Direct methanol fuel cell extension

Direct methanol fuel cells, extensive discussion and review of various types of fuel cells and advances made in the performance of DMFC s since their inception... 

Fuel Cell Reactions. Low temperature fuel cells such as proton exchange membrane fuel cells (PEMFC) or direct methanol fuel cells (DMFC) employ large amounts of noble metals such as Pt and Ru. There has been extensive research to replace these expensive metals with more available materials. A few studies considered transition metal nitrides as a potential candidate. In an anode reaction of DMFC, Pt/TiN displayed the electroactivity for methanol oxidation (53). Pt/TiN deposited on stainless steel substrate showed the high CO tolerance in voltammogram performed with a scan rate of 20 mV/s and 0.5 M CH3OH - - 0.5 M H2SO4 electrolyte. The bifunctional effect of Pt and TiN for CO oxidation was mentioned as observed between Pt and Ru in commercial PtRu/C catalysts. 

Normally, the kinetics of ORR and OER occurring at the cathode of fuel cells, including direct methanol fuel cells (DMFCs) is very slow. In order to speed up the ORR kinetics to reach a practical usable level in a fuel cell, ORR catalyst is needed at the air cathode. Platinum (Pt)-based materials are the most practical catalysts used in PEM technology. These Pt-based catalysts are too expensive to make fuel cells commercially viable, and hence extensive research over the past several decades has been focused on development of alternative catalysts. These alternative electrocatalysts include noble metals and allo37S, carbon materials, quinone and its derivatives, transition metal macrocyclic compounds, transition metal chalcogenides, transition metal carbides and transition metal oxides. In this chapter, we focus on both noble and nonnoble electrocatalysts being used in air cathodes and the kinetics and mechanisms O2 reduction/oxidation reaction (both ORR and OER), catal37zed by them. 

In addition to carbon and graphite-based extended reaction zone supports, Ti mesh has been fairly extensively investigated for direct methanol fuel cells in both acid and alkaline conditions, and also for formic acid cells [218, 305-307, 309-313]. Compared to three-dimensional carbons, Ti mesh has the advantage of a... 

In comparison with the extensive research and development of catalysts for PEMFC and DMFC, the development of catalysts for DEFCs has drawn a surge of interest recently in recent years due to its bio-fuel characteristic, its ability to eliminate the toxicity issue of methanol as in direct methanol fuel cells, and its high energy density. Carbon-supported PtRu, a well-known catalyst for DMFCs, was naturally studied for DEFCs [59], but lacks high activity for ethanol oxidation due to a high propensity of Ru to form RuOH at the oxidation potential region. 

Nafion , which is one of the best PEMs available today, satisfies requirements b (for gases only) d and e, and perhaps even requirement c. However, the conductivity of Nafion drops rapidly with decreasing relative humidity (RH), methanol permeability through Nafion is very high (a disadvantage for direct methanol fuel cells), and the material is presently extremely expensive ( 700 m ), although cost reductions with increased production rates have been projected by the manufacturer. These drawbacks have prompted an extensive effort to improve the properties of Nafion and identify alternate materials to replace Nafion . 

Direct methanol fuel cells are the most extensively funded (and consequently studied) fuel cells at present. Will they ever replace Li-ion batteries in applications for mobile electronic devices, such as laptops, mobile phones, video cameras and of course electric cars. Leaving prophecy to the reader, let us just make the following... 

In recent decades, direct alcohol fuel cells (DAFCs) have been extensively studied and considered as possible power sources for portable electronic devices and vehicles in the near future. The application of methanol is limited due to its high volatility and toxicity, although it is relatively easily oxidized to CO2 and protons. So other short chain organic chemicals especially ethanol, ethylene glycol, propanol, and dimethyl... 

The electrochemical oxidation of methanol has been extensively studied on pc platinum [33,34] and platinum single crystal surfaces [35,36] in acid media at room temperature. Methanol electrooxidation occurs either as a direct six-electron pathway to carbon dioxide or by several adsorption steps, some of them leading to poisoning species prior to the formation of carbon dioxide as the final product. The most convincing evidence of carbon monoxide as a catalytic poison arises from in situ IR fast Fourier spectroscopy. An understanding of methanol adsorption and oxidation processes on modified platinum electrodes can lead to a deeper insight into the relation between the surface structure and reactivity in electrocatalysis. It is well known that the main impediment in the operation of a methanol fuel cell is the fast depolarization of the anode in the presence of traces of adsorbed carbon monoxide. 

Among aU the alcohols, ethanol has being subject of extensive studies because it is a green fuel and can be easily obtained as biofuel. The schematic of direct ethanol fuel cell is presented in Fig. 4b, while Fig. 4c shows the onset on the oxidation potential of methanol and ethanol for different alloy catalyst. 

The interest in formic acid oxidation (FAO) rose up in the 1970s with the aim of shedding light on the mechanism of methanol oxidation beyond the commercial interest in direct formic acid oxidation in fuel cells [90]. The FAO in acid solution was extensively investigated on surfaces of platinum [91-100] The FAO on other pure metallic surfaces seems to have been restricted to the palladium surface [98, 101-104]. In the 1980s, the remarkable contribution was done by the studies on the influence of the ad-atom in the activity of the platinum electrode [91—94]. In the 1990s, superficial spectroscopic techniques were employed to describe the electrochemical mechanism on palladium surface [98, 101—103] as well as platinum surface [97, 98, 105]. In the last 10 years, there was a triplication of publications about the FAO, specially driven by the use of nanoparticles. 

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