Electrochemical half-cells fuel oxidation reaction

This section addresses the role of chemical surface bonding in the electrochemical oxidation of carbon monoxide, CO, formic acid, and methanol as examples of the electrocatalytic oxidation of small organics into C02 and water. The (electro)oxidation of these small Cl organic molecules, in particular CO, is one of the most thoroughly researched reactions to date. Especially formic acid and methanol [130,131] have attracted much interest due to their usefulness as fuels in Polymer Electrolyte Membrane direct liquid fuel cells [132] where liquid carbonaceous fuels are fed directly to the anode catalyst and are electrocatalytically oxidized in the anodic half-cell reaction to C02 and water according to... 

A bioelectrochemical system (BES) is an electrochemical device used to convert electrical energy into chemical energy and vice versa. A BES consists of an anode and a cathode compartment, often separated by an ion-selective membrane. The anode is the site of the oxidation reaction which liberates electrons to the electrode and protons to the electrolyte the cathode is the site of the reduction reaction, which consumes the electrons to reduce a final electron acceptor. To maintain electroneutrality of the system, protons (or other cations) need to migrate to the cathode through the ion-selective membrane. Depending on the half-cell potentials of the electrodes, a BES can be operated either as a microbial fuel cell (MFC), in which electric energy is generated, or as a microbial... 

The other member of the family of low-temperature fuel cells utilizing liquid methanol as a fuel and oxygen/air as oxidant is the direct methanol fuel cell (DMFC). The half-cell electrochemical reactions in DMFC are... 

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. 

The main elemental principle of a fuel cell is the direct electrochemical redox reaction that produces the electrical current. In the hydrogen/oxygen fuel cell, the redox reaction is composed of two electrochemical half equations - the hydrogen oxidation reaction (HOR) at the anode ... 

Fuel cells are electrochemical cells where the chemical energy of the fuel was converted into electricity for power generation with high efficiency [1,2]. Industrial purified hydrogen and air are often used in fuel cells to eliminate any pollution or emission, which is known as proton exchange membrane fuel cells (PEMFCs). In a typical PEMFC, a steam of hydrogen is deUvered to the anode side of the membrane electrode assembly (MEA) [3,4], At the anode, it is catalyzed by platinum (Pt) and split into protons and electrons. This oxidation half-cell reaction is represented as follows ... 

Oxidation of CO is also important in fuel cell applications. By combining the half reaction for the CO2/CO couple, equation (a), with electrochemical reduction of O2, fuel cells may achieve a maximum open circuit potential given by IlSlfCOj/CO) - (02/H20) = 1.34 . In practice, electrocatalysts are required to lessen the normally high kinetic overpotentials for electrodic CO oxidation. An example of a CO/O2 fuel cell which operates at the relatively low T of 80°C by employing [Rh(CO)2Br2] as the electrocatalyst and the Rh couple to mediate CO oxidation is shown below . 

The best catalysts for the electrochemical oxidation and production of hydrogen are platinum metal and the hydrogenase enzymes. Both catalyze the reaction of two protons with two electrons to form H2, as shown in Equation 7.1. Because of its superior catalytic rates and overpotentials compared to other metals and because of its high stabihty compared to hydrogenase enzymes, platinum is currently used as the catalyst for both half reactions (the oxidation of H2 and the reduction of O2) in polymer electrolyte membrane (PEM) fuel cells, which have been proposed for automotive transportation [1]. However, the high cost of platinum provides a strong impetus for developing less expensive alternatives. 

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