Transcript
Direct Methanol Fuel Cell (DMFC)
Abstract:
Direct Methanol Fuel Cell (DMFC) is often considered as a promising electrochemical generator for various applications, including micro sources. Direct Methanol Fuel Cell or DMFCs are a subcategory of proton exchange fuel cell in which methanol is used as a fuel f uel cell. here the main advantages are the ease of transport of methanol is used as a fuel, an energy density yet reasonable sustainable li!uid at all environmental conditions. "fficiency is !uite low for these cells, so they are targeted to especially to portable applications, where the energy and power density are more important than efficiency. efficiency. #nfortunately, #nfortunately, serious limitations are still remain and need to be solved before development of such devices. Challenges concern the various component of DMFC both anodic and cathodic reaction need more suitable electrodes, as well as the electrolytic membrane should be concerned.
Abstract:
Fuel cells are considered as future device for converting the chemical energy into electrical energy without having any movable parts. Fuel cell can be classified according to wor$ing temperature% high, medium and low (ambient) temperature system or referring to the pressure of operation% high, medium and low (atmospheric) pressure system. &t wor$s on the principal of oxidation reduction mechanism using special type of 'olymer "lectrolyte Membrane ('"M) which only allows proton to exchange through it. Direct Methanol Fuel Cell (DMFC) is advantageous in terms of operation conditions as well as its reliability over the other types of fuel cells such as, l$aline Fuel Cell (FC), Molten Carbon Fuel Cell (MCFC), 'olymer "lectrolyte Membrane Fuel Cell ('"MFC), olid *xide Fuel Cell (*FC), 'hosphoric cid Fuel Cell ('FC). Direct Methanol Fuel Cell (DMFC) wor$s in the same way as a 'olymer "lectrolyte Membrane Fuel Cell ('"MFC) with a difference that methanol and water are split into protons, electrons and C* + at the anode. he main advantages are the ease of transport of methanol, an energydense yet reasonably stable li!uid at all environmental condition, methanol can be produced from biomass or natural gas and the lac$ of complex steam reforming (used to generate hydrogen from fossil fuel) operations. he efficiency is presently !uietly low for these cells so they are targeted especially to portable applications, where energy and power density are more important than efficiency. #sing methanol as primary fuel has its advantages over pure hydrogen. *ne of the most significant is that fact that methanol can be stored as a li!uid over a wide temperature range ( -℃ to /0. ℃) and therefore avoids many of the pitfalls of hydrogen storage. 1i!uid methanol on the other hand can be stored in cheap plastic containers and is an excellent carrier fuel that hydrogen can be extracted from to power fuel cells. he reasons behind the poor efficiency are firstly, the low reaction $inetics of methanol oxidation reaction at anode, secondly, the thic$ness of anode catalyst layer. thic$ catalyst layer increases the ohmic resistances as well as mass transfer resistances. 2ow a days, fuel cell technology especially in DMFCs which is being for long as the most difficult fuel cell technology due to methanol crossover and catalytic inefficiency, steady progress has been made such as catalysis, electrolysis, electrode structure, theoretical understanding of gas diffusion and fuel cell engineering.
Abstract:
Direct Methanol Fuel Cell (DMFC) is simulated in se!uential mode in a 3ero dimensional mode to represent the electrochemical reaction on both electrodes. &t is shown that this approach is predicted the harmful methanol f low across the polymer electrolyte membrane('"M), the cross over and the resulting loss of potential on the cathode , caused by the mixed potential that is build between the parasitic cathodic methanol and the oxygen reduction .
Abstract:
Fuel Cells are electrochemical reactions that reali3ed the direct conversion of chemical energy of reactants to electrical energy. mong the different fuel cell types, the DMFC with the polymer electrolytic membrane('"M) as electrolyte and li!uid water 4 methanol mixture as energy carrier is a promising power source of vehicular and various portable application, li$e laptops. Multimedia e!uipments, and mobile power supplies, these type of fuel cell has several advantages, such as low emission, a potentially renewable li!uid fuel with a high power dencity,as well as fast and convenient refueling.
Abstract:
Direct Methanol Fuel Cells(DMFCs)are currently investigated as alternative power source to batteries for portable applications because they can offer higher energy densities. 5owever, two factors limit the performance of DMFC systems% crossover of methanol from anode to cathode and the slow $inetics of the electrochemical oxidation of methanol at the anode. he crossover of methanol lowers the system efficiency and decreases cell potential due to corrosion at the cathode. he $inetics of DMFCs are complicated because the reaction mechanism involves adsorption of methanol and several reaction steps including the oxidation of C*, where the electrochemical oxidation of methanol occurs. Catalysis studies have attempted to analy3e possible reaction pathways to find the main pathway of methanol oxidation. Most studies conclude that the reaction can proceed according to multiple mechanisms. 5owever, it is widely accepted that the most significant reactions are the adsorption of methanol and the oxidation of C*. the reaction mechanism that will be used in to model performance of DMFCs.
Abstract:
*ne of the most promising applications of Direct Methanol Fuel Cells (DMFCs) presently concerned with the field of portable power sources . &n this regard, increasing interest is devoted towards the miniaturi3ation of these fuel cell devices in order to replace the current 1iion batteries. heoretically, methanol has a superior specific energy density (/666 7h8$g) in comparison with the best rechargeable battery, lithium polymer and lithium ion polymer (/66 7h8$g) systems. his means longer conversation times using mobile phones, longer times for use of laptop computers and more power available on these devices to support consumer demand. nother significant advantage of the DMFC over the rechargeable battery is its potential for instantaneous refuelling. hese significant advantages ma$e DMFCs an exciting development in the portable electronic devices mar$et .#nfortunately, DMFC operation at low temperatures re!uires a high noble metal loading to enhance the $inetics of the methanol electrooxidation reaction and counteract the poisoning effects at the cathode due to the methanol crossover . &n order to reduce ohmic drop, mass transport and manufacturing problems deriving by the use of thic$ electrodes, the present DMFC catalysts for low temperature applications are usually unsupported 't and 't9u alloys :;6;+<. =et, the presence of catalyst agglomeration effects in unsupported catalysts significantly limits their utili3ation in polymer electrolyte fuel cell systems. &n this wor$, an >?@ 't9u (;%; a8o) alloy supported on Aulcan BC+ and a /6@ 't8Aulcan BC+ were inhouse prepared and utili3ed in DMFCs as anode and cathode catalysts, respectively. hese carbon supported catalysts associate high metal surface area to a suitable concentration of the active phase that allows to maintain a low electrode thic$ness. he influence of noble metal loading on the performance of a DMFC operating at low temperatures (6/6C) has been investigated. his effect has been correlated to catalyst utili3ation and electrocatalytic activity at the different temperatures.
Abstract:
Direct methanol fuel cell (DMFC) is a device that converts chemical energy in Methanol to useful electrical energy. he DMFC cells are fabricated by synthesi3ing Membrane "lectrode ssembly (M"). Methanol is oxidi3ed to carbon dioxide at the anode. 'rotons pass through the membrane and electrons through the external electrical circuit. hey combine with oxygen at the cathode to form water. he actual cell voltage of direct methanol fuel cell is less than theoretical voltage due to losses involved in the fuel cell operation. MaEor losses are due to methanol cross over and slow reaction $inetics (activation losses). For example, during the reaction process, some !uantity of methanol permeates through the membrane from the anode side to the cathode. his process $nown as methanol crossover (MC), reduces the efficiency of the DMFC as the carbon atoms in methanol poisons the cathodes catalyst. Moreover, the methanol which has crossed over becomes Gwasted and cannot be reused as a fuel in the anode side.
Abstract:
he polyvinylidene fluoridesulfonated polystyrene composite membrane with proton exchange performance, denoted as 'ADF', was prepared using a thermally induced polymeri3ation techni!ue. he thermal stability of the 'ADF ' composite membrane was investigated using thermo gravimetric (H) analysis. he complex formation of the composite membrane was ascertained by Fourier transform infrared spectroscopy (F&9). he surface compositions of the 'ADF' membrane were analy3ed using Bray photoelectron spectroscopy (B'). he morphology of the composite membrane was characteri3ed by environmental scanning electron microscopy (""M). he proton conductivity of the 'ADF' membrane was measured using impedance spectroscopy in the hydrated condition. he 'ADF' membrane has a stronger hydrophilic character than the pristine 'ADF membrane and the polyvinylidene fluoride polystyrene composite membrane ('ADF'), which is caused by the incorporation of sulfonic acid groups. he proton conductivity and the methanol permeability of the 'ADF' membrane measured at +-> I . lthough 'ADF ' composite membrane possesses the lower oxidative stability than 2afion;; membrane, the composite membrane displays lower methanol permeability than the 2afion;; membrane, and the selectivity (the ratio of proton conductivity and methanol permeability) of the composite membrane is almost +6 times than that of 2afion;;.
