Direct methanol fuel cells cathode electrode

Convert P, Countanceau C, Cromgneau P, Gloaguen F, Lamy C (2001) Electrodes modified by electrodeposition of CoTAA complexes as selective oxygen cathodes in a direct methanol fuel cell. J Appl Electrochem 31 945-952... 

A direct methanol fuel cell consists of two electrodes—a catalytic methanol anode and a catalytic oxygen cathode—separated by an ionic conduc-... 

PEMFC)/direct methanol fuel cell (DMFC) cathode limit the available sites for reduction of molecular oxygen. Alternatively, at the anode of a PEMFC or DMFC, the oxidation of water is necessary to produce hydroxyl or oxygen species that participate in oxidation of strongly bound carbon monoxide species. Taylor and co-workers [Taylor et ah, 2007b] have recently reported on a systematic study that examined the potential dependence of water redox reactions over a series of different metal electrode surfaces. For comparison purposes, we will start with a brief discussion of electronic structure studies of water activity with consideration of UHV model systems. 

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 ... 

The electrodes in the direct methanol fuel cell (DMFC) (i.e. the anode for oxidising the fuel and the cathode for the reduction of oxygen) are based on finely divided Pt dispersed onto a porous carbon support, and the electro-oxidation of methanol at a polycrystalline Pt electrode as a model for the DMFC has been the subject of numerous electrochemical studies dating back to the early years ot the 20th century. In this particular section, the discussion is restricted to the identity of the species that result from the chemisorption of methanol at Pt in acid electrolyte. This is principally because (i) the identity of the catalytic poison formed during the chemisorption of methanol has been a source of controversy for many years, and (ii) the advent of in situ IR culminated in this controversy being resolved. 

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. 

One energy application of methanol in its early stages of development is the direct methanol fuel cell (DMFC). A fuel cell is essentially a battery in which the chemicals are continuously supplied from an external source. A common fuel cell consists of a polymer electrolyte sandwiched between a cathode and anode. The electrodes are porous carbon rods with platinum... 

For EIS measurements of a direct methanol fuel cell (DMFC), the anode is supplied with an aqueous solution of methanol at a concentration such as 1 M and using controlled flow rates. The cathode is operated on either air, oxygen, or hydrogen, with controlled flow rate and pressure [43], In order to measure the anode EIS, the DMFC is fed with hydrogen gas instead of air or oxygen, to eliminate the contributions of the cathode. This cathode is normally denoted as a dynamic hydrogen electrode (DHE). Thus, the anode impedance spectra between the anode and the DHE can be obtained in a complete fuel cell. 

DMFC research at LANE in FY 2002 has focused primarily on fundamental issues relevant to potential portable and transportation applications of direct methanol fuel cells, such as cathode and anode electrocatalysis, electrode composition and structure, membrane properties and MEA design. Substantial progress has been achieved in cathode research. 

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-... 

H+) Produced by the dissociation of Hj at the anode to the cathode, (3) Prevention of the associated electron flow through the membranes forcing them to flow in the external circuit to the cathode to produce DC current, and (4) Support for the catalyst loaded on the electrodes. When Hj is replaced by methanol as a fuel in liquid form in direct methanol fuel cell (DMFC), the dissociation of methanol solution at the anode produces protons that are transported through the hydrated PEM to the cathode, where a reduction of O2 produces water in the presence of the protons. To qualify PEM for commercial application in PEMFC and DMFC, it should have a combination of properties including (Maiyalagan and Pasupathi 2010 Neburchilov et al. 2007 Nagarale et al. 2010) ... 

Bunazawa H, Yamazaki Y (2008) Influence of anion ionomer content and silver cathode catalyst on the performance of alkaline membrane electrode assemblies (MEAs) for direct methanol fuel cells (DMFCs). J Power Sources 182(1) 48-51... 

Yet, the most interesting results for ORR on Fe-Pd/WC catalyst are those obtained in the presence of alcohol. The electrode response for Fe-Pd/WC system in oxygen saturated acid has not been affected even at high concentrations of methanol, whereas the ORR on conventional catalyst Pt/C was completely restrained since the dominant reaction was basically methanol oxidation rally. Such results suggested that Pd-Fe/WC/C could be an excellent candidate for direct methanol fuel cell (DMFC) cathode because of its inert activity toward methanol oxidation as seen in Fig. 23.3. The utilization of a completely inert catalyst to methanol oxidation is one of the important criteria for DMFCs to operate at higher power densities since the issue of methanol crossover is unavoidable and can cause dramatic loss in cell performance, especially with common catalysts that are active... 

The above analysis can also be used in rotating disc electrode (RDE) test, where the difference in half wave potentials is used as AE or for the positive electrode of an electrolysis cell or for both the anode and the cathode of an alkaline fuel cell and direct methanol fuel cell, where the anode also suffers high overpotential losses. 

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