Methanol In Acidic Media Research Articles

Synthesis of Ni-MOF loaded Pt nanoparticle composites for the electro-oxidation of methanol in acidic media

A series of Pt/Ni-MOF nanocomposites with different atom molar ratio of Pt/Ni were synthesized by the traditional hydrothermal method. Various methods including element mapping, X-ray diffraction (XRD) were employed to characterize the crystal structure and surface morphology of the materials. TEM (Transmission Electron Microscopy) confirms that the Pt nanoparticles are highly dispersed onto the Ni-MOF nanosheet surface, which can provide an abundance of active sites for efficient oxidation of methanol. Electrochemical measurements showed that Catalyst b (the atomic molar ratio of Pt to Ni is 2:1 in the precursor materials) exhibited a higher oxidation current density in MOR and larger electrochemically active surface area (ECSA) than other catalysts with different atomic ratios and commercial Pt/C. Meanwhile, the synthesized catalysts showed long-term activity and good resistance to toxicity.

Facile synthesis of PEG-glycerol coated bimetallic FePt nanoparticle as highly efficient electrocatalyst for methanol oxidation

Direct methanol fuel cell (DMFC) has shown excellent growth as an alternative candidate for energy sources to substitute fossil fuels. However, developing cost-effective and highly durable catalysts with a facile synthesis method is still challenging. In this prospect, a facile strategy is used for the preparation of hydrophilic Fe-Pt nanoparticle catalyst via a polyethylene glycol-glycerol route to utilize the advantages of nanostructured surfaces. The synthesized electrocatalysts are characterized by XRD, XPS, TEM, EDS and FTIR to confirm their structure, morphology, composition, and surface functionalization. The performance of the catalysts towards methanol oxidation reaction (MOR) was investigated by cyclic voltammetry and chronoamperometry in both acidic and alkaline media. The Fe-Pt bimetallic catalyst exhibits better current density of 36.36 mA cm−2 in acidic medium than in alkali medium (12.52 mA cm−2). However, the high If/Ib ratio of 1.9 in alkali medium signifies better surface cleaning/regenerating capability of catalyst. Moreover, the catalyst possessed superior cyclic stability of ~ 80% in the alkaline electrolyte which is 1.6 times higher than in the acidic one. The better stability and poison tolerance capacity of catalyst in alkaline media is attributed to the OH− ions provided by the electrolyte which interact with the metal species to form M-(OH)x and reversibly release OH− and regenerate metal surface for further oxidation reactions. But synergism provided by Fe and Pt gives better activity in acidic electrolyte as Pt is favourable catalyst for dehydrogenation of methanol in acidic medium. This study will be useful for designing anodic electrocatalysts for MOR.

Platinum nanoparticles/phosphotungstic acid nanorods anchored poly(diphenylamine) nanohybrid coated electrode as a superior electro-catalyst for oxidation of methanol

Solvation of energy crises is the need of the era which urges for alternate energy resources. Direct methanol fuel cells (DMFCs) are an integral part of alternate energy and fuel concerns. This study demonstrates the facile fabrication of polydiphenylamine/phosphotungstic acid/platinum (PDPA/PTA/Pt) nanocomposites modified electrode via electrodeposition method for efficient electro-oxidation of methanol in acidic medium. The physicochemical characterization of PDPA/PTA/Pt nanocomposite modified electrode morphology using SEM with EDX mapping, and crystallinity behavior was examined using powder XRD analysis. The morphology of the PDPA/PTA/Pt nanocomposites demonstrates that the size of Pt nanospheres is ~200 nm, and the size of PTA nanorods is ~300 nm in the PDPA matrix. The electrochemical properties were also evaluated using cyclic voltammetry, chronoamperometric and electrochemical impedance studies techniques. The PDPA/PTA/Pt nanocomposite modified electrode showed superior electrocatalytic activity, higher current density (14.807 mA cm−2), longer stability and durability (30 min), and excellent catalytic poisoning tolerance to carbonaceous species accumulation towards methanol electro-oxidation reaction (MEOR), which is because of the synergistic existence of Pt nanospheres and PTA nanorods with PDPA matrix which enhances the electron transfer. The obtained results proved that the developed electro-catalyst is an excellent alternative for efficient MEOR in fuel cells applications.

Excellent electrocatalysis of methanol oxidation on platinum nanoparticles supported on carbon-coated silicon

The prepared carbon-coated silicon (Si@C) material was blended with graphite powder together to form the specific carbon paste electrode with different mass percent X% of Si@C (CPE-Si@C(X%)). The electrochemical impedance spectroscopy (EIS) was performed on the prepared CPE-Si@C and the pure carbon paste electrode (CPE), and the results show that the CPE-Si@C (X%) electrode has a smaller charge transfer resistance. Pt/CPE and Pt/CPE-Si@C(X%) electrodes were prepared by electrodepositing Pt particles on CPE-Si@C and CPE, and the obtained electrodes were used for electrocatalytic oxidation of methanol in acid media. The results show that the activity of Pt/CPE-Si@C(X%) electrode for electrocatalytic oxidation of methanol was higher than that of Pt/CPE electrode, and the mass peak current density of Pt/CPE-Si@C(10%) electrode for electrocatalytic oxidation of methanol reached 321 mA mg−1, which was 1.8 times higher than that of Pt/CPE electrode. The Pt/CPE-Si@C (10%) electrode and the Pt/CPE electrode were characterized by chronoamperometry. The results show that Pt/CPE-Si@C (10%) has a better stability of activity and stronger tolerance against CO poisoning.

The three-dimensional carbon nanosheets as high performance catalyst support for methanol electrooxidation

In this paper, we perform three typical oxidation treatments, such as O3, HNO3 and H2O2, to modify the surface structure of the novel three dimensional carbon nanosheets (3D CNSs). The different treatment generates kinds of oxygenated functional groups on the surface of support. One of them, the CNSs treated by ozone produces the greatest amount of carboxyl groups and keeps the original morphology, which can be used as the excellent support for the electrochemical oxidation of methanol in acidic medium. Through various characterizations, it is discovered that the PtCo/CNSs-1 shows the excellent lamellar structure, good crystallinity, abundant pore structure and large interlayer spacing, which provide ultrahigh specific surface area, superb electron and ionic conductivity. Furthermore, the superfine PtCo alloy nanoparticles evenly deposits on the 3D CNSs, which reveals superior electrocatalytic performance. More importantly, the capacity of anti-poisoning of which is enhanced obviously.

Electrochemical activity of Ni-montmorillonite/Vulcan XC-72R carbon black nano-catalyst for the oxidation of methanol in acidic medium

Direct methanol fuel cell is claiming to be the most main power source in future as a clean energy source, for which methanol is used as fuel. In the present study, nickel nanoparticles were synthesized by green route in the presence of montmorillonite (Ni-MMT). Then the electrochemical activity of prepared nanocomposite was investigated in methanol oxidation reaction in acidic medium. In the process of nickel nanoparticle synthesis, the natural substrate montmorillonite was used as capping agent and Allium jesdianum water extract was used as the source of reducing agent for the first time. The Ni-MMT sample was characterized by UV–Vis, XRD, SEM and EDX techniques. Production of nickel nanoparticles in the proposed green method is confirmed by absorption peak of 405 nm in UV–Vis spectrum. The average particle size of Ni-MMT was determined as 20.80 nm. The oxidation of methanol in acidic medium was studied by cyclic voltammetry using Ni-MMT-modified carbon paste electrode (Ni-MMT/CPE). Methanol was oxidized on the modified electrode surface at 0.3 V. Also, the catalytic current of methanol oxidation was 3 mA in H2SO4 electrolyte which is significantly more than unmodified CPE. The concentration of 0.5 M for H2SO4 was obtained as the optimum electrolyte for the oxidation of methanol. Methanol can be catalyzed in the concentration range of 0.1–0.5 M by the prepared nanostructured catalyst.Graphic abstractNi nanoparticles in montmorillonite (Ni-MMT) which was prepared by Allium jesdianum extract have a good electrocatalytic effect on methanol oxidation.

Hydrothermal Syntheses of NiO−GO Nanocomposite on 3D Nickel Foam as a Support for Pt Nanoparticles and its Superior Electrocatalytic Activity towards Methanol Oxidation

AbstractIn this project, Pt/NiO−GO nanocatalyst is grown on nickel foam (NF) and, its catalytic activity towards electrochemical oxidation of methanol in acidic media is studied. The first step is devoted to the synthesis of NiO−GO support by a hydrothermal method. Then Pt nanoparticles (∼34.3 nm) are electrodeposited on this supporting material. Hydrothermal and electrochemical deposition conditions are optimized. Surface of modified NF was inspected for physical characterization and Chemical composition by some techniques such as field emission scanning electron microscopy (FESEM), energy‐dispersive X‐ray spectra (EDS), and X‐ray diffraction (XRD). In the electrochemical section, the catalytic performance of Pt/NiO−GO/NF towards methanol oxidation is investigated by cyclic voltammetry and chronoamperometry measurements. The electrochemical impedance spectroscopy (EIS) is elected to deliberate charge transfer resistance on the catalyst surface. Mass activity, electrochemical surface area (ECSA) and durability of prepared catalysts are compared with commercial Pt/C. Deliberations prove the superiority of Pt/NiO−GO/NF towards methanol oxidation in acidic media. The Superior quality of synthesized nanocatalyst that is attributed to the synergetic effect of the NiO−GO support material and Pt nanoparticles, indicate that Pt/NiO−GO/NF can be successfully used as the anode in the direct methanol fuel cell (DMFC).

Pt[sbnd]CoN supported on TiN-modified carbon nanotubes (Pt[sbnd]CoN/TiN–CNT) as efficient oxygen reduction reaction catalysts in acidic medium

Herein, new catalysts for the oxygen reduction reaction (ORR) (PtCoN nanoparticles supported on TiN–carbon nanotubes (CNTs)) were successfully prepared via the simple polymerized complex method and heat treatment in NH3. Through this facile two-step synthesis, metal chlorides were first transformed to the corresponding oxides, then reduced to metal particles or nitrides. The synthesized PtCoN/TiN–CNT electrocatalysts showed excellent electrochemical activity for oxygen reduction and high tolerance against methanol in acidic medium. The ORR onset potential of Pt0.3CoN/TiN–CNT (0.812 V vs. RHE) is higher than that of 40 wt% commercial Pt/C (0.789 V vs. RHE) due to the synergistic effect between nano-platinum particles and metal nitrides. The TiN-coated CNT support provided high electron transfer rate and catalytic tolerance in methanol solution. The number of transferred electrons was examined by rotating ring-disk electrode measurements, which concurred with the result of the Koutecky–Levich equation for a four-electron mechanism.

Enhanced electrocatalytic performance of platinum nanoparticles on thiolated polyaniline-multiwalled carbon nanotubes for methanol oxidation.

Pt nanoparticles (PtNPs) well-dispersed on thiolated polyaniline (TPANI)-multiwalled carbon nanotubes (MWCNTs) were prepared for enhanced electrocatalytic oxidation of methanol in acidic media. Briefly, the preparation of nanocomposites was carried out via microwave-assisted thiol–ene reaction of 2,5-dimercapto-1,3,4-thiadiazole (DMcT) with oxidized PANI, which was synthesized in the presence of MWCNTs, yielding TPANI-MWCNTs; then, PtNPs were deposited on TPANI-MWCNTs by a microwave-assisted method to obtain PtNPs/TPANI-MWCNT nanohybrids. Fourier transform infrared spectroscopy, cyclic voltammetry (CV), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and inductively coupled plasma-atom emission spectroscopy were used to study relevant nanohybrid properties. TEM showed that PtNPs were well dispersed on TPANI-MWCNTs. TGA showed that PtNPs/TPANI-MWCNTs exhibited better thermal stability than PtNPs/TPANI-MWCNTs and PtNPs/MWCNTs. CV studies showed that PtNPs/TPANI-MWCNT-modified glassy carbon electrode (GCE) exhibited a larger electrochemically active surface area and higher electrocatalytic performance toward methanol electro-oxidation compared with those of PtNPs/PANI-MWCNTs/GCE and PtNPs/MWCNTs/GCE. Also, the PtNPs/TPANI-MWCNTs/GCE electrode possessed high stability and maintained 86% of its initial catalytic activity after 1000-cycle CV in 1.0 M CH3OH + 0.5 M H2SO4.

Probing the surface fine structure through electrochemical oscillations.

In the course of (electro)catalytic reactions, reversible and irreversible changes, namely the formation of adsorbed poisons, catalyst degradation, surface roughening, etc., take place at distinct time-scales. Reading the transformations on the catalyst surface from the measurement of the reaction rates is greatly desirable but generally not feasible. Herein, we study the effect of random surface defects on Pt(100) electrodes toward the electro-oxidation of methanol in acidic media. The surface defects are gently generated in situ and their relative magnitudes are reproducibly controlled. The system was characterized under conventional conditions and investigated under an oscillatory regime. Oscillatory patterns were selected according to the presence of surface defects, and a continuous transition from large amplitude/low frequency oscillations (type L) on smooth surfaces to small amplitude/high frequency oscillations (type S) on disordered surfaces was observed. Importantly, self-organized potential oscillations were found to be much more sensitive to the surface structure than conventional electrochemical signatures or even other in situ characterization methods. As a consequence, we proved the possibility of following the surface fine structure in situ and in a non-invasive manner by monitoring the temporal evolution of oscillatory patterns. From a mechanistic point of view, we describe the role played by surface defects and of the adsorbed and partially oxidized, dissolved species on the oscillations of type S and L.

Influence of the Metallic Load of Pt/C and Pt0.6-Ru0.4/C Nanowires on the Electrochemical Oxidation of Methanol in Acid Medium

Influence of the Metallic Load of Pt/C and Pt0.6-Ru0.4/C Nanowires on the Electrochemical Oxidation of Methanol in Acid Medium

Facile Fabrication of Platinum-Cobalt Alloy Nanoparticles with Enhanced Electrocatalytic Activity for a Methanol Oxidation Reaction

Decreasing the cost associated with platinum-based catalysts along with improving their catalytic properties is a major challenge for commercial direct methanol fuel cells. In this work, a simple and facile strategy was developed for the more efficient preparation of multi-walled carbon nanotube (MWCNT) -supported Pt/CoPt composite nanoparticles (NPs) via solution plasma sputtering with subsequent thermal annealing. Quite different from general wet synthesis methods, Pt/CoPt composite NPs were directly derived from metal wire electrodes without any additions. The obtained Pt/CoPt/MWCNTs composite catalysts exhibited tremendous improvement in the electro-oxidation of methanol in acidic media with mass activities of 1719 mA mg−1Pt. This value is much higher than that of previous reports of Pt-Co alloy and commercial Pt/C (3.16 times) because of the many active sites and clean surface of the catalysts. The catalysts showed good stability due to the special synergistic effects of the CoPt alloy. Pt/CoPt/MWCNTs can be used as a promising catalyst for direct methanol fuel cells. In addition, this solution plasma sputtering-assisted synthesis method introduces a general and feasible route for the synthesis of binary alloys.

Strategic synthesis of platinum@ionic liquid/carbon cathodic electrocatalyst with high activity and methanol tolerance for the oxygen reduction reaction

Improving the electrocatalytic activity and methanol tolerance of cathodic Pt electrocatalyst for the oxygen reduction reaction (ORR) is very important for accelerating commercial viability of direct methanol fuel cells. In this work, the highly dispersed Vulcan XC-72 carbon supported 1-butyl-3-methylimidazolium chloride (BmimCl) ionic liquid modified Pt nanoparticles (Pt@BmimCl/XC-72) composites are synthesized successfully by simple NaBH4 reduction method in the presence of BmimCl ionic liquid. In the method, the interaction between BmimCl ionic liquid and K2PtCl4 results in the generation of ultrafine BmimCl-PtII complex precipitate, which is responsible for the well dispersion and small particle size of final Pt@BmimCl/XC-72 composites. During the synthesis, the Pt nanoparticles are modified by BmimCl simultaneously due to the strong N-heterocycle-Pt interaction. The as-prepared Pt@BmimCl/XC-72 composites exhibit significantly improved activity and selectivity for the ORR in the presence of methanol in acidic media compared to Pt/XC-72 composites prepared by general NaBH4 reduction method.

Biochar from pyrolysis of cellulose: An alternative catalyst support for the electro-oxidation of methanol

In the present study, the biochar produced by fast pyrolysis at 350 °C of untreated and acid-treated cellulose are evaluated as supports of CuRu@Pt core-shell nanoparticles (2.9–3.5 nm) for the electro-oxidation of methanol in acid media. Carbon materials and the supported core-shell nanoparticles were characterized by physicochemical and electrochemical techniques. Cyclic voltammetry and chronoamperometry were used to study the activity of the catalysts. The nanocatalyst supported onto the biochar from acid-treated cellulose exhibited high electroactive surface area (38 m2/g) and high performance in the methanol electro-oxidation reaction, reaching TON values of 0.151 molec. (sites s)−1 at 0.5 V. This contribution provides a new approach for the utilization of an inexpensive carbon material precursor as cellulose to design alternative catalytic systems and their emerging applications in electrocatalysis.

Carbon-supported Pt-free catalysts with high specificity and activity toward the oxygen reduction reaction in acidic medium

Specific carbon-supported Pt-free catalysts (Pd, PdFe, PdIr and PdFeIr) toward the oxygen reduction reaction (ORR) were developed. With this end, materials with high and low activity toward the ORR and the methanol oxidation reaction (MOR) were synthesized by the borohydride method (BM). Physicochemical characterization was carried out by several x-ray techniques, such as x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD) and x-ray dispersive energy (EDX). The ORR was studied at these materials in absence and presence of methanol in acidic medium in a half-cell configuration by the rotating disk electrode (RDE) technique. Additionally, the performance of the catalysts was evaluated as cathode material in a direct methanol fuel cell (DMFC) station. Main results indicate enhanced catalysis toward the ORR and improved tolerance toward the methanol by Fe and Ir insertion into the material, respectively. Membrane electrode assembly (MEA) with a cathode containing PdFeIr/C catalyst yields elevated performance in DMFC, while the electrode cost is dramatically reduced.

Evaluation of Activity of Platinum-Ruthenium-Cobalt/Graphene Catalysts towards Methanol Oxidation

In this study a series of PtRuCo/GR with the different molar ratios were prepared by microwave-assisted heating of the reaction mixture consisting of H2PtCl6, RuCl3, CoCl2 and ethylene glycol. The Transmission Electron Microscopy and Inductively Coupled Plasma Optical Emission Spectroscopy were employed to characterize the synthesized PtRuCo/GR catalysts. The electrocatalytic activity of the synthesized catalysts towards the oxidation of methanol was investigated by means of cyclic voltammetry and chronoamperometry. It was found that the PtRuCo/GR catalysts with the Pt:Ru:Co molar ratios equal to 1:2:2, 1:1.7:5.6 and 3.5:1:23 were prepared. The PtRuCo/GR catalyst with the Pt:Ru:Co molar ratio equal to 3.5:1:23 has a higher electrocatalytic activity towards the oxidation of methanol in acidic medium as compared with that of other synthesized catalysts.

Influence of Structural Effects on Platinum Electrodes in the Preferential Adsorption of CO and Methanol in Acid Media

Methanol has been the subject of many studies in the last decade within the possible fuels for the fuel cell technology. As known the methanol electro-oxidation pathway on platinum follows by formation of formic acid, carbon monoxide and finally carbon dioxide and water. In this work it is shown the influence of structural effect on platinum electrodes for the electro-oxidation of CO and methanol. Moreover, it is shown the effect of the CO adsorption on platinum on methanol electro-oxidation. Methanol electro-oxidation follows a different sequence of the potential dependence depending on surface orientation. The highest potential for CO electro-oxidation was observed on Pt(111) followed by Pt(100), and Pt(110). There are two groups of platinum surfaces for methanol electro-oxidation: self-cleaning, and self-poisoning. Self-cleaning reduce the potential of the COads electro-oxidation whereas self-poisoning increase the potential of the COads electro-oxidation.

Synthesis, Characterization and Properties of the Graphene Supported Pt-Co Nanocatalysts Towards the Electro-Oxidation of Methanol

Among the different types of fuel cell technologies, direct methanol fuel cells (DMFCs) are the most suitable for mobile and portable electronic applications. The development of cost-effective, active, and stable catalysts, able to substitute Pt or allow reducing the amount of it in low temperature fuel cell anodes is still in progress. In our previous works [1, 2] it has been shown that the graphene supported platinum-cobalt catalysts prepared by means of microwave synthesis enhance electrocatalytic activity towards the oxidation of borohydride and ethanol in an alkaline medium and are promising anode materials for direct borohydride fuel cells (DBFCs) and ethanol fuel cells (DEFCs). In this study investigation of activity of the graphene supported platinum-cobalt catalysts with the different Pt:Co molar ratios, fabricated by the rapid microwave heating method, towards the electro-oxidation of methanol in an acidic medium is presented. The Pt-Co/GR catalysts with the Pt:Co molar ratios equal to 1:3, 1:6, 1:20, 1:50 and 1:60 were prepared by microwave-assisted heating of required amounts of Pt(IV), Co(II) and ethylene glycol at a temperature 170 oC for 30 min. For comparison, the graphene supported Pt catalyst was also prepared at 170 oC for 30 s. The Pt loading in the synthesized catalysts was near 0.1 mg Pt cm-2. The electrochemically active surface areas of Pt in the synthesized Pt/GR and Pt-Co/GR catalysts were determined from the cyclic voltammograms of the mentioned catalysts recorded in a deaerated 0.5 M H2SO4 solution at a sweep rate 50 mV s-1 by calculating the charge associated with hydrogen adsorption (220 µCcm-2) and are 0.7 cm2 for Pt/GR and 5.2, 2.9, 1.6, 1.0 and 0.5 cm2for the Pt-Co/GR catalysts with the Pt:Co molar ratios equal to 1:3, 1:6, 1:20, 1:50 and 1:60, respectively. Values of the electrochemically active surface areas of the investigated Pt-Co/GR catalysts are 1.4-7.5 times higher than those of the Pt/GR catalyst. Electrochemical properties of Pt-Co/GR were investigated towards the electro-oxidation of methanol in acidic medium by means of cyclic voltammetry and chronoamperometry and compared with those of the bare graphene supported Pt catalyst. It has been determined that the Pt-Co/GR catalysts with the Pt:Co molar ratios equal to 1:3, 1:6, 1:20 exhibit an enhanced electrocatalytic performance for methanol electro-oxidation as compared with that of bare graphene supported platinum catalyst. Methanol oxidation current density values are ca. 2.1-3.2 times higher at the Pt-Co/GR catalysts with the above mention Pt:Co molar ratios than those at the Pt/GR catalyst. Highest electrocatalytic activity towards the electro-oxidation of methanol in acidic medium shows the graphene supported Pt-Co catalyst with the Pt:Co molar ratios equal to 1:3 and 1:6 as compared with that of catalysts with higher Pt:Co molar ratios and Pt/GR. These results obtained show that the Pt-Co/GR catalysts with the different Pt:Co molar ratios could have promising future as catalysts for DMFC.

Evaluation of Activity of Platinum-Ruthenium-Cobalt/Graphene Catalysts Towards Methanol Oxidation

A simple approach – microwave synthesis was used to prepare platinum-ruthenium-cobalt/graphene catalysts (denoted as Pt-Ru-Co/GR). A series of Pt-Ru-Co/GR with the different molar ratios were prepared by microwave-assisted heating of the reaction mixture consisting of H2PtCl6, RuCl3, CoCl2 and ethylene glycol. The Transmission Electron Microscopy (TEM) and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) were employed to characterize the synthesized Pt-Ru-Co/GR catalysts. The electrocatalytic activity of the synthesized catalysts towards the oxidation of methanol and CO was investigated by means of cyclic voltammetry and chrono-techniques. The electrochemically active surface areas of the prepared catalysts were determined from the cyclic voltammograms of the Pt-Ru-Co/GR catalysts recorded in a deaerated 0.5 M H2SO4 solution at a sweep rate of 50 mV s–1 by calculating the charge associated with hydrogen adsorption (220 µC cm-2). It was found that the Pt-Ru-Co/GR catalysts with the Pt:Ru:Co molar ratios equal to 1:2:2, 1:1.7:5.6 and 3.5:1:23 were prepared. The EDX analysis confirm the presence of Pt, Ru and Co nanoparticles in the investigated PtCoRu/GR catalysts. It has been determined that the Pt-Ru-Co/GR catalyst with the Pt:Ru:Co molar ratio equal to 3.5:1:23 has a higher electrocatalytic activity towards the oxidation of methanol in acidic medium as compared with that of other synthesized catalysts.

Influence of Structural Effects on Platinum Electrodes in the Preferential Adsorption of CO and Methanol in Acid Media

The complete methanol electro-oxidation on platinum single crystal electrodes produces CO2, H2O and 6 e- in acidic medium. However methanol adsorption is sensitive to the platinum surface orientation, showing different reactivity for different platinum crystallographic planes. In this work, it was studied the preferential adsorption and oxidation of carbon monoxide (CO) and methanol in acid media on polycrystalline and low index planes of platinum single crystals. In the experimental procedure carbon monoxide was bubbled in methanol solution with the platinum electrode polarized at 0.1 V vs. RHE. Then, the potential was scanned from 0.1 to 0.8 or 1.0 V vs ERH depending on platinum single crystal electrode. From Figure 1a the carbon monoxide oxidation occurs at potential above 0.6 V vs. RHE for all platinum surfaces. Besides data from Figure 1b methanol oxidation on Pt(111), Pt(100) and polycrystalline platinum electrodes exhibited high potential, above 0.8 V (RHE). After adsorption of carbon monoxide on platinum electrodes, on polycrystalline platinum and Pt(100) the peak maximum occurred at more positive potential compared with methanol reaction. In this case methanol oxidation only was promoted after carbon monoxide oxidation reaction. On Pt(100) and Pt(111) the adsorption of CO contributed to reduce the potential for methanol oxidation. Thus, these experiments suggest that carbon monoxide competes with methanol for adsorption on platinum electrode. For polycrystalline Pt and Pt(110) single crystals, the mixture CO+CH3OH showed potential of oxidation larger than with pure reactants. On the other hand, on Pt (111) and Pt(100) the oxidation of methanol happens at potential above that for the mixture of methanol and carbon monoxide, so that, it is possible that the electrochemical reaction follows different pathways on these surfaces. Figure 1. (a) first potential scan at platinum electrodes in 0.2 M CH3OH + 0.1M H2SO4, obtained at 10 mV s-1. Insert show CO peak between 0.2 – 0.4 V (RHE). (b) Potential peak maximum dependence for CO, CH3OH and CO + CH3OH oxidation. Acknowledgedment:CNPq for financial support (process 150885/2012-1).