浅析6063铝型材表面"铝丝印"的成因与对策

从金属腐蚀学的观点出发，分析了“铝丝印”形成的电化学腐蚀机理，并提出了具体的解决措施。     

Atmospheric Plasma Deposition: A New Pathway in the Design of Conducting Polymer‐Based Anodes for Hydrogen Fuel Cells

In this study, we explored thin films of nanofibrous functionalised conducting plasma polyaniline (pPANI) with platinum deposited by an atmospheric plasma deposition process for the potential design of anodes for hydrogen fuel cell applications. We observed that the incorporation of such a polymer, characterised by both electronic and ionic conductivity, associated with a catalyst in a 3D porous network, could lead to an increased probability of the three‐phase contact to occur. In this context, aniline was mixed with functionalised platinum nanoparticles and used as the precursor. The role of these functionalised nanoparticles was not only to act as the catalyst for fuel cell purposes, but also as nucleation sites promoting the formation of the nanofibrous pPANI thin film during the plasma polymerisation. The morphology of the thin film was analysed by scanning electron microscopy and the efficiency, in terms of energy conversion, was assessed in a single fuel cell test bench.     

Preparation of KOH‐doped PVA/PSSA Solid Polymer Electrolyte for DMFC: The Influence of TiO2 and PVP on Performance of Membranes

The development of low cost alkaline anion solid exchange membranes requires high ionic conductivity, low liquid uptake, strong mechanical properties and chemical stability. PVA/PSSA blends cross‐linked with glutaraldehyde and decorated with titanium dioxide nanoparticles introduce advantages relative to the pristine membrane of PVA and PVA/PVP membranes due to their improved electrical response and low methanol uptake/ swelling ratio allowing their use in alkaline direct methanol fuel cells.     

Toward Fully‐ and Semi‐passive Operation of a Liquid‐Fed Direct Methanol Fuel Cell

This work reports the performance characteristics of a liquid‐fed direct methanol fuel cell (DMFC) operated in both fully‐ and semi‐passive conditions. For the latter case, a blower is used to provide forced air convection at the cathode so as to reveal how and how much a passive DMFC suffers from its structural constraint and also the mass and heat transfer limitations. The results based on the fully passive operation suggest that the cell performance is greatly affected by the level of methanol concentration. In this study, 2 M performs the best when the cell uses different structural setups. Besides, the effects of ambient temperature and the cathode self‐heating mechanisms are also explored under a fully passive condition. For the semi‐passive operation, forced air convection is proved to be helpful in enhancing oxygen delivery but may lead to faster heat and water dissipation and thus significantly reduces the cell performance. An optimal blowing intensity is obtained when the blower operates at a half speed. When the cathode diffusion layer is removed, the effects of active air supply become weakened. Considering the limited performance improvement and parasitic losses caused by a blower, we believe the self‐breathing mode is still an attractive choice.     

Electrochemical Performance of MnO2‐based Air Cathodes for Zinc‐air Batteries

This paper compares the oxygen reduction on four MnO₂‐based air cathodes assembled in home‐made electrochemical cells, with some particular observations on α‐MnO₂ cathode. The results show that the catalytic activity decreases in the following order: electrolytic MnO₂ (EMD) > natural MnO₂ (NMD) > β‐MnO₂ > α‐MnO₂. The maximum power density of the zinc‐air battery with EMD as the catalyst reaches up to 141.8 mW cm⁻² at the current density of 222.5 mA cm⁻², which is about 60%, 20% and 10% higher than that of α‐MnO₂ (90.0 mW cm⁻² at 120.3 mA cm⁻²), β‐MnO₂ (121.5 mW cm⁻² at 150.4 mA cm⁻²) and NMD (128.2 mW cm⁻² at 207.8 mA cm⁻²), respectively. It is believed that its unique crystal structure and biggest BET surface area make EMD have the smallest charge transfer resistance (R_ct), thus EMD has the highest activity.     

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.     

Catalytic Oxidation of Methanol by Aqueous POM on Al2O3 Supported Catalysts and Electrochemical Performance of POM

Phosphomolybdic acid (H₃PMo₁₂O₄₀, POM) was attempted to be used as the energy‐storage agent in this paper to avoid some problems of the direct methanol fuel cell (DMFC), such as catalyst poisoning and methanol permeation. Catalytic oxidation of methanol by aqueous POM on Al₂O₃ supported catalysts with Pt and Ru active metal was evaluated in the presence of liquid water. The process takes advantage of the high catalytic activities of platinum for methanol oxidation. The effects of temperature, reaction time, and methanol concentration on activity were observed. The catalytic activity of Pt/Al₂O₃ is better than that of Ru/Al₂O₃ for the oxidation of methanol by POM. The methanol conversion rate reached 93.55% on the Pt/Al₂O₃ at 80 °C after reaction for 1 h. The electrochemical experiments indicate that POM shows a larger current density in redox processes on an Au electrode than methanol. The redox process of reduced POM is a reversible multi‐electron transfer process.     

Investigation of a Novel Catalyst Coated Membrane Method to Prepare Low‐Platinum‐Loading Membrane Electrode Assemblies for PEMFCs

In this work, a novel catalyst coated membrane (CCM) approach–a catalyst‐sprayed membrane under irradiation (CSMUI)–was developed to prepare MEAs for proton exchange membrane fuel cell (PEMFC) application. Catalyst ink was sprayed directly onto the membrane and an infrared light was used simultaneously to evaporate the solvents. The resultant MEAs prepared by this method yielded very high performance. Based on this approach, the preparation of low‐platinum‐content MEAs was investigated. It was found that for the anode, even if the platinum loading was decreased from 0.2 to 0.03 mg cm^–2, only a very small performance decrease was observed; for the cathode, when the platinum loading was decreased from 0.3 to 0.15 mg cm^–2, just a 5% decrease was detected at 0.7 V, but a 35% decrease was observed when the loading was decreased from 0.15 to 0.06 mg cm^–2. These results indicate that this approach is much better than the catalyst coated gas diffusion layer (GDL) method, especially for the preparation of low‐platinum‐content MEAs. SEM and EIS measurements indicated ample interfacial contact between the catalyst layer and the membrane.     

Start‐Up and Load‐Change Behavior of a Catalytic Burner for a Fuel‐Cell‐Based APU for Diesel Fuel

The catalytic burner CAB 4 was developed for a fuel‐cell‐based diesel‐APU (auxiliary power unit) with a capacity of 14.5 kW_th,APU. In order to operate a catalytic burner in such an APU, several requirements must be met. Normal operation involves combustion of anode off‐gas from the fuel cell. If the fuel cell malfunctions or if the gas quality is insufficient, the burner must also be able to fully convert the reformate while by‐passing the fuel cell. It must be possible to catalytically ignite the burner using a reformate with increased CO‐concentration. The burner must fully convert all combustible components in the fuel‐gas at all operating points. The energy contained in the fuel gas is utilized in the CAB to generate superheated steam with no oscillations and to supply this steam to the autothermal reformer. When the fuel processing system is being shut down, the burner should be able to continue providing steam for sweeping the downstream reactors for a limited period of time. Catalytic ignition of the CAB 4 was demonstrated with a reformate containing up to 5 mol.% CO. The behavior of the burner was characterized in steady‐state operation, during load changes, during transitions in the operating mode, and during shut‐down.     

Investigation of the Ethanol Electro‐Oxidation in Alkaline Membrane Electrode Assembly by Differential Electrochemical Mass Spectrometry

The fuel cell differential electrochemical mass spectrometry (FC‐DEMS) measurements were performed for studying the ethanol oxidation reaction (EOR), using alkaline membrane electrode assemblies (MEAs) made up of nanoparticle Pt catalyst and alkaline polymeric membranes. The obtained results indicate that in an alkaline medium, ethanol undergoes significantly more complete electro‐oxidation to CO₂ than in an acidic MEA using the same Pt anode. The CO₂ current efficiency (CCE) can be compared for acidic and alkaline MEA with similar electrochemical active area on the anode side. The CCE estimated, in case of alkaline MEA with Pt anode, is around 55% at 0.8 V/RHE, 60 °C and 0.1 M ethanol. In comparison, under similar conditions, acidic MEAs using the same anode catalyst show only 2% CCE. This might indicate that the C–C bond scission rates are much higher in alkaline media. However, the mechanism of ethanol oxidation in alkaline media is not exactly known. CO₂ produced in electrochemical reaction forms soluble carbonates in the presence of aqueous alkaline electrolyte. This makes it difficult to study ethanol oxidation in alkaline media using FTIR or model DEMS systems. The alkaline polymer electrolyte membranes as used in this study for making alkaline MEAs provide an important opportunity to observe CO₂ produced during EOR using FC‐DEMS system.     

Performance and Durability of Membrane Electrode Assemblies Based on Radiation‐Grafted FEP‐g‐Polystyrene Membranes

Membrane electrode assemblies (MEAs) based on radiation‐grafted proton exchange membranes developed at PSI have shown encouraging performance in the past in hydrogen and methanol fuelled polymer electrolyte fuel cells. In this study, the effect of the pre‐treatment of crosslinked radiation‐grafted FEP membranes prior to lamination with the electrodes on the performance of the MEAs was investigated. Two approaches were assessed separately and in combination: (1) the impregnation of the radiation‐grafted membranes with solubilised Nafion®, and (2) the use of a swollen vs. dry membrane. It is found that the combination of coating the membrane with Nafion® ionomer and hot‐pressing the MEA with the membrane in the wet state produce the best single cell performance. In the second part of the study, the durability of an MEA, based on a radiation‐grafted FEP membrane, was investigated. The performance was stable for 4,000 h at a cell temperature of 80 °C. Then, a notable degradation of the membrane, as well as the electrode material, started to occur as a consequence of either controlled or uncontrolled start‐stop cycles of the cell. It is assumed that particular conditions, to which the cell is subjected during such an event, strongly accelerate materials degradation, which leads to the premature failure of the MEA.     

The Operation of HT‐PEM Fuel Cells Coupled to Lithium Ion Batteries in a Fleet of Light Passenger Vehicles

High temperature polymer electrolyte membrane (HT‐PEM) fuel cells offer some advantages over their low temperature equivalent, but there have been relatively few reports into their use in vehicles. This paper describes the power train design and operation of a fleet of Microcab H2EV vehicles. The power train consisted of a HT‐PEM fuel cell coupled via a DC/DC convertor to a lithium iron phosphate traction battery, which was then connected to two Lynch motors. The integration and operation of all the major power train components is described. Also described here is the vehicle control unit that uses digital and analog communications to provide overall management of the vehicle. Details are given of all the safety systems designed into the vehicle. Some data describing the performance of the H2EV power‐train during typical drive cycles is presented, which shows that the system was functional. It is concluded that HT‐PEM fuel cell light vehicles are viable, but the heating and cooling time of the fuel cell needs to be significantly reduced.     

Theoretical Model for the Optimal Design of Air Cooling Systems of Polymer Electrolyte Fuel Cells. Application to a High‐Temperature PEMFC

The cooling system of a high‐temperature PEM fuel cell with a nominal electric power of 1.5 kW for a combined heat and power unit (CHP) has been designed using a thermochemical model. The 1D model has been developed as a simple, predictive, and useful tool to evaluate, design, and optimize cooling systems of PEM fuel cells. As proved, it can also be used to analyze the influence of different operational and design parameters, such as the number and geometry of the channels, or the air flow rate, on the overall performance of the stack. To validate the model, predicted results have been compared with experimental measurements performed in a commercial 2 kW air‐forced open‐cathode stack. The model has then been applied to calculate the air flow required by the designed prototype stack as a function of the power output, as well as to analyze the influence of the cooling channels configuration (cross‐section geometry and number) on the heat management. Results have been used to select the optimum air‐fan cooling system, which is based on compact axial fans.     

Effects of Microstructural Functional Layers on Flat‐Tubular Solid Oxide Fuel Cells

The functional layer of a flat‐tubular solid oxide fuel cell (SOFC) is examined using a three‐dimensional microscale electrode model. SOFC electrodes essentially include two types of layers: a structural layer and a functional layer. The structural layers, which are the anode support layer and the cathode current collector layer, are composed of large particles with a high porosity that facilitates gas diffusion. The functional layers consist of small particles with a low porosity that increases the triple phase boundary (TPB) reaction area and reduces the activation overpotential. In the model, the particle diameter and functional layer thickness are adjusted and analyzed. The effects of the two parameters on the performance of the functional layer are monitored in the contexts of several multilateral approaches. Most reactions occurred near the electrode–electrolyte interface; however, an electrode design that included additional TPB areas improved the electrode performance. The role of the functional layer in a flat‐tubular SOFC is examined as a function of the functional layer particle size and thickness. The performance of a cell could be enhanced by preparing a functional layer using particles of optimal size and thickness, and by operating the device under conditions optimized for these parameters.     

A Layered Perovskite EuBaCo2O5+δ for Intermediate‐Temperature Solid Oxide Fuel Cell Cathode

A layered perovskite EuBaCo₂O_5+δ (EBCO) has been prepared by a solid‐state reaction, and evaluated as potential cathode for intermediate‐temperature solid oxide fuel cells. Structural characterizations are determined at room temperature using powder X‐ray diffraction and transmission electron microscopy technique. The good fits to the XRD data by Rietveld refinement method are obtained in the orthorhombic space group (Pmmm). The lower average thermal expansion coefficient, 14.9 × 10^–6 °C^–1 between 100 and 800 °C, indicates its better thermal expansion compatibility with conventional electrolytes, compared with the other cobalt‐containing cathode materials. The high electrical conductivity and large oxygen nonstoichiometry at intermediate temperatures suggest the effective charge transfer reactions including electron conduction and oxide‐ion motion in cathode. As a result, a highly electrochemical activity towards the oxygen reduction reaction is achieved between 600 and 700 °C, as evidenced by low area‐specific resistances, e.g. 0.14–0.5 Ω cm². In addition, cathodic overpotential and oxygen reduction kinetics of the EBCO cathode have also been studied.     

Model for the Degradation Performance of a Single‐Cell Direct Methanol Fuel Cell under Varying Operational Conditions

The effect of varying operating parameters on the degradation of a single‐cell direct methanol fuel cell (DMFC) with serpentine flow channels was investigated. Fuel cell internal temperature, methanol concentration, and air and methanol flow rates were varied in experimental tests and fuel cell performance was chronologically recorded. A DMFC semi‐empirical performance model was developed to predict the polarization curves of the DMFC and validated at different operating conditions. Performance degradation was observed and modeled over time by a linear regression model. Unlike previous studies, the cumulative exposure of the operating factors to the fuel cell was considered in the degradation analysis. The degradation model shows the cell voltage generation capacity does not significantly degrade. However, the Tafel slope of the cell changes with cumulative exposure to methanol concentration and air flow, and the ohmic resistance changes with cumulative exposure to temperature, methanol and air flow.     

Fabrication and Power Densities of Anode‐Supported Solid Oxide Fuel Cells with Different Ni‐YSZ Anode Functional Layer Thicknesses

We investigated an appropriate preparation condition for anode‐supported SOFCs: (La,Sr)MnO₃/cathode functional layer/YSZ/Ni‐YSZ were fabricated with and without a Ni‐YSZ anode functional layer (AFL) via the tape‐casting method, where the AFL thicknesses were controlled from approximately 20 to 80 μm. The warpage depended on the co‐sintering temperature of the electrolyte/AFL/anode‐support half‐cells, indicating that similar shrinkage of the electrolyte/AFL/anode support is significant for lower warpages. The electrical properties of SOFCs with AFLs were compared to those of SOFCs without AFLs. In this regard, the use of an AFL decreased the ohmic and activation polarization resistances due to both the decrease in contact resistance between the electrolyte and the AFL and the increase in three‐phase boundaries. However, the polarization diffusion increased when an AFL was employed, because AFL layers are denser than the anode support. The maximum power densities of samples with AFL were higher than those of SOFCs without AFLs, indicating that the decrease in both ohmic and activation‐polarization resistances is more significant for improving the power densities, as compared to the concentration polarization resistance.     

Preparation and Electrochemical Properties of Sr‐doped K2NiF4‐type Cathode Material Pr1.7Sr0.3CuO4 for IT‐SOFCs

A novel K₂NiF₄‐type oxide Pr_1.7Sr_0.3CuO₄ (PSCu) is studied to obtain its electrochemical properties as the cathode for intermediate‐temperature solid oxide fuel cells (IT‐SOFCs). The PSCu cathode powder and Ce_0.8Sm_0.2O_1.9 (SDC) electrolyte powder were synthesized by sol‐gel method and glycine‐nitrate method, respectively. The crystal structure of PSCu powder and PSCu‐SDC composite powder were identified with X‐ray diffraction (XRD). It is shown that PSCu belongs to tetragonal K₂NiF₄‐type and has good chemical compatibility with SDC. The thermal expansion coefficient (TEC) of PSCu is close to that of SDC. The conductivity of PSCu tested with four‐probe method exhibits a semiconductor‐pseudometal transformation at 400–450 °C, where the maximum conductivity of 103.6 S cm⁻¹ is obtained. The polarization test indicates the area specific resistance (ASR) of PSCu decreases with increasing temperature, reaching 0.11 Ω cm² at 800 °C. The activation energy of oxygen reduction reaction during 600–800 °C is 1.19 eV. The single fuel cell performance test reveals the open circuit voltage (OCV) and resistivity of PSCu reduce with increasing temperature, but the power density ascends with increasing temperature. The maximal power density is 243 mW cm⁻² at 800 °C, and the corresponding current density and OCV are 633 mA cm⁻² and 0.77 V, respectively.     

Influence of Deposition Temperature of GDC Interlayer Deposited by RF Magnetron Sputtering on Anode‐Supported SOFC

Gadolinia‐doped ceria (GDC) film, as a barrier layer to prevent chemical reaction between yttria‐stabilized zirconia (YSZ) electrolyte and Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3–δ (BSCF)–GDC cathode, is deposited by radio frequency (RF) magnetron sputtering on YSZ electrolyte, and the influence of deposition temperature on Ni–YSZ/YSZ/GDC/BSCF–GDC single cell performance is investigated. The SEM results show that the GDC film deposited at 30 °C exhibits a porous structure, whereas the GDC film deposited at 400 °C has a dense structure. The single cells show excellent performance when the deposition temperature is above 250 °C, whereas the single cells show poor performance when the deposition temperature is below 200 °C. The large difference in cell performance occurs from their large difference in polarization resistance. The porous structure of GDC interlayer, which cannot well prevent the reaction between BSCF and YSZ, is responsible for the poor performance of the cells with GDC interlayer deposited at a temperature below 200 °C.     

Start‐Up of HT‐PEFC Systems Operating with Diesel and Kerosene for APU Applications

Fuel‐cell‐based auxiliary power units offer power generation with reduced fuel consumption and low emissions. A very promising system is the combination of an autothermal reformer with a high‐temperature polymer electrolyte fuel cell. A fast start‐up procedure is a crucial requirement for the use of this system as an auxiliary power unit. This paper reports on the development of a suitable start‐up strategy for a 10 kW_el auxiliary power unit with a start‐up burner. A commercially available diesel burner was tested as a start‐up device. A dynamic MATLAB/Simulink model was developed to analyze different start‐up strategies. With the currently available apparatus and start‐up burner it takes 2,260 s before power generation can begin according to simulation results. The fuel processor alone would be ready for operation after 1,000 s. An optimization of the fuel cell stack with regard to its thermal mass would lead to a start‐up time of 720 s. A reduction to 600 s is possible with a slight customization of the start‐up burner.