The characterization of Pt/Sn catalyst for the electrochemical oxidation of methanol

Enhancement of methanol electro-oxidation was observed on Pt alloy-SPE (solid polymer electrolyte) electrodes in a sulfuric acid solution, on which the catalytic activity was higher than that on a plain Pt-SPE or a second metal-electrodeposited Pt-SPE. Such Pt alloy-SPEs were prepared by a reducing agent penetration method; the reducing agent penetrated from one face of the SPE membrane to the other face, which contacted the mixture of metal ion solutions. Then, at the latter face of the SPE membrane, Pt alloy was formed, which was confirmed by x-ray diffraction. Such Pt alloy on SPE exhibited a partly amorphous character in the case of PtSn and PtRu alloy-SPEs. The electrodes studied were PtAuRu, PtRu, PtSn, and PtRuSn alloy-SPEs. For a specific alloy system, it was found that amorphous Pt alloy-SPEs exhibited the higher catalytic activity than the crystalline ones. The order of catalytic activity among them was cPtRuSn > aPtSn > aPtAuRu at 50~ where a and c denote amorphous and crystalline, respectively. The kinetic parameters were observed to be different among the Pt alloy-SPEs. It was discussed from those parameters that the adsorption state of the adsorbed intermediate from a methanol molecule depended on the kind of electrode. The highest activities were observed on PtRuSn alloy-SPE at 50 and 6O~ which were 33 mA. cm -2 and 50 mA 9 cm -2 at 0.4 V vs. RHE in 1M CH3OH + 0.5M H2SO4 as apparent current densities, or 90 and 130 ~A 9 cm -3 as true current densities with respect to the surface of Pt, respectively.Methanol electro-oxidation in acidic solution has been receiving attention as a process at a methanol fuel cell anode (1-10). Therefore, the enhancement of catalytic activity of the electrode material for the electro-oxidation was widely studied with respect to practical application of a methanol fuel cell (1-10). Pt is used as the main material, since it has the highest catalytic activity among single metals over a wide potential range and the modification of Pt metal is presently a major subject for the development of a catalytically active anode. Thus, the surface or bulk composition of a Pt electrode was modified by a second metal through mechanical mixing (2), submonolayer electrodeposition (1, 4, 5), alloy formation (8), and possibly sputtering (or ion plating). Second-metal modification has been extensively carried out by Janssen and Moolhuysen who summarized the second-metal effect in the case of submonolayer electrodeposition (4, 5), where Sn and Ru as second metals gave 1O0 and 25 times more enhanced catalytic activity than a Pt metal itself, respectively.On the other hand, the Pt electrode interface was modified by being bonded into the solid polymer electrolyte (SPE) matrix (9); Pt-SPE was thus formed by the reducing agent penetration method (1, 9-11). The catalytic activity of Pt-SPE toward the methanol electro-oxidation was pronounced in its durability during prolonged polarization (9, 10). Accordingly, dual modification by the second metal and also the SPE matrix has been carried out by su...

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“…[5] as schematically shown in Fig. 13A, the current per unit area, the current density, i, is expressed by…”

Section: I Imentioning

confidence: 99%

Platinum Alloy Electrodes Bonded to Solid Polymer Electrolyte for Enhancement of Methanol Electro‐oxidation and Its Reaction Mechanism

Aramata

Masuda

1991

J. Electrochem. Soc.

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“…Furthermore, this enhancement applies only to "fresh" surfaces, and is limited to surfaces which have experienced only a few sweeps through the potential region where "poisons" might be generated. With our apparatus, we were not able to make a systematic and satisfactory study of the catalysis of "aged" surfaces, which could be more representative of the catalysis in fuel cells [24]. It may even be the case that our observation of anticatalysis associated with tin in some experiments, e.g.…”

mentioning

confidence: 91%

Electrochemical oxidation of methanol on tin-modified platinum single-crystal surfaces

Haner¹,

Ross²

1991

J. Phys. Chem.

124

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“…This type of study is feasible when catalysts such as Pt−Sn are used, which activate C−H bonds and accomplish oxidation more efficiently than bare Pt at low potentials. The oxidation of small organic molecules, including MeOH, − ,− , formaldehyde, − , formic acid, − ,,,− carbon monoxide, ,− ,− EtOH, ,,− acetaldehyde, , n -PrOH, , i -PrOH, ,,, BuOH, ethylene glycol, − glyoxal, glyoxylic acid, , and oxalic acid 41 has been studied at Pt electrodes and Pt modified with Sn. However, different methods of e...…”

Section: Introductionmentioning

confidence: 99%

“…We have used electrochemical co-deposition as the method for preparing electrodes modified with the binary catalyst Pt−Sn. The electrochemical oxidation of MeOH on co-deposited Pt−Sn has been previously studied and has been shown to be superior to electrodeposited Pt alone. ,,, The oxidation of EtOH has been studied for Pt substrates with adsorbed Sn atoms . However, the use of electrodeposited catalysts, with the possibility of generating small catalyst particles, is more compatible with use in a fuel cell.…”

Section: Introductionmentioning

confidence: 99%

Electrocatalytic Oxidation of Small Carbohydrate Fuels at Pt−Sn Modified Electrodes

1998

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The electrocatalytic oxidations of water-soluble alcohols and diols and some other small organic molecules (MeOH, EtOH, 2-fluoroethanol, 2,2-difluoroethanol, 2,2,2-trifluoroethanol, CH2(OH)2, ethylene glycol, n-PrOH, i-PrOH, 1,4-butanediol, 1,3-propanediol, 1,2-propanediol, t-BuOH, neopentyl alcohol, benzyl alcohol, 2-Me-1-PrOH, formic acid, acetaldehyde, acetic acid, propionaldehyde, propionic acid, acetone, glycolaldehyde, glyoxal, glycolic acid, glyoxylic acid, oxalic acid) have been compared in aqueous 0.5 M H2SO4 at C and Au electrodes modified with an electrodeposited Pt−Sn catalyst at low (−0.1 to 0.5 V vs SCE) potentials. The Pt−Sn catalyst is electrochemically deposited and forms as a smooth deposit on Au electrodes. At a catalyst loading of ∼0.5 mg/cm2 the electrodeposition of the Pt−Sn catalyst results in formation of adherent ∼0.8 μm size particles on C electrodes. In general, for organic molecules containing only C, H, and O with two or more carbon atoms, the presence of H atoms on both the α- and β-carbon results in a relatively negative potential for onset of catalytic current (usually between −0.1 and −0.2 V vs SCE) at Pt−Sn compared to Pt alone. Of the alcohols and diols studied, formaldehyde (which exists in aqueous solutions as the hydrated form, CH2(OH)2) shows the highest electrocatalytic currents at the Pt−Sn catalyst. The ultimate product, via HCOOH, is CO2. EtOH is oxidized only to acetic acid on Pt−Sn electrodes. The EtOH and n-PrOH oxidation yields, determined by exhaustive electrolysis, are 4 e- per molecule, while i-PrOH yields only 2 e- per molecule. We confirmed the generation of acetic acid, propionic acid, and acetone as the final products for the oxidations of EtOH, n-PrOH, and i-PrOH, respectively, by 13C NMR and/or GCMS. The electron yield of the oxidation of ethylene glycol at Pt−Sn surfaces is only 4 e- per molecule instead of the value of 8 e- per molecule expected for the oxidation of ethylene glycol to oxalic acid. Glycolic acid (CHOCOOH) is the oxidation product by GCMS. This substance is not electrocatalytically oxidized on Pt−Sn at potentials negative of ∼ +0.4 V vs SCE in comparison to the −0.1 V vs SCE onset for ethylene glycol oxidation. MeOH, the molecule with the highest electron yield on Pt−Sn (6 e- per molecule), unfortunately shows the most positive potential onset for oxidation among the group of alcohols compared in this study, while the two intermediates along the path of oxidation to CO2, formaldehyde, and formic acid are oxidized on Pt−Sn at very negative potentials compared to MeOH. Thus, the conversion of MeOH to formaldehyde is the efficiency-determining step in the oxidation of MeOH to CO2.

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The characterization of Pt/Sn catalyst for the electrochemical oxidation of methanol

Cited by 61 publications

References 3 publications

Platinum Alloy Electrodes Bonded to Solid Polymer Electrolyte for Enhancement of Methanol Electro‐oxidation and Its Reaction Mechanism

Platinum Alloy Electrodes Bonded to Solid Polymer Electrolyte for Enhancement of Methanol Electro‐oxidation and Its Reaction Mechanism

Electrochemical oxidation of methanol on tin-modified platinum single-crystal surfaces

Electrocatalytic Oxidation of Small Carbohydrate Fuels at Pt−Sn Modified Electrodes

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