The Global Energy Association: Today’s interlocutor, Prof Masahiro Watanabe was nominated in the category of “Fuel cells and hydrogen energy” for “proposing several novel concepts in bimetallic alloy catalysts such for fuel cell anodes and cathodes, which are now being used in commercialized co-generation systems and fuel cell vehicles”. Recently our viewers recalled what anodes and cathodes are from the school physics course and are well prepared. Prof Watanabe, please tell us a bit about your researching activities?
Masahiro Watanabe: Life-policy of my research works is; first understanding the essential requirements in the important industrial application, then go back to the basic science, and feedback the results for the application in co-operation with industries.
My work on fuel cell catalysts started at the end of 1960th on the anode catalysts for direct oxidation of liquid fuels such as MeOH, enlightened by listening a lecture at an international meeting on a possibility of appearance of fuel cell cars in 1980th. Before my work, pure Pt was only good catalyst but still required the large amounts of Pt to get a good performance.
Therefore, I tried to improve the catalytic activity of the anode catalyst by alloying of various combinations and compositions among the precious metals, of which preparation became possible by my original simple & repeatable method, called“Ti Ranney Method”. I found a common new behavior on the alloys that relatively active elements such as Pt (A-group) can be enhanced dramatically by alloying with non-active elements such as Ru (B-group), realizing 20-30 times higher activity for MeOH oxidation and 1000 times for formic acid oxidation at ca. 50-50% combination, but A-A or B-B alloys showed only the dilution effect to each activity. So, I hypothesized that each element in the A-B alloys plays different role, e.g., adsorb intermediate species from fuel molecule and oxidant species from H2O, respectively, and enhance the slowest oxidation step.
To prove this hypothesis, controlled amounts of B-atoms were electrodeposited stepwise of less than one-atomic layer on A metal surface, regarded as a mono-layer alloy. The catalytic behaver of the mono-layer alloy depending on the composition coincides very well with that of the bulky alloy. This new method has been applied to development of new catalysis for various reactions, opened a new science area of“Catalysis by Ad-Atoms”.
Based on the results found above, I extended my work to develop highly dispersed catalysts on high surface area supports applicable to practical fuel stacks. For example, the preparation of Pt-Ru alloy/CB has developed and the activity has been referred as the standard by researchers and engineers for a long time. My alloys produced by the some companies is now uniquely used in commercialized DMFC and Ene-Farm.
In 1980th, I started to work on structures of the gas-diffusion layer and catalyst layer to get high performance fuel cell stack, where catalyst particles can fully play for the catalysis at the anode and cathode. This concept and information have been widely accepted in the practical fuel cell productions up to now.
From the end of 1980th, I started and has focused more on Polymer type fuel cells. For FCV applications, the performance and durability of the cathode catalysts is most important issue because the cathode reaction is 2-3 orders of magnitude lower than that at the anode supplied pure H2. I have first discovered that alloying Pt with non-precious metals such as Fe, Ni, Co enhances the activity by 10-20 times higher at 30-50 at. % of the latter content via the modification of electronic structure of the formed alloys.
By the detailed analysis with various modern analysis tools, we found that the located in vicinity of alloy surface dissolved out but the remaining Pt atoms rearranged in closed packing state, forming Pt skin layer and protecting non-precious metals inside of the alloy from further dissolution. The electronic structure of Pt skin is still modified by that of underlid alloy, resulting in the notable enhancement, mentioned above.
After the publication of these results at the end of 1990th, many research works have been done by many researchers as the so-called core-shell catalysts. I am very happy that this Pt-Co alloy supported on CB is now practically used on “Toyota Mirai”, which I am now driving.
Being evaluated such works mentioned above, we have awarded Government funds (totally ca. 150M US$) for the construction Clean Energy Research Center (2001) and then Fuel Cell Nanomaterials Center (2008) for fuel cell researches, from MEXT and METI (NEDO).
Works have been accelerated at the research centers by many staffs, PhD students, research engineers from co-operating companies and institutes.
“Nano-capcel method” for the preparation of catalysts is the one of important research products, which realizes precise control of the size and composition and uniformity of the dispersion state of catalyst particles on supporting materials, resulting in an exceptionally high activity and the stability.
The ceramic support materials with high electric conductivity and with good gas-diffusion structures, which we newly invented, becomes the key materials for the anode and cathode catalysts for the next generation FCVs or new heavy duty applications such as long-driving trucks etc.
We can see many publications by other groups on electrocatalysts, demonstrating high activities of alloys with a specific crystallite structure or low cost with non-noble metals or carbon-alloys, but most of them have not been used in the practical systems because of the lack of the viewpoint on the stability, unfortunately.
People say that Pt is expensive. However, the Pt loading of 10g/100kW or less in FC stack can be acceptable for the wide penetration of FCVs in the market, since it is the PGM loading level in wildly spread IC engine cars (>1000M in the world) for the post-treatment of the exhaust gas.
The Global Energy Association: You worked on several types of fuel cells including direct methanol fuel cells, polymer electrolyte ones, phosphoric acid ones, and solid oxide fuel cells. It is clear that each of them has its own qualities, but still – which one will be the battery of the future?
Masahiro Watanabe: Fuel cells are crucial as electricity production tools from H2 with the highest conversion efficiency in the forthcoming H2 society.
Among them, polymer electrolyte fuel cells (PEFCs) have features of the capability of the quick start at the operation condition between -40 to 100 ℃, with exceptionally high stack power density, resulting in the compact systems, e.g., >4kW/L approaching to that of IC engines, with short fueling time, and long driving distances (500-1000 km) by one fuel charging.
Thus, PEFCs have attracted enormous interest for various applications, which have first been commercialized as “Ene-Farm” of >200 thousand units since 1998 for the residential co-generation of electricity and heat in Japan. Hydrocarbon based membranes are being developed, e.g., by my group, which can operate temperature at an expanded temperature region, then the application of PEFCs can be expanded to distributed electric power stations with much higher efficiency.
They have also applied to fuel cell vehicles (FCVs) as their power sources. The application is quickly expanding not only for passenger cars but also heavy duty trucks, trains or ships or forklifts or mobile compact power sources for wheel-chair, robots, drones etc.
On the other hand, solid Oxide Fuel Cells (SOFCs) operate at 650-1000 deg. C, with further higher electric conversion efficiency than PEFCs. Small-size SOFCs have been commercialized as Ene-Farm already in Japan and also as power generation systems in several countries. By the reduction of their production cost, the LNG-fueled application will be expanded much more in near future.
Direct Methanol Fuel Cells can find a niche for them in maintenance-free portable or small stational power sources.
The Global Energy Association: If we are talking about hydrogen, it is no use forgetting about the fact that it may come from completely different sources. Thus, blue hydrogen is made from LNG, while the green one is produced from water and can surely be considered a renewable source of energy. So, what are, in your opinion, the prospects of each of them considering the future energy mix?
Masahiro Watanabe: In view of achievement of the suppression of gross emission of CO2 <20% level at 2050, the uses of renewable energies such as solar or wind, etc. are of cause essential.
However, these green energies have problems to be solved, e.g., such as instability during the operation in second, hour, day and seasons and also their geometrically uneven distribution. For their applications, therefore, it is crucial to develop the science/technology for the efficient conversion/storage of them as electric or chemical energies.
Compared to battery storage system, the green H2 is the best as chemical conversion/storage system having no limitation of the volume and timing of uses, however the time is needed for the construction of the plants and infrastructures to be able to cover the future energy consumption.
Therefore, LNG is currently the most reliable and acceptable energy resource to be replaceable from petroleum, coal or nuclear power plant (NPP) in all over the world, to lower CO2 emission or avoid the serious NPP accident. Unfortunately, until 2050 we may not be able to shift enough to the renewable energies in every countries, so that the stepwise replacement of LNG as blue H2 with renewable energies in possible areas should be considered.
The blue hydrogen made from LNG is now used in fuel cells as commercialized co-generation systems and power sources for fuel cell vehicles, showing the over-all energy efficiencies more than 90% and 65%, respectively. The efficiencies, based on LNG, are by ca.2 times higher than that of the conventional fire power plants or internal combustion engines. These efficiencies has been demonstrated to be improved farther by >10%, based on H2, which clearly demonstrate that the fuel cell systems become the best tool to consume the green H2, tooThe large volume use of the blue H2 may be considered as one of the best-mix energies for power-generations with H2 or H2+LNG combustion or for SOFCs, for which so-called CCS (Carbon dioxide Capture & Storage) has to be developed similtaniously.
The Global Energy Association: Various experts from all over the world put their faith in hydrogen-powered cars as a future alternative for the electric vehicles. Will we really be able drive H2 cars without fear of being left without recharging somewhere in the middle of the desert?
Masahiro Watanabe: “Toyota Mirai” commercialized after 200 thousand km driving tests in various modes including severe weather conditions such as Alaska or Death Valley. I am driving the first version Mirai for 5 years without any mechanical trouble and can drive >500km with 5kg H2 only of 5 min. fueling time.
It is easy to check the possible driving distance and find a H2 refueling station in web-site, although there is still a limitation of the drivability. Our Government has promoted to construct 160 H2-fueling stations so far and plans to construct 320 and 480, until 2025 and 2030, respectively.
After 2030, therefore, people can drive everywhere in Japan. The same situation has started in several developed countries in the world. The systematic construction of H2 fueling stations in the developing stage of H2 society may solve such a fear of H2 being empty during peoples driving.
I learned previously in Makinsey report that the construction of H2 infrastructure could be a half, compared to that of the electric infrastructure for Battery EVs.
