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The influence of microporous layer (MPL) design parameters for gas diffusion layers (GDLs) on the performance of polymer electrolyte fuel cells (PEFCs) was clarified. Appropriate MPL design parameters vary depending on the humidification of the supplied gas. Under low humidification, decreasing both the MPL pore diameter and the content of polytetrafluoroethylene (PTFE) in the MPL is effective to prevent drying-up of the membrane electrode assembly (MEA) and enhance PEFC performance. Increasing the MPL thickness is also effective for maintaining the humidity of the MEA. However, when the MPL thickness becomes too large, oxygen transport to the electrode through the MPL is reduced, which lowers PEFC performance. Under high humidification, decreasing the MPL mean flow pore diameter to 3 μm is effective for the prevention of flooding and enhancement of PEFC performance. However, when the pore diameter becomes too small, the PEFC performance tends to decrease. Both reduction of the MPL thickness penetrated into the substrate and increase in the PTFE content to 20 mass% enhance the ability of the MPL to prevent flooding.

Abstract Lithium ion conducting polymer electrolytes were prepared by mixing insoluble lithium tetrakis(pentafluorobenzenethiolato) borate (LiTPSB) with poly(vinylidene fluoride) (PVDF) or poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP). Their films were prepared by hot pressing and are investigated for ionic conductivity and thermal properties. LiTPSB is insoluble in PVDF. Ionic conductivity was largely dependent on the salt content for LiTPSB–PVDF composite polymer electrolytes, and exhibited higher ionic conductivity than homogeneous LiTFSI–PVDF based polymer electrolytes. Melting point and crystallinity of PVDF were independent on LiTPSB content, resulting in no difference for melting point and crystallinity between pure PVDF and LiTPSB–PVDF. Ionic conductivity was effectively improved by incorporation of 18-crown-6 or kryptofix222 for LiTPSB–PVDF based polymer electrolytes.

Abstract Residual stresses in the electrolytes of segmented-in-series solid oxide fuel cells (SIS-SOFCs) and anode-supported cells (ASCs) were estimated at room temperature by X-ray diffraction. In the SIS-SOFCs, the residual stresses in the electrolyte were smaller than in the ASCs and did not change significantly after redox cycling. For both designs, numerically calculated values of the residual stresses in the electrolyte were found to be comparable to the experimental results. Next, in order to simulate the reoxidation reaction, the anode was subjected to forced expansion, and the residual stresses were estimated at high temperatures. It was found that in the SIS-SOFC, the dimensional changes and residual stresses were smaller than those in the ASC. The high redox tolerance of the SIS-SOFC is considered to stem from the fact that the electrically insulated substrate prevents the expansion and deformation of the positive electrode–electrolyte–negative electrode structure.

Several years ago, Li/Na carbonate (Li2CO3/Na2CO3) was developed as the electrolyte of molten carbonate fuel cells (MCFCs) in place of the usual Li/K carbonate (Li2CO3/K2CO3) to the advantage of a higher ionic conductivity and lower rate of cathode NiO dissolution. To estimate the potential of Li/Na carbonate as the MCFC electrolyte, the dependence of the cell performance on the operating conditions and the behavior during long-term performance was investigated in several bench-scale cell operations. The obtained data on the performance of Li/Na cells was analyzed to estimate the impact of voltage losses by using a performance model and discussed in comparison with the data of conventional Li/K cell performance.

Retaining optimum acid-contents in membranes and electrodes is critical to maintaining the performance and durability of acid-doped high-temperature (HT) polymer-electrolyte-membrane fuel cells (PEMFCs). Since the distribution of acids is influenced by the operating and compression conditions of the stack, there is great demand for understanding the behavior of individual membrane-electrode-assemblies (MEAs) while operating the cells in a stack. In this study, an in-situ diagnosis method using electrochemical impedance spectroscopy (EIS) is implemented during the durability test of an HT-PEMFC stack. Adopting a lumped equivalent-circuit model, the specific parameters are obtained from EIS results, and the changes of the values are compared with the performance loss of individual MEA. From this analysis it can be concluded that the main cause of performance degradation of the stack is due to the loss of electrolytes in the cathode, which leads to an increase in the proton transport resistance of cathode catalyst layers. In addition to the proton transport loss in the cathode, the charge transfer resistance of the oxygen reduction reaction has contributed to the performance decay of the stack. The causes of the increase in the cathode charge transfer resistance for each cell of the stack are discussed.

The anodic performance enhancement of solid oxide fuel cells (SOFCs) by introducing penetrating electrolyte structures was investigated using a random resistor network model considering the transport of electrons and ions, and the electrochemical reaction in composite anodes. The composite anode was modeled as a mixture of ionic and electronic particles, randomly distributed at simple cubic lattice points. The dependence of the anodic polarization resistances on the volume fraction of the electronic phase, the thickness of the anode, and the insertion of various penetrating electrolyte structures were explored to obtain design criteria for best performing composite anodes. The network simulation showed that the penetrating electrolyte structures are advantageous over flat electrolytes by enabling more efficient use of electrochemical reaction sites, and thereby reducing the polarization resistances.

Abstract Regarding the reliability of the polymer electrolyte membrane (PEM) fuel cell, the advancement of fuel, thermal and water management techniques of the system have been critically investigated. In this study, a 1 kW class PEM fuel cell stack is built with an Aciplex-S™ membrane, which is integrated to be automatically controlled in a hydrogen-fueled power generation system of a 80 cm ×70 cm ×120 cm single unit with a dc/ac inverter which produces 220 VAC power. Intensive and systematic care should be taken especially with the longer cell stack which is being operated under repeated current load change. The automatically controlled fuel-feed and thermal management system achieved in this study can markedly enhance the fuel efficiency and the reliability of the cell stack. The devices in the sub-systems are all electrically controlled versions to be manipulated on a touch screen via a PLC unit. The thermal and fuel-feed control logic are pre-built-in the CPU of the PLC unit based on an early study of cell stack evaluation. In addition, the power inverting and dummy load unit is coupled to the power generation system, and an additional data acquisition system has been constructed.

Abstract Sodium borohydride (NaBH 4 ) in the presence of sodium hydroxide as a stabilizer is a hydrogen generation source with high hydrogen storage efficiency and stability. It generates hydrogen by self-hydrolysis in aqueous solution. In this work, a Co–B catalyst is prepared on a porous nickel foam support and a system is assembled that can uniformly supply hydrogen at >6.5 L min −1 for 120 min for driving 400-W polymer electrolyte membrane fuel cells (PEMFCs). For optimization of the system, several experimental conditions were changed and their effect investigated. If the concentration of NaBH 4 in aqueous solution is increased, the hydrogen generation rate increases, but a high concentration of NaBH 4 causes the hydrogen generation rate to decrease because of increased solution viscosity. The hydrogen generation rate is also enhanced when the flow rate of the solution is increased. An integrated system is used to supply hydrogen to a PEMFCs stack, and about 465 W power is produced at a constant loading of 30 A.

Abstract Gel polymer electrolytes consisted of poly(alkylene oxide) (PAO), LiBF 4 or LiClO 4 , and aprotic solvents (γ-butyrolactone (GBL) and/or ethylene carbonate (EC)) were prepared and the conductivity was measured. The conductivity was very high and similar to that of the organic liquid electrolytes. The performance of Li | gel polymer electrolyte | LiCoO 2 cell was measured and compared to that of the cell with the liquid electrolyte corresponded. The cell with the gel electrolyte showed a decrease of capacity at high-rate discharge and low temperature owing to concentration polarization.