Alcohol oxidation reaction electrocatalysis

Chapter 1 discusses the current status of electrocatalysts development for methanol and ethanol oxidation. Chapter 2 presents a systematic study of electrocatalysis of methanol oxidation on pure and Pt or Pd overlayer-modified tungsten carbide, which has similar catalytic behavior to Pt. Chapters 3 and 4 outline the understanding of formic acid oxidation mechanisms on Pt and non-Pt catalysts and recent development of advanced electrocatalysts for this reaction. The faster kinetics of the alcohol oxidation reaction in alkaline compared to acidic medium opens up the possibility of using less expensive metal catalysts. Chapters 5 and 6 discuss the applications of Pt and non-Pt-based catalysts for direct alcohol alkaline fuel cells. 

For a given electrochemical system, the increase of the voltage efficiency is directly related to the decrease of the overpotentials of the oxygen reduction reaction, t]c, and alcohol oxidation reaction, T]a, which needs to enhance the activity of the catalysts at low potentials and low temperature, whereas the increase of the faradic efficiency is related to the ability of the catalyst to oxidize completely or not the fuel into carbon dioxide, i.e. it is related to the selectivity of the catalyst. Indeed, in the case of ethanol, taken as an example, acetic acid and acetaldehyde are formed at the anode [10], which corresponds to a number of electrons involved of 4 and 2, respectively, against 12 for the complete oxidation of ethanol to carbon dioxide. The enhancement of both these efficiencies is a challenge in electrocatalysis. 

However, the kinetics of alcohol oxidation reaction (AOR) is sluggish and Pt is considered as the best electrocatalyst for oxidation of alcohols in acid medium [9,10]. The electrocatalysis of AOR involves a multi-electron transfer and multi-step mechanism with formation of many... 

DMFCs and direct ethanol fuel cells (DEFCs) are based on the proton exchange membrane fuel cell (PEM FC), where hydrogen is replaced by the alcohol, so that both the principles of the PEMFC and the direct alcohol fuel cell (DAFC), in which the alcohol reacts directly at the fuel cell anode without any reforming process, will be discussed in this chapter. Then, because of the low operating temperatures of these fuel cells working in an acidic environment (due to the protonic membrane), the activation of the alcohol oxidation by convenient catalysts (usually containing platinum) is still a severe problem, which will be discussed in the context of electrocatalysis. One way to overcome this problem is to use an alkaline membrane (conducting, e.g., by the hydroxyl anion, OH ), in which medium the kinetics of the electrochemical reactions involved are faster than in an acidic medium, and then to develop the solid alkaline membrane fuel cell (SAMFC). 

Metal oxide electrodes have been relatively infrequently employed in electro-organic reactions and, even in those cases which have been moderately well studied, there are still some questions regarding the reaction mechanisms, e.g. whether a surface oxide species mediates the organic transformation or not in the case of oxidation reactions. The study of certain types of model organic compounds, e.g. alcohols and aldehydes, at metal oxide electrodes could lead to further insight into oxide electrocatalysis. 

The goal of maximum energy generation by oxidation of carbonaceous species often thwarted detailed examination of occasional selective oxidations, such as ethylene oxidation to acetaldehyde on Pd or Au (28, 29, 370) or to ethylene oxide on Ag (330) or methanol and benzyl alcohol oxidation to formates and benzaldehyde, respectively (6-32, 54, 250, 333). Product yields were usually determined at one potential only or even galvanostatically (330), and the combined effects of potential, catalyst, reactant concentration, and cell design or mixing on reaction selectivity are unknown at present. Thus, reaction mechanisms on selective electrocatalysis are not well understood with few exceptions. For instance, ethylene oxidation on solid pal-... 

Another aspect that has emerged in the last few years in the electrocatalysis of alcohol oxidation is a consideration of the support used for the catalyst nanoparticles. The support may influence the electrocatalysis of the reaction through more than one effect. The support may influence the dispersion of the catalyst nanoparticles and usually an increase in the dispersion will increase the cmrent density because of the increase in the... 

Recent intensive research efforts have led to the development of less expensive and more abundant electrocatalysts for fuel cells. This book aims to summarize recent advances of electrocatalysis in oxygen reduction and alcohol oxidation, with a particular focus on low- and non-Pt electrocatalysts. The book is divided into two parts containing 24 chapters total. All the chapters were written by leading experts in their fields from Asia, Europe, North America, South America, and Africa. The first part contains six chapters and focuses on the electro-oxidation reactions of small organic fuels. The subsequent eighteen chapters cover the oxygen reduction reactions on low- and non- Pt catalysts. 

The effectiveness of the Pt-modified diamond electrodes for the electrocatalysis of fuel cell reactions was examined. We have tested their electrocatalytic activities for O2 reduction and alcohol oxidation. Figure 19.7 compares O2 reduction currents for the as-deposited diamond, the as-deposited diamond/Pt, honeycomb 60 x 500 nm/Pt and the 400 nm x 3 xm/Pt electrodes in 1 M H2SO4... 

In order to obtain a reaction rate sufficient for a technical process, the material inside the decomposer should be activated with molybdenum or tungsten carbide instead of simple iron oxide. In this case, the reaction rate using ethanol or propanol to form the corresponding alcoholates is sufficient, too. Higher alcoholates can only be produced in this way with help of a micro-heterogeneous electrocatalysis and/or the help of ultrasonic energy [29-31]. 

Electrocatalysis in DAFC anodes is complex because the reaction mechanism involves adsorption of alcohol and several elementary reaction steps including the CO oxidation. Figure 8.2 shows a possible network of reaction pathways by which the electrochemical oxidation of methanol occurs. Since more than 50 years detailed catalysis studies have attempted to analyze possible reaction pathways to find the main pathway of methanol oxidation [11, 12] (see next Section). Most studies conclude that the reaction can proceed according to multiple mechanisms and that the most significant reactions are the adsorption of the alcohol and the oxidation of CO. 

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