Catalysts for Methanol Oxidation

Abstract

Methanol electroxidation proceeds via a multistep reaction. Herein, mechanisms of reaction and reaction rates of sub-set of the mechanism on different surfaces are discussed. Platinum is a reasonable catalyst for the first methanol electroxidation steps (dehydrogenation), but not for the last (CO electroxidation). Hence, alloying Platinum with a second metal was used as a strategy to enhance the rate of the last step. Accordingly, enhanced rates of CO electroxidation are attained by modifying the bonding energy of the adsorbate to the catalyst or by promoting the formation of oxygenated species at lower overvoltage. Finally, new perspectives on the field of methanol catalysts are commented including the search for catalysts that promote early onset of oscillations, i.e. under lower overvoltage. IntroductionMethanol is the typical fuel with one carbon (C1) atom for fuel cells. Methanol was one of the first small molecules chosen to study the oxidation on platinum group metals in the very early beginning of electrocatalysis. In that time, the oxidation of other C1 molecules such as formic acid and formaldehyde (interest in CO oxidation came latter with the oxidation of reformatted gases) were investigated as a model oxidation because their elementary steps were supposedly present in the mechanism of methanol oxidation. From the point of view of CO 2 emission, methanol has, among the other small molecules, the highest energy production per unit of produced

Fundamentals of Electrochemistry with Application to Direct Alcohol Fuel Cell Modeling

“…The CO groups remain adsorbed to the catalyst, blocking the active reaction sites. This produces a sharp reduction of the effective catalyst surface area, which also reduces cell performance [25,[40][41][42]. To mitigate this effect, binary Pt-based catalysts include a secondary metal, such as Sn or Ru [42][43][44][45][46][47][48][49][50][51][52]; the blockage of active sites is alleviated via a bifunctional mechanism that allows the absorption of hydroxyl groups at lower potentials on the secondary metal, thus favoring further oxidation of Pt-adsorbates blocking the active catalyst sites [53][54][55].…”

“…The methanol oxidation reaction (MOR) takes place in multiple steps [39], and some of them lead to the production of undesirable intermediate products, such as CO [25,[40][41][42]56]. Due to the multiple species involved, the reaction is slower and more complex than Reaction (3), which leads to significantly lower current densities in DMFCs than in hydrogen PEMFCs.…”

Simultaneous Pt deposition and nitrogen doping of graphene as efficient and durable electrocatalysts for methanol oxidation

“…As a key component of DMFCs, Pt based catalysts are still under widespread investigation and have shown exciting performance [4]. However, to move towards their successful commercialization, focusing solely on their catalytic activity is not sufficient enough.…”

Thorough Analysis of the Effect of Temperature on the Electro-Oxidation of Formic Acid

“…In some direct liquid fuel cells, formic acid is oxidized in the anode, 12 either because it is used as the main fuel or because it is formed as an intermediate in the electro-oxidation reaction of other fuel, such as methanol. 13,14 Moreover, formic acid is also a common product in the electrochemical reduction of carbon dioxide. 15,16 The FAEOR has been extensively studied on platinum and palladium catalysts or materials based on these metals.…”