Fuel cells cathodic reaction

Fischer-Tropsch, 178 for back-bonding, 17 for direct bonding, 17 formic acid, 141 FTIR characterizations, 291 fuel cell, 47, 185, 290, 320 fuel cell catalyst, 290 fuel cell cathode reactions, 303... 

The fan curves were measured and implemented in the model. Changing air parameters due to increased humidity resulting from the fuel cell cathode reaction were also taken into consideration. It was shown that the influence of the water on the temperature distribution is less than 1%. 

Clearly, PEM fuel cell cathode reactions are very complex. 

The first reported electroorganic synthesis of a sizeable amount of material at a modified electrode, in 1982, was the reduction of 1,2-dihaloalkanes at p-nitrostyrene coated platinum electrodes to give alkenes. The preparation of stilbene was conducted on a 20 pmol scale with reported turnover numbers approaching 1 x 10. The idea of mediated electrochemistry has more frequently been pursued for inorganic electrode reactions, notably the reduction of oxygen which is of eminent importance for fuel cell cathodes Almost 20 contributions on oxygen reduction at modified... 

Paradoxically, all these significant recent contributions to the theory of the ORR, together with most recent experimental efforts to characterize the ORR at a fuel cell cathode catalyst, have not led at aU to a consensus on either the mechanism of the ORR at Pt catalysts in acid electrolytes or even on how to properly determine this mechanism with available experimental tools. To elucidate the present mismatch of central pieces in the ORR puzzle, one can start from the identification of the slow step in the ORR sequence. With the 02-to-HOOads-to-HOads route appearing from recent DFT calculations to be the likely mechanism for the ORR at a Pt metal catalyst surface in acid electrolyte, the first electron and proton transfer to dioxygen, according to the reaction... 

Such bimetallic alloys display higher tolerance to the presence of methanol, as shown in Fig. 11.12, where Pt-Cr/C is compared with Pt/C. However, an increase in alcohol concentration leads to a decrease in the tolerance of the catalyst [Koffi et al., 2005 Coutanceau et ah, 2006]. Low power densities are currently obtained in DMFCs working at low temperature [Hogarth and Ralph, 2002] because it is difficult to activate the oxidation reaction of the alcohol and the reduction reaction of molecular oxygen at room temperature. To counterbalance the loss of performance of the cell due to low reaction rates, the membrane thickness can be reduced in order to increase its conductance [Shen et al., 2004]. As a result, methanol crossover is strongly increased. This could be detrimental to the fuel cell s electrical performance, as methanol acts as a poison for conventional Pt-based catalysts present in fuel cell cathodes, especially in the case of mini or micro fuel cell applications, where high methanol concentrations are required (5-10 M). 

Fuel Cell Anode Reaction Cathode Reaction... 

In a PEM fuel cell, the CDLs are where the electrochemical reactions occur for electric power generation. For example, for H2/air (O2) PEM fuel cells, the reactions occurring at the anode and cathode catalyst layers are as follows ... 

The literature reviewed in sections 2—6 represents significant advances made in the last 20 years in our understanding of solid oxide fuel-cell cathodes. At the same time, however, this work has also underscored how complex the oxygen reduction reaction is, mak-... 

Fig. 5. (a) Working principle of a solid oxide fuel cell, (b) Sketch of possible reaction paths of the oxygen reduction reaction, taking place on a particle of a solid oxide fuel cell cathode. 

A porous anode and cathode are attached to each surface of the membrane, forming a membrane-electrode assembly, similar to that employed in SPE fuel cells. Electrochemical reactions (electron transfer-l-hydrogenation) occur at the interfaces between the ion exchange membrane and electrochemically active layers of electrodes. Electrochemical reductive HDH occurred at the interfaces between the ion exchange membrane and the cathode catalyst layer when an electrical current is applied between the electrodes ... 

E25.17 Electrocatalysts are compounds that are capable of reducing the kinetic barrier for electrochemical reactions (barrier known as overpotential). While platinum is the most efficient electrocatalyst for accelerating oxygen reduction at the fuel cell cathode, it is expensive (recall Section 25.18 Electrocatalysis). Current research is focused on the efficiency of a platinum monolayer by placing it on a stable metal or alloy clusters your book mentions the use of the alloy PtsN. An example would be a platinum monolayer fuel-cell anode electrocatalyst, which consists of ruthenium nanoparticles with a sub-monolayer of platinum. Other areas of research include using tethered metalloporphyrin complexes for oxygen activation and subsequent reduction. 

Reaction 6 may involve an [H-H]+(ads) intermediate. The hydrogen electrode reactions are of interest from the standpoint of hydrogen-consuming fuel cells, competing reactions in various battery systems, the generation of hydrogen gas by water electrolysis, and the complementary cathodic reaction in metal corrosion in aqueous environments. The predominant pathway and rate-determining steps have been identified on a few metal electrode surfaces (30). 

Decrease the platinum content of the oxygen reduction reaction catalysts in fuel cell cathodes to meet the DOE 2010 precious-metal-loading goals of 0.2 g/rated kW. 

The catalytic activity of the oxygen reduction reaction (ORR) at the fuel cell cathode is known to be relatively slow, presumably because it is a 4-electron (e ) mechanism ... 

Morozan A, Jousselene B, Palacin S (2011) Low-platinum and platinum free catalysts for the oxygen reduction reaction at fuel cell cathodes. Energy Environ Sci 4 1238-1254... 

Norskov JK, Rossmeisl J, Logadottir A, Lindquist L, Kitchin JR, Bligaard T, Jonsson H (2004) Origin of the overpotential for the oxygen reduction reaction at a fuel cell cathode. J Phys ChemB 108 17886-17892... 

In summary, the RDE results indicate that ORR kinetics obtained on Pd/C and Ag/C catalysts were comparable to that on Pt/C, with reactions primarily through a 4e ORR pathway but with 50-100 mV larger overpotentials. However, Pd oxidization at fuel cell cathode working potentials can be a hindrance for its practical application in AEMFCs. Balancing cost, performance, and durability, Ag/C catalysts have been identified by several research groups as the preferred cathode catalysts to replace Pt/C for AEMFC applications. The performance of Ag/C catalysts as compared with Pt/C catalysts in AEMFCs is presented here. 

The local appearance of the reaction product is determined by the current-carrying ion. While for acidic fuel cells the reaction product shows up at the cathode (oxidant side), it is the anode (fuel side) for alkaline fuel cells. In case of C-containing fuels, e.g., methanol, a second reaction product containing the oxidized carbon appears at the... 

Electrode Kinetic and Mass Transfer for Fuel Cell Reactions For the reaction occurring inside a porous three-dimensional catalyst layer, a thin-film flooded agglomerate model has been developed [149, 150] to describe the potential-current behavior as a function of reaction kinetics and reactant diffusion. For simplicity, if the kinetic parameters, such as flie exchange current density and diffusion limiting current density, can be defined as apparent parameters, the corresponding Butler-Volmer and mass diffusion relationships can be obtained [134]. For an H2/air (O2) fuel cell, considering bofli the electrode kinetic and the mass transfer, the i-rj relationships of the fuel cell electrode reactions within flie catalyst layer can be expressed as Equations 1.130 and 1.131, respectively, based on Equation 1.122. The i-rj relationship of the catalyzed cathode reaction wifliin the catalyst layer is... 

Pt-based alloys have been developed for many years to improve the catalytic activity of the oxygen reduction reaction and the methanol oxidation reaction, and reduce Pt loading in the catalyst layers of the PEM fuel cell cathode and anode. Great progress has been made in recent years in terms of alloy activity screening, alloy mechanism discovery, and alloy stability investigation. 

When NOx are present in the air and/or in fuel cell cathode, NO is easily oxidized to NO2. Mohtadi et al. [98] performed a cyclic voltammetry (CV) study on a fuel cell after it was exposed to NO2 and foimd no oxidation peaks corresponding to adsorbed NO2 species on the Pt surface. This indicated that the poisoning effects of NO2 do not appear to be a catalyst poisoning issues instead, they suggested [98] that the ionomer and/or the catalyst-ionomer interface could be affected by NO2 exposiue through the following reaction ... 

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