An infrared-responsive poly(acrylamide-co-butyl methacrylate)/polyacrylic acid/multi-wall carbon nanotube (MWCNT) interpenetrating network hydrogel was prepared, and its temperature response was observed. This hydrogel exhibits an upper critical solution temperature (UCST)-type temperature response; it swells at temperatures above the UCST and shrinks at temperatures below the UCST. Gravimetric measurements of the gels revealed that the infrared-induced temperature rise of the MWCNTs and subsequent cooling could be the cause of the recurrent swelling and shrinking. However, the degree of swelling was reduced by the addition of MWCNTs despite their exothermicity.

Because of worldwide industrialization and increasing population, we are facing a problem concerning the availability of clean water. Therefore, the desalination of saline water using a reverse osmosis (RO) membrane is very important technology for producing a large amount of clean water. RO membrane technology has been well developed over the past 50 years. Although remarkable progress has been made in the fabrication of membranes, there is still a challenge to produce reliable membranes with antifouling properties, high mechanical strength, high tolerance to chlorine attack and a minimum thickness of the membrane barrier layer to provide a high flux. Multi-wall carbon nanotubes (CNT) have been added to the active layer of aromatic polyamide (PA)-RO membranes, with interesting results, such as better robustness. This review considers recent work on the synthesis, structure, performance, etc. of CNT/PA nanocomposite membranes.

The ion adsorption/desorption behavior of single-wall carbon nanotube capacitor electrodes revealed by galvanostatic charge/discharge tests, cyclic voltammetry (CV), X-ray diffraction (XRD), Raman spectroscopy, and electrochemical quartz-crystal microbalance (EQCM) measurements are reviewed. It was found that capacitance of SWCNT capacitor electrodes depends not only on the surface area, but also on the electrical density of states (DOS) of the SWCNTs. It was also found that the inner tube space of SWCNTs is used for ion-storage. Smaller-diameter SWCNTs showed a higher gravimetric capacitance at low current densities. On the other hand, large diameter SWCNTs showed a better rate performance. The ion adsorption/desorption dynamics of SWCNT electrodes were examined by the EQCM method. The results obtained indicate that in addition to traditional ion adsorption-type charge compensation, ion desorption-type charge compensation dynamics occur inside the SWCNTs. The dependence of the rate performance of SWCNT electrodes on the tube-diameter can be explained by this mechanism. By combining the above knowledge, we propose a new type of electrochemical energy storage device which uses the redox reaction of iodine ions in the hollow space of SWCNTs.

Carbon nanotubes (CNTs) are known to be a material with excellent properties, and their use in various fields has been highly anticipated. However, the commercialization of CNT composites has not progressed as expected. The reason for this is that their appropriate use was not sufficiently defined. This report discusses some promising applications of CNT composite materials for the near future.

Recent progress in thermoelectric materials based on single-wall carbon nanotubes (SWCNTs) is considered from fundamental and practical points of view. This progress has recently been driven by social requirements in energy harvesting, as well as significant interest in terms of materials preparation and fundamental physical transport properties. The latest thermoelectric properties of SWCNT-based materials have achieved a figure of merit (zT) as high as ca. 0.1, comparable to those of inorganic semiconductors such as silicon. Along with structural control and doping chemistry, several exotic applications including thermal energy harvesting for the Internet of Things (IoT) and invisible sensing are described.

The performance of polymer electrolyte fuel cells (PEFCs) depends on the oxygen reduction reaction (ORR) at the cathode. Although platinum-supported carbon black has been used as the ORR catalyst in PEFCs, the use of platinum makes the cells expensive. Recently, platinum-free catalysts have been developed as cheap and long-life alternatives for excellent ORR catalytic activity. This review focusses on the acidic ORR catalytic activity of modified carbon nanotubes (CNTs) such as nitrogen-doped CNTs and defect-induced CNTs.

Reaction sites of graphite electrodes of lithium-ion batteries covered with solid electrolyte interphase (SEI) was studied with electrochemical methods using molecular probes. In part 1, in order to clarify the effect of SEIs on the kinetics of lithium-ion transfer at electrolyte/electrode interface, the relation between the interfacial lithium-ion transfer resistance (R_ct) and electrochemical double-layer capacitance (C_dl) or standard rate constant (k⁰) of [Ru(NH₃)₆]^2+/3+ was investigated. 1/R_ct increased in proportional to the value of k⁰ and C_dl, and the proportional constants depended on the SEI-forming additives. In addition, activation energy was almost the same values. These results indicate that pre-exponential factor of Arrhenius equation for lithium-ion intercalation/deintercalation reaction depends on the nature of SEIs. In part 2, co-intercalation reactions of solvated lithium-ion into graphite in symmetric and asymmetric glyme-based electrolyte solutions was investigated to elucidate why SEI can suppress co-intercalation reactions. In all glyme solutions, the overpotential caused by vinylene carbonate (VC)-derived SEI was larger than that by ethylene carbonate (EC)-derived SEI. In addition, for asymmetric glymes, the overpotential was much larger than the other glymes and lithium-ion intercalation reactions took place in VC-based solution. These results were caused by its large steric hindrance and it can be concluded that the size of ionic path is an important factor that determines the suppression of the co-intercalation reaction.