A numerical simulation study of fluid flow, heat and mass transfer in a proton exchange membrane fuel cell (PEMFC) was performed. The three-dimensional continuity, momentum, and mass transport equations were discretized by the finite volume technique on the staggered mesh and solved by the SIMPLE algorism. The electrochemical reaction at the catalyst layer was considered in the model. Effects of flow rate, flow field, and channel configuration on current density distribution were examined to optimize the fuel cell design for high-energy efficiency and high power density performance. Simulation results show that insufficient inlet gas flow rate and low humidity would reduce the performance of the fuel cell. The effect of channel depth on current density and flow field was also presented.
Gas diffusion electrodes consisting of three layers, i.e., Pt/C catalyst layer (CL), hydrophobic gas-diffusion layer (GDL) and carbon backing layer (CBL), for polymer electrolyte fuel cells (PEFC) were investigated to clarify the relation between the electrochemical performance and the microstructure. We focused on effects of the GDL coating and the content of wet-proofing material (tetrafluoroethylene-hexafluoropropylene, FEP) in the CBL on the electrode performances with the constant composition of the CL. It was found that the hydrophobic GDL is effective to enhance the O2 diffusivity and the catalyst utilization. A high performance due to high O2 diffusivity was observed for the electrode by using the CBL without any FEP treatment at a relatively low air utilization operation. In contrast, the FEP treatment was found to be effective for the application to, for example, co-generation type fuel cells, which require the operation at relatively high potential and high utilization of air, e.g., 0.8 V and 40%.
Dependence of water partial pressure (PH2O) on the protonic conductivities of phosphate glasses made by a condensation-polymerization process below liquidus temperature has been investigated. Protonic conductivities of Sr-Ba-Pb + W-phosphate glass at 373 K were 4×10-5 and 6×10-4 S/cm, at PH2O = 0.035 and 0.485 atm, respectively. The PH2O dependence of conductivity for this glass is lower than that for Nafion. When operating under a non-humidified condition, the conductivity remains unchanged with time, and the fuel cell using the glass electrolyte was able to generate power continuously. The phosphate glass is one of the new candidate materials for electrolyte used in fuel cells.
A liquid organic electrolyte system for lithium ion batteries with LiCoO2 cathode containing phenyl group compounds as electrolyte additives has been studied. Cycle performance of LiCoO2 cathode charged to 4.5 V using electrolyte with additives were increased remarkably in comparison with that of electrolyte without additives. The correlation between the highest molecular orbitals (HOMO) energy and the oxidation potential of the additives is roughly linear.
In order to examine the effect of sonic waves on photocatalysis, sonophotocatalysis of oxalic acid was performed. The yield of CO2 increased about 31 times larger than that in the case of photocatalysis. The yield was twice larger than the sum of yields of photocatalysis and sonolysis. Synergistic effects were observed in an Ar atmosphere. In the case of air surroundings, however, synergistic effect could not be observed.