The electrochemical performance of porously sintered iron-based negative electrodes was examined to assess their suitability for application to high performance alkaline rechargeable batteries. Atomized iron-based powders with and without sulfur were used as raw materials of the electrodes. In order to clarify the discharge-charge mechanism, effects of additives such as K2S, Bi2S3 and LiOH on the electrochemical reaction were also discussed based on the results of cyclic voltammetry in conjunction with changes in the chemical bonds along with the depth from the electrode surface. It was found that the electrochemical performance of the iron electrodes (atomized iron-based powders without sulfur) was improved when K2S was added to the electrolyte of 8 M KOH. The discharge capacity was two times larger than those having the LiOH or Bi2S3 additive in the electrolytes. Furthermore, the discharge curves showed three distinct potential plateaus at about −1.0, −0.9 and −0.7 V vs. Hg/HgO, indicating that oxidation reaction was induced by sulfur additive in the electrolyte. It was revealed by X-ray photoelectron spectroscopy (XPS) analysis that the surface of the iron was uniformly covered with FeS of about 200 nm in thickness in the vicinity of the electrode surface. It is obvious from the XPS spectra that formation of FeS was the primary reaction on the electrode surfaces. Owing to the above-mentioned reaction, the discharge capacity for the negative electrodes fabricated with the sulfur-containing iron-based atomized powders increased with the number of cycles and reached 200 mAhg−1(Fe) at the 15th cycle, and maintained the behavior up to 25 cycles with a Coulombic efficiency of around 100%.

Ultrathin layers of oppositely charged poly͑diallyldimethylammonium chloride͒ ͑PDDA͒ and Nafion were alternately deposited on negatively charged phenylsilsesquioxane ͑PhSiO 3/2 ͒ microparticles via layer-by-layer assembly. An extremely small amount of Nafion was used for the layers. The average thickness of a Nafion layer was estimated to be 2.6 nm from the amount of deposited Nafion and the density. A monolithic sheet was obtained from PhSiO 3/2 particles with PDDA and the Nafion multilayer when the particles were pressed at 70 MPa. Fenton's test, differential thermal analysis, and thermogravimetry revealed that PhSiO 3/2 particles are chemically and thermally stable. The monolithic samples prepared using PDDA/Nafion-multilayer-coated PhSiO 3/2 particles showed proton conductivities ϳ4 orders of magnitude higher than those of samples without multilayers, and their conductivity reached about 10 −5 S/cm at 80°C and 80% relative humidity.

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Microbial fuel cells equipped with SPEEK-MEA (SPEEK-MFC) and Nafion-MEA (Nafion-MFC) were constructed with organic waste as electron donor and lake sediment as inoculum and were then evaluated comprehensively by electrochemical and microbial analyses. The proton conductivity of SPEEK was several hundreds-fold lower than that of Nafion 117, whereas the oxygen mass and diffusion transfer coefficients of SPEEK were 10-fold lower than those of Nafion 117. It was difficult to predict which was better membrane for MFC based on the feature of membrane. Analyses of polarization curves indicated that the potential of electricity production was similar in both MFCs, as the SPEEK-MFC produced 50-80% of the practical current density generated by the Nafion-MFC. Chronopotentiometry analyses indicated that the Nafion-MEA kept the performance longer than the SPEEK-MEA for long period, whereas performance of both anodes improved on time. Multidimensional scaling analyses based on DGGE profiles revealed the anolytic and biofilm communities of the SPEEK-MFC had developed differently from those of the Nafion-MFC. Clone library analyses indicated that Geobacter spp. represented 6.3% of the biofilm bacterial community in the Nafion-MFC but not detected in the SPEEK-MFC. Interestingly, the clone closely related to Acetobacterium malicum strain HAAP-1, belonging to the homoacetogens, became dominant in both anolytic and biofilm communities of the SPEEK-MFC. It was suggested that the lower proton conductivity of SPEEK-MEA allowed the bacteria closely related to strain HAAP-1 to be dominant specifically in SPEEK-MFC. These results indicated that Nafion-MFC ranked with SPEEK-MFC and that MEAs had strong selective pressure for electricity-producing bacterial community.