Because of the world-wide progress of global warming and climate change, the introduction of CO2-free renewable energies, such as solar, wind, hydro, and geothermal powers, is demanded.
We are studying electrochemical energy conversion systems, using hydrogen, to use renewable energy at dsired time and place.
For example, hydrogen can be produced by electrolysis, using surplus renewable electricity without the emission of CO2.
The CO2-free hydrogen is stored till when electricity is insufficient or transported to where electricity is insufficient, and converted to electricity, using a fuel cell on-site.
This concept is expected to lead to the achievement of the energy circulation without the emission of CO2.
Our research projects, national projects and collaborative projects with our industrial partners, are on the subjects of basic technology of water electrolysis, direct electrochemical synthesis of chemical hydrides, and innovative fuel cell catalysts toward the production, transportation, and conversion of hydrogen, respectively.
Sophistication of water electrolysis technologies
Water electrolysis is one of the most fundamental reactions in electrochemistry and has been industrialized for a long time.
Water electrolysis is recently regarded as key technologies to achieve large-scale production of CO2-free hydrogen from renewable energy.
However, there are a lot of issues to be solved to adapt water electrolysis to renewable energy with a large fluctuation.
Our group are developing common method and electrolyzer to evaluate electrode performances, and mechanisma for catalyst degradation, which we expect to accerelate industrial development of electrolyzers.
The development of new materials that is durable under fluctuating power of renewable energy is also quite important for the above technology.
Alkaline water electrolysis has advantages in cost and scale, but its components are likely degraded under flutuating power and start/stop operation.
We are analyzing reverse current caused in the electrolyzer via precise measurement and simulation, using small-sized bipolar electrolyzer, and are developing new coating materials and self-repairing catalysts to achieve high durability of electrodes.
Solid-polymer electrolyte (SPE) water electrolyzers which were developed on the basis of the structure of polymer electrolyte fuel cells (PEFCs), have attracted increasing attention because of their high energy efficiencty and tolerance to fluctuating power.
Current SPE water electrolyzer require much precise metals, such as iridium and platinum; therefore, we are developing new technologies to reduce their amounts.
We are also studying the basics of cell design of SPE water electrolyzers, using anlysis techniques developed for PEFCs.
Direct electrochemical synthesis of chemical hydrides
Hydrogen, the lightest element in nature, exits as gas at ambient atmosphere, which causes large costs for long-range transportation.
The use of hydrogen carrier, such as liquid hydrogen, chemical hydrides, and ammonia, have extensively been investigated to solve this problem.
We are focusing on the use of chemical hydrides and its efficient production.
Toluene, a representative chemical hydride, accommodate three molecules of H2 per a molecule. The volume of a hydrogenated toluene, methylcyclohexane (MCH), corresponds to the 1/500 volume of the gaseous H2.
One of the biggest advantages of MCH is its storage and transportation via an infrastructure for gasoline.
Currently, MCH is synthesized by the chemical reaction of toluene with H2 which was produced by water electrolysis; however, the energy efficiency of this process is not so high.
We have developed a new electrolyzer for direct electrochemical synthesis of MCH without the production of H2, applying the design of PEFC cells.
We also join the JST CREST project organized by Prof. Atobe in YNU to apply the above technology for large-scale electrochemical synthesis of various valuable organic compounds.
Innovative fuel cell catalysts
Among fuel cells, polymer electrolyte fuel cells (PEFCs) are useful and have been practically realized for residential fuel cells and fuel cell vehicles because of their relatively low operation temperature (from room temperature to approx. 80 °C) and high energy efficiency.
Much platinum-based catalysts are used in the current PEFCs; therefore, the reduction of the usage of platinum-group metal elements is crucial for future PEFCs.
In addition, the degradation of catalysts, such as platinum and carbon supports, is also problematic.
Our group has focused on developping highly active and durable catalysts consisting of metal oxides for PEFCs.
The development of metal-oxide-based catalysts with high activity like platinum is quite challenging; however, we are tuckling to this issue to realize the catalytic mechanism of metal oxides from structural and mechanistic understanding of catalytic active sites via materials synthesis, physicochemical characterizations, electrochemical analyses.
