We are trying to simultaneously carry out two processes in a fuel cell: dehydrogenation from organic hydrides, which is an endothermic reaction, and power generation, which is an exothermic reaction. By studying the operating conditions (cell temperature, etc.) of the solid oxide fuel cell in detail, we have succeeded in recovering toluene from methylcyclohexane, one of the organic hydrides, while generating electricity.

This achievement shows the possibility of power generation using less energy than the dehydrogenation reaction, without using dehydrogenation facilities, which were conventionally required (Fig. 1). The recovered toluene production rate was 94%. Additionally, it has been shown that by changing the conditions, oxygen groups can be introduced into the aromatic backbone using a fuel cell.

Solid oxide fuel cells with high operating temperatures can achieve high power generation efficiency due to their high reaction activity. However, the formation of water at the fuel electrode dilutes the fuel, resulting in Nernst loss. To prevent this, proton-conducting ceramic fuel cells are attracting attention. In our laboratory, we are also investigating the effect of the intermediate layer, focusing on Ba-based electrolytes, with the aim of applying them as chemical reactors.

We are working on the direct synthesis of useful chemicals such as methane and methanol by electrochemical reduction of CO2 (carbon recycling). As basic research, we are using lithography, a semiconductor technology, to fabricate a novel composite electrode (Fig. 1) on a silicon substrate by combining different metals with different CO adsorption capacities, aiming to continuously generate multi-electron reduction. By adjusting the spacing between the different metals, we have succeeded in decreasing the amount of CO, a two-electron reduction product, and increasing the amount of methane, an eight-electron reduction product. We plan to work on improving the efficiency in the future.

The issues with CO2 electrolysis reduction are the low solubility of CO2 in the electrolyte and the hydrogen evolution reaction (HER), which is a side reaction. As a solution to this, we use a gas diffusion electrode (GDE), and by supplying CO2 as a gas from the gas diffusion layer side and causing a reaction at the three-layer interface of catalyst, electrolyte and CO2 gas, we can expect to improve the reaction rate and suppress HER. In our laboratory, we are investigating ways to improve performance by electrodepositing catalysts onto GDE (Fig. 2), applying ionomers to promote ion transport, and coating micro-porous layers used in solid polymer electrolyte fuel cells.

We have synthesized a boron carbonitride catalyst and are investigating the electrolytic synthesis of ammonia at room temperature and pressure under a nitrogen gas supply. Although its Faraday efficiency and yield are still low, we have found that its properties vary depending on the pH and potassium ion of the electrolyte.

Safe use of hydrogen is essential to realize a carbon-neutral society. To ensure this safety, we are studying the relationship between hydrogen behavior and mechanical properties in materials used in hydrogen infrastructure. Using low-strain rate tensile tests, we have shown that hydrogen embrittlement behavior is governed by the distribution of hydrogen concentration in steel. During elastic deformation, hydrogen-enhanced decohesion (HEDE) dominates due to increased interstitial hydrogen content, while in the plastic deformation region, dislocation migration becomes more active, and hydrogen accumulation in defects progresses due to increased hydrogen penetration from surface defects. In addition, hydrogen-enhanced local plasticity (HELP) is found to be dominant in the deformation region (Fig. 1)

The difference in fracture surface morphology between tests in an external high-pressure hydrogen environment and tests on hydrogen-charged materials revealed that the hydrogen embrittlement behavior is different. When using materials in a hydrogen environment, the stress (strain) and the environment are considered to have a significant influence on the safety of the materials.