Supported Pt and Pt–Ru catalysts prepared by potentiostatic electrodeposition for methanol electrooxidation

Methanol electrooxidation was investigated on Pt–Ru electrocatalysts supported on glassy carbon. The catalysts were prepared by electrodeposition from solutions containing chloroplatinic acid and ruthenium chloride. Bulk composition analysis of the Pt–Ru catalyst was performed using an X-ray detector for energy dispersive spectroscopy analysis (EDX). Three different compositions were analyzed in the range 0–20 at.% Ru content. Tafel plots for the oxidation of methanol in solutions containing 0.1–2 M CH₃OH, and in the temperature range 23–50 °C showed a reasonably well-defined linear region. The slope of the Tafel plots was found to depend on the ruthenium composition. The lower slope was determined for the Pt catalyst, varying between 100 and 120 mV dec⁻¹. The values calculated for the alloys were higher, ranging from 120 to 140 mV dec⁻¹. The reaction order for methanol varies from 0.5 to 0.8, increasing with the ruthenium content. The activation energy calculated from Arrhenius plots was found to change with the catalyst composition, showing a lower value around 30 kJ mol⁻¹ for the alloys, and a higher value, of 58.8 kJ mol⁻¹, for platinum. The effect of ruthenium content is explained by the bifunctional reaction mechanism.     

Promotional effect of Ni–Co/ordered mesoporous carbon as non-noble hybrid electrocatalyst for methanol electro-oxidation

Journal of Applied Electrochemistry - The development of a ternary hybrid catalytic system, inclusive of Ni species/Co species/ordered mesoporous carbon (catalyst/co-catalyst/support) and its...     

Mesoporous Pt–Ni catalyst and their electro catalytic activity towards methanol oxidation

Mesoporous Pt/Ni architecture has been prepared by template assisted electrochemical deposition of Pt–Ni over anodized aluminum oxide template followed by controlled de-alloying with nitric acid. Surface characteristics of the ordered bimetallic mesoporous Pt/Ni structure were systematically characterized through XRD, SEM, AFM and XPS analyses. It is designated by XPS analysis that presence of Ni significantly modifies surface characteristics and electronic states of Pt accompanied with a downshift in the d-band character of Pt. Mesoporous morphology is highly beneficial to offer readily accessible Pt catalytic sites for methanol oxidation reaction. The prepared bimetallic Pt/Ni was used as electro catalyst for DMFC. Comparison of electrocatalytic activity of bimetallic mesoporous Pt/Ni with bimetallic smooth Pt/Ni was interrogated using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy analyses. Distinctly enhanced electrocatalytic activity with improved CO tolerance associated with bimetallic mesoporous Pt/Ni electrode towards methanol oxidation stems from a synergy existing between mesoporous structure with bi-metallic composition.     

Pt/Co和Pt/Ni双金属纳米溶胶制备及催化制氢

采用化学共还原法制备聚乙烯吡咯烷酮(PVP)稳定的Pt/Co和Pt/Ni双金属纳米溶胶,采用UV-Vis、TEM等对所合成的Pt/Co和Pt/Ni双金属纳米溶胶进行表征,研究了化学组成对双金属纳米溶胶催化剂催化NaBH4水解制氢的影响. 结果表明,所制双金属纳米溶胶的平均粒径约为2.0 nm,双金属纳米溶胶的催化能力高于单金属Pt, Co, Ni纳米溶胶,Pt/Co和Pt/Ni双金属纳米颗粒优异的催化性能可归因于电荷转移效应,Co或者Ni原子与Pt原子之间发生的电荷转移效应使得Pt原子带负电而Co或者Ni原子带正电,荷电的Pt和Co、Ni原子成为催化反应的活性中心,促进了催化反应的进行.     

Porous Pt/γ-Al2O3 catalytic membrane reactors prepared using mesitylene solvated Pt atoms

The opportunity of using mesitylene solvated Pt atoms for the deposition of Pt catalyst on inorganic membranes is shown. The catalytic activity of the membrane reactor has been tested using the hydrogenation of benzene as model reaction. The performance of the membrane reactor has been compared with that of a conventional packed bed using -Al₂O₃ powder impregnated with Pt. The effect of the feeding configuration has been investigated, and the results show a membrane effect due to the different degrees of accessibility of pores of different size. For alumina powder we have obtained an activation energy of 12.9 kcal/mol, which well agrees with the data reported in literature. The membrane reactor, instead, exhibited an activation energy ca. 60% lower. The preliminary porometry results have shown a slight effect of the platinum deposition process on membrane permeability.     

Preparation, characterization, and application of alkaline leached Ni/Zn–Ni binary coatings for electro-oxidation of methanol in alkaline solution

The Ni–Zn binary coating was electrochemically deposited on a copper electrode. Then, it was etched in a concentrated alkaline solution (30 wt% NaOH) to obtain a porous electrocatalytic surface suitable for methanol electro-oxidation in alkaline solution. The surface compositions of coatings before and after alkaline leaching were determined by atomic absorption spectroscopy and energy dispersive X-ray analysis. The surface morphologies were investigated by scanning electron microscopy. It was found that the leached Ni–Zn coating has a porous structure. Electrocatalytic activity toward the methanol electro-oxidation was assessed by cyclic voltammetry and electrochemical impedance spectroscopy techniques. The activation of electrode related to the removal of existing corrosion products and formation of pores and cracks during alkaline leaching. Cyclic voltammetry studies confirmed that the alkaline leaching process improved the activity of Ni–Zn coating in comparison with smooth Ni deposit for the methanol electro-oxidation.     

Ni–Mo and Ni–W sulfide catalysts prepared by decomposition of binary thiometallates

Ni–Mo and Ni–W sulfide catalysts with atomic ratio R = 0.5 (Ni/(Ni + M), with M = Mo or W) prepared by decomposition of Ni-impregnated thiometallates were evaluated in the reaction of thiophene hydrodesulfurization. Catalysts derived from impregnated thiometallates (DTI samples) presented improved catalytic activity and higher synergistic effect than catalysts prepared by co-precipitation (HSP samples) despite the fact that co-precipitated catalysts showed larger surface area. Structure characterization by high-resolution electron microscopy (HREM) and X-ray diffraction (XRD) revealed different crystalline phases in DTI and HSP catalysts. A mixture of phases (MS₂, NiS_1.03 and MO₂) was observed in catalysts obtained by co-precipitation. Only the poorly crystalline MS₂ phase was observed in DTI catalysts suggesting that the Ni promoter is very well dispersed on the chalcogenide structure.     

Pt–NiO/C anode electrocatalysts for direct methanol fuel cells

Pt catalyst was supported on Vulcan XC-72R containing 5 wt.% NiO using NaBH₄ as a reducing agent. The prepared catalyst was heat-treated at 400 °C. XRD, TEM and EDX analyses were applied to characterize Pt–NiO/C electrocatalyst. The introduction of NiO reduces the particle size of Pt crystallites. The electrocatalytic activity of Pt–NiO/C electrocatalysts was examined towards methanol oxidation reaction in 0.5 M H₂SO₄ solution using cyclic voltammetry and chronoamperometry techniques. A three fold increment in the oxidation current density was gained at Pt–NiO/C electrocatalyst compared to Pt/C one. The corresponding chronoamperograms showed high steady state current density values suggesting better stability of Pt–NiO/C electrocatalyst towards the carbonaceous poisoning species. The enhanced electrocatalytic performance and the long-term cycle durability of Pt–NiO/C electrocatalyst are attributed to the strong interaction between Pt and NiO and the formation of small Pt crystals.     

Stability of Pt–Co/C and Pt–Pd/C based oxygen reduction reaction electrocatalysts prepared at a low temperature by a combined impregnation and seeding process in PEM fuel cells

The stability of Pt–Co/C and Pt–Pd/C electrocatalysts relative to that of a commercial Pt/C catalyst was measured in terms of the loss of the electrochemical surface area (ESA). The electrocatalytic activity was investigated in an acidic solution (0.3 M H₂SO₄) and in a single PEM fuel cell under H₂/O₂ conditions. In the acidic solution, the ESA of the catalyst decreased as the number of repeated potential cycles increased, which is likely to be due to dissolution of the different metals contained within the catalyst structure. In the fuel cell environment, the deterioration of the cell performance increased as the number of repeated potential cycles increased. Thus, the loss of cell performance may be related to the loss of the ESA. In addition, the loss of the catalyst’s ESA affected the cell performance at low-, medium-, and high- current densities, indicating a loss of either the activation potential or an ohmic loss. Among the three electrocatalysts evaluated, the Pt–Co/C based one exhibited the highest electrocatalytic activity in both the acidic solution and in the fuel cell environment.     

Sintering behavior of Ni–Zn ferrite powders prepared by molten-salt synthesis

Ni_0.5Zn_0.5Fe₂O₄ powders were prepared by a novel molten-salt synthesis method. The effects of calcination processes of the powders on their sintering behaviors were investigated. Compared with the synthesis by traditional solid-state reaction, the proposed molten-salt method can significantly reduce the synthesis temperature of Ni_0.5Zn_0.5Fe₂O₄ from 800 to 550°C below, and the prepared powders have relatively high sintering activity at low temperature, which can thus decrease the sintering temperature. However, the abnormal growth of grains is easy to occur during sintering, thus resulting in uneven grain size. In particular, during the molten-salt synthesis, the holding time for calcination is a dominant factor affecting the activity and crystallization degree of the resultant powders. From the point of view of increasing the density of sintered bodies, the optimal conditions for synthesizing Ni_0.5Zn_0.5Fe₂O₄ powder by the proposed molten-salt synthesis is 400°C for 6 h. In addition, the saturate magnetization of the finally obtained ferrite ceramics has nothing to do with the preparation processes, while their coercivity depends on their densification and grain size caused by their different processing routes.     

Electrochemical characterization of Ni–P and Ni–Co–P amorphous alloy deposits obtained by electrodeposition

Ni–P and Ni–Co–P amorphous alloy deposits were obtained by electrodeposition at 80 °C on carbon steel substrates. The influence of the electrolyte Co²⁺ concentration and of applied current density was investigated. The corrosion behaviour of amorphous and crystalline deposits was evaluated by polarization curves and electrochemical impedance spectroscopy in NaCl 0.1 M solution at room temperature. Impedances were measured for samples under total immersion (free potential against time) and for polarized samples in predefined regions of the polarization curves. It was found that the alloy deposit composition is highly affected by the composition of the electrolyte but displays no significant dependence on applied current density. The results showed that the presence of Co on Ni–P amorphous alloys improves the deposit performance in the studied corrosive medium. It was also verified that the amorphous structure provides higher corrosion resistance to both Ni–P and Ni–Co–P alloys.     

Photocatalytic degradation of methanol on titania and titania–silica aerogels prepared by non-alkoxide sol–gel route

Titania and titania–silica aerogels were prepared by alkoxide or non-alkoxide sol–gel route and subsequent supercritical drying with carbon dioxide at low temperature. The resulting aerogels having high surface area and mesoporosity were used as photocatalysts for gas phase methanol degradation reaction. Photocatalytic degradation reactions were carried out on titania and titania–silica aerogels, and commercial Degussa P-25 titania. The photocatalytic activities of titania and titania–silica aerogels were higher than that of the P-25. While the conversion of methanol degradation over the P-25 catalyst was only 50–60%, that for the titania aerogel was observed to be above 98% due to the higher specific surface area and the well developed mesoporous structure. In spite of lower titania contents, much higher surface area and high dispersion of titania of titania–silica aerogel gave rise to the high photocatalytic activity in comparison to those of titania aerogels. Moreover, titania–silica aerogel was also used for the photodegradation and adsorption hybrid system. It was observed that the high removal efficiency for methanol was caused by the combination of higher catalytic activity and adsorption capacity.     

Catalytic oxidation of gas-phase mercury over Co/TiO2 catalysts prepared by sol–gel method

Co/TiO₂ catalysts prepared by sol–gel method were studied for gas-phase mercury oxidation in this paper. Experimental results revealed that the optimal loading of Co was 7.5%, which yielded more than 90% oxidation efficiency within the temperature range of 120–330 °C. The high activity was mainly attributed to the enrichment of well dispersed Co₃O₄. We also found that oxygen performed a key role in mercury oxidation process, while HCl could corrode the oxidized mercury and release it to gas phase. Thereafter, a modified Mars–Maessen mechanism was proposed and the possible simultaneous oxidization of NO and mercury was studied.     

Photocatalytic hydrogen production from methanol aqueous solution under visible-light using Cu/S–TiO2 prepared by electroless plating method

Cu was loaded on the S-doped TiO₂ by electroless plating method. The prepared Cu/S–TiO₂ exhibited high photocatalytic activity for hydrogen generation, and the yield is up to 7.5 mmol h^− 1 g^− 1cat in methanol solution. Their physical structure and chemical properties were characterized by UV–Vis, XRD, XPS and EXAFS. The copper species were CuO and Cu₂O, and the sample showed excellent visible light absorption ability. Comparing with the sample prepared by chemical reducing method, the electroless plated copper on S–TiO₂ was highly dispersed, which could facilitate photo-generated charges capture, transfer and separation.     

Electrodics of methanol oxidation on Pt-f-multiwalled carbon nanotube composite, prepared by γ-radiolysis

We report the electrodics of methanol oxidation on Pt-multiwalled carbon nanotube composites (Pt-f-MWCNTs), prepared by γ-radiolysis of K₂PtCl₆ in the presence of HOOC-functionalized multiwalled carbon nanotubes. The electrocatalytic activity for the methanol oxidation was studied using cyclic and linear sweep voltammetric techniques on the stationary indium tin oxide and rotating gold disc electrodes, respectively. Higher values of oxidative (anodic) current were obtained using Pt-f-MWCNTs compared to the polycrystalline Pt electrode. This phenomenon is attributed to the synergistic effect of oxy groups on MWCNTs, which alleviate CO poisoning. The electrodics of the reaction at various temperatures was studied using linear sweep voltammetry (LSV) on a rotating disc gold electrode, modified with the composite. From the Koutecky-Levich plots, the standard rate constant (k⁰) was determined to be 7.9 ± 1.9 × 10⁻⁸ cm s⁻¹.     

Hydrodeoxygenation of p-cresol on unsupported Ni–P catalysts prepared by thermal decomposition method

Unsupported Ni–P catalysts were prepared from the mixed precursor of NiCl₂ and NaH₂PO₂ by thermal decomposition method, and their catalytic activities were measured using the hydrodeoxygenation (HDO) of p-cresol as probe. The effects of the H₂PO₂⁻/Ni^2 + molar ratio in the precursor and the thermal decomposition temperature on the catalyst purity, crystallite size and HDO activity were studied. The HDO of p-cresol on these Ni–P catalysts proceeded with two parallel pathways yielding methylbenzene and methylcyclohexane as final products. The higher HDO catalytic activity of the catalyst was attributed to its bigger crystallite size and purer phase of Ni₂P.