We demonstrate the efficient chemical vapor deposition synthesis of singlewalled carbon nanotubes where the activity and lifetime of the catalysts are enhanced by water. Water-stimulated enhanced catalytic activity results in massive growth of superdense and vertically aligned nanotube forests with heights up to 2.5 millimeters that can be easily separated from the catalysts, providing nanotube material with carbon purity above 99.98%. Moreover, patterned, highly organized intrinsic nanotube structures were successfully fabricated. The water-assisted synthesis method addresses many critical problems that currently plague carbon nanotube synthesis.

We have succeeded in synthesizing vertically aligned doubled-walled carbon nanotube (DWNT) forests with heights of up to 2.2 mm by water-assisted chemical vapour deposition (CVD). We achieved 85% selectivity of DWNTs through a semi-empirical analysis of the relationships between the tube type and mean diameter and between the mean diameter and the film thickness of sputtered Fe, which was used here as a catalyst. Accordingly, catalysts were engineered for optimum DWNT selectivity by precisely controlling the Fe film thickness. The high efficiency of water-assisted CVD enabled the synthesis of nearly catalyst-free DWNT forests with a carbon purity of 99.95%, which could be templated into organized structures from lithographically patterned catalyst islands.

We propose a statistical and macroscopic analysis to estimate the catalyst activity of water-assisted growth (super-growth) of single-walled nanotubes (SWNT) and to characterize SWNT forests. The catalyst activity was estimated to be 84% (+/-6%), the highest ever reported. The SWNT forest was found to be a very sparse material where SWNTs represent only 3.6% of the total volume. This structural sparseness is believed to play a critical role in achieving highly efficient growth.

Highly efficient single-walled carbon nanotube (SWNT) growth from Fe-Mo nanoparticle catalysts made by colloidal synthesis is demonstrated by water-assisted chemical vapor deposition. In a 10 min growth time, SWNT forests with heights up to 1.5 mm were synthesized possessing a 2.8 nm average diameter, carbon purity above 99.99%, and Brunauer-Emmett-Teller (BET) surface area of 1200 m 2 /g, which rivals SWNTs grown from sputtered Fe thin films. Realization of high efficiency SWNT growth using catalysts prepared by economical and scalable wet processes opens up a cost-effective route toward the mass production of SWNT forests.

After optimization of the preparation procedure and the alloy composition of a PtCo catalyst, we found that MEA of the PtCo catalyst could show better I-V performance than that of a Pt catalyst. To improve the stability of a carbon support, we have evaluated various types of carbon, and we found a graphitized carbon could show better stability than a normal carbon. We also evaluated the PtCo catalyst on the graphitized carbon to achieve both better ORR activity and better stability of carbon, but the PtCo catalyst on the graphitized carbon could not show any ORR activity improvement due to the larger particle size of PtCo. After exploring new carbons, we could find a unique carbon which has higher surface area and better stability than a normal carbon. We prepared the PtCo catalyst on the carbon, and this catalyst could show good balance between the ORR activity and the carbon stability.

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The synergistic extraction of aluminium(III) and gallium(III) with 2,4-pentanedione (Hacac) in heptane from a weakly acidic solution was investigated in the presence of 3,5-bis(trifluoromethyl)phenol (BTMP). A large enhancement of the extraction of metal(III) was ascribed to the formation of outer-sphere complexes between metal(III) chelates and BTMP in the organic phase. Furthermore, an IR study demonstrated that the outer-sphere complexes were formed by the hydrogen bond between the hydroxy hydrogen atom of BTMP and the oxygen atoms of metal(III) chelates. The formation constants of the outer-sphere complexes with BTMP were determined and compared with those with 3,5-dichlorophenol (DCP) to understand the steric effect of the phenol derivative in this synergistic extraction. The bulky trifluoromethyl-group of BTMP and the short oxygen–oxygen nonbonded distance of Al(acac)3 resulted in a steric repulsion between two BTMP molecules to prevent the formation of Al(acac)3·3BTMP, although Al(acac)3·3DCP, Ga(acac)3·3BTMP, and Ga(acac)3·3DCP could be formed. Such a steric effect on outer-sphere complexation improves the separation efficiency between aluminium(III) and gallium(III) in the present synergistic extraction.

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