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Thermodynamic hydrogen oxidation

Hydrogen oxidation according to Eq. (5) is possible above 0 V. If hydrogen evolution occurs at the negative electrode and the H2 evolved reaches the positive electrode, from the thermodynamic situation the reaction that is to be expected is ... [Pg.161]

In order to overcome unfavorable thermodynamics, hydrogen must be oxidatively removed (either by superacid or added oxidant). Considering the abundance of methane in nature, the conversion of natural gas into branched liquid hydrocarbons in the gasoline range is of immense interest. [Pg.553]

The potency of an electrocatalyst is usually defined in terms of the potential required to carry out a specific process at a prescribed rate, or current, per unit area of electrode. Platinum, for example, promotes hydrogen evolution and hydrogen oxidation in aqueous electrolytes, at very high rates at potentials very close to the thermodynamic redox potential for the reaction H+(aq) I e - - ViH2(g), that is, small overpotentials, T. Hence, it is a far more potent electrocatalyst than, for example, Hg or carbon, for which the onset for either reaction occurs at potentials far removed from that predicted value, that is, large T. ... [Pg.193]

A number of processes in living systems result in the transfer of electrons (oxidation and reduction) and can be understood in thermodynamic terms. Oxidation is the loss of electrons or hydride (H ) ions (but not hydrogen [H" ] ions) by a molecule, atom, or ion. Reduction is the gain of electrons or hydride (H ) ions by a molecule, atom, or ion. Transfer of one hydride ion results in the transfer of two electrons. [Pg.72]

Yet, changing over to higher temperatures implies a certain diminution of thermodynamic indices of the fuel cells. The Gibbs free energy - AG of hydrogen oxidation by oxygen decreases with increasing temperature. It amounts to 1.23 eV at 25°C but... [Pg.191]

Rollins JB, Conboy JC (2009) Kinetics and thermodynamics of hydrogen oxidation and oxygen reduction in hydrophobic room-temperature ionic liquids. J Electrochem Soc 156 B943-B954... [Pg.164]

The knowledge of enthalpies of dissociations for M —H, M —R, M —C(0)R, and Y —C(0)R (Y = H, R) bonds allows the estimation of enthalpies of various organome-tallic reactions (Table 4.4). This table shows that the following reactions are thermodynamically favorable oxidative addition of hydrogen, CO insertion into the M —R bond, olefin insertion into the M —H bond, and olefin insertion into the M —R bond. Oxidative addition of aldehydes to the transition metal complexes is possible. However, due to the near-zero value of the enthalpy of this reaction, oxidative addition of aldehydes does not occur easily in the above-mentioned processes. Thermodynamically unfavorable are oxidative addition of the unstrained C —C bonds, oxidative addition of C — H bonds, and CO insertion into the M — H bonds. [Pg.203]

Aluminum exhibits good resistance to atmospheric corrosion and to corrosion in neutral solution. The reason is that in this pH range it is protected by a thermodynamically stable oxide film (Figure 2.18). In acidic or alkaline environments, aluminum oxide dissolves and the metal corrodes rapidly with simultaneous formation of hydrogen. In presence of chloride ions, pitting corrosion may occur. [Pg.522]

Exactly, the same kinetics of adsorption and desorption of oxygen as well as the reaction of adsorbed oxygen (0(s)) have also been used before to model hydrogen oxidation (Karakaya and Deutschmann, 2013). The surface reaction kinetics for CO oxidation is given in Table 2.1. The reaction kinetics are thermodynamically consistent at temperatures of 273—1273 K. [Pg.63]

The thermodynamics of the reactions was established as a function of voltage by calculating the stability of the reaction intermediates and the overpotential of the reaction could be linked directly to the proton and electron transfer (Norskov et al, 2004). A Tafel-Heyrovsky-Volmer three-step reaction model (Wang et al, 2006) for the hydrogen oxidation is considered at the anode, while a Damjanovic three-step reaction model (Malek et al, 2008) for the oxygen reduction mechanism is assumed at the cathode. Assuming non-interaction between adsorbed intermediate species and... [Pg.71]

Methanol electro-oxidation is a complex reaction involving the transfer of six electrons and several catalytic steps. Although the thermodynamic potential for the full electro-oxidation of methanol in acid electrolytes is close to that of hydrogen oxidation, the overall reaction is much more demanding due to the multi-electron transfer steps to form carbon dioxide. The half reaction is ... [Pg.98]

In the previous section, we discussed fuel cell thermodynamics. However, in reality, fuel cell operation with an external load is much more practical than in a thermodynamic state. When a H2/air PEM fuel cell outputs power, the half-electrochemical reactions will proceed simultaneously on both the anode and the cathode. The anode electrochemical reaction expressed by Reaction (l.I) will proceed from H2 to protons and electrons, while the oxygen from the air will be reduced at the cathode to water, as expressed by electrochemical Reaction (l.II). For these two reactions, although the hydrogen oxidation reaction (HOR) is much faster than the oxygen reduction reaction (ORR), both have limited reaction rates. Therefore, the kinetics of both the HOR and the ORR must be discussed to achieve a better understanding of the processes occurring in a PEM fuel cell. [Pg.14]

What prompted the present study was our recent discovery that the protein carbonyl allysine (adipic semialdehyde) can become further oxidized into 2-aminoadipic acid (2-AAA) (see Scheme I). In human skin, this thermodynamically stable oxidation endproduct of lysine, accumulated to a much larger extent than its precursor measured as 6-hydroxynorleucine. This finding implied that hydrogen peroxide mediated oxidation was important in the extracellular matrix and raised the question whether intracellular long-lived proteins, such as the crystallins were also subject to lysyl oxidation and 2-AAA formation. [Pg.93]


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See also in sourсe #XX -- [ Pg.179 ]




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