Hydrogen direct methanol fuel cell

The generated potential via exergonic reactions in direct fuel cells is partly used to promote electrode reactions (kinetic overpotential), while in indirect fuel cells, the fuel is first processed into simpler fuels (to reduce the kinetic overpotential) via conventional catalytic reactors, or CMRs, in which temperature is used as the key operating parameter to accomplish the desired kinetics and equilibrium conversions. Among the direct fuel cells, e.g., PEMFCs use hydrogen, direct methanol fuel cell (DMFC) uses methanol, while the SOFC can operate directly on natoral gas (Figiue 15.3). However, in indirect fuel cells, a complex fuel must be suitably reformed into simpler molecules such as H2 and CO before it can be used in a fuel ceU. 

Besides chemical catalytic reduction of carbon dioxide with hydrogen, which is already possible in the laboratory, we are exploring a new approach to recycling carbon dioxide into methyl alcohol or related oxygenates via aqueous eleetrocatalytic reduction using what can be called a regenerative fuel cell system. The direct methanol fuel cell... 

Fuel cells can run on fuels other than hydrogen. In the direct methanol fuel cell (DMFC), a dilute methanol solution ( 3%) is fed directly into the anode, and a multistep process causes the liberation of protons and electrons together with conversion to water and carbon dioxide. Because no fuel processor is required, the system is conceptually vei"y attractive. However, the multistep process is understandably less rapid than the simpler hydrogen reaction, and this causes the direct methanol fuel cell stack to produce less power and to need more catalyst. 

The Pt/Ru catalyst is the material of choice for the direct methanol fuel cell (DMFC) (and hydrogen reformate) fuel cell anodes, and its catalytic function needs to be completely understood. In the hrst approximation, as is now widely acknowledged, methanol decomposes on Pt sites of the Pt/Ru surface, producing chemisorbed CO that is transferred via surface motions to the active Pt/Ru sites to become oxidized to CO2... 

For isolating the overpotential of the working electrode, it is common practice to admit hydrogen to the counter-electrode (the anode in a PEMFC the cathode in a direct methanol fuel cell, DMFC) and create a so-called dynamic reference electrode. Furthermore, the overpotential comprises losses associated with sluggish electrochemical kinetics, as well as a concentration polarization related to hindered mass transport ... 

Direct hydration, of ethylene, 10 538 Direct hydrogenation, 6 827 Direct immunosensors, 14 154 Direct ingot (dingot) method, 25 409 Direct initiation, 14 270 Direct injection (DI) diesel engines, 12 421 Direct inlet injection, gas chromatography, 6 383, 415-416 Directional couplers, 17 446 Directional drilling techniques, in sulfur extraction, 23 572 Directive 89/107/EEC (EU), 12 36 Direct liquefaction, 6 827 Direct marketing, technical service personnel and, 24 343 Direct metal nitridation, 17 211-213 aerosol flow reactor, 17 211-212 Direct methanol fuel cells (DMFC),... 

A particular version of the PEFC is the direct methanol fuel cell (DMFC). As the name implies, an aqueous solution of methanol is used as fuel instead of the hydrogen-rich gas, eliminating the need for reformers and shift reactors. The major challenge for the DMFC is the crossover of methanol from the anode compartment into the cathode compartment through the membrane that poisons the electrodes by CO. Consequently, the cell potentials and hence the system efficiencies are still low. Nevertheless, the DMFC offers the prospect of replacing batteries in consumer electronics and has attracted the interest of this industry. 

Polyphosphazene-based PEMs are potentially attractive materials for both hydrogen/air and direct methanol fuel cells because of their reported chemical and thermal stability and due to the ease of chemically attaching various side chains for ion exchange sites and polymer cross-linking onto the — P=N— polymer backbone. Polyphosphazenes were explored originally for use as elastomers and later as solvent-free solid polymer electrolytes in lithium batteries, and subsequently for proton exchange membranes. 

A direct-methanol fuel cell is very similar to the hydrogen fuel cells in this review, with the exception of the fuel. In a direct-methanol fuel cell, methanol is fed instead of hydrogen and reacts according to the reaction... 

The purpose of the present review is to summarize the current status of fundamental models for fuel cell engineering and indicate where this burgeoning field is heading. By choice, this review is limited to hydrogen/air polymer electrolyte fuel cells (PEFCs), direct methanol fuel cells (DMFCs), and solid oxide fuel cells (SOFCs). Also, the review does not include microscopic, first-principle modeling of fuel cell materials, such as proton conducting membranes and catalyst surfaces. For good overviews of the latter fields, the reader can turn to Kreuer, Paddison, and Koper, for example. 

Most fuel cells are powered by hydrogen, which can be fed to the fuel cell system directly or can be generated within the fuel cell system by reforming hydrogen-rich fuels such as methanol, ethanol, and hydrocarbon fuels. Direct methanol fuel cells (DMFCs), however, are powered by pure methanol. 

Direct methanol fuel cell technology is relatively new compared to that of fuel cells powered by pure hydrogen, and research and development are roughly 34 years behind that of other fuel cell types. Nonetheless, the DMFC appears to be the most promising as a battery replacement for portable applications such cellular phones and laptop computers, and a number of manufacturers are already introducing commercial versions of these applications. 

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