Polymer-electrolyte fuel cells electrode potential

Figure 6.5. Impedance spectra for the oxygen reduction reaction at three different electrode potentials a 0.8 V b 0.7 V c 0.6 V. The microporous layer (loading 3.5 mg/cm2) of the electrode has varying PTFE content ( ) 10 ( ) 20 (A) 30 (+) 40 wt% [5], (Reprinted from Journal of Power Sources, 94(1), Song JM, Cha SY, Lee WM. Optimal composition of polymer electrolyte fuel cell electrodes determined by the AC impedance method, 78-84, 2001, with permission from Elsevier and the authors.)...

This review considers what we believe to be a suitable method to solve a range of electrochemical related problems in science and engineering, i.e., Adomian decomposition. The method is applied to several problems related to the analysis of three dimensional electrodes.4,5 The typical structure of three dimensional electrodes is shown schematically in Figure 1, in terms of two types of electrode. Figure la, is appropriate for electrodes connected by an electrolyte as typically used in synthesis or in batteries, while Figure lb is for electrodes as used in fuel cells, e.g., polymer electrolyte fuel cells (PEMFC). In general the models are concerned with determining the concentration and potential (and current) distributions in the structure. 

Figure 6.1. Impedance spectra at several electrode potentials for H2/02 PEFCs with 30 wt% Pt/C, 0.4 mg Pt/cm2 and 0.7 mg Nafion /cm2 electrodes, Nafion 117 membrane at T = 25°C and atmospheric gas pressure a full range of frequency (0.05 Hz to 10 kHz) b details of the high-frequency region (o) 0.925 V, (A) 0.9 V, (V) 0.875 V, and (+) 0.65 V [4], (Reprinted from Electrochimica Acta, 43(24), Paganin VA, Oliveira CLF, Ticianelli EA, Springer TE, Gonzalez ER. Modelistic interpretation of the impedance response of a polymer electrolyte fuel cell, 3761-6, 1998, with permission from Elsevier and the authors.)...

FIGURE 6.11 Relation between the current density-potential curve against the RHE (reversible hydrogen electrode) of stainless steel (left) and anode and cathode polarization curve of a polymer electrolyte fuel cell (right). (With kind permission from Springer Science+Business Media, Polymer Electrolyte Fuel Cell Durability. Influence of metallic bipolar plates on the durability of polymer electrolyte fuel cells. 2009. pp. 243-256. Scherer, J., Munter, D., and Strobel, R.)... 

Fig. 1 Comparison of the current density-potential curve of stainless steel (left) and the anode and cathode polarization curve of a polymer electrolyte fuel cell (right). RHE reversible hydrogen electrode...

Fuel cell researchers have also investigated other reference electrodes, such as a pseudo-reference electrode constructed by inserting a micro-sized carbon filament between two polymer electrolyte membranes [73], The main advantage of pseudoreference electrodes is their easy implementation, although one disadvantage is that their DC potential is unknown. However, this DC potential may not be that critical because EIS measurements mainly rely on the AC perturbation signal from which the impedance is calculated. 

The construction of a cell permitting both FTIR measurements and electrochemical impedance measurements at buried polymer/metal interfaces has been described [266]. Ingress of water and electrolyte, oxidation (corrosion) of the aluminum metal layer, swelling of the polymer and delamination of the polymer were observed. A cell suitable for ATR measurements up to 80°C has been described [267]. The combination of a cell for ATR measurements with DBMS (see Sect. 5.8.1) has been developed [268]. It permits simultaneous detection of stable adsorbed species and relatively stable adsorbed reaction intermediates (via FTIR spectroscopy), quantitative determination of volatile species with DBMS and elucidation of overall reaction kinetics. An arrangement with a gas-fed electrode attached to the ATR element and operated at T = 60°C has been reported [269]. In this study, the establishment of mixed potentials at an oxygen consuming direct methanol fuel cell in the presence of methanol at the cathode was investigated. With infrared spec-... 

PANI-NTs synthesized by a template method on commercial carbon cloth have been used as the catalyst support for Pt particles for the electro-oxidation of methanol [501]. The Pt-incorporated PANl-NT electrode exhibited excellent catalytic activity and stabUity compared to 20 wt% Pt supported on VulcanXC 72R carbon and Pt supported on a conventional PANI electrode. The electrode fabrication used in this investigation is particularly attractive to adopt in solid polymer electrolyte-based fuel cells, which arc usually operated under methanol or hydrogen. The higher thermal stabUity of y-Mn02 nanoparticles-coated PANI-NFs on carbon electrodes and their activity in formic acid oxidation pomits the realization of Pt-free anodes for formic acid fuel cells [260]. The exceUent electrocatalytic activity of Pd/ PANI-NFs film has recently been confirmed in the electro-oxidation reactions of formic acid in acidic media, and ethanol/methanol in alkaline medium, making it a potential candidate for direct fuel cells in both acidic and alkaline media [502]. 

Al-air fuel cells, Zn-Mn02 and Al-Mn02 cells, were assembled with anodes, cathodes and alkaline solid polymer electrolyte membranes. The electrochemical cells showed excellent cell power density and high electrode utilization. Therefore, these PVA-based solid polymer electrolyte membranes have great advantages in the applications for all-solid-state alkaline fuel cells. Some other potential applications include small electrochemical devices, such as supercapacitors and 3C electronic products. 

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