Tailoring electrochemical efficiency of hydrogen evolution by fine tuning of TiOx/RuOx composite cathode architecture

Here we report an approach to design composite cathode based on TiO_x nanotubes decorated with RuO_x nanowhiskers for efficient hydrogen evolution. We tailor catalytic activity of the cathodes by adjustment of morphology of TiO_x nanotubular support layer along with variation of RuO_x loaded mass and assess its performance using electrochemical methods and wavelet analysis.The highest energy efficiency of hydrogen evolution is observed in 1 M H₂SO₄ electrolyte to be ca. 64% at −10 mA/cm² for cathodes of the most developed area, i.e. smaller diameter of tubes, with enhanced RuO_x loading. The efficiency is favored by detachment of small hydrogen bubbles what is revealed by wavelet analysis and is expressed in pure noise at wavelet spectrum. At increased current density, −50 or −100 mA/cm², better efficiency of composite cathodes is supported by titania nanotubes of larger diameter due to an easier release of large hydrogen bubbles manifested in less periodic events appeared in the frequency region of 5–12 s at the spectra.We have shown that efficiency of the catalysts is determined by a pre-dominant type of hydrogen bubble release at different operation regimes depending on specific surface and a loaded mass of ruthenia.     

Low precious metal loading porous transport layer coating and anode catalyst layer for proton exchange membrane water electrolysis

A mixed metal oxide-coated Ti felt was constructed for use as a porous transport layer (PTL) in a proton exchange membrane (PEM) water electrolyzer. The PTL was fabricated by coating Ti felt with 0.43 mg_TaOx cm^?2 and 1 mg_Ir + Ru cm^?2 IrO₂–RuO₂-TaO_x using a thermal decomposition method. The coated Ti felts exhibited high conductivity, mass transport performance, stability and oxygen evolution reaction (OER) catalytic activities. The stability of IrO₂–RuO₂-TaO_x coating obviously improved than traditional electroplated Pt coating. Using the PTL, a single cell performance of 1.836 V @ 2000 mA cm^?2 was achieved at 80 °C under ambient pressure with 1 mg cm^?2 of precious metal in anode CL. However, the precious metal loading is about 2 mg cm^?2 in common PEM electrolyzer anode catalyst layer (CL). The IrO₂–RuO₂-TaO_x-coated Ti felt proved to be a promising low-cost PTL for PEM water electrolysis with high performance.     

Synthesis and electrochemical properties of nano-composite IrO2/TiO2 anode catalyst for SPE electrolysis cell

A composite catalyst of nano-grade IrO₂/TiO₂ powder is synthesized by Adams’ fusion method for reducing overvoltage of solid polymer electrolyte (SPE) cell and cost-down of noble metal catalyst, simultaneously. The IrO₂/TiO₂ catalysts, which has a porous composite nanostructure, are prepared according to molar ratio of Ir and Ti element with a specific surface area of 34.1–55.3 m² g^?1. It is found that crystal structure of TiO₂ is more dominated by the rutile phase than by Anatase. For a SPE system, total catalyst loading of anode which made of TiO₂ and IrO₂ is prepared as low as 0.77 mg cm^?2 or less, in which the loading amount of the IrO₂ only is set to 0.6 mg cm^?2 or less. The anode catalyst layer of about 10 ? thickness is coated on the membrane (Nafion 212) for the membrane electrode assembly (MEA) by the decal method. The strong adhesion between the catalyst electrode the membrane is observed by Scanning electron microscopy (SEM). Linear sweep voltammetry (LSV) results shows that the nano-composite IrO₂/TiO₂ catalysts has better oxygen evolution reaction (OER) than that of the synthesis IrO₂ only. Finally, the IrO₂/TiO₂ catalysts is applied as anode electrode for SPE cells and it is observed that in spite of the lower loading amount of the IrO₂ less than 0.5 mg cm^?2, working voltage of 1.68 V is observed at a current density of 1 A cm^?2 and operating temperature of 80 °C.     

Activity and stability optimization of RuxIr1-xO2 nanocatalyst for the oxygen evolution reaction by tuning the synthetic process

IrO₂ and RuO₂ are known as two of the best catalysts for the oxygen evolution reaction (OER) in acidic electrolyte. It is reported that RuO₂ has higher OER catalytic activity, while IrO₂ possesses better electrochemical stability during the OER process in acid. Therefore, many combined strategies have been proposed to utilize the advantages of both IrO₂ and RuO₂ catalysts in water electrolysis applications. In this article we describe how, by tuning the wet-chemical synthesis process in which the Ir precursor is added after the synthesis of RuO₂ nanoparticles (NPs) (two-step), the Ru_0.5Ir_0.5O₂ NPs have been synthesized to improve the OER catalytic activity in both acidic and alkaline media. In detail, the specific OER activity of the Ru_0.5Ir_0.5O₂ NPs (with a particle size of ca. 10 nm) is 48.9 μA cm⁻² at an overpotential ŋ = 0.22 V (vs. RHE) and 21.7 μA cm⁻² at ŋ = 0.27 V (vs. RHE) in 0.1 M HClO₄ and 0.1 M KOH, respectively. These values are higher than those for the one-step (Ir_0.5+Ru_0.5)O₂ NPs (obtained by contemporaneously adding both Ru and Ir precursors), which are 19.5 and 15.5 μA cm⁻² at the same measuring conditions, respectively. Additionally, with more IrO₂ component distributed on the particle surface, the two-step Ru_0.5Ir_0.5O₂ NPs show better OER catalytic stability than RuO₂ NPs.     

Zeolite-templated IrxRu1−xO2 electrocatalysts for oxygen evolution reaction in solid polymer electrolyte water electrolyzers

Ir_xRu_1−xO₂(1 ≥ x ≥ 0) with nanorod structure were successfully synthesized by employed pre-filling the Ir and/or Ru guest species into the peripheral-pore of NH₂-modified as-synthesized SBA-15 and explored as electrocatalyst for oxygen evolution reaction (OER) in water electrolyzers. Various physicochemical parameters for zeolite template and/or Ir_xRu_1−xO₂ were obtained by SEM, TEM, XRD, EDX and N₂ gas absorption/desorption measurements. The morphology for prepared Ir_xRu_1−xO₂ samples with individual and/or cluster nanorods was changed with the component difference. Cyclic voltammetry, linear sweep voltammetry, electrochemical impedance spectroscopy, steady state polarization curves and stability tests were performed to investigate the catalytic activity and stability of these electrocatalysts for OER. The cell with catalyst RuO₂ showed best catalytic performance with the lowest onset potential (1.374 V at 10 mA cm⁻²), which may be ascribed to regular nanoclusters and larger outer active surface area. Meanwhile, the cell stability tests suggested that the addition of IrO₂ in Ir_xRu_1−xO₂ improved the stability of the RuO₂ catalyst.     

The Fe3+ role in decreasing the activity of Nafion-bonded IrO2 catalyst for proton exchange membrane water electrolyser

Fe³⁺ is a common ion contaminant for the proton exchange membrane water electrolyser (PEMWE). In this work, three-electrode-system was employed to study the effect of Fe³⁺ on Nafion-bonded IrO₂ catalyst which is conventional anode catalyst for PEMWE. Study results showed that Fe³⁺ contamination decreased IrO₂ catalytic activity significantly only when the following two conditions were both satisfied: 1) Nafion resin exists in working electrode; 2) working electrode potential was over 1.471 V (vs. NHE) which is around the initial voltage of oxygen evolution reaction (OER). Besides, the contaminated working electrode activity was recovered to about 16% by being immersed into 3 M H₂SO₄ solution, but it was recovered to about 59% by ethanol washing method. These study results revealed that Fe³⁺ plays a role of catalyst for H₂O₂ production during OER process, which leads to Nafion resin decomposition. The degradation products covered working electrode surface, and thus decreased effective active sites of IrO₂. Nafion degradation was further confirmed by analyzing 1) F⁻ content in anode water and 2) FTIR of contaminated Nafion membrane.     

Enhanced ethanol oxidation on PbOx-containing electrode materials for fuel cell applications

The synthesis, characterization and utilization of lead oxide-based catalysts, deposited by the sol–gel method on carbon powder to be used as anode in direct ethanol fuel cells (DEFC) is described. For comparison, other materials, based on Ru and Ir (and mixtures of Ru, Ir or Pb) were tested in the same experimental conditions. X-ray diffraction analysis showed that the Pb was deposited on carbon powder as a mixture of PbO and PbO₂ molecular structures. The catalysts Pt-(RuO₂-PbO_x) and Pt-(RuO₂-IrO₂) exhibited significantly enhanced catalytic activity for the ethanol oxidation as compared to Pt/C commercial powder. Quasi-steady-state polarization curves showed that the composites Pt-(RuO₂-PbO_x)/C and Pt-(RuO₂-IrO₂)/C started the oxidation process in very low potentials (155 and 178 mV, respectively). So, the addition of metallic oxides by the sol–gel route to Pt is presented as a very interesting way to prepare materials with high catalytic activity for direct ethanol fuel cell systems. Current–time studies also showed the good performance of the Pt-(RuO₂-PbO_x) catalyst due to smaller poisoning of the material as the process advances.     

Enhancing the activity of a SiC–TiO2 composite catalyst for photo-stimulated catalytic water splitting

In this work, effort has been made to design an efficient catalyst for the photo-stimulated water splitting reaction, starting with the modification of TiO₂ (P25) to enhance its activity. A SiC(1 wt%)–TiO₂ composite material shows an activity as high as twice of that of TiO₂. NiO_x, an electron collector, promotes the activity of TiO₂, while IrO₂, a hole capturer, enhances the hydrogen evolution rate of SiC. A SiC(1 wt%)–NiO_x/TiO₂ three-component and an IrO₂/SiC(1 wt%)–NiO_x/TiO₂ four-component composite materials produce 30% and 100% more H₂ than the NiO_x/TiO₂ catalyst during the first 5 h, respectively, with ethanol used as the sacrificial reagent. Furthermore, the SiC(1 wt%)–NiO_x/TiO₂ catalyst is active under visible light, while the NiO_x/TiO₂ catalyst shows no activity under the same irradiation condition. 3C-SiC has a narrow band gap and its band edge well compensates that of the TiO₂. The enhancing effect of dopants on the SiC(1 wt%)–TiO₂ composite material is sensitive to the location of the modifiers, which further proves that an efficient separation of the charge carriers is crucial to the overall activity of the composite catalyst.     

Highly efficient Ru/TiO2‐NiAl mixed oxide catalysts for CO selective methanation in hydrogen‐rich gas

Selective CO methanation (CO‐SMET) is viewed as an effective H₂‐rich gas purification technique for proton exchange membrane fuel cells. In this work, improved composite‐supported Ru catalysts were developed for the CO‐SMET process. Mixed metal oxides (MMOs) obtained by calcination of layered double hydroxides precursor were used as an effective catalyst supports. After incorporation of TiO₂, the resulting TiO₂‐MMO composites were expected to have an enhanced catalytic performance. Therefore, a series of TiO₂‐NiAl layered double hydroxides was successfully prepared via 1‐pot deposition method. After calcination, the derived TiO₂‐NiAl MMO‐supported Ru catalysts obtained by impregnation method showed excellent catalytic performance for CO‐SMET reaction. The catalyst could deeply remove the CO outlet concentration (<10 ppm) with a high selectivity (>50%) over the wide low‐temperature window (175‐260°C). Furthermore, the catalyst also showed high stability with no deactivation during a long‐term durability test (120 h). Based on X‐ray diffraction, Fourier transform infrared, Raman, thermogravimetric differential scanning calorimetry, N₂ adsorption‐desorption, temperature‐programmed reduction, scanning electron microscopy, and transmission electron microscopy analyses, the enhanced catalytic performance of the TiO2‐NiAl MMO‐supported Ru catalyst was found to be related to the higher dispersion of Ru nanoparticles, partially reduced NiO species, and the increased specific surface area and structural stability of the support. The facile synthesis strategy proposed herein may open a new window for the efficient production of high‐quality H₂.     

Characterization of RuO2·xH2O with various water contents

Hydrous ruthenium oxides (RuO₂·xH₂O) with different contents of water (x) were prepared by annealing commercial RuO₂·2.6H₂O powders at different temperatures. The morphologies and crystalline structures of RuO₂·xH₂O were investigated using transmission electron microscope (TEM) and selected area electron diffraction (SAED) techniques. From the TEM images, it was observed that the particle size of RuO₂·xH₂O increased with increasing annealing temperature. From the SAED patterns, it was observed that RuO₂·xH₂O powders became an amorphous phase at annealing temperatures <116 °C and became a crystalline phase at annealing temperatures above 116 °C. Amorphous RuO₂·xH₂O prepared at 116 °C reached its maximum specific capacitance as a result of proton insertion into the bulk of RuO₂ but with smaller Ru–Ru distance in the local structure. The more disordered structure induced by proton insertion was obtained by SAED pattern from a sample annealed at 116 °C. The possible connection between the microstructure and specific capacitance of RuO₂·xH₂O is discussed.     

Experimental validation of the “EasyTest Cell” operational principle for autonomous MEA characterization

The paper presents the experimental validation of the “EasyTest Cell” operational principle via comparative electrochemical tests on MEAs carried out in three types of electrochemical hydrogen energy conversion (EHEC) testing cells: conventional polymer electrolyte membrane fuel cells (PEMFC) and polymer electrolyte membrane water electrolyzers (PEMWE), properly equipped with all the required auxiliaries (products conditioning and supplying, reagents removal, etc.), and the simple, autonomous EasyTest Cell. Along with EasyTest Cell validation and demonstration of its advantages, the influence of argon pressure during sputtering on the electrode characteristics, including gas diffusion limitations was investigated. The electrodes under investigation were magnetron sputtered C/Ti/IrO_x (IrO_x loading in the range 0.12–0.4 mg cm⁻²), C/Ti/IrO_x/Pt/IrO_x (IrO_x 0.08/Pt 0.06/IrO_x 0.08 mg cm⁻²), sputtered at various argon pressure C/Ti/Pt (0.15 and 0.25 mg cm⁻²), and commercial ELAT electrode (V.21, Lot # MB030105-1, Pt loading 0.5 mg cm⁻², E-TEK). The results obtained proved the reliability, simplicity (running-periphery-free) and broadened experimental possibilities of EasyTest Cell over PEMFC and PEMWE single cell testing. Thus, significant cost reduction and resource saving in R&D laboratory can be achieved. Moreover, validation of EasyTest Cell contributes not only to testing facilitations, but potentially to standardization of MEA testing since it gives possibilities for precise control and more uniform distribution of the working parameters applied to the testing object, which are both compulsory for performance comparison and qualifying.     

Sputtered Ir–Ru based catalysts for oxygen evolution reaction: Study of iridium effect on stability

Magnetron sputtered low-loading iridium-ruthenium thin films are investigated as catalysts for the Oxygen Evolution Reaction at the anode of the Proton Exchange Membrane Water Electrolyzer. Electrochemical performance of 50 nm thin catalysts (Ir pure, Ir–Ru 1:1, Ir–Ru 1:3, Ru pure) is tested in a Rotating Disk Electrode. Corresponding Tafel slopes are measured before and after the CV-based procedure to compare the activity and stability of prepared compounds. Calculated activities prior to the procedure confirm higher activity of ruthenium-containing catalysts (Ru pure > Ir–Ru 1:3 > Ir–Ru 1:1 > Ir pure). However, after the procedure a higher activity and less degradation of Ir–Ru 1:3 is observed, compared to Ir–Ru 1:1, i.e. the sample with a higher amount of unstable ruthenium performs better. This contradicts the expected behavior of the catalyst. The comprehensive chemical and structural analysis unravels that the stability of Ir–Ru 1:3 sample is connected to RuO₂ chemical state and hcp structure. Obtained results are confirmed by measuring current densities in a single cell.     

Direct hydrodeoxygenation of cellulose and xylan to lower alkanes on ruthenium catalysts in subcritical water

Nano particles of Ru, Rh, Pd, Ir, Pt, and Au, protected by polyvinyl pyrrolidone (PVP), were applied to the hydrodeoxygenation of cellulose and xylan in water and 5 MPa H₂ at 543 K. The distributions of products generated from cellulose and xylan were roughly similar to each other under the present reaction conditions, and therefore, the former was intensively studied. The Ru-PVP catalyst afforded mainly methane and lower alkanes, rather than producing water soluble organic compounds, such as diols and alcohols, that were formed with the use of the other catalysts. The changes in the product distributions with reaction temperature and time indicated that the reaction consisted of two consecutive reactions: cellulose or xylan → water soluble compounds → hydrogenolysis. The first transformation was promoted in subcritical water, and the second step was catalyzed by the Ru catalyst. The Ru catalyst that was supported on CeO₂, γ-Al₂O₃, or activated carbon yielded a similar product distribution to that on Ru-PVP; however, the loading of Ru on TiO₂, ZrO₂, SiO₂–Al₂O₃, or SiO₂ resulted in the increment of diols. After the reaction a small portion of the CeO₂ and most of the SiO₂–Al₂O₃ and SiO₂ were dissolved in water, and a portion of the Al₂O₃ was transformed to boehmite AlO(OH) from the γ-alumina. Little change in the catalytic activity however was observed upon the reuse of Ru/Al₂O₃ in the second run.     

Novel (Ir,Sn,Nb)O2 anode electrocatalysts with reduced noble metal content for PEM based water electrolysis

A solid solution of IrO₂, SnO₂ and NbO₂, denoted as (Ir,Sn,Nb)O₂, of compositions (Ir_1−2xSn_xNb_x)O₂ with x = 0, 0.125, 0.20, 0.25, 0.30, 0.35, 0.40, 0.425 and 0.50 has been synthesized by thermal decomposition of a homogeneous mixture of IrCl₄, SnCl₂·2H₂O and NbCl₅ ethanol solution coated on pretreated Ti foil. The (Ir,Sn,Nb)O₂ thin film of different compositions coated on Ti foil has been studied as a promising oxygen reduction anode electrocatalyst for PEM based water electrolysis. It has been identified that (Ir,Sn,Nb)O₂ of composition up to x = 0.30 [(Ir_0.40Sn_0.30Nb_0.30)O₂] shows similar electrochemical activity compared to pure IrO₂ (x = 0) resulting in ∼60 mol.% reduction in noble metal content. On the other hand, (Ir,Sn,Nb)O₂ of composition x = 0.20 [(Ir_0.20Sn_0.40Nb_0.40)O₂] shows only 20% lower activity compared to pure IrO₂ though the noble metal oxide, IrO₂ loading is reduced by 80 mol.%. The accelerated life test of the anode electrocatalyst for 48 h followed by elemental analysis of the electrolyte shows that (Ir,Sn,Nb)O₂ improves the stability of the electrode in comparison to pure IrO₂ electrocatalyst in oxygen reduction processes. The excellent electrochemical activity as well as long term structural stability of (Ir,Sn,Nb)O₂ during water electrolysis has been discussed using first-principles calculations of the total energies, electronic structures, and cohesive energies of the model systems.     

Highly efficient methanol oxidation on durable PtxIr/MWCNT catalysts for direct methanol fuel cell applications

Development of highly active and durable Pt based anode materials with higher utilization of Pt is quite crucial towards the commercial viability of direct methanol fuel cells (DMFCs). Herein, multi-walled carbon nanotube supported Pt_xIr nanostructures (Pt_xIr/MWCNT) are successfully prepared by one-pot wet chemical reduction without any surfactants. The role of Ir content and its bi-functional mechanism on kinetics of methanol oxidation reaction (MOR) was studied. The MOR on Pt_xIr/MWCNT follows Langmuir-Hinshelwood mechanism by successive oxidative removal of CO. The co-existence of IrO₂ plays a vital role as catalytic promotor. Amongst, Pt₂Ir/MWCNT shows enhanced electrocatalytic activity (mass activity (MA), 933.3 mA/mg_Pt) and durability (13.8% loss of MA after 5000 potential cycles) thru the well-balanced electronic and bi-functional effects. This study implies that the optimized composition of Pt₂Ir/MWCNT exhibits efficient methanol oxidation and could be a potential catalyst for direct methanol fuel cells.     

Oxygen reduction at carbon supported ruthenium–selenium catalysts: Selenium as promoter and stabilizer of catalytic activity

Carbon supported ruthenium-based catalysts (Ru/C) for the oxygen reduction in acid electrolytes were investigated. A treatment of Ru/C catalysts with selenious acid had a beneficial effect on catalytic activity but no influence on intrinsic kinetic properties, like Tafel slope and hydrogen peroxide generation. Reasons for the increased activity of RuSe_x/C catalysts are discussed. Potential step measurements suggest that at potentials around 0.8 V (NHE) a selenium or selenium-oxygen species protects the catalyst from formation of inactive RuO₂-films. This protective effect leads to an enhanced activity of RuSe_x/C compared to Ru/C. No evidence was found for a catalytically active stoichiometric selenium compound. The active phase may be described as a ruthenium suboxide RuO_x (x < 2) layer integrated in a RuSe_y phase or RuSe_yO_v (y < 2, v < 2) layer at the particle surface.     

Role of the composition and preparation method in the activity of hydrotalcite-derived Ru catalysts in the catalytic partial oxidation of methane

Hydrotalcite-derived Ru catalysts were tested in the catalytic partial oxidation of CH₄ to produce syngas. The effect of Ru content, oxidic matrix composition, and preparation procedure on chemical–physical properties and performances of catalysts was studied. Bulk catalysts (0.25 and 0.50 wt.% Ru) were obtained via Ru/Mg/Al hydrotalcite-type (HT) precursors with carbonates or silicates as interlayer anions. A supported catalyst was prepared by impregnation on a calcined Mg/Al–CO₃ HT. Ru/γ-Al₂O₃ was evaluated for comparison. Both the Ru dispersion and the interaction with the support decreased as the Ru loading increased and when silicates were present due to RuO₂ segregation. Regardless of the Ru loading, carbonate-derived catalysts performed better than those containing silicates. The increased Ru loading improved the initial activity, but deactivation occurred after high temperature tests. Stability tests for shorter contact times over a 0.25 wt.% bulk sample obtained from Ru/Mg/Al HT with carbonates showed a tendency to deactivate at 750 °C.     

Catalytic transfer hydrogenation of furfural to furfuryl alcohol over Fe3O4 modified Ru/Carbon nanotubes catalysts

In this study, magnetic Fe₃O₄ modified Ru/Carbon nanotubes (CNTs) catalysts were used to achieve the catalytic transfer hydrogenation of furfural (FF) to furfuryl alcohol (FFA), with alcohols as the solvent and hydrogen donors. According to the result of the catalyst characterization, Fe₃O₄ promoted the formation of Ru⁰ species. The effects of Fe₃O₄ loading and different hydrogen donors on the catalytic transfer hydrogenation of FF were tested, and the reaction parameters and catalyst stability were also analyzed. It is found that Fe₃O₄ effectively enhanced the activity of Ru/CNTs in catalytic transfer hydrogenation of FF, the catalytic activity was optimized at the Fe₃O₄ loading of 5 wt%, and the optimal hydrogen donor was i-propanol. Moreover, the Ru–Fe₃O₄/CNTs could be easily collected for further use and possessed excellent stability. The mechanism of the catalytic transfer hydrogenation of FF using Ru–Fe₃O₄/CNTs was discussed, and the corresponding catalyst activity groups included metal Ru sites and RuO_x-Fe₃O₄ Lewis acid sites, which account for the excellent catalytic activity of transfer hydrogenation.     

Investigation of supported IrO2 as electrocatalyst for the oxygen evolution reaction in proton exchange membrane water electrolyser

Indium tin oxide (ITO) was used as a support for IrO₂ catalyst in the oxygen evolution reaction. IrO₂ nanoparticles were deposited in various loading on commercially available ITO nanoparticle, 17–28 nm in size using the Adam's fusion method. The prepared catalysts were characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The BET surface area of the support (35 m²/g) was 3 times lower than the unsupported IrO₂ (112.7 m²/g). The surface area and electronic conductivity of the catalysts were predominantly contributed by the IrO₂. The supported catalysts were tested in a membrane electrode assembly (MEA) for electrolyser operation. The 90% IrO₂-ITO gave similar performance (1.74 V@1 A/cm²) to that of the unsupported IrO₂ (1.73 V@1 A/cm²) in the MEA polarisation test at 80 °C with Nafion 115 membrane which was attributed to a better dispersion of the active IrO₂ on the electrochemically inactive ITO support, giving rise to smaller catalyst particle and thereby higher surface area. Large IrO₂ particles on the support significantly reduced the electrode performance. A comparison of TiO₂ and ITO as support material showed that, 60% IrO₂ loading was able to cover the support surface and giving sufficient conductivity to the catalyst.     

Metal oxide promoters for methanol electro-oxidation

Noble metal oxides (IrO_x, RuO_x) and valve metal oxides (SnO_x and VO_x) have been investigated as promoters of Pt electrocatalyst for methanol oxidation in acidic environment. Pt modification was made using low oxide content (5 wt%) in order to evaluate the possibility of using such oxide promoter in a multifunctional catalyst. At this low level of oxide content, IrO_x provided a larger promoting effect than RuO_x. This occurred in the absence of specific alloying with Pt and also in the presence of lower catalyst dispersion. The electrocatalytic enhancement produced by the valve metal oxides was significantly lower than IrO_x and RuO_x. These results are interpreted in terms of the different water displacement mechanism for the various oxides. Such evidences seem to indicate that a multifunctional catalyst may represent a valid route to enhance methanol electro-oxidation.