deduced from such gradients. 

Figure 5. Reactor and catalyst gradients application to a heterogeneous catalyst.

M. Santis, S. A. Preunberger, A. Reiner, and F. N. Biichi. Homogenization of the current density in polymer electrolyte fuel cells by in-plane cathode catalyst gradients. 

Another preparation method for gradient array is gel-transfer eleetrodeposition, whieh was developed by Hiller and coworkers. This method involves the controlled diffusion of precursor metal salts into a hydrated gel from spatially distinct locations, followed by an eleetrodeposition to create a surface composition gradient. As illustrated in Figure 12.2(a), a ternary catalyst gradient was created by diffusing precursor metal salts, from three different locations, into a... 

Figure 12.2. (a) Schematic of synthesis routine for a multi-component catalyst gradient by gel-transfer method, (b) Optical image of concentration gradient of Pt /Ru /Rh in agarose gel [12]. (Reproduced by permission of ECS—The Electrochemical Society, from Jayaraman S, Hillier AC. Electrochemical synthesis and reactivity screening of a ternary composition gradient for combinatorial discovery of fuel cell catalysts.)... 

A non-uniform electrode was introduced in 1989 [73]. In this electrode, the electrocatalyst concentration increased along the direction parallel to the electrode substrate. It is expected that the effect of increased catalyst loading in the direction of gas flow could balance the effect of diminishing reactants in the gas stream. In this way, the reaction rate could be substantially uniform across the electrode surface. Prasanna et al. [74] employed the catalyst-gradient method for single fuel cell fabrication, and found that it was an effective way to reduce Pt loading without... 

Besides the catalyst gradient in the catalyst layer, other components such as the hydrophobic agent (PTFE) and proton conductive polymer (Nafion) may also need to be adjusted in order to optimize gas/water transportation and electron/proton transfer. It can be expected that the catalyst layer adjacent to the gas diffusion layer side should be more hydrophobic to ensure much more of the reactants penetrates the inside of the electrode. While near the membrane side, more proton conductive polymer is needed to ensure a continuous network for proton conduction. Therefore, a non-uniform catalyst layer with a decreasing PTFE loading and an increasing Nafion content along the through-plane direction from GDL to membrane should be more efficient. 

Prasanna M, Cho EA, Kim HI, Oh IH, Lim TH, Hong SA. Performance of proton-exchange membrane fuel cells using the catalyst-gradient electrode technique. J Power Sources 2007 166 53-8. 

Figure 23.30. Comparison of the cumulative carbon corrosion following a 24-h 1.2 V potentiostatic hold at 80 °C in 1 M H2SO4 for two commercial carbons COl, C02 and one heat-treated carbon C03, and platinum and Pt/Co alloy catalysts on these carbons [95]. (Reprinted from Journal of Power Sources, 166(1), Prasanna M, Cho EA, Kim H-J, Oh I-H, Lim T-H, Hong S-A, Performance of proton-exchange membrane fuel cells using the catalyst-gradient electrode technique, 18-25, 2007, with permission from Elsevier.)...

Use Catalyst Gradients in Reactor This is similar to item 2. Here, a larger fraction of inert solid is used where hot spots are anticipated. This minimizes hot spots but also results in a larger reactor. 

Jayaraman, S., Hillier, A.C. Construction and reactivity mapping of a platinum catalyst gradient using the scanning electrochemical microscope. Langmuir 2001, 17, 7857-7864. 

Jayaraman S and Hillier A C (2001) Construction and Reactivity Mapping of a Platinum catalyst Gradient Using the Scanning Electrochemical Microscope, Langmuir, 17, pp. 7857-7864. 

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