Browsing by Author "Kim, Nam Dong"

Now showing 1 - 3 of 3
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    Atomic cobalt on nitrogen-doped graphene for hydrogen generation
    (Nature Publishing Group, 2015) Fei, Huilong; Dong, Juncai; Arellano-Jiménez, M. Josefina; Ye, Gonglan; Kim, Nam Dong; Samuel, Errol L.G.; Peng, Zhiwei; Zhu, Zhuan; Qin, Fan; Bao, Jiming; Yacaman, Miguel Jose; Ajayan, Pulickel M.; Chen, Dongliang; Tour, James M.
    Reduction of water to hydrogen through electrocatalysis holds great promise for clean energy, but its large-scale application relies on the development of inexpensive and efficient catalysts to replace precious platinum catalysts. Here we report an electrocatalyst for hydrogen generation based on very small amounts of cobalt dispersed as individual atoms on nitrogen-doped graphene. This catalyst is robust and highly active in aqueous media with very low overpotentials (30 mV). A variety of analytical techniques and electrochemical measurements suggest that the catalytically active sites are associated with the metal centres coordinated to nitrogen. This unusual atomic constitution of supported metals is suggestive of a new approach to preparing extremely efficient single-atom catalysts.
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    Three-Dimensional Networked Nanoporous Ta2O5–x Memory System for Ultrahigh Density Storage
    (American Chemical Society, 2015) Wang, Gunuk; Lee, Jae-Hwang; Yang, Yang; Ruan, Gedeng; Kim, Nam Dong; Ji, Yongsung; Tour, James M.; Richard E. Smalley Institute of Nanoscale Science and Technology
    Oxide-based resistive memory systems have high near-term promise for use in nonvolatile memory. Here we introduce a memory system employing a three-dimensional (3D) networked nanoporous (NP) Ta2O5-x structure and graphene for ultrahigh density storage. The devices exhibit a self-embedded highly nonlinear I-V switching behavior with an extremely low leakage current (on the order of pA) and good endurance. Calculations indicated that this memory architecture could be scaled up to a ∼162 Gbit crossbar array without the need for selectors or diodes normally used in crossbar arrays. In addition, we demonstrate that the voltage point for a minimum current is systematically controlled by the applied set voltage, thereby offering a broad range of switching characteristics. The potential switching mechanism is suggested based upon the transformation from Schottky to Ohmic-like contacts, and vice versa, depending on the movement of oxygen vacancies at the interfaces induced by the voltage polarity, and the formation of oxygen ions in the pores by the electric field.
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    Ultrahigh strength, modulus, and conductivity of graphitic fibers by macromolecular coalescence
    (AAAS, 2022) Lee, Dongju; Kim, Seo Gyun; Hong, Seungki; Madrona, Cristina; Oh, Yuna; Park, Min; Komatsu, Natsumi; Taylor, Lauren W.; Chung, Bongjin; Kim, Jungwon; Hwang, Jun Yeon; Yu, Jaesang; Lee, Dong Su; Jeong, Hyeon Su; You, Nam Ho; Kim, Nam Dong; Kim, Dae-Yoon; Lee, Heon Sang; Lee, Kun-Hong; Kono, Junichiro; Wehmeyer, Geoff; Pasquali, Matteo; Vilatela, Juan J.; Ryu, Seongwoo; Ku, Bon-Cheol; The Carbon Hub
    Theoretical considerations suggest that the strength of carbon nanotube (CNT) fibers be exceptional; however, their mechanical performance values are much lower than the theoretical values. To achieve macroscopic fibers with ultrahigh performance, we developed a method to form multidimensional nanostructures by coalescence of individual nanotubes. The highly aligned wet-spun fibers of single- or double-walled nanotube bundles were graphitized to induce nanotube collapse and multi-inner walled structures. These advanced nanostructures formed a network of interconnected, close-packed graphitic domains. Their near-perfect alignment and high longitudinal crystallinity that increased the shear strength between CNTs while retaining notable flexibility. The resulting fibers have an exceptional combination of high tensile strength (6.57 GPa), modulus (629 GPa), thermal conductivity (482 W/m·K), and electrical conductivity (2.2 MS/m), thereby overcoming the limits associated with conventional synthetic fibers.