JAPANESE

Next Generation Research Incubator

Research and Development of High-Efficiency Energy Conversion System Using Sunlight, Water and Hydrogen for the Nonuse of Fossil Fuels

The future of clean energy production lies in perfecting the nanoscale details of fuel cell components to create an innovative carbon-neutral energy system

The race is on to find ways to replace our reliance on fossil fuels with clean, sustainable methods of generating power. Current solar and hydrogen technologies are not yet efficient enough to produce energy on a large scale. With this in mind, researchers from the High-Efficiency Energy Conversion program aim to improve current solar and hydrogen fuel cells, while finding ways to reduce the pollutants already in the environment.

“We hope to develop efficient energy conversion systems that don’t emit carbon dioxide and pollutants,” says Nagahiro Hoshi, lead researcher on the program. “We will create a system that generates power fueled by sunlight and water. To do this, we must perfect the structures of the nanomaterials used to make solar and hydrogen fuel cells to optimize their ability to harness energy.”

Hoshi’s team works with various nanostructures, including nanoparticles, single-crystal surfaces and organic nanoassemblies, to build devices that can capture as much energy as possible without wastage.

Enhancing energy conversion

The surface structures of catalysts used in solar cells and hydrogen fuel cells can have a remarkable impact on conversion efficiency. For example, the orientation of atoms on a solar cell’s surface significantly affects the distribution of light across the cell. One way of enhancing a solar cell is to coat its surface with a dye. The atomic make-up of the dye contributes to the cell’s ability to generate electric current when exposed to light, providing it is adsorbed onto an appropriate surface.

The researchers recently explored the effects of using a zinc porphyrin (ZnP) dye on single-crystal titanium dioxide (TiO2) substrate surfaces. They trialed three different TiO2 substrates and found that their surface structures significantly altered the ability of the ZnP dye to generate an electric current efficiently. In fact, one of the ZnP TiO2 substrates had an incident photon-to-current conversion efficiency 13 times higher than one of the others.

Hoshi attributes the high conversion efficiency on this substrate to the bent configuration of the adsorbed porphyrin ring, which results in a shorter distance between the ring and surface. Such attention to detail in terms of nanoscale surface structures will generate the breakthroughs needed to create highly efficient, scalable and cost-effective solar power.

At present, hydrogen is mainly manufactured by using heat and pressure to separate it from natural gases. But since this also creates large amounts of carbon dioxide, scientists are exploring ways to generate hydrogen from water instead. When burned, hydrogen releases only water and steam, and it has the potential to fuel all kinds of systems. Hoshi’s team has developed a hydrogen-based method that could transform excess carbon dioxide into usable fuel.

“We are researching photocatalysts capable of decomposing pollutants such as carbon oxides, ammonia and waste oil,” says Hoshi. “We have had recent success in investigating the photocatalytic conversion of carbon dioxide into methane — the reaction pressure needed to reduce the carbon dioxide was created using hydrogen gas.”

To help realize this vision of a zero-emission society, Hoshi and his team welcome collaborations with researchers and private companies interested in this burgeoning field of nanotechnology.