钛基金属氧化物涂层电极的研究进展

钛基金属氧化物涂层电极又称DSA,是一种新型不溶性阳极电极。综述了钛基金属氧化物涂层电极的研究进展,包括钛基钌系涂层电极、钛基铱系涂层电极、钛基二氧化锰电极和钛基二氧化铅电极。介绍了不同钛基涂层电极材料的制备方法、性能特点和应用情况,并对其今后的发展方向作了展望。     

Performance of quaternized poly(vinyl alcohol)-based electrolyte membrane in passive alkaline DEFCs application: RSM optimization approach

Direct ethanol fuel cells (DEFCs) have emerged as potential tools for producing sustainable energy for portable devices due to their high energy density and their safe and nontoxic fuel source. However, the main problem of DEFCs is the sluggish oxidation of ethanol and fuel crossover from the anode side to the cathode side. Nafion membranes are commonly used as the electrolyte membrane in DEFCs, but they have a high production cost and high ethanol permeability. Thus, this work studies the performance of an alternative electrolyte membrane that is based on a quaternized poly(vinyl alcohol) (QPVA) polymer in passive alkaline DEFCs. The composition of the QPVA-based membranes was optimized with potassium hydroxide (KOH) as an ion charge carrier and by the inorganic filler graphene oxide (GO). The membrane properties were influenced by KOH and GO. The effect of these two parameters on the performance of the QPVA-based membranes was investigated for its ion-exchange capacity and ionic conductivity and selectivity using the response surface methodology to optimize the membrane composition. The QPVA-based membranes were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and field emission scanning electron microscope. The membrane properties were influenced by KOH concentration doping and GO filler loading, which affect the membrane selectivity and, consequently, the overall performance of the passive alkaline DEFCs. Finally, the maximum power density of the passive DEFCs was improved from 5.8 to 11.3 W cm⁻² at 30 °C, 13.7 mW cm⁻² at 60 °C, and 19.3 mW cm⁻² at 90 °C, respectively, in ambient air. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47526.     

Co-PVP的制备及其对乙醇在碱性介质中的电催化性能

以乙二醇为溶剂,聚乙烯吡咯烷酮K-30（PVP）为络合保护剂,采用液相还原法制备纳米复合催化材料Co-PVP,以Co-PVP材料制备了Co-PVP-C电极（Co含量为3%）,采用循环伏安法、计时电流法、交流阻抗等研究了其对乙醇在碱性介质中电化学氧化的催化性能和催化机理。结果表明,产物为单质Co与PVP的复合颗粒材料,平均粒径约12 nm,呈球形,分散性好。以1.0 mol/L C2H5OH＋1.0 mol/L KOH为电解液,0.22 V电位下电流密度达到22 mA/cm2。当金属离子初始浓度为20 mmol/L,反应温度为0℃时,制备的Co-PVP材料对乙醇的电化学氧化具有较好的催化活性。     

Effect of support on the apparent activity of palladium oxide in catalytic methane combustion

The support effect on the low temperature catalytic oxidation of methane over palladium catalysts was studied by comparing a series of metal oxides as the support. Samples of 0.010 g/g Pd catalysts supported on different grades and/or phases of TiO₂, Al₂O₃, and ZrO₂ were prepared via incipient impregnation and their catalytic activity was evaluated using a laboratory plug-flow reactor. The specific surface area of the supports determined by nitrogen adsorption varied from about 13-220 m²/g. Initial experiments conducted with titania (anatase) as a support showed a low apparent activity and a poor thermal stability. Focusing on anatase, we have successfully improved its thermal stability by additions of Al₂O₃ or by doping with CeO₂, or La₂O₃. However, contrary to expectations based on some information in the literature, we have found that the activity decreased in the sequence of Al₂O₃ > ZrO₂ > TiO₂, and was not a direct function of specific surface area. This was especially evident in the case of titania. The surface structure of the support and the nature of its interaction with the active component PdO seem to play a far more important role in activity than the apparent specific surface area. Moreover, anatase-supported catalysts present a very rapid deactivation, whereas rutile-supported catalysts are relatively stable. The observed phenomena could potentially be related to the interaction between support and the active phase of palladium. Several models have been proposed to describe the strong metal-support interaction, but either charge transfer or encapsulation seems to be the most probable.     

Electrochemical oxidation of ethylene glycol on Pt-based catalysts in alkaline solutions and quantitative analysis of intermediate products

Electrocatalytic activities of Pt/C, Pt-Ru/C, and Pt-Ni/C for the oxidation of ethylene glycol in a basic solution are evaluated by cyclic voltammetry and quasi-steady state polarization. Based on the results of Tafel slopes from quasi-steady state polarization, the catalytic activities for ethylene glycol oxidation are in the order of Pt-Ru/C > Pt-Ni/C > Pt/C. The analysis of intermediate products for ethylene glycol oxidation by higher performance liquid chromatograph (HPLC) demonstrates that the degree of ethylene glycol oxidation is dependent on catalysts. Pt-Ru/C shows the highest current densities for ethylene glycol oxidation, but shows lower fuel utilization. On the other hand, Pt-Ni/C shows higher ability to cleavage C–C bonds, but is suffered from catalyst poisoning. To improve the tolerance for catalyst poisoning, we construct a novel Pt-Ni-SnO₂/C catalyst, compare its catalytic activities, and evaluate the intermediates. Pt-Ni-SnO₂/C shows superior catalytic activities for ethylene glycol oxidation, resulting in the highest degree of complete electro-oxidation of ethylene glycol to CO₂.     

Catalytic activity of dual catalysts system based on nano-manganese oxide and cobalt octacyanophthalocyanine toward four-electron reduction of oxygen in alkaline media

The electrocatalysis of the dual functional catalysts system composed of electrolytic nano-manganese oxide (nano-MnOx) and cobalt octacyanophthalocyanine (CoPcCN) toward 4-electron reduction of oxygen (O₂) in alkaline media was studied. Nano-MnOx electrodeposited on the CoPcCN monolayer-modified glassy carbon (GC) electrode was clarified as the nano-rods with ca. 10-20 nm diameter by scanning electron microscopy. The peak current for O₂ reduction at the dual catalysts-modified GC electrode increases largely and the peak potential shifts by ca. 160 mV to the positive direction in cyclic voltammograms compared with those obtained at the bare GC electrode. The Koutecký-Levich plots indicate that the O₂ reduction at the dual catalysts-modified GC electrode is an apparent 4-electron process. Collection efficiencies obtained at the dual catalysts-modified GC electrode are much lower than those at the GC electrode and are almost similar to those at the Pt nano-particles modified GC electrode. The obtained results demonstrate that the dual catalysts system possesses a bifuctional catalytic activity for redox-mediating 2-electron reduction of O₂ to HO₂⁻ by CoPcCN as well as catalyzing the disproportionation of HO₂⁻ to OH⁻ and O₂ by nano-MnOx, and enables an apparent 4-electron reduction of O₂ at a relatively low overpotential in alkaline media. In addition, it has been found that the cleaning of the dual catalysts-modified electrode by soaking in 0.1 M sulfuric acid solution enhances its catalytic activity toward the reduction of O₂.     

Electrochemical behaviour of metal hexacyanoferrate converted to metal hydroxide films immobilized on indium tin oxide electrodes—Catalytic ability towards alcohol oxidation in alkaline medium

In this work, we demonstrate a simple method to modify indium tin oxide (ITO) electrodes in order to perform electro-catalytic oxidation of alcohols in alkaline medium. Metal hexacyanoferrate (MHCF) films such as nickel hexacyanoferrate (NiHCF) and copper hexacyanoferrate (CuHCF) were successfully immobilized on ITO electrodes using an electrochemical method. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were employed to characterize the structural and morphological aspects of MHCF films. Cyclic voltammetry (CV) was used to study the redox properties and to determine the surface coverage of these films on ITO electrodes. Electrochemical potential cycling was carried out in alkaline medium in order to alter the chemical structure of these films and convert to their corresponding metal hydroxide films. SEM and XPS were performed to analyze the structure and morphology of metal hydroxide modified electrodes. Electro-catalytic oxidation ability of these films towards methanol and ethanol in alkaline medium was investigated using CV. From these studies we found that metal hydroxide modified electrodes show a better catalytic performance and good stability for methanol oxidation along with the alleviation of CO poisoning effect. We have obtained an anodic oxidation current density of ∼82 mA cm⁻² for methanol oxidation, which is at least 10 fold higher than that of any metal hydroxide modified electrodes reported till date. The onset potential for methanol oxidation is lowered by ∼200 mV compared to other chemically modified electrodes reported. A plausible mechanism was proposed for the alcohol oxidation based on the redox properties of these modified electrodes. The methodology adapted in this work does not contain costlier noble metals like platinum and ruthenium and is economically viable.     

Transformation of an alcohol in the presence of a ketone as a model reaction to characterize the acidity and the basicity of oxide catalysts

The reaction of cyclopentanol in the presence of cyclohexanone at 350°C over amorphous solids or zeolites led to alkenes and hydrogen transfer products. It was shown that these products were formed respectively on the acid sites and on the basic sites of the catalysts. Consequently, this reaction made it possible to estimate at the same time the acid and basic properties of the catalysts.     

Influences of zinc oxide and an organic additive on the electrochemical behavior of pure aluminum in an alkaline solution

The corrosion behavior of pure aluminum in inhibited and uninhibited 4 MKOH was investigated by means of hydrogen collection, polarization curve measurement and electrochemical impedance spectroscopy (EIS). The results showed that the corrosion of pure aluminum was greatly inhibited by the addition of ZnO and dimethyl amine epoxy propane (designated as DE). EIS and EDAX analyses revealed that ZnO produces its effect by depositing on the aluminum surface, which increases the overpotential of hydrogen evolution. It was also found that the addition of DE could greatly improve the deposition of zinc layers.     

Effect of supports on catalytic activity of chromium oxide-based catalysts in the dehydrogenation of propane with CO2

Dehydrogenation of propane in the presence and absence of CO₂ over CrO_x/SiO₂ and CrO_x/Al₂O₃ catalysts with Cr loading between 0.7–20.4 wt% was discussed. It was found that the nature of support strongly effects on the catalytic performance in the dehydrogenation with CO₂. Over the CrO_x/SiO₂ catalyst CO₂ enhance the propene yield, whereas over the CrO_x/Al₂O₃ catalyst the yield and selectivity of propene in the presence of CO₂ strongly decrease. The effect of steam on catalytic performance of the tested catalysts was also discussed.     

Competitiveness of CO2 capture from an industrial solid oxide fuel cell combined heat and power system in the early stage of market introduction

In this article, it was investigated whether potentially low-cost CO₂ capture from SOFC systems could enhance the penetration of SOFC in the energy market in a highly carbon-constrained society in the mid-term future (up to year 2025). The application of 5 MWe SOFC systems for industrial combined heat and power (CHP) generation was considered. For CO₂ capture, oxyfuel combustion of anode off-gas using commercially available technologies was selected. Gas turbine (GT-) CHP plant was considered to be the reference case.Technical results showed that despite the energy penalties due to CO₂ capture and compression, net electrical and heat efficiencies were nearly identical with or without CO₂ capture. This was due to higher heat recovery efficiency by separating SOFC off-gas streams for CO₂ capture. However, CO₂ capture significantly increased the required SOFC and heat exchanger areas.Economic results showed that for above 40-50 $ t⁻¹ CO₂ price, SOFC-CHP systems were more economical when equipped with CO₂ capture. CO₂ capture also enabled SOFC-CHP to compete with GT-CHP at higher cell stack production costs. At zero CO₂ price, cell stack production cost had to be as low as 140 kW⁻¹ for SOFC-CHP to outperform GT-CHP. At 100 $ t⁻¹ CO₂ price, the cell stack production cost requirement raised to 350 $ kW⁻¹. With CO₂ capture, SOFC-CHP still outperformed GT-CHP at a significantly higher cell stack production cost above 900 $ kW⁻¹.     

On the simultaneous use of La0.75Sr0.25Cr0.5Mn0.5O3−δ as both anode and cathode material with improved microstructure in solid oxide fuel cells

A new concept of a solid oxide fuel cell (SOFC) using simultaneously the same electrode material at the anode and cathode sides with improved microstructure is proposed. We have found that La_0.75Sr_0.25Cr_0.5Mn_0.5O_3−δ (LSCM) can be considered as a good candidate for such configuration, symmetrical fuel cells (SFCs), due to its enhanced electrochemical properties in both reducing and oxidising conditions. LSCM-based SFCs offer promising performances, e.g., 0.5 and 0.3 W cm⁻² at 950 °C using H₂ and CH₄, respectively as fuels. Finally, the optimisation of the microstructure has been achieved via a novel facile procedure, using poly(methyl methacrylate) PMMA microspheres as templates.     

Effect of the metal oxide loading on the activity of silica supported MoO3 and V2O5 catalysts in the selective partial oxidation of methane

Precipitated silica catalysts loaded with either MoO₃ (0.2–4.0 wt%) or V₂O₅ (0.2–5.3 wt%) have been studied in the selective partial oxidation of methane to formaldehyde with molecular oxygen at 520 °C. The functionality of the SiO₂ surface towards the formation of HCHO is significantly promoted by V₂O₅, while it is depressed by the MoO₃.