Methanol polarization curves

In the circuit, Rs is the electrolyte resistance, CPE indicates the double-layer capacitance, Rc, is the methanol oxidation charge-transfer resistance, while R1 and Cl are the mass transfer related resistance and capacitance (mainly due to methanol adsorption or CO coverage). The physical expression of these parameters can be deduced from the reaction kinetics. In the methanol oxidation reaction, the overall charge transfer rate is the sum of each charge-transfer step (rct). The Faradaic resistance (Rj) equals the inverse of the DC polarization curve slope ... 

Fig. 53 Comparison of DMFC polarizations curves at 80 °C with anode feed of 0.5 M methanol solution and the air cathode operating at zero backpressure for a cell with a Nafion 115 membrane and a cell with a polyaromatic membrane of lower methanol permeability [105].

The electrode-electrolyte assembly was investigated in a single cell test station. After installing the MEA in the fuel cell housing, water was supplied to the anode and cathode backing layers and the cell was warmed-up step-wise from room temperature to 145°C. The polarization curves obtained for the fuel cells equipped with the Nafion-silica and Nafion-silica-PWA membranes, under same conditions in presence of oxygen feed at cathode and 2M methanol solution at anode, are reported in Fig. 6. 

Pt/Ru which displayed a negative shift of the polarization curves and a decrease in the degree of poisoning compared with pure platinum. Pt/Sn also displays greater activity for methanol oxidation compared to pure Pt. However, it was not as promising as Pt/Ru catalyst. 

Fig. 1.20 Steady-state galvanostatic polarization curves for the oxidation of 1.0 M methanol on Pt/Sn electrodes in 0.5 M sulfuric acid at room temperature. Effect of perfiuoroalkanesulfonic acid additives upon ease of methanol electrooxidation.

Fig. 2.23 (a) Comparison of the CO stripping of the three colloidal catalysts, (b) Steady-state polarization curves along with simulated curves for methanol oxidation of the three different 30wt.% PtRu/Vulcan XC-72 catalysts (symbols) at two different temperatures (22 and 60°C). Conditions fixed delay of 5 min, methanol concentration 1 M in the working electrode compartment, flow rate 10Lh . ... 

Depending on the conductivity of the solutions the ohmic drop may vary considerably in organic solvents. Whereas in solutions of primary (waterlike) alcohols such as methanol, ethanol (EtOH) and propanol polarization curves with ohmic drop corrections can be obtained it is impossible to make similar measurements in non water-like solvents such as long chain alcohols, halogenated hydrocarbons and other aprotic solvents. 

Fig. 5.9 Comparison of polarization curves for ORR on (a) Pt/C and (b) Pd-Co-Pt in 0.1 mol L H2SO4 with and without 0.1 mol L methanol 1,600 rpm scan rate 5 mV s (Reproduced from Ref [30] with kind permission of The Electrochemical Society 2012)...

Omran et al. have proposed a 3D, single phase steady-state model of a liquid feed DMFC [181]. Their model is implemented into the commercial computational fluid dynamics (CFD) software package FLUENT . The continuity, momentum, and species conservation equations are coupled with mathematical descriptions of the electrochemical kinetics in the anode and cathode channel and MEA. For electrochemical kinetics, the Tafel equation is used at both the anode and cathode sides. Results are validated against DMFC experimental data with reasonable agreement and used to explore the effects of cell temperature, channel depth, and channel width on polarization curve, power density and crossover rate. The results show that the power density peak and crossover increase as the operational temperature increases. It is also shown that the increasing of the channel width improves the cell performance at a methanol concentration below 1 M. 

Fig. 2.4 Power density and polarization curves of a Pt/WC anode MEA with a 2 M methanol concentration and a flow rate of 4 ml/min at various operating temperatures [23]...

A lot of papers have been addressed to the methanol oxidation on Pt-Ru catalyst in acidic media, and excellent reviews have been done by Spendelow et al. [24] and Petrii [25]. Conversely, few works have been addressed to the MOR on Pt-Ru catalysts in alkali media. Firstly, Petrii et al. [26] compared the polarization curves of methanol electrooxidation in an alkaline solution under steady-state conditions... 

Fig. 17.6 Comparison of polarization curves for ORR on Pd2Co/C in oxygen-saturated 0.1 M HCIO4 solution with and without 0.1 M methanol rotation rate 900 rpm sweep rate 10 mV s . The inset is the cyclic voltammetry of Pd2Co/C nanoparticles m nitrogen-saturated 0.1 M HCIO4 + 0.1 M methanol solutions sweep rates 20 mV s [19]...

In the 1920 s, E. MQller and his co-workers made a series of studies on the anodic oxidation of methanol, formaldehyde, and formic acid which represent the first extensive mechanistic investigation of these compounds, although the principles of electrode kinetics had not yet been formulated. Muller did not establish mechanisms for these reactions however, many of his observations have been later confirmed and his studies were among the first with a comparison of polarization curves on several noble metals including platinum, palladium, rhodium, iridium, osmium, rubidium, gold, and silver (cf. Figure 1). As was usual at that time, Muller discussed his results in terms of polarization, rather than in terms of current or reaction rate. 

We will assume that the methanol concentration does not vary significantly across the ACL. Figure 2.11 illustrates the system of coordinates and the typical profile of the overpotential ri x) in the ACL. To emphasize that we are on the anode side, the axis x is now directed toward the membrane so that the polarization curve of the ACL is 7i(ji) (Figure 2.11). 

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