Kensuke Takechi

Bio: Kensuke Takechi is an academic researcher from Toyota. The author has contributed to research in topics: Electrolyte & Battery (electricity). The author has an hindex of 23, co-authored 85 publications receiving 3495 citations. Previous affiliations of Kensuke Takechi include University of Notre Dame & Kyushu University.

Quantum Dot Solar Cells. Tuning Photoresponse through Size and Shape Control of CdSe−TiO2 Architecture

Abstract: Different-sized CdSe quantum dots have been assembled on TiO2 films composed of particle and nanotube morphologies using a bifunctional linker molecule. Upon band-gap excitation, CdSe quantum dots inject electrons into TiO2 nanoparticles and nanotubes, thus enabling the generation of photocurrent in a photoelectrochemical solar cell. The results presented in this study highlight two major findings: (i) ability to tune the photoelectrochemical response and photoconversion efficiency via size control of CdSe quantum dots and (ii) improvement in the photoconversion efficiency by facilitating the charge transport through TiO2 nanotube architecture. The maximum IPCE (photon-to-charge carrier generation efficiency) obtained with 3 nm diameter CdSe nanoparticles was 35% for particulate TiO2 and 45% for tubular TiO2 morphology. The maximum IPCE observed at the excitonic band increases with decreasing particle size, whereas the shift in the conduction band to more negative potentials increases the driving force and favors fast electron injection. The maximum power-conversion efficiency

Avoiding short circuits from zinc metal dendrites in anode by backside-plating configuration.

Abstract: Portable power sources and grid-scale storage both require batteries combining high energy density and low cost. Zinc metal battery systems are attractive due to the low cost of zinc and its high charge-storage capacity. However, under repeated plating and stripping, zinc metal anodes undergo a well-known problem, zinc dendrite formation, causing internal shorting. Here we show a backside-plating configuration that enables long-term cycling of zinc metal batteries without shorting. We demonstrate 800 stable cycles of nickel-zinc batteries with good power rate (20 mA cm(-2), 20 C rate for our anodes). Such a backside-plating method can be applied to not only zinc metal systems but also other metal-based electrodes suffering from internal short circuits.

Intrinsic Barrier to Electrochemically Decompose Li2CO3 and LiOH

Abstract: It is widely acknowledged that Li2CO3 and LiOH as side-products in the operation of a Li–air cell should be completely removed in the cycling to avoid cumulative negative effect on the cycling performance. However, the understanding of their electrochemical decomposition is limited. We report a mechanistic analysis of the intrinsic barrier to electrochemically decompose Li2CO3 and LiOH. Our first-principles study reveals that the decomposition is rate-limited by the electrochemical extraction of Li+, whereas the chemical release of anions is barrierless once the applied voltage overcomes the energy penalty to generate a Li-deficient surface. The voltage necessary for the decomposition of Li2CO3 is predicted to be in the range of 4.38–4.61 V, whereas for LiOH it is in the range of 4.67–5.02 V. The maximum charge efficiency to decompose Li2CO3 and LiOH in the operation of a Li–air cell is estimated to be 66% and 61%, respectively. The high intrinsic barrier originates from the energy cost of oxidizing redox...

Outdoor performance of large scale DSC modules

Abstract: To elucidate possible challenges for outdoor practical use of dye-sensitized solar cells, outdoor performance of large scale DSC modules made of series-connected 64 DSC cells have been examined for a half year. This is almost the first long term outdoor test of full-fledged DSC modules. Although DSC modules still need the larger area than conventional Si solar cell modules to attain the same rated output because of lower rated energy conversion efficiency, the measured data teach that DSC modules yearly generated 10–20% more electricity than conventional crystalline-Si modules of the same rated output power. This result also teaches that the energy conversion efficiency obtained by the certified measurement under 1 Sun condition does not always coincide with the electricity generated outdoors yearly, and is not a crucial measure to evaluate the performance of solar cells. The outputs of four modules showed similar monotonous slow and steady decreases, showing potential outdoor use of DSC. Simultaneously, it indicates that there are still remaining challenges to overcome one by one in attaining higher performance keeping long term stability.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Dye-Sensitized Solar Cells

Abstract: Dye-sensitized solar cells (DSCs) offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency. DSC research groups have been established around the worl ...

Toward Safe Lithium Metal Anode in Rechargeable Batteries: A Review.

Abstract: The lithium metal battery is strongly considered to be one of the most promising candidates for high-energy-density energy storage devices in our modern and technology-based society. However, uncontrollable lithium dendrite growth induces poor cycling efficiency and severe safety concerns, dragging lithium metal batteries out of practical applications. This review presents a comprehensive overview of the lithium metal anode and its dendritic lithium growth. First, the working principles and technical challenges of a lithium metal anode are underscored. Specific attention is paid to the mechanistic understandings and quantitative models for solid electrolyte interphase (SEI) formation, lithium dendrite nucleation, and growth. On the basis of previous theoretical understanding and analysis, recently proposed strategies to suppress dendrite growth of lithium metal anode and some other metal anodes are reviewed. A section dedicated to the potential of full-cell lithium metal batteries for practical applicatio...

A review on the visible light active titanium dioxide photocatalysts for environmental applications

Abstract: Fujishima and Honda (1972) demonstrated the potential of titanium dioxide (TiO2) semiconductor materials to split water into hydrogen and oxygen in a photo-electrochemical cell. Their work triggered the development of semiconductor photocatalysis for a wide range of environmental and energy applications. One of the most significant scientific and commercial advances to date has been the development of visible light active (VLA) TiO2 photocatalytic materials. In this review, a background on TiO2 structure, properties and electronic properties in photocatalysis is presented. The development of different strategies to modify TiO2 for the utilization of visible light, including non metal and/or metal doping, dye sensitization and coupling semiconductors are discussed. Emphasis is given to the origin of visible light absorption and the reactive oxygen species generated, deduced by physicochemical and photoelectrochemical methods. Various applications of VLA TiO2, in terms of environmental remediation and in particular water treatment, disinfection and air purification, are illustrated. Comprehensive studies on the photocatalytic degradation of contaminants of emerging concern, including endocrine disrupting compounds, pharmaceuticals, pesticides, cyanotoxins and volatile organic compounds, with VLA TiO2 are discussed and compared to conventional UV-activated TiO2 nanomaterials. Recent advances in bacterial disinfection using VLA TiO2 are also reviewed. Issues concerning test protocols for real visible light activity and photocatalytic efficiencies with different light sources have been highlighted.