Alcohol Fuels Research Articles

Pd/CNT Catalysts for Electrochemical Oxidation of Small Organic Molecules in Alkaline Media

The development of the alkaline anion exchange membrane (AEM) for the direct liquid fuel cell opened up opportunities for the use of new fuels (that oxidized inefficiently in PEM fuel cells) and new catalysts (that corroded easily in PEM fuel cells). In this work, we explore the effect of a CNT support for Pd catalysts for the oxidation of various alcohol and formate fuels in alkaline media. We found that the CNT support provided a significant advantage over standard, activated carbon support in several of the fuels. The increase in oxidation rate in formate, for example, was 5-fold. However, the oxidation rate of propanol was not significantly enhanced by the CNT support. We are presently exploring the scientific reason for the enhanced oxidation rates by the CNT support using XRD and XPS analysis. Masel, et al, suggested that in formic acid the CNT provides enhancement due to its electronic properties, and a shift in Pd 3d5/2­ binding energy supports this. However, we are presently investigating why the promotion in alkaline media is so much greater than in acidic media, even for the formate (compared with formic acid).

(Invited) Electrocatalysis in Low Temperature Fuel Cells

Electrocatalysis, i.e. the heterogeneous catalysis of electrochemical reactions occurring at the electrode-electrolyte interface, has mainly concerned technological developments related either to energy storage (e.g. water electrolysis) or to energy conversion (e.g. fuel cells) [l, 2]. However, except for the hydrogen electrode which is now well known, and the oxygen electrode which has been extensively studied, other catalytic electrodes for the direct oxidation of soluble fuels, need much more investigations. Among them primary alcohols are particularly interesting as fuels in a Direct Oxidation Fuel Cell (DOFC), because of several favorable features, such as a high theoretical energy density (4 to 9 kWh kg-1 compared to 33 kWh kg-1 for molecular di-hydrogen) and a great facility of handling. Moreover alcohols, which may be produced from the biomass, are very convenient fuels due to a lot of advantages: high solubility in aqueous electrolytes, relatively high reactivity, ease of storage and supply, small toxicity (except for methanol). They can be directly electro-oxidized in a Direct Alcohol Fuel Cell (DAFC) working at low temperature [3]. This explains why many fundamental investigations were undertaken in the last three decades on the electrochemical oxidation of several alcohols: methanol [4, 5], ethanol [3, 6, 7], glycerol [8], etc. and also on related compound, such as carbon monoxide [9], etc. Until now, the most promising and most studied fuels for application in a DOFC, with the direct oxidation of the organic molecule, are methanol and ethanol. However, a lot of electrocatalytic problems still arise due to the relative complexity of the reaction mechanisms. These include the effect of the molecular structure of the organic compound, the nature and structure of the adsorbed intermediates, the nature and structure of the electrode material, the pH and the anions of the supporting electrolyte, and the role of the water adsorption residues. Furthermore, the catalyst structure, such as particle size, composition and degree of alloying, are also of great importance, since most of the alcohol oxidation reactions are structure sensitive. On the other hand the synthesis of plurimetallic catalysts is one way to reduce the platinum group metal loading in order to reduce the cost of a DAFC system. Thus the key research topics for practical applications are the following: ● the investigation of reaction mechanisms on new anode electrocatalysts, by combination of several catalytic materials (including platinum), each of them being able to activate a given path of the mechanism ; ● the optimization of the electrode catalysts in terms of composition, particle size, metal loading and accessibility to the reactants. Detailed oxidation mechanisms of several alcohols (methanol, ethanol, and glycerol) will be discussed and will be correlated to the nature and structure of the electrocatalysts.

PdCu/C Catalysts for the Electrochemical Oxidation of Renewable Polyalcohols

The development of the alkaline anion exchange membrane (AEM) for the direct liquid fuel cell opened up opportunities for the use of new fuels (that oxidized inefficiently in PEM fuel cells) and new catalysts (that corroded easily in PEM fuel cells). The first fuel studied in depth was ethanol because it oxidizes much more efficiently in alkaline media than acidic media. However, the same palladium catalyst that oxidizes ethanol in alkaline media can also be used to oxidize several other alcohol fuels including polyalcohols such as ethylene glycol (EG), propylene glycol (PG), and glycerol (G). Therefore, we recently demonstrated a flexible fuel direct liquid fuel cell that operated on alcohols such as ethanol, EG, PG, and G. However, these fuels all oxidize more slowly then ethanol, requiring significant kinetic improvement to be used practically. We tested various combinations of Pd:Cu and compared them in each polyalcohol fuel, EG, PG, and G. We observed that any quantity of Cu added to the Pd produced an increase in oxidation rate compared with pure Pd for all three polyalcohol fuels. We also observed a down-shift in d-band center as observed by XPS. We hypothesize that the addition of Cu to the Pd results in a combination of the electronic and bifunctional effects. The electronic effect is caused by perturbations in the electronic structure of Pd, the primary catalyst, induced by the Cu. The bifunctional effect is caused by the co-catalysis of Pd and Cu directly on the surface of the catalyst.

Effective Nickel and Ruthenium Modified Palladium Anode Catalysts for Ethylene Glycol Oxidation in Alkaline Medium

As one of the attractive fuels in the direct alcohol fuel cell applications, the ethylene glycol electrooxidation was investigated in alkaline medium on Pd-based bimetallic catalysts (PdM/C, where M = Ni, Ru). These electrode materials were synthesized by polyol method, using ethylene glycol as both solvent and reducing agent. The resulted anode catalysts displayed effectiveness toward the oxidation of ethylene glycol. The latter molecule was also scrutinized as potential fuel which can be converted by cogeneration into energy (5.2 kWh kg-1) and particularly to added value product. Ex situanalytical measurements with liquid chromatography/Mass spectrometry provided evidences on the identification of glycolate as the main reaction product on the PdM/C anode materials (Figure 1). The identification of some adsorbed intermediates and the final reaction products, was also supported by combining electrochemical (cyclic voltammetry, chronoamperometry) and in situreflectance infrared spectroscopy experiments. The PdNi/C catalyst showed the highest intrinsic catalytic activity for the ethylene glycol oxidation. From FTIR experiments our findings gave evidences that the initial molecule skeleton was conserved and carbon monoxide was observed in a low amount. Acknowledgements R. Garcia Da Silva gratefully acknowledges FAPESP (2012/07464-0; 2013/25632-0) and CNPq for his fellowship. Reference L.M. da Palma, T.S. Almeida, V.L. Oliveira, G. Tremiliosi-Filho, E.R. Gonzalez, A.R. de Andrade, K. Servat, C. Morais, T.W. Napporn, K.B. Kokoh, RSC Adv., 4, 64476 (2014). Figure 1. Glycolate1isolated and identified by LC-MS as the main compound issued from the ethylene glycol oxidation at the Pd-M/C (M = Ni and Ru) catalysts in alkaline medium. Figure 1

Nanostructured Graphene-Supported Pt-NiTiO3 Catalyst for the Oxygen Reduction Reaction for Alkaline Direct Alcohol Fuel Cells Applications

The catalytic activity for the ORR of graphene-supported Pt-NiTiO3 (Pt-NiTiO3/G) catalyst was evaluated in 0.5 M KOH. NiTiO3 nanoparticles were synthesized via a wet-chemical method. XRD analysis confirmed the formation of crystalline NiTiO3 nanoparticles with a size of ca. 25 nm. Then, nanostructured 20% Pt-NiTiO3/G catalyst (Pt:NiTiO3 ratio of 1:1) was obtained by the microwave assited polyol method. The titanate-based catalyst showed a high cataytic activity for the ORR in 0.5 M KOH electrolyte. It also showed enhanced tolerance to methanol and ethanol, compared to Pt/C and Pt/Gr catalysts. The results suggest that Pt-NiTiO3/G electrocatalyst is a good candidate for Alkaline Fuel Cells applications.

On the Possibilities of Using Alternative Fuels in ICE Powered Lawn Mowers and Tractors to Meet Phase III Emissions Standards

There is a need to use alternative fuels in Internal Combustion Engines (ICE) powered lawn care equipment used around residential, office and reserved areas. This will enable this equipment to meet Phase III emissions standards set by the Environmental Protection Agency. One method of reducing emissions from trimmers, lawn mowers, tractors and blowers is to use alcohol fuels in the next generation of ICE powered devices and also, to make it adaptable to operate on flex-fuels. These devices are not only a great source of noise pollution, they are also a major source of hydrocarbon, NOx and CO emissions in the residential neighbourhood from spring to the fall seasons, hence, the need to mandate the use of alcohol and flex fuels to lowers emissions. These changes will require a slight modification of the engine, by way of increasing the compression ratio on one hand, and modifying the fuel system: tank, fuel lines, and fuel dispensing system (carburetor) to meet flex-fuel requirements. This proposed engine modification will meet Phase 3 emissions standards as alcohol fuels possess superior combustion characteristics and lower emissions.

GS0702 多成分アルコール混合燃料を用いた小型ディーゼル機関の性能改善について

In late years, the fuel consumption of diesel engine remarkably improves, and it is superior in the environmental performance. The biofuel attracts attention as an alternative fuel of the petroleum fuel. In this study, experiment has been carried out to examine the combustion characteristic for small diesel engine by using multicomponent alcohol fuels. The main results are as follows; 1) Net thermal efficiency decreases by using DGM addition fuel for small diesel engine. 2) NOx emissions by using propanol and DGM addition fuels decrease than that of light oil at any engine load. 3) HC emissions by using propanol and DGM addition fuels are almost constant or decrease than the light oil.

Polyaniline films photoelectrochemically reduce CO2 to alcohols.

In this communication, we demonstrate that polyaniline, the very first example of an organic semiconductor, is a promising photocathode material for the conversion of carbon dioxide (CO2) to alcohol fuels. CO2 is a greenhouse gas; thus using solar energy to convert CO2 to transportation fuels (such as methanol or ethanol) is a value-added approach to simultaneous generation of alternative fuels and environmental remediation of carbon emissions. Insights into its unique behavior obtained from photoelectrochemical measurements and adsorption studies, together with spectroscopic data, are presented. Through a comparative study involving various conducting polymers, a set of criteria is developed for an organic semiconductor to function as a photocathode for generation of solar fuels from CO2.

Thermodynamic analysis of syngas production and carbon formation on oxidative steam reforming of butanol

Theoretical calculations of chemical equilibrium were adopted to explore the syngas production of oxidative steam reforming of butanol (OSRB). The results indicated that when the H2O/C4H9OH molar ratio was 3 and the O2/C4H9OH molar ratio was 1.5, the thermal neutrality temperature reached 602 °C, generating a corresponding H2 yield of 59.3%, a CO yield of 39.5%, and reforming efficiency of 65.1%. Additionally, when the OSRB was at moderate temperatures (400–800 °C), adding an appropriate amount of O2 effectively inhibited coke formation and exerted only a minor effect on butanol reforming efficiency. The analysis of the coking boundaries indicated that at the same H2O/C1 molar ratio, alcohol fuels with higher carbon numbers (butanol > ethanol > methanol) produced higher degrees of coke formation. However, if OSRB was used, the amount of H2O and O2 addition was able to be controlled to inhibit coke formation and reduce the coke formation zone considerably.

A comparison of butanol and ethanol flame development in an optical spark ignition engine

The work was concerned with experimental study of the turbulent flame development process of ethanol and butanol fuels in an optically accessed spark ignition research engine. The fuels were evaluated in a single cylinder engine equipped with full-bore overhead optical access and operated at typical stoichiometric part-load conditions. High-speed natural light (or chemiluminescence) imaging and simultaneous in-cylinder pressure data measurement and analysis were used to understand the fundamental influence of both low and high carbon content in alcohol fuels on turbulent flame propagation and subsequent mass burning with the potential to solidify butanol’s reputation as a possible mainstream fuel additive. Overall, it was concluded that the butanol blend tested was similar to the ethanol blend tested in terms of combustion duration, pressure development and flame radius development. This was to be expected with equal oxygen weighting but further highlights butanol’s ability to surpass ethanol as one of the gasoline industry’s fuel additive of choice.

Effects of direct injection timing and premixed ratio on combustion and emissions characteristics of RCCI (Reactivity Controlled Compression Ignition) with N-heptane/gasoline-like fuels

This paper presents an experimental study on the combustion and emissions characteristics of Reactivity Controlled Compression Ignition (RCCI) combustion with n-heptane/gasoline-like fuels are researched on a single-cylinder engine. The effects of injection timing and premixed ratio are investigated. The experimental results indicate that with the advance of the direct injection timing, the ignition delay increases for all three fuels and ethanol has the longest ignition delay. The CO (carbon monoxide) and soot emissions gradually decrease while the NOx emissions increase for the three different fuels. However, HC (hydrocarbon) emissions monotonically decrease with gasoline but initially increase and then decrease with the alcohol fuels. When comparing gasoline and ethanol with the same premixed ratio and direct injection timing, the combustion phase with ethanol as port fuel occurs later than that of gasoline, especially with a higher premixed ratio. Moreover, ethanol has lower NOx and soot emissions than those of gasoline, indicating that ethanol as an alternative fuel can improve emissions in the RCCI combustion mode.

Ozone applied to the homogeneous charge compression ignition engine to control alcohol fuels combustion

The present investigation examines the impact of seeding the intake of an HCCI engine with ozone, one of the most oxidizing chemical species, on the combustion of three alcohol fuels: methanol, ethanol and n-butanol. The research was performed through engine experiments and constant volume computations. The results showed that increasing the ozone concentration led to an improvement in combustion coupled with a combustion advance. It was also observed, by comparing the results for each fuel selected, that n-butanol is the most impacted by ozone seeding and methanol the least. Further analyses of the experimental results showed that the alcohol fuel combustion can be controlled with ozone, which presents an interesting potential. Finally, computation results confirmed the experimental results observed. They also showed that in presence of ozone, alcohol fuels are not initially oxidized by molecular oxygen but by O-atoms coming from the ozone decomposition.

Adaptive air distribution in an ejector burner for the utilisation of methanol-mixed fuels

Numerous studies have focused on the utilisation of alcohol fuels because of the energy crisis. However, the combustion efficiency and stability of alcohol fuels are unacceptable. This study proposed an ejecting combustion method for utilising methanol-mixed fuels and numerically investigated the characteristics of adaptive air distribution in an ejector burner. The geometrical parameters of the ejector burner were optimised and validated by an experiment. Results show that the suction effect of negative pressure in the mixing chamber and the entrainment effect of fuel jet flow both play important roles for an ejector burner to draw air. The positions of ejector nozzle exit locating at the suction chamber axis and low operating pressure are beneficial for obtaining a stable air distribution. Molar entrainment ratio (MER) rapidly increases with an increase in parameter α, which is defined as the ratio of throat diameter to nozzle exit diameter, but declines with increasing ejector back pressure. In the experiment, the changing rate of MER is less than 6.4%, and combustion efficiency is higher than 99.2% in the load range of 20–120%, which is highly consistent with that of the simulation. The optimised burner could automatically distribute air supply and facilitate stable combustion.

Preliminary Investigation on the Electrochemical Activity of Butanol Isomers as Potential Fuel for Direct Alcohol Fuel Cell

A preliminary investigation of electrocatalytic oxidation activity of butanol isomers has been carried out to study their potential as fuels for direct alcohol fuel cells. The electrochemical study was carried out on Pt and Pd electrodes using a three electrode cell set up in alkaline media. The primary alcohol isomers of butanol were observed to behave similarly in their electrochemical reactions whereas 2-butanol showed completely different oxidation features on both catalysts. For example, no poisoning effects were observed for 2- butanol unlike for the primary butanol isomers. In contrast, tert-butanol did not show any oxidation reaction on Pt and Pd electrodes. Furthermore, Pd was not active at all in acidic media for butanol oxidation. The reactivity of butanol isomers were found to be in the order n-butanol>iso-butanol>2-butanol>tert-butanol based on the oxidation current density values

Electrocatalyst for Direct Alcohol Fuel Cells

The direct conversion of methanol in acidic environment at platinum ruthenium catalysts is the standard process in today’s direct methanol fuel cells. The high cost related to the relative high platinum loading and the user reluctance to use methanol hinder a wider market spread of this otherwise quite mature technology. Therefore catalysts for the alcohol conversion in alkaline environment were investigated allowing reducing the use of platinum group metals. In addition the use of other alcohols as fuel was investigated in both alkaline and acidic environment including high temperature polymer electrolyte fuel cell conditions. It will be shown that palladium is a good catalyst for the alcohol oxidation in alkaline environment if alloyed with other metals. It will further be shown rhodium as alloying metal can enhance ethanol oxidation in an acidic environment already at ambient temperature and even stronger at HT-PEMFC conditions.

Exploring the limits of a down-sized ethanol direct injection spark ignited engine in different configurations in order to replace high-displacement gasoline engines

The paper presents a layout of a highly boosted Ethanol Direct Injected engine in order to explore the limits of down-sizing for replacing high-displacement gasoline engines, which represents a powerful means of reducing fuel consumption and engine-out emissions at reduced production costs. The substitution of high-displacement engines (2.4- or 3.0-l) by a down-sized turbocharged Ethanol Direct Injected engine is studied. This document describes the detailed layout of all engine hardware and in particular, the cylinder head structure including the optimized intake and exhaust manifolds as well as implemented direct injection injectors. The work continues with a presentation of the experimental data obtained at the engine test rig. A series of experimental data is also presented for the down-sized engine mounted in a car as a replacement for its original high-displacement engine. Substantial fuel consumption gains are obtained as well as values of engine torque for the down-sized, down-speeded prototype engine, which makes it possible to replace engines with much higher displacements. As a result the maximum obtained efficiency of the 1.4l prototype engine with twin-stage compressor reaches a value of 3250kPa brake pressure at 44% efficiency. The present work is a very new and different approach compared to previous published studies on ethanol and down-sized engines due to the fact that the Brazilian hydrated ethanol fuel (7% water content) has a major charge effect compared to North American and European Gasoline and alcohol fuels (consult Table 1). This means that more aggressive down-sizing, turbo-charging and mixture stratification approaches can be applied as the following chapters will explain in detail.

New Direct Alcohol and Hydrogen Fuel Cells for Naval and Aeronautical Applications (PILCONAER)

In the current context of demand for reliable, low cost and low environmental impact energy sources, many countries and companies are mostly focused on fuel cells (FC) in fields as transportation and stationary power generation and portable devices. Lately, FCs have begun to be applied in naval and aeronautical systems due to its high efficiency, low noise and environmental advantages. These applications could range from propulsion systems to auxiliary power units (APU). The main problems associated with the use of FCs in these areas are the current high cost due to the materials used, i.e. Nafion and Pt, the lack of durability testing in these specific conditions, security issues to flammability and high H2 pressures and low availability as a fuel, or the toxicity of methanol used as a fuel, and specific parameters such as weight in aircraft applications and volume in marine applications. Currently it is working on each of these issues, and at this point the ethanol as direct fuel is considered crucial. The use of ethanol as fuel has the advantage of easy transportation, storage and refueling, and is nontoxic. Bioethanol is a promising energy source, produced from raw materials containing sugar or starch. These raw materials exists in all parts of the world and is renewable, which involves the use of local energy sources contributing to the diversification of energy supply, reducing import dependence, increasing security of supply and generating new opportunities for agriculture. The main objective of the proposal is the development of low power stacks (stacks) fed with methanol (DMFC) and ethanol (DEFC) based on the development of new catalysts and membranes. The materials are considered first from the point of view of application in FCs fed with H2 (PEMFC) to be optimized and used on FCs fed directly with alcohols. An important particular objective is the development of cells fed with ethanol in alkaline medium in order to eliminate the use of Pt as the catalyst and increase the efficiency of the electrochemical FC while cost is decreased. The proposed development of new FCs fed with alcohols, especially ethanol, is considered a technology of sustainable use, further commitment to the restoration of the natural environment and biodiversity conservation. The consortium combines groups: skilled in synthesis and characterization of materials (CSIC); expert in the development and evaluation of FC stacks (UPM and INTA) and with the ability to develop physical and mathematical models to predict the behavior of the fuel cell equipped for the MEAs fabricated (UCM). Four companies have shown interest in the proposal, as well as participation according to preliminary results.

Progress and recent trends in reactivity-controlled compression ignition engines

Low-temperature combustion is an emerging engine technology that has the ability to yield low NOx and soot emissions while maintaining high fuel efficiency. Low-temperature combustion strategies include homogeneous charge compression ignition, premixed charge compression ignition, reactivity-controlled compression ignition and partially premixed combustion. These low-temperature combustion strategies use early fuel injections to allow sufficient time for air–fuel mixing before combustion. According to the literature, some low-temperature combustion strategies are not promising for future automotive and power generation applications due to difficulties in controlling the heat release rate and the lack of a combustion phasing control mechanism. To mitigate these problems, the reactivity-controlled compression ignition combustion concept was introduced. Reactivity-controlled compression ignition is a dual-fuel partially premixed combustion concept, which uses port fuel injection of a low-reactivity fuel (e.g. gasoline, natural gas and alcohol fuels) and direct injection of a high-reactivity fuel (e.g. diesel and biodiesel) with blending inside the combustion chamber to increase the combustion duration and to provide phasing control. Combustion phasing is controlled by the relative ratios of the two fuels, and the combustion duration is controlled by spatial stratification between the two fuels. This article begins by an overview of the different low-temperature combustion strategies and demonstrates some advantages of reactivity-controlled compression ignition, over homogeneous charge compression ignition and premixed charge compression ignition combustion strategies in regard to fuel flexibility and combustion controllability. A comprehensive review of recent research on various aspects of reactivity-controlled compression ignition and comparisons of thermal efficiency and pollutant emissions over conventional diesel combustion is also presented. This article presents the significance of reactivity-controlled compression ignition strategy as a promising solution for future automotive engines and discusses future research directions.

Preliminary Investigation on the Electrochemical Activity of Butanol Isomers as Potential Fuel for Direct Alcohol Fuel Cell

Low molecular weight alcohols have been proposed as promising alternative fuels to H2 in low temperature fuel cells due to their liquid nature, high energy density, availability in nature and easy handling1. Methanol and ethanol have been widely studied as fuel for direct alcohol fuel cell (DAFC); however methanol is toxic whereas ethanol is non-toxic and can be produced by fermentation of sugar. However, there is on-going public debate on the ethics of utilizing food stocks for fuel production instead of nutrition2. An alternate renewable source, which does not compete with the food, is required for a sustainable long-term energy production. Thus, 2nd generation bio-fuels are produced from non-food based feedstock such as lignocellulose biomass (LCB)2-3. Butanol is considered as a 2nd generation bio-fuel with better infrastructure compatibility than ethanol. These C4 alcohols have higher energy content, lower water adsorption, and better blending ability with gasoline than ethanol and is considered as a promising substitute for gasoline in automobiles2-3. In fuel cell, butanol provides 24 electrons on complete oxidation compared to 12e- and 6e- from ethanol and methanol respectively. In this regard, with the recent developments in the bio-butanol production, butanol has the potential to be used as fuel for DAFC. However increasing carbon will increase the number of possible intermediates and complicates the reaction pathway and thus reduces the efficiency. Within this study, different butanol isomers were examined as potential fuel for DAFC using a three electrode cell set up on Pt and PtSn electrodes prepared by electrodeposition on glassy carbon both in acid and alkaline media. The Sn coverage was calculated from the difference in the hydrogen desorption charge before and after the Sn deposition. A clear difference in behaviour was observed for different butanol isomers in the cyclic voltammetry (CV) indicating their different oxidation activity. N-butanol and iso-butanol showed similar CV features whereas 2-butanol and ter-butanol showed completely different CV features. Ter-butanol was found to be inactive for electrochemical oxidation at room temperature on Pt. Comparing the CV of Pt in butanol and acid, it was clear that the presence of OHads is necessary to initiate the n-butanol and iso-butanol oxidation on Pt. To enhance this, an oxophilic metal (Sn) was added to Pt so as to initiate the water dissociation at a lower potential. The PtSn electrode showed an improved oxidation activity compared to Pt with a pre-peak at ~500 mV (Figure 1) lower than the onset potential found using Pt for n-butanol oxidation in acidic media. Since this pre-peak appears at a potential region where PtOx is not formed, the oxygenated species for the butanol oxidation was assumed to be provided by the Sn on the catalyst surface 4. The higher activity of PtSn was thought to be due to a bi-functional mechanism where the water dissociate on Sn surface to provide OHads at lower potential which helps in the removal of poisoning species CO from the Pt as CO2 (equation1-2). The activation energy calculated at the pre-peak, 0.25 V vs. Ag/AgCl (3M NaCl) for the PtSn was about ~11 kJ mol-1 which is significantly lower than that on pure Pt at the first anodic peak, 0.7 V vs. Ag/AgCl-3M NaCl (25 kJ mol-1). The lower activation energy on PtSn at lower potential could be attributed to their effectiveness in the dissociative adsorption and oxidation of butanol 5. These results suggests PtSn could be an active catalyst for n-butanol electro oxidation and shows promise for further studies on long chain organic molecules. Sn+H2O --> Sn-OHads +H++e- (1)Pt + COads + Sn-OHads --> CO2 + H+ +e- (2) Figure 1. The voltammogram of Pt and PtSn electrodes (a) Pt and PtSn in in 0.1M H2SO4 and (b) Pt and PtSn in 0.1M BtOH+0.1M H2SO4 . Scan rate 50 mVs-1. Sn coverage ~25%. Reference (1) (a) Catalysts for Alcohol-fuelled Direct Oxidation Fuel Cells; Liang, Z. X.; Zhao, T. S., Eds.; Royal Society of Chemistry, Cambridge, UK, 2012(b) Song, S.; Maragou, V.; Tsiakaras, P. Journal of Fuel Cell Science and Technology 2006, 4, 203. (2) Dürre, P. Biotechnology Journal 2007, 2, 1525. (3) Tao, L.; He, X.; Tan, E. C. D.; Zhang, M.; Aden, A. Biofuels, Bioproducts and Biorefining 2014, 8, 342. (4) (a) Gupta, S. S.; Singh, S.; Datta, J. Materials Chemistry and Physics 2009, 116, 223(b) Beyhan, S.; Coutanceau, C.; Léger, J.-M.; Napporn, T. W.; Kadırgan, F. International Journal of Hydrogen Energy 2013, 38, 6830. (5) Sen Gupta, S.; Singh, S.; Datta, J. Materials Chemistry and Physics 2010, 120, 682. Figure 1

Electrocatalysis of Direct Methanol and Ethanol Oxidation in Polymer Electrolyte Fuel Cells

In recent decades, significant efforts have been focused on the direct electrochemical oxidation of alcohol and hydrocarbon fuels. Organic liquid fuels are characterized by high energy density and the electromotive force associated with their electrochemical combustion to CO2 is comparable to that of hydrogen combustion to water. Among the liquid organic fuels, methanol and ethanol have promising characteristics in terms of reactivity at low temperatures, storage and handling. Compared with ethanol, methanol has the significant advantage of faster reaction kinetics and higher selectivity to CO2 formation for the electrochemical oxidation process. Highly dispersed carbon-supported bimetallic PtRu and PtSn alloy catalysts are widely recognized among the most performing anode formulations for these processes. Alloying Pt with Ru and Sn promotes oxidation of methanol and ethanol by the adsorption of OH species at considerably lower overpotentials and, thus, favoring the occurrence of a bifunctional mechanism. Furthermore, the electronic effect caused by a second metal on the neighboring Pt atoms affects the strength of CO adsorption on the catalyst surface. This causes a decrease of the coverage of poisoning CO intermediate species. Catalysts characterized by a high degree of alloying and metallic behavior on the surface appear to be very active towards methanol oxidation. However, beside the alloyed catalysts, noble metal oxides (IrOx, RuOx) and valve metal oxides (SnOx, TiOx and VOx) can be suitable promoters for methanol and ethanol oxidation in acidic environment. An effective use of such oxide promoters in combination with the alloy catalysts can provide a multifunctional catalytic system. Recent studies carried out in our laboratory have shown that IrOx can give rise to a significant promoting effect, even larger than that of RuOx, both in the case of methanol and ethanol oxidation. Whereas, the electrocatalytic enhancement produced by the valve metal oxides is generally lower than IrOx and RuOx but well evident. These results are interpreted in terms of the different water displacement mechanisms for the various oxides and the related effects on adsorbed CO removal. The effect of temperature is also discussed with reference to the coverage of adsorbed methanolic residues or change in selectivity in the case of ethanol electro-oxidation. For the ethanol oxidation process, anode catalyst selectivity towards CO2, acetic acid and acetaldehyde reaction products is discussed in relation to the alloy and oxide content in the catalyst. In particular, SnOx species on the surface of Sn-rich Pt-Sn-based electrocatalyst appear to assist the further oxidation of ethanolic adsorbates, leading to larger yields of acetic acid and CO2. In addition to the enhancement of reaction rates, there is an effect of the promoter on the stability of the bimetallic alloy as evidenced by accelerated stress tests. All these evidences seem to indicate that a multifunctional catalyst may represent a valid route to enhance performance and reliability of methanol and ethanol electro-oxidation processes at low temperature.