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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.

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.

Abstract In this paper, electrolyte solutions of ethylene carbonate (EC) and ethylene methylene carbonate (EMC) with different salts as LiPF6, LiBF4 and LiN(SO2C2F5)2 were prepared and characterized using Pulsed Field Gradient (PFG) NMR and DSC. Cation transport numbers, τ+, ranging between 0.37 and 0.49 were obtained. The maximum value of 0.49 was obtained in the case of a 0.5 M solution of LiBF4 in 2:8 EC:EMC. The DSC data suggest that the increase of EMC stabilizes the electrolyte solution towards low temperature, and that a 2:8 EC:EMC ratio assures good stability at low temperature to the electrolyte solution. While LiN(SO2C2F5)2 seems to score the best in terms of low temperature stability, LiPF6 may offer the best cost/performances compromise.

Abstract A fundamental study on direct ammonia fuel cells with a molten hydroxide electrolyte was conducted. The electrochemical oxidation of ammonia on Pt electrode in a molten NaOH–KOH electrolyte was investigated by cyclic voltammetry and mass spectrometry. Ammonia was proved to be oxidized to N2 on the Pt electrode during anodic polarization in the molten hydroxide electrolyte. Furthermore, the direct ammonia fuel cell, i.e., Pt gas diffusion electrode|molten NaOH–KOH electrolyte|Pt gas diffusion electrode, was assembled and operated at 200–220 °C. The cell achieved the maximum power density of ca. 16 mW cm−2 at 220 °C with the supply of NH3 and humidified O2 to the anode and cathode, respectively. The mechanism of ammonia oxidation over Pt electrodes in a molten hydroxide electrolyte was discussed based on the results obtained.

Abstract Lithium bis(oxalto)borate (LiBOB) is quite effective to prevent vigorous decomposition of propylene carbonate (PC) at the graphite anode of a Li-ion battery during Li insertion. PC is a very good solvent that is inexpensive, has high conductivity and a low melting point; however, the power capability of PC electrolyte containing LiBOB is unsatisfactory. In an attempt to improve the power capability of the LiBOB/PC electrolyte, mixed electrolytes containing both LiBOB and LiClO4 were examined. An integrated fiber felt of highly graphitized carbon was used as the working electrode and the performance was evaluated by cyclic voltammetry (CV), constant current followed by constant voltage charge (CCCV) and constant current discharge. The CV produced a stable peak for Li extraction, but the peak height was as low as half that obtained in a conventional electrolyte such as a 1:1 mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) containing 1 M LiClO4. However, the peak height in PC, containing 1/49 M LiBOB and 1 M LiClO4, became 1.5 times higher than that in PC containing 1 M LiBOB. The peak height was increased further using a 1:1 mixture of PC and acetonitrile (AN) containing 1/49 M LiBOB and 1 M LiClO4, although the cycleability was poor. A similar tendency was observed with the CCCV test. The CV peak height was plotted against the ionic conductivity of several solvents and showed no linear relationship, implying that the reaction activity was influenced by the solid electrolyte interphase (SEI) formed. The charge transfer resistance was evaluated by impedance spectroscopy. The results revealed that not only the surface film resistance but also the charge transfer resistance was markedly increased in the electrolyte containing LiBOB; however, they were reduced by the addition of LiClO4.

Abstract A PEFC (polymer electrolyte fuel cell) with a large power generation area of 140 mm × 160 mm has spatial distributions of the water content of the MEA (membrane electrode assembly) and the electric current produced that depend on the flow rate and relative humidity of the supplied gas. When 49 NMR (nuclear magnetic resonance) surface coils arranged in 7 rows × 7 columns were inserted into the PEFC, two-dimensional spatial distributions of the water content of the MEA and the electric current could be measured from the acquired NMR signals. The water content of the MEA was calculated from the intensity of the NMR signal, and the electric current distribution was determined by an inverse analysis that reproduces the spatial distribution of the resonance frequency of the NMR signals. The PEFC, which was supplied with hydrogen and oxygen at a high humidity of 80 %RH, generated electric power at 130 A over the whole area of the MEA. On the other hand, under a low humidity of 40 %RH and low flow rate conditions, the water content of the MEA became high in the midstream and downstream regions, and a high electric current was generated in these regions.