Study of the Electrochemical Activities of Mo-Modified Pt Catalysts, for Application as Anodes in Direct Methanol Fuel Cells: Effect of the Aggregation Route

Abstract

Electrocatalysts with constant metallic composition, consisting of carbon-supported platinum and molybdenum phases, were synthesized following the thermolysis (thr) and borohydride (bhr) reduction methods and using different metallic precursors. The obtained electrocatalysts were characterized by X-ray energy-dispersive spectrometry, X-ray diffraction and high resolution transmission electron microscopy. Their activities were studied by cyclic voltammetry. Different surface structures were obtained and the electrochemical activities toward methanol oxidation were compared. Pt, MoO 2 and MoO 3 phases were well identified with the characterization techniques used. However, the electrochemical responses obtained from both sample series were considerably different, suggesting that the arrangement and relationships between active phases strongly depend on the synthesis method and aggregation sequence of the metallic precursors, and being the cause of different catalytic activities and stabilities of molybdenum oxide phases. The bhr method offered higher activity than the thr method. Among the sample series obtained by bhr method, the catalyst obtained by platinum deposition on the previously synthesized molybdenum on carbon, led to the highest overall activity. Fuel Cells represent one of the most promising options for generating electricity with high efficiency and low environmental impact. The Direct-Methanol Fuel Cell (DMFC) is a low-temperature cell where methanol is directly supplied as fuel to the anode compartment, without any previous reforming. Furthermore, methanol can be stored and transported in liquid phase, it can be obtained from biomass, and its complete oxidation can yield a high energy density.1 Platinum has been recognized as the most active catalyst for the methanol oxidation reaction and it has been employed in the formulation of such materials. However, the formation of different organic intermediates, adsorbed on Pt surfaces during methanol electrooxidation, causes the poisoning of active sites and decreases the catalyst efficiency. Several studies indicate that the modification of the Pt catalyst with other transition metal can lead to good results in oxidizing methanol at a low potential (lower than in pure Pt). 2On the other hand, it is well known that bimetallic materials show increased activity toward the CO electro-oxidation reaction, yielding CO 2 . Studies on catalytic effects that take place on bimetallic surfaces, obtained from pure metals and modified by the deposition of a second metal, are closely related to the technological development of low temperature fuel cells. Some researchers have emphasized the use of CO as a test molecule to show the electronic effect associated with this reaction. The CO desorption energy is apparently related to strong intermetallic bonds and mixed orbitals of the active phases. Hence, a catalyst with high activity toward methanol oxidation must also have high activity for CO oxidation.3 This activity is explained by some authors in terms of the so-cal...

Water Molecular Adsorption on the Low-Index Pt Surface: A Density Functional Study

“…The said modified Pt-based catalysts described in our literature reviews involve the addition of other metals, e.g. Pt-Ru [7][8], Pt-Co [9], Pt-Cu [10], Pt-Mo [11], Pt-Pd [12], PtRu-Mo [13] -and even Pt-Ru-O-Ir catalyst systems [14]. However, we will not discuss in detail the processes in DMFCs, but we focus on the fundamental part of H2O-Pt systems as one of the reaction steps in MOR, in a scientific perspective.…”

Effect of the Preparation Method on the Electrocatalytic Activity of Pt-Sn/Nanotubes Catalysts Used in DMFC

“…3 To produce a useful electrocatalyst, significant efforts have been made to decrease the amount of Pt used and to overcome the problem of CO poisoning. [4][5][6][7][8] The solutions involve the use of secondary metals such as Ru, [9][10][11] Sn, 10,[12][13][14] Pd, 11,12 Mo, 15,16 W, 17,18 Rh 6,19,20 and Cr 21,22 to promote the catalytic activity and the oxidation of the chemisorbed CO. Recently, utilization of PtSn over different carbonaceous materials as anode catalysts has been studied for methanol oxidation by several groups.…”

Active Pt-Nanocoated Layer with Pt–O–Ce Bonds on a CeOx Nanowire Cathode Formed by Electron Beam Irradiation

“…Recently, the metal platinum (Pt)–oxide support interaction has been attracting much attention for maximization of activity on Pt/C in MEA. Both of anodic 4 − 34 and cathodic 35 − 56 electrocatalytic reactions on Pt-loaded CeO 2 , 4 − 21 , 35 − 44 TiO 2 , 22 − 25 , 45 − 49 SnO 2 , 26 − 30 , 50 − 53 WO 3 , 31 , 32 , 46 , 54 MoO 2 , 33 , 55 or NbO 2 34 , 56 were examined for MEA application in previously published works.…”

“…Recently, the metal platinum (Pt)–oxide support interaction has been attracting much attention for maximization of activity on Pt/C in MEA. Both of anodic − and cathodic − electrocatalytic reactions on Pt-loaded CeO 2 , − ,− TiO 2 , − ,− SnO 2 , − ,− WO 3 , ,,, MoO 2 , …”