Anodic Oxidation of Methanol Using a New Base Electrocatalyst

Abstract

Preparation of a new electrocatalyst for the anodic oxidation of methanol in sulfuric acid is described.The catalyst shows a high degree of passivity in hot sulfuric acid, and a modest electrocatalytic activity toward the methanol reaction.Anodic oxidation of methanol, the reaction employed on the anode of the direct methanol fuel cell, is conventionally carried out using noble electrocatalysts. The best of these has been found to be a codeposited mixture of platinum and ruthenium. The use of base materials as anode catalysts requires, in addition to electrocatalytic activity, a low corrosion rate in the cell electrolyte. We present here some preliminary results of measurements of the anodic oxidation of methanol using a newly synthesized base electrocatalyst: this catalyst is passivated by the highly aggressive electrolyte.The direct methanol fuel cell (DMFC) is a prospective power source for several applications, the most important of which is as an easily refuelable power stack in the electrically driven vehicle.' 1-4 The required anodic reaction is the direct oxidation of methanol to carbon dioxide, as CH 3 OH + H 2 O -CO2 + 6H + + 6e-. The DMFC requires use of acidic electrolytes, either in aqueous or solid forms. This fact, coupled with their high electrocatalytic activity, requires that noble electrocatalysts are employed. Currently, the most effective of these for the methanol reaction is a platinum/ruthenium alloy in the ratio variously given as between 9:1 and 1:1. -8 The notion of base electrocatalysts for the DMFC anode has been mooted before, 9 ' 2 but the results have given low oxidation current densities, and the catalyst corrosion rates have not been well defined. We describe below the results from a new electrocatalyst which we have synthesized from base materials, containing no noble metal.The electrocatalyst was prepared from nickel nitrate and sodium tungstate (both analytical grade) as starting materials.These were dissolved in double-distilled water as separate solutions to concentrations of 0.1 mol dm -3 .The pH of the tungstate solution was adjusted to 5.9 using nitric acid. The tungstate solution was then added dropwise over several hours to the nickel solution to small excess of Ni 2+ , with continuous stirring. Nickel tungstate was thereby precipitated and was filtered, washed, and dried. The nickel tungstate was then reduced in a furnace at 823°C for 8 h under an atmosphere of 80% hydrogen, 20% methane. After reduction, the material was furnace-cooled under argon. This formed the final electrocatalytic material. X-ray diffraction of the catalyst showed the presence of two components in addition to some graphite. One was tungsten carbide (WC). The other showed peaks similar to those of metallic nickel, but shifted relative to the standard diffraction pattern of the pure metal.' 3 We believe that these are due to nickel containing dissolved tungsten in solid solution, and probably carbon as well, but the full identity of this component has not been resolved. However, at 800 0 C, the solu...

Electrocatalysis by nanocrystalline tungsten carbides and the effects of codeposited silver

“…In previous methods, where tungsten carbides (as well as other carbides) were produced by gas-phase reduction of W(VI) using methane/hydrogen mixtures, much carbon was also deposited [8][9][10][11], and this was detected by XRD. The advantage of this high-temperature solid-state synthesis is therefore the production of clean W 2 C/WC surfaces, without residual carbon coated on the surface: no carbon peaks were observed in the XRD patterns in Fig.…”

“…Burstein). oxidation catalysis [7] and methanol electrocatalysis [8][9][10]. Sputtered nickel tantalum carbide has shown electrocatalytic activity as both an anode and cathode [11].…”

Synthesis of Nanoparticulate Tungsten Carbide Under Microwave Irradiation

“…T ungsten carbide (WC) has been studied as a nonnoble anode electrocatalyst for acidic low‐temperature fuel cells. Experiments have been carried out using the material as an electrocatalyst for the anodic oxidation of hydrogen 1–4 and methanol 5,6 . The dimensions of the WC crystals influence the electrocatalyst performance; decreasing the WC particle size from 500 to 600 nm to 200 nm was reported to increase electrocatalytic activity significantly 3 .…”

Nanosized tungsten carbide synthesized by a novel route at low temperature for high performance electrocatalysis

“…WC has been proposed to partially or totally replace the noble metals like Pt to reduce the cost11121314151617181920212223242526. WC as catalyst was firstly used for alkane isomerization and showed a high catalytic activity which is comparable with Pt1011.…”

“…Philip et al pointed out that the catalytic activity of WC on hydrogen oxidation was one hundred thousandth of Pt catalyst23. But the catalytic activity of WC on methanol oxidation was not so bad2425. Nakazawa et al reported that the electronegative WC could absorb the hydrogen in methanol, leading to the dehydrogenation and oxidation of methanol26.…”