Proton catalyst durability

Wang X, Li WZ, Chen ZW, Waje M, Yan YS. 2006. Durability investigation of carbon nanotube as catalyst support for proton exchange membrane fuel cell. J Power Sources 158 154-159. 

Liu, X., Chen, J., Liu, G., Zhang, L., Zhang, H., and Yi, B. (2010) Enhanced long-term durability of proton exchange membrane fuel cell cathode by employing Pt/Ti02/C catalysts. Journal of Power Sources, 195 (13), 4098-4103. 

This survey focuses on recent developments in catalysts for phosphoric acid fuel cells (PAFC), proton-exchange membrane fuel cells (PEMFC), and the direct methanol fuel cell (DMFC). In PAFC, operating at 160-220°C, orthophosphoric acid is used as the electrolyte, the anode catalyst is Pt and the cathode can be a bimetallic system like Pt/Cr/Co. For this purpose, a bimetallic colloidal precursor of the composition Pt50Co30Cr20 (size 3.8 nm) was prepared by the co-reduction of the corresponding metal salts [184-186], From XRD analysis, the bimetallic particles were found alloyed in an ordered fct-structure. The elecbocatalytic performance in a standard half-cell was compared with an industrial standard catalyst (bimetallic crystallites of 5.7 nm size) manufactured by co-precipitation and subsequent annealing to 900°C. The advantage of the bimetallic colloid catalysts lies in its improved durability, which is essential for PAFC applicabons. After 22 h it was found that the potential had decayed by less than 10 mV [187],... 

Because of its lower temperature and special polymer electrolyte membrane, the proton exchange membrane fuel cell (PEMFC) is well-suited for transportation, portable, and micro fuel cell applications. But the performance of these fuel cells critically depends on the materials used for the various cell components. Durability, water management, and reducing catalyst poisoning are important factors when selecting PEMFC materials. 

PEM fuel cells operate at relatively low temperatures, around 80°C. Low temperature operation allows them to start quickly (less warm-up time) and results in less wear on system components, resulting in better durability. However, they require that a noble-metal catalyst (typically platinum) be used to separate the hydrogen s electrons and protons, adding to system cost. The platinum catalyst is also extremely sensitive to CO poisoning, making it necessary to employ an additional reactor to reduce CO in the fuel gas if the hydrogen is derived from an alcohol or hydrocarbon fuel. This also adds cost. Developers are currently exploring platinum/ruthenium catalysts that are more resistant to CO. 

Proper water management in proton exchange membrane fuel cells (PEMFCs) is critical to PEMFC performance and durability. PEMFC performance is impaired if the membrane has insufficient water for proton conduction or if the open pore space of the gas diffusion layer (GDL) and catalyst layer (CL) or the gas flow channels becomes saturated with liquid water, there is a reduction in reactant flow to the active catalyst sites. PEMFC durability is reduced if water is left in the CL during freeze/thaw cycling which can result in CL or GDL separation from the membrane,1 and excess water in contact with the membrane can result in accelerated membrane thinning.2... 

A typical PEFC, shown schematically in Fig. 1, consists of the anode and cathode compartments, separated by a proton conducting polymeric membrane. The anode and cathode sides each comprises of gas channel, gas diffusion layer (GDL) and catalyst layer (CL). Despite tremendous recent progress in enhancing the overall cell performance, a pivotal performance/durability limitation in PEFCs centers on liquid water transport and resulting flooding in the constituent components.1,2 Liquid water blocks the porous pathways in the CL and GDL thus causing hindered oxygen transport to the... 

Co-Exchanged Zeolites. Hydrothermal durability of Co-zeolites usually depends on the nature of the parent zeolite, Co exchange level, preparation method, etc. Existence of both Co and Bronsted acid sites in zeolites can play a synergistic role for catalyzing NOx reduction reaction with HCs however, the protonic sites induce catalyst deactivation by Not only can the... 

In fuel cells, well known catalyst is produced from carbon black-supported Pt particles (Pt/C) for hydrogen and oxygen redox reactions which occurs at anode and cathode but conventional Pt/C catalyst has low durability and can be easily poisoned by carbon monoxide. Electrospun Pt/ruthenium, Pt/rhodium, and Pt nanowires have been produced and compared with Pt/C showing better performance in a proton exchange membrane fuel cell (PEMFC). 

Samsung SDI has developed a prototype of DMFC for use in laptops which is quoted to have a durability almost twice as compared to other systems being developed. SAIT has reduced the amount of catalyst required by 50 %, by developing a mesoporous carbon material, which supports highly efficient 3 nm nanocatalyst particles. In addition, SAIT has developed a unique concept of nanocomposite membrane to reduce methanol crossover by more than 90 %. This composite uses a 30-100 pm thick proton-conducting membrane with a proton conductivity of 0.1 S.cm . The DMFC has an energy density of 650 Wh dm , and fed with about 200 cm of liquid methanol can supply power to a laptop for about 15 h. The cell measures 23 cm x 8.2 cm x 5.3 cm, and its weight is less than 1 kg [60]. 

Wang Z B, Zuo P J, Chu Y Y, Shao Y Y and Yin G P (2009), Durability studies on performance degradation of Pt/C catalysts of proton exchange membrane fuel cell. International Journal of Hydrogen Energy, 34,4387 394. 

The catalyst layer thickness typically ranges between 5 and 20 pm for proton exchange membrane (PEM) fuel cells. A variation of 2 pm that can hardly be observed under an optical microscope could mean a thickness difference of 40 to 10%. A 40% difference will cause a significant variation in the fuel cell performance and durability. It is absolutely imacceptable if there are membrane areas in the active region that are not covered by the catalyst at all. 

The ideal additive would enhance proton conductivity and stabihty. One demonstration of this was in a composite PFSA membrane using Pt nanoparticles supported on titania or silica [63]. The composite membranes when employed in MEAs demonstrated unhumidifled fuel cell performance comparable to that of a similar humidified fuel cell. Whether adding Pt to the membrane will help durability or hurt it is still a matter of some debate [64, 65]. Unfortunately, it is not commercially feasible at this time to add additional Pt to the MEA and so this approach while novel is not practical. The HPAs are known peroxide decomposition catalysts and so these inorganic oxides have been demonstrated to improve performance and decompose peroxide in fuel cells and if they could be immobilized would present a practical solution to this problem [66]. 

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