Anion Conduction in Solid Electrolytes Probed by Water Transport Measurement

The application of inorganic materials as electrolyte of alkaline fuel cell is an important task to achieve noble-metal-free and high-temperature-resistant fuel cells. In the present study, water transport during ion conduction through solid electrolyte was measured to seek inorganic materials with anion conduction. We discovered the anion conduction in layered oxide NaCo2O4. Although LiCoO2 has the similar layered structure to NaCo2O4, this oxide showed cation conduction

Water Transport during Ion Conduction in Anion-Exchange and Cation-Exchange Membranes

Water transport during ion conduction through an anion-exchange membrane (AEM) immersed in an aqueous solution of HNO3 and KOH was investigated. We have developed an apparatus to accurately measure small changes in volumes of the aqueous solution at each side of the membrane by capillary tubes during the passage of an electronic current through the membrane. In contrast to the previously reported apparatus, the present apparatus can be applied to an AEM in various aqueous solutions of electrolytes, and measurements under conditions close to those in actual solid alkaline fuel cells are therefore possible by using alkaline solutions. The water-transport number for AEM in HNO3 was larger than that in KOH, indicating the importance of selecting the appropriate aqueous solution of electrolytes. It is possible to determine whether anions or cations are conductors in electrolyte membranes with unknown properties. © 2009 The Electrochemical Society

Development of Direct-Ethanol Anion-Conducting Solid Alkaline Inorganic Fuel Cell

Anion-conducting solid alkaline inorganic fuels cell was developed. This fuel cell could be operated at high temperature of 110℃. NaCo2O4 showed OH- conduction and activity for oxygen reduction reaction. The Fe-Co-Ni alloy catalyst prepared in this experiment showed activity not only for hydrogen oxidation reaction but also for ethanol oxidation reaction. Completely precious metal-free fuel cell composed of NaCo2O4 and Fe-Co-Ni cell was made. The cell generated a high output power density of 64 mW/cm2 directly from ethanol at current density of 160 mA/cm2

Performance of Solid Alkaline Fuel Cells Employing Layered Perovskite-Type Oxides as Electrolyte

Layered perovskite-type oxides were characterized by electrochemical measurement. Five kinds of perovskite oxides (LaSr3Fe3O10, NaLaTiO4, Sr4Co1.6Ti1.4O8(OH)2 ・xH2O, RbLaNb2O7 and LaFeO3) were used as electrolyte of fuel cells. Every perovskite oxide could generate current and high open circuit voltage (>0.8 V). The results were attributed to hydroxide ion (OH-) conduction resulting from reduction and H2O treatments. This hypothesis suggests that the possibility of a new alkaline fuel cell by using layered perovskite as electrolyte

Development of New Anion-Conducting Layered Perovskite-Type Oxide Electrolytes

Layered perovskite oxide LaSr3Fe3O10 (LSFO) was characterized by electrochemical measurements and XRD. The H2 sensing property of the oxide with 15wt% Pd/LSFO anode catalyst in H2 at room temperature was examined. As for H2 sensing, the potential about 0.9 V was gained in the presence of H2 without cathode catalyst. Furthermore, the membrane potential for concentration cell of NaOH with LSFO showed negative value, and the potential with anion exchange membrane (AEM) also showed negative value. These results suggest that LSFO shows OH- conductivity and the possibility of a new type fuel cell by using LSFO as electrolyte

Sodium cobalt oxide as a non-platinum cathode catalyst for microbial fuel cells

Platinum has long been the best catalyst for microbial fuel cells (MFCs), but its high cost and limited resources have prompted us to find more abundant and less expensive alternatives. In this study, the potential of a sodium cobalt oxide (NaCo2O4) as a cathode catalyst for MFCs was investigated. A catalyst ink, prepared by mixing 50 wt% of Ketjenblack with NaCo2O4, was applied (4 mg cm−2 as NaCo2O4) to a waterproofed carbon to make an air-cathode. The activity of oxygen reduction reaction of the cathode was measured by the linear sweep voltammetry technique. The NaCo2O4 cathode exhibited about 50–90% current density of a cathode made with platinum-on-carbon catalyst at the same electric potential. This NaCo2O4 cathode was fit into a MFC, which was then run to treat synthetic wastewater. It exhibited the current density of about 3 A m−2. No decline in the current density or performance was observed over several days of operation. It exhibited the highest power density of 0.6 W m−2. Optimization of the cathode preparation conditions may further improve the cathode performance. This study suggests a promising potential of NaCo2O4 as a cathode catalyst for MFCs. Keywords: Microbial fuel cells, Air-cathode, Non-platinum catalyst, Oxygen reduction reaction, Voltammetr

Improving CO Tolerance of Pt2Ru3/C Catalyst by the Addition of Tin Oxide

SnOx-modified Pt2Ru3/C catalysts were post-treated in different atmospheres at various temperatures to improve the catalytic activity for H2/CO electro-oxidation. The structures of the Pt2Ru3/C and SnOx/Pt2Ru3/C catalysts were characterized by X-ray diffraction. Electrochemical activities were evaluated by CO stripping voltammetry and single cell test. The SnOx/Pt2Ru3/C catalysts had a lower onset potential for CO electro-oxidation and greater cell voltage than the Pt2Ru3/C catalyst under high CO concentrations. The SnOx/Pt2Ru3/C catalyst treated in 5 % H2/Ar at 150℃ exhibited the greatest CO tolerance due to that the post-treatment caused the conversion of SnO2 to SnOx (1≤ x ≤2) without destroying PtRu alloy structure

Effect of Reduction Temperature of Fe-Co-Ni/C Catalyst on the Solid Alkaline Fuel Cell Performance

In this present work, the effect of reduction temperature of Fe-Co-Ni/C anode catalyst on the solid alkaline fuel cell performance was investigated. Fe-Co-Ni/C anode catalysts were prepared by the impregnation method, and reduced at 360℃, 500℃, and 900℃ in hydrogen flow for 2 h. The order of the maximum power density was as follows: Fe-Co-Ni/C with reduction at 360℃ > reduction at 500℃ > reduction at 900℃. The maximum power density of 17 mW cm^[-2] was obtained for the cell with Fe-Co-Ni/C anode reduced at 360℃. The order of the particle size was as follows: Fe-Co-Ni/C with reduction at 360℃ < reduction at 500℃ < reduction at 900℃. Fe-Co-Ni/C reduced at 360℃ with the smallest particle size showed the highest activity for hydrogen oxidation reaction