Methanol fuel cell voltage

Interestingly, the PEMFC may also operate directly on methanol. Naturally, the problems associated with high coverage of various intermediates will be present, as mentioned above, as well as additional problems such as loss of methanol over the membrane. Nevertheless, it is possible to operate a methanol fuel cell with a voltage around 0.4 V and a reasonable current, to power small mobile devices such as portable computers and cell phones and make them independent of connection to the conventional power net. For more details on fuel cells we refer the reader to L. Carr-ette, K.A. Friedrich and U. Stimming, Fuel Cells 1(1) (2001) 5-39. 

Fuel cells incorporating lithographic methods and masking/deposition/etching protocols have been fabricated on Si wafers and thereby satisfy two critical needs in a standard fuel cell collection of electrons (current collectors) and controlling the flow field of fuel and oxidant. Kelley et al. produced a miniature direct methanol fuel cell (DMFC) with a current— voltage and fuel utilization performance that matched standard-sized DMFCs prepared in-lab.A working volume for the miniature DMFC of 12 mm was reported, with an operational performance of 822 W h kg at 70 °C. ... 

The platinum/ruthenium mixture is then fired with the same firing cycle. The ratio of platinum to ruthenium is 1 1 [2,50] with the effective concentration, based on the flat area of the disc, applied to the substrate being 4 mg cm" [35,51]. The voltage-discharge curves of a coimnercially available fuel cell (H-Tec Methanol Fuel Cell Junior) was characterized. The cell was disassembled and the Ag-coated borosilicate anode was inserted and retested. 

The first of these possibilities has the advantage of keeping the fuel cell at a higher temperature and thus realizing a better electrical performance. Shukla et al. (1995) have described such a direct methanol fuel cell. A temperature of 200 C was maintained in an evaporator for a 2.5 M aqueous methanol solution. The fuel cell s working temperature was lower. At a temperature of 100°C current density of 200 mA/cm could be realized at a voltage of about 0.5 V (the total platinum content of both electrodes was 5 mg/cm ). 

The operating efficiency of direct methanol fuel cells is greatly lowered because of methanol crossover. This effect leads to unproductive methanol consumption and to a marked decrease in working voltage, caused by the action of methanol on the oxygen electrode potential. So far, only two options can be seen to lessen or completely... 

In direct formic acid fuel cell, at a temperature of 70 C and a working voltage of 0.4 V, a power density of about 50mW/cm was attained in 12M formic acid. For comparison, the power density in a typical methanol fuel cell under the same conditions is about 30 mW/cm. ... 

With the experience gathered in the development of direct methanol fuel cells, platinum-ruthenium catalysts were used for the anodic process in the first studies on direct formic acid fiiel cells. Then, it was shown that much better electrical characteristics can be obtained with palladium black as the catalyst. Importantly, with this catalyst, one can work at much lower temperatures. In particular, at a temperature of 30°C power densities of 300 mW/cm were obtained with a voltage of 0.46 V, and about 120 mW/cm with a voltage of 0.7 V. Considering all these special features, it will be very convenient to use formic acid as a reactant in fuel cells of small size, for power supply in portable equipment, ordinarily operated at ambient temperature. 

Comprehensive EXAFS reviews on catalysis have been recently published. These encompass studies concerning surface mediated electrochemical processes and catalytic solids under environmental conditions. The first set of studies examined the local structural changes in the metal occurring in tandem with redox processes under voltage control. " Recent work in this area examines the stability of bimetallic Pt-Ru electrodes and their performance in the hydrogen oxidation reaction in the presence of CO or direct methanol fuel cells. Studies reviewed involving supported metal catalysts concern, in the first place, the reduction process " while other studies also consider the oxidation process and reduction under inert gases. All of these studies make an attempt to understand the relevance of the metal support interface... 

Simoglou A, Argyropoulos P, Martin EB, Scott K, Morris AJ, Taama WM (2001) Dynamic modeling of the voltage response of direct methanol fuel cells and stacks. Part II feasibility study of model-based scale-up and scale down. Oiem Eng Sci 56 6761-6772... 

The performance of a fuel cell is characterized by its output voltage and current density, which is defined as the current per unit area of the cell. The fuel cell voltage drops at higher currents due to increasing catalytic activation losses, ionic and electronic resistances in the cell, and mass transport limitations. The cell efficiency is therefore proportional to the ratio of measured voltage to the ideal cell voltage (1.23 V and 1.21 V for hydrogen and methanol at 25 °C, respectively). 

From a perasal of Fig. 24, it is apparent that the Pd/MWCNT anode is particularly suitable for the oxidation of ethanol which shows the highest open circuit voltage (OCV, 0.74 V) and peak power density (18.4 mW cm at 0.2 V) out of the three fuels investigated. Notably, the performance trend in the passive DAFC is different from that observed in the half cell where glycerol provides the highest peak current density (Fig. 13). On the other hand, the lower performance of both the direct methanol fuel cell (DMFC) and the direct glycerol fuel cell (DGFC) as compared to the DEFC is in line with the chronopotentiometric experiments illustrated in Fig. 13. 

In a direct methanol fuel cell (DMFC) since the voltage losses due to both ORR and the methanol oxidation reaction (MOR) are significant, the OCV loss is the summation of both. 

Many statements and descriptions are plain and brief, but they are the crystallization of many years of my experience and research. You ll explore fundamental questions Will the catalyst particles be able to participate in the electrochemical reaction if they are fully covered by a thin ionomer film What can the limiting current density be based on the mass transport of air How severe will the voltage loss be if a thin layer of liquid water forms How can you quickly assess catalytic activity difference based on voltage difference in V-I curves How can a direct methanol fuel cell work using neat methanol How high can H2and O2 gases be pressurized within a PEM electrolyzer ... 

Much worse is the situation with a direct methanol fuel cell (DMFC) anode. For this electrode, jcrit is very low, about 20mAcm (Table 23.1). This means that at a working current of 100 mAcm , a typical DMFC anode operates in the double-Tafel regime, which dramatically increases the anode polarization voltage. 

Table 2 Micro-FC prototypes, incorporating mesoporous silicon in the core system, reported in the hterature for DHFC (direct hydrogen fuel cell), DMFC (direct methanol fuel cell), and RHFC (reformed hydrogen fuel cell). Aacttve is the active surface, OCV the open circuit voltage of the cell, PP the power peak during the test, fuel A and K are the fuels provided at anode (A) and cathode (K), T° is the temperature during the test, RT is the room temperature, MeOH is methanol and EtOFI is ethanol...

A. A. Kulikovsky. The voltage current curve of a direct methanol fuel cell Exact and fitting equations. Electrochem. Comm., 4 939-946, 2002b. 

Many research groups have reported the fuel cell performance of Pt nanoparticles supported on CNTs at the cathode of H2/O2 fuel cells or direct methanol fuel cells [63, 65, 66, 68, 69, 71, 81, 87, 188, 189, 191-193]. It has been shown that the performance of a CNT-based MEA is better than that of conventional Pt/C MEA [65, 71, 81, 189, 191-193]. For example, Matsumoto and coworkers [193] conducted the fuel cell tests of the MEA with CNTs used as a support for Pt catalysts at the cathode. The authors concluded that enhancements in PEM fuel cell performance are observed by using the CNT cathode in comparison to a conventional carbon cathode in a low current density region (Figure 14.27). The voltage drop above 400 mA/cm was ascribed to the proton diffusion. 

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