二甲醚生产技术（上）

综述了二甲醚的生产技术     

Preliminary Study on Direct Operation of LT‐SOFCs Based on GDC Electrolyte Film With DME Fuel

Direct operation of anode‐supported cone‐shaped tubular low temperature solid oxide fuel cells (LT‐SOFCs) based on gadolinia‐doped ceria (GDC) electrolyte film with dimethyl ether (DME) fuel was preliminarily investigated in this study. The single cell exhibited maximum power densities of 500 and 350 mW cm^–2 at 600 °C using moist hydrogen and DME as fuel, respectively. A durability test of the single NiO‐GDC/GDC/LSCF‐GDC cell was performed at a constant current of 0.1 A directly fuelled with DME for about 200 min at 600 °C. The results indicate that the single cell coking easily directly operated in DME fuel. EDX result shows a clear evidence of carbon deposition in the anode. Further studies are needed to develop the novel anti‐carbon anode materials, relate the carbon deposition with anode microstructure and cell‐operating condition.     

Experimental Study of Internal Reforming on Large‐area Anode Supported Solid Oxide Fuel Cells

The effect of endothermic internal steam reformation of methane and exothermic fuel cell reaction on the temperature of a planar‐type anode‐supported solid oxide fuel cell was experimentally investigated as a function of current density and fuel utilization. We fabricated a large‐area (22 × 33 cm²) cell and compared temperature profiles along the cell using 30 thermocouples inserted through the cathode end plate at 750 °C under various conditions (Uf ∼50% at 0.4 A cm⁻²; Uf ∼70% at 0.4 A cm⁻²; Uf ∼50% at 0.2 A cm⁻²) with hydrogen fuel and methane‐steam internal reforming. The endothermic effect due to internal reforming mainly occurs at the gas inlet region, so this process is not very effective to cool down the hot spot created by the exothermic fuel cell reaction. This eventually results in a larger temperature difference on the cell. The most moderate condition with regards to thermal gradient on the cell corresponds to high fuel utilization (Uf ∼70%) and low current density (∼0.2 A cm⁻²). The electrochemical performance was also measured, and it was found that the current–voltage characteristics are comparable for the cell operated under hydrogen fuel and internal steam reforming of methane because of lower polarization resistance with high partial pressure of water vapor.     

Gas Diffusion Layers for Proton Exchange Membrane Fuel Cells Using In situ Modified Carbon Papers with Multi‐walled Carbon Nanotubes Nanoforest

Gas diffusion layers (GDLs) in the proton exchange membrane fuel cells (PEMFCs) enable the distribution of reactant gases to the reaction zone in the catalyst layers by controlling the water in the pore channels apart from providing electrical and mechanical support to the membrane electrode assembly (MEA). In the present work, we report the in situ growth of carbon nanotubes nanoforest (CNN) directly onto macro‐porous carbon paper substrates. The surface property as analysed by a Goniometer showed that the CNN/carbon paper surface is highly hydrophobic. CNN/carbon paper was employed as a GDL in an MEA using Nafion‐212 membrane as an electrolyte and evaluated in single cell PEMFCs. While the GDLs prepared by wire‐rod coating process have major performance losses at lower humidities, the in situ CNN/carbon paper, developed in this work, shows very stable performance at all humidity conditions demonstrating a significant improvement for fuel cell performance. The CNN/carbon‐based MEAs showed very stable performance with power density values of ∼1,100 and 550 mW cm^–2, respectively, both using O₂ and air as oxidants at ambient pressure.     

Effect of Ru/CGO versus Ni/CGO Co‐Infiltration on the Performance and Stability of STN‐Based SOFCs

Electrolyte supported cells (ESC), with Sc₂O₃‐stabilized ZrO₂ (ScSZ) electrolytes, Gd‐doped ceria (CGO) or M/CGO (M = Ni, Ru) infiltrated Sr_0.94Ti_0.9Nb_0.1O₃ (STN94) anodes and LSM/YSZ cathodes, were evaluated for their initial performance and long‐term stability. Power density for the Ru/CGO infiltrated cell reached ∼0.7 W cm^–2 at 850 °C, 4% H₂O/H₂, whereas the Ni/CGO infiltrated cell reached ∼0.3 W cm^–2, with the current morphologies and loadings. Operation at 0.125 A cm^–2, 850 °C, feeding 50% H₂O/H₂ to the anode and air to the cathode, for a period >300 h, showed superior stability for the Ru/CGO infiltrated cell, with ∼0.04 mV h^–1 degradation rate, when compared to the Ni/CGO infiltrated cell (∼0.5 mV h^–1). For the Ni/CGO case, the observed degradation has been tentatively linked to initial changes in the electrochemical active area and long‐term detrimental interactions between components.     

Enhancing the Efficiency of SOFC‐Based Auxiliary Power Units by Intermediate Methanation

Fuel‐cell‐based auxiliary power units benefit from the high power density and fuel flexibility of solid oxide fuel cells (SOFCs), facilitating straightforward onboard fuel processing of diesel or jet fuel. The preferred method of producing the fuel gas is autothermal reforming, which to date has shown the best practical applicability. However, the resulting reformate is poor in methane, so that cell cooling is not supported by internal methane steam reforming. Accordingly, large flow rates of excess air are required to cool the stack. Hence, the power demand of the cathode air blower significantly limits the net electrical power output of the system and large cathode flow channels are required. The present work examines attempts to further increase the system efficiency in middle‐distillate‐fueled SOFC systems by decreasing the cathode air flow rates. The proposed concept is generally based on inducing endothermic methane steam reforming (MSR) inside the cells by augmenting the methane content in an upstream methanation step. Methanation, however, can only yield significant methane production rates if the reaction temperature is limited. Therefore, four process layouts are presented that include different cooling measures. Based on these setups, the general feasibility and the benefit of intermediate methanation are demonstrated.     

Catalytic Influence of Oxide Component in Ni‐Based Cermet Anodes for Ammonia‐Fueled Solid Oxide Fuel Cells

Recently, the promising prospect of ammonia as a hydrogen carrier for solid oxide fuel cells (SOFCs) has attracted significant interests. In this work, the effects of temperature, fuel content, and total flow rate of anode gas on the performance of Ni/yttria‐stabilized zirconia (Ni/YSZ) anode for ammonia‐fueled SOFCs were investigated. Based on obtained results, the utilization route of ammonia on Ni/YSZ anode was discussed; the results of electrochemical experiments were related with the catalytic decomposition bahavior of ammonia over Ni/YSZ. Moreover, the catalytic activity for ammonia decomposition and anode performance of Ni/samarium‐doped ceria (Ni/SDC) and Ni/yttrium‐doped barium cerate (Ni/BCY) were also investigated. Among these anode materials, Ni/BCY exhibited the highest ammonia decomposition activity and anode performance for ammonia‐fueled SOFCs at intermediate temperatures.     

Shortened Carbon Nanotubes as Enhanced Support for High‐performance Platinum Catalysts

Carbon nanotubes (CNTs) were shortened from 5 to 15 μm to ca. 200 nm using ball milling with ethanol as the milling aid agent, and a platinum catalyst with these shortened carbon nanotubes (SCNTs) as the support was prepared by a high‐pressure colloidal method. It was found that this catalyst with SCNTs showed much higher activity than a platinum catalyst with normal CNTs as support; for methanol anodic oxidation, the activity of the Pt/SCNTs was 50% higher than that of the Pt/CNTs, and the Pt/SCNTs also showed higher activity for the cathodic reduction of oxygen. The Pt/SCNTs were characterised by X‐ray diffraction scanning and transmission electron microscropy. It is suggested that the significant performance enhancement when SCNTs are used as support might result from the generation of new surfaces and defects, the opening of closed nanotubes in the process of milling, higher platinum dispersion on the shortened nanotubes and the interaction of platinum nanoparticles with the SCNTs.     

Evaluation of the Performance of Platinum Nanoparticle–Titanium Oxide Nanotubes as a New Refreshable Electrode for Formic Acid Electro‐oxidation

Platinum nanoparticles (Pt‐NP) are deposited on the surface of titanium oxide nanotubes (TN) by microemulsion method. Highly ordered TN on a pure titanium substrate are successfully fabricated by anodizing of titanium. The morphology and surface analysis of Pt‐NP/TN electrodes were investigated using scanning electron microscopy and X‐ray diffraction spectroscopy, respectively. The electro‐oxidation of formic acid on Pt‐NP/TN electrodes in acidic medium was studied by cyclic voltammetry and chronoamperometry methods. The results showed that the oxidation peak currents on the Pt‐NP/TN electrode for formic acid oxidation are several times larger than a smooth platinum electrode and confirmed the better electro‐catalytic activity and stability of these new electrodes. The photocatalytic properties of titanium oxide make the Pt‐NP/TN electrode reusable after a short UV treatment, and the electro‐oxidation current density of Pt‐NP/TN electrode after UV‐cleaning can be re‐established. So Pt‐NP/TN electrode has a good application potential to fuel cells.     

A Low Cost Large‐Area Solid Oxide Cells Fabrication Technology based on Aqueous Co‐Tape Casting and Co‐Sintering

Aqueous‐based tape casting is a low‐cost and environment friendly technology. In this paper, large‐area fuel electrode‐supported solid oxide cells (SOCs) were fabricated by this technology in conjunction with co‐sintering process. A 10 cm × 10 cm single cell with NiO/Zr_0.92Y_0.08O_2–δ fuel electrode, Zr_0.92Y_0.08O_2–δ electrolyte and La_0.6Sr_0.4Co_0.2Fe_0.8O_3+δ/Ce_0.9Gd_0.1O_2+δ air electrode has been successfully developed with improved electrode microstructure and hence the cell performance with the maximum power density of 534 mW cm^–2 at 850 °C with humidified H₂ as the fuel and air as the oxidant has been achieved. The optimal slurry formulations used in the fabrication of SOC were summarized for future reference purpose.     

Tailoring Electrochemical Property of Layered Perovskite Cathode by Cu‐doping for Proton‐Conducting IT‐SOFCs

Layered perovskite oxide YBaCuCoO_5+x (YBCC) was synthesized by an EDTA‐citrate complexation process and was investigated as a novel cathode for proton‐conducting intermediate temperature solid oxide fuel cells (IT‐SOFCs). The thermal expansion coefficient (TEC) of YBCC was 15.3 × 10⁻⁶ K⁻¹ and the electrical conductivity presented a semiconductor‐like behavior with the maximum value of 93.03 Scm⁻¹ at 800 °C. Based on the defect chemistry analysis, the electrical conductivity gradually decreases by the introduction of Cu into Co sites of YBaCo₂O_5+x and the conductor mechanism can transform from the metallic‐like behavior to the semiconductor‐like behavior. Thin proton‐conducting (BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3–δ) BZCYYb electrolyte and NiO–BZCYYb anode functional layer were prepared over porous anode substrates composed of NiO–BZCYYb by a one‐step dry‐pressing/co‐firing process. Laboratory‐sized quad‐layer cells of NiO‐BZCYYb / NiO‐BZCYYb / BZCYYb / YBCC with a 20 μm‐thick BZCYYb electrolyte membrane exhibited the maximum power density as high as 435 mW cm⁻² with an open‐circuit potential (OCV) of 0.99 V and a low interfacial polarization resistance of 0.151 Ωcm² at 700 °C. The experimental results have indicated that the layered perovskite oxide YBCC can be a cathode candidate for utilization as proton‐conducting IT‐SOFCs.     

Palladium/Cobalt Coated on Multi‐Walled Carbon Nanotubes as an Electro‐catalyst for Oxygen Reduction Reaction in Passive Direct Methanol Fuel Cells

This work reports the synthesis of Pd‐based alloy electrocatalysts of Co supported on multi‐walled carbon nanotubes (MWCNTs) and their evaluation as cathode materials in a passive direct methanol fuel cell (PDMFC). The X‐ray diffraction (XRD) analysis showed well‐defined reflections corresponding to a face centered cubic phase of palladium. As compared to the Pd/MWCNT electrocatalyst, the bimetallic alloy electrocatalysts with the different Pd_xCo atomic ratios showed highly enhanced mass activity (MA) for the oxygen reduction reaction (ORR); however, the significant enhancement in the specific activity (SA) by a factor of about 1.2–5.6 for the ORR was found on the Pd_xCo alloy electrocatalysts in the presence and absence of methanol electrolyte solution. This enhancement SA in of the Pd‐based electrocatalysts was correlated to the changes in the lattice parameter and Pd_xCo surface composition. Surface area changes of Pd‐based electrocatalysts supported on MWCNT were evaluated using an accelerated durability test (ADT). The results obtained using the ADT were correlated to the performance of the Pd‐based electrocatalysts in the PDMFC. A better performance was obtained for the cell using Pd₃Co/MWCNT (2.53 mW cm^–2) compared to Pd/MWCNT (1.64 mW cm^–2) and Pt/C‐Electrochem (1.20 mW cm^–2) as cathode in the PDMFC. In the presence and absence of methanol the impedance Bode spectra showed one time constant that associated to follow a four electron pathway.     

Adsorption of Sulfur‐Containing Species on LaCrO3 (001) Surface: A First‐Principles Study

Density functional theory calculations are employed to investigate the adsorption of sulfur‐containing species on the (001) surface of LaCrO₃ (LCrO). Molecular adsorption is found to be stable with H₂S binding preferentially at O site on the LaO‐terminated surface. The adsorption of H₂S molecule leads to the electrons transferring from the substrate to the molecule and the charges rearrangement within the molecule. In addition, the adsorption of the corresponding S‐containing dissociated species (SH and S) is investigated. SH and S are found to be preferentially bind at the Cr site. We further predict the adsorption energies of sulfur‐containing species increase following the sequence H₂S<SH<S for all the adsorption sites on LCrO (001) surface. Based on the adsorption energy comparison, LCrO is more sulfur‐tolerant than traditional Ni‐based anode materials, which is qualitatively in line with available experimental results. This study provides a scientific basis for rational design of sulfur‐tolerant anode materials for SOFCs.     

Performance and Evaluation of Cu‐based Nano‐composite Anodes for Direct Utilisation of Hydrocarbon Fuels in SOFCs

The anodes for direct utilisation of hydrocarbon fuels have been developed by using Cu/Ceria‐based nano‐composite powders. The CuO/GDC/YSZ–YSZ or CuO/GDC‐GDC nano‐composite powders were synthesised by coating nano‐sized CuO and CeO₂ particles on the YSZ or GDC core particles selectively by the Pechini process. Their microstructures and electrical properties have been investigated with long‐term stability in reactive gases of dry methane and air. The anodes fabricated using Cu‐based nano‐composite anodes showed almost no carbon deposition until 500 h in dry CH₄ atmosphere. The type of an electrolyte‐supported single cell in conjunction with the Cu/Ceria‐based anode must be selected together for the low melting temperature of Cu/CuO. The GDC electrolyte supported unit cell with the Cu/GDC–GDC anode showed the maximum power density of 0.1 Wcm^–2 and long‐term stability for more than 500 h under electronic load of 0.05 Acm^–2 at 650 °C in dry methane atmosphere.     

One‐Step Preparation of Pt on Pretreated Multiwalled Carbon Nanotubes for Methanol Electrooxidation

For the first time, intermittent microwave heating (IMH) is a one‐step technique applied to pretreat the multiwalled carbon nanotubes (MWCNTs) in H₂O₂ solution. The approach does not require washing and filtration of the sample, thus significantly reducing the loss of the material and treatment time. The IMH associated with H₂O₂ treatment, is optimised to fabricate efficient support for Pt electrocatalyst. Both as‐received and treated MWCNTs are used as Pt electrocatalyst supports, respectively. It demonstrates that the treated MWCNTs supported Pt has much better electrocatalytic performance than that of untreated MWCNTs supported Pt. The Pt on MWCNTs treated with an IMH irradiation mode in 10 s on and 20 s off for 5 times, shows the best performance for methanol oxidation. This work provides a novel approach to simply and economically fabricate an efficient MWCNT support at a large scale, for high performance Pt electrocatalysts.     

Degradation Mechanism of Anode‐Supported Solid Oxide Fuel Cell In Planar‐Cell Channel‐Type Setup

The degradation mechanism of anode‐supported planar solid oxide fuel cells is investigated in the present work. We fabricate a large‐area (10 cm × 10 cm) cell and carry out a long‐term test with the assembly components. A constant current of ∼0.4 A cm^–2 is applied to the cell for ∼3,100 h, and the furnace temperature is controlled in the sequence 750–800–750 °C to investigate the effect of operating temperature and thermal cycling on the degradation rate. Impedance spectra and current–voltage characteristics are measured during the operation in order to trace any increase in Ohmic and non‐Ohmic resistance as a function of time. The degradation rate is rapid during the operation at the higher temperature of ∼800 °C compared to that during the operation at ∼750 °C. Even after cooling down to ∼750 °C, that rate is still accelerated. The main contribution to the cell degradation is from an increase in the Ohmic resistance. Postmaterial analyses indicate that the cathode is delaminated at the electrolyte/cathode interface, which is attributed to the difference in thermal expansion coefficient (TEC). Thus, the present results emphasize the importance of matching the TEC between cell layers, especially under severe operating conditions such as long duration and complex thermal cycling.     

Modelling and Performance Evaluation of Solid Oxide Fuel Cell for Building Integrated Co‐ and Polygeneration

Models of fuel cell based combined heat and power systems, used in building energy performance simulation codes, are often based on simple black or grey box models. To model a specific device, input data from experiments are often required for calibration. This paper presents an approach for the theoretical derivation of such data. A generic solid oxide fuel cell (SOFC) system model is described that is specifically developed for the evaluation of building integrated co‐ or polygeneration. First, a detailed computational cell model is developed for a planar SOFC and validated with available numerical and experimental data for intermediate and high temperature SOFCs with internal reforming (IT‐DIR and HT‐DIR). Results of sensitivity analyses on fuel utilisation and air excess ratio are given. Second, the cell model is extended to the stack model, considering stack pressure losses and the radiative heat transfer effect from the stack to the air flow. Third, two system designs based on the IT‐DIR and HT‐DIR SOFCs are modelled. Electric and CHP efficiencies are given for the two systems, as well as performance characteristics, to be used in simulations of building integrated co‐ and polygeneration systems.     

Efficient Anchorage of Palladium Nanoparticles on the Multi‐Walled Carbon Nanotubes as Electrocatalyst for the Hydrazine Electrooxidation in Strong Acidic Solutions

A facile homogeneous precipitation–reduction reaction method, which involves PdCl₂ → PdO · H₂O → Pd⁰ reaction path, is used to synthesize the multi‐walled carbon nanotubes (MWCNTs) supported Pd nanoparticles (Pd/MWCNTs) catalysts. The particle size of Pd/MWCNTs catalysts can be easily tuned by controlling the hydrolysis temperature of PdCl₂. X‐ray diffraction (XRD) and transmission electron microscopy (TEM) measurements show the particle size of Pd/MWCNTs catalysts increases with hydrolysis temperature of PdCl₂, which is ascribed to the fact that the particle size of PdO · H₂O nanoparticles increases with hydrolysis temperature of PdCl₂. At the lower hydrolysis temperature, the as‐prepared Pd/MWCNTs catalyst possesses the higher dispersion and the smaller particle size. Consequently, the resultant Pd/MWCNTs catalyst exhibits the big electrochemical active surface area and the excellent electrocatalytic performance for hydrazine electrooxidation in strong acidic solutions. In addition, the electrochemical measurement indicate that particle size effect of Pd‐NPs occurs during the N₂H₄ electrooxidation. In brief, the mass activity and specific activity of the Pd/MWCNTs catalyst increases and decreases with decreasing the particle size of Pd‐NPs for the N₂H₄ electrooxidation, respectively.     

Highly Stable Pd‐Based Catalytic Nanoarchitectures for Low Temperature Fuel Cells

The multiwalled carbon nanotubes (MWCNTs) are treated with hydrofluoric acid (HF) aqueous solution so as to make enlarged micropores on the nanotube walls. Normally, there are no chemical bonds between the metal nanoparticles and the support. Therefore, the large contact area between metal nanoparticles and the support would decrease the possibility of nanoparticle agglomeration or their detachment from the support. The obtained large micropores to which the meal nanoparticles are attached can efficiently achieve the above advantages. In the experiment, the catalytic activity and the stability of Pd supported on HF treated MWCNTs (Pd/MWCNT_HF) catalyst are evaluated by potential cycling for ethanol oxidation. The voltammetric data suggest that the obtained enlarged micropores on the treated nanotube walls can anchor the metal nanoparticles so effectively that it can overcome the agglomeration or detachment from the surface of the MWCNT. Pd/MWCNT_HF catalyst shows improved stability.     

Mn‐Stabilised Microstructure and Performance of Pd‐impregnated YSZ Cathode for Intermediate Temperature Solid Oxide Fuel Cells

The effect of Mn alloying on PdO powder and Pd‐impregnated Pd + YSZ cathode for the O₂ reduction reaction in intermediate temperature solid oxide fuel cells has been studied in detail. The microstructure, thermal stability, electrochemical activity and performance stability of the powder and cathode were analysed using thermal gravimetric analysis, X‐ray diffraction, scanning electron microscopy/energy dispersive spectroscopy and electrochemical impedance spectroscopy. The results indicate that an addition of 5 mol.‐% Mn effectively inhibits the growth and coalescence of Pd and PdO particles at high temperatures and stabilises the microstructure of the powders and the electrode; as a consequence, the electrochemical performance and stability of the cathode are significantly improved. The electrochemical performance of the Pd + YSZ and Pd_0.95Mn_0.05 + YSZ cathodes so prepared is much better than that of the conventional LSM‐based cathodes and is also comparable with the mixed ionic and electronic conducting oxide cathodes such as LSCF.