Rod-shaped manganese dioxide (MnO2) nanoparticles with three different crystallographic phases, namely α-, β-, and γ-MnO2, were hydrothermally prepared. The products were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), Brunaure-Emmett-Teller (BET) method, and electrochemical measurements as cathode materials for secondary lithium-ion batteries. The crystalline phase of MnO2 depended mainly on the Mn concentration of precursor solution and reaction temperature whereas it was not influenced by the pH value of precursor solution. All the samples were obtained as secondary particles composed of rod-shaped nanoparticles and the sizes of α- and γ-MnO2 were smaller than that of β-MnO2. In electrochemical tests, the γ-MnO2 had the highest initial capacity of 190 mA h g−1 among three different crystal phases and maintained better performance than the other crystallographic samples in the subsequent discharge/charge cycles. As a result, the electrochemical performance of MnO2 depends on the crystal structure rather than the particle size.
The polymer electrolyte fuel cell (PEFC) is expected as the future automotive power source. However, the PEFC is inferior to the current gasoline engine in the response to the load change such as the acceleration of the vehicle. The main reason of inferiority in such response is the difficulty of quick increase in steam supply to the MEA. In order to solve such difficulty, we made the study of the MPL having the ability to keep water to be supplied to the ion exchange membrane in running short of steam supply. The MPL is one of the parts constituting the MEA. We developed the prototype of the MPL containing the material, the activated carbon which has the ability to keep water. In the experiment to stop supply of the steam during the generation of electricity, the MEA using this prototype MPL could generate electricity longer than the MEA using the conventional MPL could do so. In this article, we showed that the MEA using this prototype MPL had the ability to keep water. Further it was showed that this water kept in the MPL could be supplied to the ion exchange membrane when steam supply to MEA decreases.
The crystalline and electronic structures of lithium insertion/extractions in trirutile LixFeF3 as well as the intercalation/deintercalation average voltages have been investigated using the density functional theory within the DFT+U framework. Our calculations give a good prediction of the average voltages with the reaction proceeds in a single phase way for the LixFeF3 (x = 0.25–0.75). The crystalline structures and electronic structures are also analyzed in detail in order to understand the effects of Li intercalation/deintercalation and the magnetic properties in trirutile LixFeF3. It is found that Li0.25FeF3 and Li0.75FeF3 are ferrimagnetic, while Li0.5FeF3 and LiFeF3 are antiferromagnetic.
One-dimensional multicomponent cellular automata, with the addition of a reactive boundary, can model electrochemical processes such as cyclic voltammetry. Electron transfer probabilities at the boundary are derived from the Butler-Volmer type kinetic equation. The model is applied successfully to coupled irreversible systems in which an escaping species is involved in addition to oxidized and reduced species.