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Pt-based cathodes in direct methanol fuel cells are promising materials for a wide range of applications. However, such materials suffer significant performance loss due to severe methanol crossover from anode to cathode, resulting in mixed potentials from methanol oxidation and oxygen reduction reaction. Herein, we proposed some facile synthesis procedures to avoid Pt active sites contamination from methanol. The strategy was to associate controlled ultrasmall Pt nanoparticles (NPs), Vulcan XC-72, and MnOx species prepared from Mn(NO3)2.4H2O. Interestingly, we have observed that depending on the synthetic pathway chosen, the methanol-tolerance ability of the material increased, suggesting different interactions among the components of the catalyst. The results indicated an improved selectivity of the system due to a synergy between Pt and MnOx. The best strategy was the immobilization of ultrasmall Pt NPs (~2 nm) on carbon black, before impregnation and thermal decomposition of MnOx, which almost wholly suppressed the methanol oxidation interference on the system. Also, the optimized cathode presented a comparable performance for ORR to the traditional Pt/C without methanol addition. To further rationalize such findings, physical and electrochemical characterizations were successfully performed, which allowed us to better understand the proposed catalysts and their different methanol-tolerance abilities.

Three carbon ceramic materials with different porosities were prepared by the sol–gel method, using HNO3, HF, and HNO3/HF as catalysts and the surface areas (SBET) of the products were determined as 246, 201, and 356 m2 g−1, respectively. The materials were characterized using N2 sorption isotherms, scanning electron microscopy, and conductivity measurements. The matrices were used as supports for the in situ immobilization of Ni(II) phthalocyanine (NiPc) on their surfaces. XPS was used to determine the Ni/Si atomic ratios of the NiPc-modified materials. Pressed disk electrodes were prepared with the NiPc-modified matrices, and tested as sensors for dopamine. The electrode prepared using nitric acid showed excellent catalytic activity for the simultaneous determination of ascorbic acid (AA) and dopamine (DA), with sensitivities of 53.02 and 104.17 μA mmol dm−3, respectively. Good repeatability was achieved, with R.S.D. values of 3.67% (AA) and 3.53% (DA), as well as high stability.

This work reports the electrocatalytic activity of 2,3,5,6-tetrachloro-1,4-benzoquinone (TCBQ)/multi-walled carbon nanotubes (MWCNT) immobilized on an edge plane pyrolytic graphite electrode for nicotinamide adenine dinucleotide (NADH) oxidation. Scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS) were used to confirms the presence of chloro after the nanotube modification with 2,3,5,6-tetrachloro-1,4-benzoquinone. The surface charge transfer constant, ks, and the charge transfer coefficient for the modified electrode, α, were estimated as 98.5 (±0.6) s−1 and 0.5, respectively. With this modified electrode the oxidation potential of the NADH was shifted about 300 mV toward a less positive value, presenting a peak current much higher than those measured on an unmodified edge plane pyrolytic graphite electrode (EPPG). Cyclic voltammetry and rotating disk electrode (RDE) experiments indicated that the NADH oxidation reaction involves 2 electrons and a heterogenous rate constant (kobs) of 3.1 × 105 mol−1 l s−1. The detection limit, repeatability, long-term stability, time of response and linear response range were also investigated.

The use of tris (2,2?-bipyridil) copper (II) chloride complex, [Cu(bipy)3]Cl2/6H2O, as a biomimetic catalyst, is reported in the construction of an amperometric sensor for dopamine. The sensor was prepared modifying a glassy carbon electrode with a Nafion † membrane doped with the complex. The optimized conditions for the sensor response were obtained in 0.25 mol dm � 3 Pipes buffer (pH 7.0) containing 150 mmol dm � 3 H2O2, with an applied potential of � /50 mV versus saturated calomel electrode (SCE). In these conditions, a linear response range between 9 and 230 mmol dm � 3 , with a sensitivity of 1.439 /0.01 nA dm 3 mmol � 1 cm � 2 and a detection limit of 4.8 mmol dm � 3 were observed for dopamine. The response time for this sensor was about 1 s, presenting the same response for at least 150 successive measurements, with a good repeatability (4.8%) expressed as relative standard deviation for n � /13. After its construction, this sensor can be used after 180 days without loss of sensitivity, kept at room temperature. The difference of the sensor response between four preparations was 4.2%. A detailed investigation about the sensor response for other eighteen phenolic compounds and five interfering species was performed. The sensor was applied for dopamine determination in pharmaceutical preparation with success. # 2002 Elsevier Science Ltd. All rights reserved.

A chemically modified electrode constructed by mixing nickel tetrasulfonated phthalocyanine (NiTsPc) immobilized on modified silica gel with carbon paste showed a redox process with a midpoint potential of 0.44 V vs sce . Experiments carried out with different supporting electrolytes suggested an effect due to the nature of the anion. The solution pH does not affect the midpoint potential but the peak current increases when the pH is decreased. The immobilization procedure causes an increase in the monomeric form of the complex. The electrochemical property of NiTsPc adsorbed onto modified silica showed good stability even in acidic media (pH=2) and the ability to catalyze the electro-oxidation of cysteine at 0.5 V vs sce .

This work describes the study of underpotential deposition (upd) of Pb on polycrystalline platinum in 0.2M HClO4 solutions using cyclic voltammetry and rotating ring-disk electrode techniques. In such conditions, a full monolayer of upd Pb corresponds to a coverage of 0.41. The adsorption of lead inhibits the adsorption of hydrogen in a non-selective way. This behaviour was explained through the comparison between the radius of the ad-atom and the substrate. It was calculated that each Pb ad-atom occupies two sites in the surface. Additionally it is shown that the presence of upd Pb significantly inhibits the oxygen reduction reaction. This effect associated to the formation of H2O2 as the final product, instead of H2O.

The electropolymerization process of pyrrole in aqueous acid medium at a gold polycrystalline electrode was followed in situ by uv—visible differential reflectance spectroscopy (UVDRS). This allows us to observe the early stages of polymerization and to monitor the film growth as a function of the number of potential cycles, or of the time of polarization at a fixed potential. The redox properties of the films were also investigated, and the uv—visible absorption bands were assigned according to the results of the literature. The effect of the incorporation of iron tetrasulfonated phthalocyanine into the polypyrrole films was also observed by UVDRS as a function of time, potential and number of cycles.

The underpotential deposition (UPD) of Cu on Pt was studied in acid media using cyclic voltammetry and rotating ring-disk electrode techniques. Experimental data at sub-monolayer levels demonstrate that ad-atom formation occurs in different energy states and no rearrangements take place in the ad-layer. Rotating ring-disk studies of the oxygen reduction reaction on Cu UPD show a strong inhibition of the reaction only in the region of diffusion control. At first, the 4 e reaction to H 2 O is inhibited in favor of the 2 e reaction to H 2 O 2 but at more negative potentials even the formation of H 2 O 2 is inhibited. A mechanism based on the degree of surface-active sites blocked by Cu ad-atoms is proposed.

A number of cobalt and iron porphyrins heat treated at temperatures as low as 400°C exhibit substantial electrocatalytic activity for O 2 reduction and reasonable stability in alkaline electrolytes. The effects of this heat treatment on the structure and overall properties of these materials, however, are not well understood. Differential thermogravimetry analyses have shown that in the case of the Co and Fe-μ-oxo forms of tetra methoxyphenyl porphyrin (TMPP) and the metal-free form as well, the onset for partial decomposition occurs at temperatures of about 400–500°C for the macrocycles either as crystals or dispersed on high area Vulcan XC-72. The results obtained with several pyrolysis—mass spectrometric techniques have indicated that the fraction of volatile nitrogen to non-nitrogen containing species generated during the heat treatment is much higher for the metal-free than for the iron-μ-oxo or CoTMPP. Microanalysis also confirms that with the Fe-μ-oxo and CoTMPP part of the nitrogen is retained. Possible models for the nature of the active sites are discussed.