Direct methanol fuel cells mechanisms

Yao, S.C., Tang, X., Hsieh, C.C., Alyousef, Y, Vladimer, M., Redder, G.K., Amon, C.H., 2006. Micro-electro-mechanical systems (MEMS)-based micro-scale direct methanol fuel cell development. Energy 31 636-649. 

Hamnett, A. Mechanism and electrocatalysis in the direct methanol fuel cell. Catalysis Today 1997, 38 (4), 445-457. 

The modification of platinum catalysts by the presence of ad-layers of a less noble metal such as ruthenium has been studied before [15-28]. A cooperative mechanism of the platinurmruthenium bimetallic system that causes the surface catalytic process between the two types of active species has been demonstrated [18], This system has attracted interest because it is regarded as a model for the platinurmruthenium alloy catalysts in fuel cell technology. Numerous studies on the methanol oxidation of ruthenium-decorated single crystals have reported that the Pt(l 11)/Ru surface shows the highest activity among all platinurmruthenium surfaces [21-26]. The development of carbon-supported electrocatalysts for direct methanol fuel cells (DMFC) indicates that the reactivity for methanol oxidation depends on the amount of the noble metal in the carbon-supported catalyst. 

The mechanism of catalyst dissolution occurs to dilfering degrees, depending upon the degree to which platinum is alloyed and what other elements are included in the alloy. Work by Piela et al. [33] suggests that PtRu alloys, as employed in direct methanol fuel cell and reformate anodes to reduce sensitivity to CO, are extremely unstable and that operation leads to ruthenium... 

The peripheral equipment needed for direct methanol fuel cells is largely analogous to that of polymer electrolyte membrane fuel cells. The mechanical basis of fuel cells and stacks on the whole consists of bipolar plates between which the sandwiched membrane-electrode assemblies are arranged. For the venting of heat, cooling plates with a circulating heat transfer agent are set up in a particular order between individual fuel cells in the stack. 

Sarma LS, Chen CH, Wang GR, Hsueh KL, Huang CP, Sheu HS, Liu DG, Lee JF, Hwang BJ (2007) Investigations of direct methanol fuel cells (DMFC) fading mechanisms. J Power Sources 167 358-365... 

The analysis of carbon materials used as catalyst support, gas diffusion layer, and current collector and bipolar plates is performed in Chap. 7. A number of carbon materials including carbon blacks, nanotubes, nanofibers, and structured porous carbon materials are analyzed and compared as catalyst support in direct methanol fuel cells. Commercial and non-commercial gas diffusion layers are described along with the role of the mesoporous layer on the fuel cell performance. Finally, synthetic graphite and carbon composites used as current collector and bipolar plates are discussed, focusing on their mechanical and electrical properties and production costs. 

Joo and co-workers [22] have discussed a new type of composite membrane, consisting of functionalised carbon nanotubes (CNT) and sulfonated polyarylene sulfone (sPAS) for direct methanol fuel cell applications. The CNT modified with sulfonic acid or platinum-rubidium (PtRu) nanoparticles were dispersed within the sPAS matrix by a solution casting method to give SOs-CNT-sPAS or PtRu-CNT-sPAS composite membranes, respectively. Characterisation of the composite membranes revealed that the functionalised CNT were homogeneously distributed within the sPAS matrix and the composite membranes contained smaller ion clusters than the neat sPAS. The composite membranes exhibited enhanced mechanical properties in terms of tensile strength, strain and toughness, which leads to improvements in ion conductivity and methanol permeability compared with the neat sPAS membrane, which demonstrates that the improved properties of the composite membranes induce an increase in power density. The strategy for CNT-sulfonated composite membranes in this work can potentially be extended to other CNT-polymer composite systems. 

Methanol (MeOH) crossover from the anode to the cathode in the direct methanol fuel cell (DMFC) is responsible for significant depolarization of the Pt cathode catalyst. Compared to Pt-based catalysts, NPMCs are poor oxidation catalysts, of methanol oxidation in particular, which makes them highly methanol-tolerant. As shown in Fig. 8.25, the ORR activity of a PANI-Fe-C catalyst in a sulfuric acid solution is virtually independent of the methanol content, up to 5.0 M in MeOH concentration. A significant performance loss is only observed in 17 M MeOH solution ( 1 1 water-to-methanol molar ratio), a solution that can no longer be considered aqueous. The changes to oxygen solubility and diffusivity, as well as to the double-layer dielectric environment, are all likely to impact the ORR mechanism and kinetics, which may not be associated with the electrochemical oxidation of methanol at the catalyst surface. Based on the ORR polarization plots recorded at... 

Zhao TS (2009) Micro fuel cells principles and applications. Elsevier, Amsterdam Zhou Y, Wang X, Wu Z, Wu X, Liu L (2011) Passive fuel delivery based on hydrophobic porous silicon for micro direct methanol fuel cells. In TREE 24th international conference on micro electro mechanical systems (MEMS), Cancun, Mexico Zhu L, Lin KY, Morgan RD, Swaminathan VV, Kim HS, Gurau B, Kim D, Bae B, Masel RI, Shannon MA (2008) Integrated micro-power source based on a micro-silicon fuel cell and a micro electromechanical system hydrogen generator. J Power Sources 185 1305-1310... 

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