Koichi Hamamoto

A functional layer for direct use of hydrocarbon fuel in low temperature solid-oxide fuel cells

Solid-oxide fuel cells (SOFCs), which consist of ceramic components, directly convert the chemical energy of a fuel into electrical energy with the highest efficiency among various kinds of fuel cells. Because SOFCs are operated at high temperatures, typically in excess of 700 °C, direct use of hydrocarbon fuel becomes possible, which minimizes the system size as well as reducing the cost. It is, however, difficult to utilize direct reforming of hydrocarbon fuel when the operating temperature is below 600 °C, which is the target for intermediate temperature SOFCs. Here, we report a new concept of an SOFC utilizing a functional layer on the surface of an anode, for the direct reformation of a hydrocarbon fuel using a micro-tubular design. Preparation of the functional layer is cost-effective and the cell with a pure-ceria (CeO2) functional layer was successfully fabricated. The cell displays practical cell performance below 500 °C using methane–water mixture as the fuel gas, and shows enhanced performance compared to systems without a functional layer.

Comprehensive Enhancement of Nanostructured Lithium-Ion Battery Cathode Materials via Conformal Graphene Dispersion

Efficient energy storage systems based on lithium-ion batteries represent a critical technology across many sectors including consumer electronics, electrified transportation, and a smart grid accommodating intermittent renewable energy sources. Nanostructured electrode materials present compelling opportunities for high-performance lithium-ion batteries, but inherent problems related to the high surface area to volume ratios at the nanometer-scale have impeded their adoption for commercial applications. Here, we demonstrate a materials and processing platform that realizes high-performance nanostructured lithium manganese oxide (nano-LMO) spinel cathodes with conformal graphene coatings as a conductive additive. The resulting nanostructured composite cathodes concurrently resolve multiple problems that have plagued nanoparticle-based lithium-ion battery electrodes including low packing density, high additive content, and poor cycling stability. Moreover, this strategy enhances the intrinsic advantages of nano-LMO, resulting in extraordinary rate capability and low temperature performance. With 75% capacity retention at a 20C cycling rate at room temperature and nearly full capacity retention at -20 °C, this work advances lithium-ion battery technology into unprecedented regimes of operation.

Low temperature densification process of solid-oxide fuel cell electrolyte controlled by anode support shrinkage

A low temperature densification process of an electrolyte for solid-oxide fuel cells (SOFCs) has been developed by utilizing controlled electrode microtubular support shrinkage. This technology enables reduction of the co-sintering temperature for the electrolyte and the electrode (anode) support to temperatures as low as 1250 °C, resulting in the realization of a new anode microstructure using conventional, commercially available materials, NiO and Sc stabilized ZrO2. The new microtubular SOFC has shown high fuel cell performances from 0.36, 0.52, and 0.56 W cm−2 and energy efficiencies of 31, 44 and 47% (lower heating value) at 600, 650, and 700 °C respectively. Impedance analysis has also shown that the main contributing factor of the cell performance varies depending upon the operating temperatures, which is of importance for further optimization of the cell structures.

Reduction and Reoxidation Reaction of Catalytic Layers in Electrochemical Cells for NOx Decomposition

The influence of reduction and reoxidation reactions on NO x decomposition properties of an electrochemical cell with a catalytic layer (NiO/yttria stabilized zirconia) has been studied. To clarify the correlation between the NO x decomposition properties and the redox reactions of NiO in the catalytic layer, we carried out the measurements of reoxidation time dependence of electric current in the temperature range of 350-600°C. The electrochemical cell with the catalytic layer was shown for the highly effective NO, decomposition properties in the presence of excess oxygen. Even if the reoxidation time increases, the current efficiency for NO x decomposition was not deteriorated at less than 400°C. However, the current efficiency has been decreased according to an increase in temperature and/or reoxidation time at over 450°C. The deterioration of current efficiency occurs with the volume expansion of the catalyst layer by the reoxidation of NiO.

Low Temperature NOx Decomposition Using Electrochemical Reactor

We attempted to fabricate and evaluate a new electrochemical reactor with an additional NOx adsorption layer on a multilayer catalytic cathode and investigated a cell operating method to achieve a low temperature operation. To clarify the capability of a NOx adsorption layer, we carried out the NOx decomposition measurements of the cell. As a result, NOx adsorption layers have improved the NOx decomposition properties though the current values of each cell were almost the same. The NO decomposition by a GDC (10mol% Gd doped CeO2) -based cell with a Pt/K/Al2O3 adsorbent took onset around 225°. It was clarified that the starting temperature and the efficiency of the NOx decomposition are heavily dependent on the adsorptivity of NOx adsorbent and the cell operating voltage mode.