Osaka University researchers develop efficient “green” hydrogen production system that operates at room temperature in air.
Hydrogen gas is a promising alternative energy source to overcome our reliance on carbon-based fuels, and has the benefit of producing only water when it is reacted with oxygen. However, hydrogen is highly reactive and flammable, so it requires careful handling and storage. Typical hydrogen storage materials are limited by factors like water sensitivity, risk of explosion, difficulty of control of hydrogen-generation. Hydrogen gas can be produced efficiently from organosilanes, some of which are suitably air-stable, non-toxic, and cheap. Catalysts that can efficiently produce hydrogen from organosilanes are therefore desired with the ultimate goal of realizing safe, inexpensive hydrogen production in high yield. Ideally, the catalyst should also operate at room temperature under aerobic conditions without the need for additional energy input.
A research team led by Kiyotomi Kaneda and Takato Mitsudome at Osaka University have now developed a catalyst that realizes efficient environmentally friendly hydrogen production from organosilanes. The catalyst is composed of gold nanoparticles with a diameter of around 2 nm supported on hydroxyapatite. The catalyst was synthesized from chloroauric acid using glutathione as a capping agent to prevent nanoparticle aggregation, resulting the formation of small size of gold nanoparticles. Glutathione-capped gold nanoparticles were then adsorbed on hydroxyapatite and glutathione was removed by subsequent calcination.
The team then added the nanoparticle catalyst to solutions of different organosilanes to measure its ability to induce hydrogen production. The nanoparticle catalyst displayed the highest turnover frequency and number attained to date for hydrogen production catalysts from organosilanes. For example, the nanoparticle catalyst converted 99% of dimethylphenylsilane to the corresponding silanol in just 9 min at room temperature, releasing an equimolar amount of hydrogen gas at the same time. Importantly, the catalyst was recyclable without loss of activity. On/off switching of hydrogen production was achieved using the nanoparticle catalyst because it could be easily separated from its organosilane substrate by filtration. The activity of the catalyst increased as the nanoparticle size decreased.
A prototype portable hydrogen fuel cell containing the nanoparticle catalyst and an organosilane substrate was fabricated. The fuel cell generated power in air at room temperature and could be switched on and off as desired. Images of the catalyst after use in the fuel cell resembled those of the unused catalyst, indicating that the hydroxyapatite-supported nanoparticle catalyst readily resisted aggregation.
Generation of hydrogen from inexpensive organosilane substrates under ambient conditions without additional energy input represents an exciting advance towards the goal of using hydrogen as a green energy source.
Will lead to checkup and early detection of serious diseases by examining breath
Research leading detection of low concentrations of gas present in exhaled human breath to health checkups and early detection and treatment of serious diseases is being performed. As gas sensors using nanomaterials can detect various gases even at low concentrations, installing such sensors in electronic healthcare devices is sought after, and research and development are being actively conducted.
Semiconductor gas sensors detect gas through reduced electrical resistance due to gas molecules attached to the surface of crystalline semiconductor materials. For this, gas sensors need a specific surface area of nanomaterials. In order to use nanomaterials for conventional gas sensors, a complicated flow was necessary, from nanomaterials synthesis to cleansing, uniform dispersion of solvent, applying on substrates, and sintering. Thus, there is a concern that manufacturing technology of such gas sensors requires significant time and labor, increasing cost.
A group of researchers led by Assistant Professor SUGAHARA Tohru at The Institute of Scientific and Industrial Research, Osaka University, succeeded in producing nanostructured gas sensor devices for detecting volatile organic compounds (VOC) in breath for the purpose of healthcare in time equivalent to or shorter than one tenth of the time required for manufacturing conventional gas sensors. This group improved conventional complicated production methods, developing a simple production method of just sintering substrates applied with materials. This gas sensor’s sensing response was comparable to the top-of-the-line sensors reported all over the world.
Since demand in healthcare products is on the rise, there is a lot of activity in research and development of sensors for checking health and disease by examining the gas components of a person’s breath. Breathalyzers for finding out who is driving drunk have already been commercialized. Recently, breath sensors for early detection of life-style diseases such as cancer and diabetes have been developed, but most of them are large, bulky and expensive. If gas sensors with high sensitivity are produced thanks to this group’s research results, portable breath sensors enabling early detection of diseases will gain popularity.
Before we have self-healing cars or buildings, we need strong materials that can fully self-repair in water-free environments. Self-healing materials work very well if they are soft and wet, but research groups have found that the ability to self-repair diminishes as materials dry out. Scientists at Osaka University are beginning to bridge this gap with rigid materials that can repair 99% of a cut on the surface in semi-dry conditions.
“The combination of physical and chemical self-healing enables materials to exhibit rapid and efficient self-healing even in a dried, hard state,” says senior author Akira Harada, a supramolecular polymer chemist at Osaka University. “Only a small amount of water vapor is needed to facilitate self-healing in the dried film state. In other words, water serves as a non-toxic glue in the self-healing process,” adds co-author Yoshinori Takashima, an associate professor at Osaka University.
Material engineers use several strategies to generate self-healing materials. They can physically embed the material with microcapsules or pathways filled with healing agents or build the material by using molecules, such as polyrotaxane, that change shape in response to damage—also called stress relaxation. Chemical self-healing materials use reversible bonds ranging from reversible chemical reactions to intermolecular interactions such as hydrogen bonding.
Harada’s lab combined physical and chemical self-healing mechanisms in their materials by using polyrotaxane as a backbone structure cross-linked by reversible interactions, in this case between boronic acid and diols. The polyrotaxane structure enables stress relaxation in recovery from a shallow dent, and the reversible nature of the bonds enables chemical self-healing from a deep cut. The combined approach allowed the materials to recover up to 80% of their strength within 10 minutes (without the combination, the materials could repair only up to 30% of their strength after an hour).
Osaka University (大阪大学 Ōsaka daigaku?), or Handai (阪大 Handai?), is a national university located in Osaka, Japan.
It is the sixth oldest university in Japan as the Osaka Prefectural Medical College, and one of Japan’s National Seven Universities. Numerous prominent scientists have worked at Osaka University such as the Nobel Laureate in Physics Hideki Yukawa.
Osaka University has 11 faculties (学部) for undergraduate programs, 16 graduate schools (大学院), 21 research institutes, 4 libraries, and 2 university hospitals.
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A group of researchers led by OSHITANI Jun (Associate Professor, Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University) and TSUJI Takuya (Associate Professor, Department of Mechanical Engineering, Graduate School of Engineering, Osaka University) examined the state of the surface of apparently fixed powder beds in which air weak enough not to move the powder is injected, and observed the following anomalous sinking phenomena, a world first:
- Unlike the case of fixed powder beds without air injection, anomalous sinking of spheres due to local fluidization of powder beds was observed.
- The final sunken depth of a sphere varied with the sphere density and air strength.
- When the sphere density is close to the powder bed density, spheres with smaller densities sank deeper than ones with bigger densities.
Sinking of objects in fluidization, in which powder is fluidized due to air injection, is used as a dry-type gravity separation technology for recycling of wastes, segregating waste plastics and non-ferrous metals. However, with this technology, only two kinds of objects with different densities, floating objects and sinking objects, can be separated at one time.
If this unique sinking phenomenon discovered by this group is used, a dry-type gravity separation technology for separating three objects with different densities can be developed, increasing the efficiency of recycling wastes.