Haruo Inoue [Chair], Specially Appointed Professor, Department of Applied Chemistry, Tokyo Metropolitan University

To realize artificial photosynthesis for sustainable and living earth there still remain many subjects to be resolved even in the current situation, where amazing scientific progress has been attained. Among them the most critical one for practical use for society should be a requirement on how energy output can exceed energy input, which is termed as “Renewable Energy Factor: REF”. Energy conversion efficiency is of course a crucial factor of energy output, but other factors of energy input such as cost for construction of facilities, operation, extraction, and transportation of energy for usage, cost for catalyst including lifetime of the catalysts etc. are practically more crucial. A definite viewpoint on how each factor involved in the REF can be breakdown into actual subject in scientific strategy should be indispensable. In this concurrent session on artificial photosynthesis, how could we get through the subjects to be resolved on the basis of state-of-the-art science and technology will be overviewed for audience to grip on the future prospect.

Takeshi Morikawa, Principal Researcher, Toyota Central R&D Labs., Inc.

Artificial photosynthesis, CO₂ reduction using sunlight energy and water, is one of the ultimate methods for addressing issues related to global warming and a fossil fuel shortage, and constructing a carbon-neutral society in the future. Systematic utilization of semiconductors and complexes are thus considered to be important to make the technology real by effective use of solar photons. Recently solar formate generation from CO₂ and H₂O was demonstrated utilizing a combination of semiconductors and complex catalysts with a solar-to-chemical conversion efficiency exceeding 4%. Further challenges for material design and development are necessary for the direct generation of solar fuels with high energy density.

Daniel G. Nocera, Professor, Department of Chemistry and Chemical Biology, Harvard University

The solar resource is unmatched in its size: more energy from the sun strikes the Earth in one hour than all of the energy consumed on the planet in an entire year. The dropping price of silicon photovoltaics is causing load defection to solar as an energy supply at an accelerated pace. This conversion to solar and, more generally, other renewable energy sources, have accordingly turned the energy research focus from generation to one of storage. The widespread implementation of solar now demands effective methods of storage. Truly disruptive improvements in energy storage technologies are limited by energy density. This limitation, however, does not apply to artificial photosynthesis, which produces fuels that possess the energy density needed for large-scale global energy storage. Research advances in artificial photosynthesis have now put society on a path to realizing a viable solar fuels industry.

Toru Setoyama, Executive Officer Fellow, Mitsubishi Chemical

Water splitting catalyzed by photo semi-conductor under sun light can provide H₂ (solar H₂) and O₂ together. CO₂ utilization combined with solar H₂ should be regarded as a final goal of artificial photo synthesis for the drastic reduction of CO₂ emission. Referring the other cases such as voltaic cell and wind turbine, introduction of renewable energy on large scale in society is not so easy due to competition with conventional infrastructures. In order to make a realistic strategy for the mitigation of climate change, we have to pick up major subjects and provide some technologies to solve them along the reliable roadmap. In order to reduce CO₂ emission as a short-term urgent issue, utilization of CH₄ with CO₂ to synthesize fuels and chemicals is reasonable from both a scientific view point and an economical view point. CH₄ is a better fossil resource than others because it can utilize CO₂ as a carbon resource.

As a CO₂ utilization technology, we can use CH₄ in a short term and solar H₂ as a final goal. I will argue the plausible strategy to introduce them.