Charge transfer oxygen reduction reaction

Therefore let us instead consider the more practical case of the tertiary current distribution. Based on the dependency of the Wagner number on polarization slope, we would predict that a pipe cathodically protected to a current density near its mass transport limited cathodic current density would have a more uniform current distribution than a pipe operating under charge transfer control. Of course the cathodic current density cannot exceed the mass transport limited value at any location on the pipe, as said in Chapter 4. Consider a tube that is cathodically protected at its entrance with a zinc anode in neutral seawater (4). Since the oxygen reduction reaction is mass transport limited, the Wagner number is large for the cathodically protected pipe (Fig. 12a), and a relatively uniform current distribution is predicted. However, if the solution conductivity is lowered, the current distribution will become less uniform. Finite element calculations and experimental confirmations (Fig. 12b) confirm the qualitative results of the Wagner number (4). 

Calvo and Balbuena examined the structure and reactivity of Pd-Pt nanoclusters with 10 atoms in the oxygen reduction reaction. In contrast with what is expected in a periodic slab calculation, they found that mixed states with randomly distributed Pd atoms in a Pt7Pd3 cluster was more stable than an ordered cluster structure due to more eflective charge transfer in the mixed state. They found that increasing the concentration of Pd in the surface favors formation of the OOH species in the first step of the reaction, but Pt atoms were needed to promote the second stage of the oxygen reduction reaction. They report that due to charge transfer eflhcts the Pd atoms have an intermediate reactivity between pure Pd and Pt, and in the mixed cluster the Pd atoms the Pd atoms act more similarly to Pt than in the ordered cluster. 

The need to convert chemical energy to electricity, efficiently and at low temperature, has increased the development of materials with electrocatalytic activity toward multi-electron charge transfer. Reactions of technical relevance are, for example, cathodic processes, such as the oxygen reduction reaction (ORR),3 13 and anodic processes, such as small organics (R-OH, where R = CH3-3-12 or CH3CH-13-17) and sugars.18-20 These complex electrochemical processes are useful in low-temperature systems such as the direct methanol FC (DMFC) or biofuel cell systems. 

In the mid-seventies, it was demonstrated that UPD metal adatoms can produce electrocatalytic effects on various electrochemical reactions. These include oxidation of small organic molecules, oxygen reduction, reactions of electroorganic synthesis, electrodeposition of metals, and charge transfers in redox couples. The oxidation of organic molecules that are... 

The oxygen reduction reaction is covered in considerable detail in a review text by Kinoshita [10]. The charge-transfer reaction itself is quite complicated, and controversy still exists around the details of which of the many possible charge-transfer mechanisms determine electrode performance. The two generalized pathways that are considered are the direct four-electron reaction ... 

Fig. 12.5 (a) Illustration of charge transfer process and oxygen reduction reaction on PDDA-CNT (b) LSV curves of ORR in an 02-saturated 0.1 MKOH solution at a scan rate of 10 mV s . The rotation rate is 1,600 rpm (reproduced with permission [51])... 

Until now, the methodology available to study charge transfer reactions at soft interfaces has been rather mature, and studies in the field have shifted to the study of catalyzed reactions such as the oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), or even oxygen evolution reaction (OER). Eor this, two classes of catalysts have been used (i) molecular catalysts and (ii) nanoparticle solid catalysts. These two approaches draw their inspiration from classical molecular catalysis and from electrocatalysis, respectively. 

At the medium frequency range, the loop is associated to the cathode charge transfer related to oxygen reduction reaction (ORR) activation losses [46]. This medium frequency loop is... 

Adlerhas investigated the behaviour of LSC porous electrodes by AC impedance spectroscopy and has found that the oxygen reduction reaction is limited by surface chemical exchange and solid state diffusion, contrary to the commonly accepted view that the electrode reactions are charge transfer limited. Furthermore he has also found that the reduction reaction extends over several micrometres and under certain conditions may approach the thickness of the electrode. Isotope exchange measurements on dense LSC deposited on a Ceo.9Cao.iOi,9 electrolyte were performed by Kawada et These experiments showed that the... 

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