Attachment of transition metal nanoparticles on nitrogen doped carbon nanotubes (MWNTs-CNx) and their further reactions.

Tesis (Maestría en Nanociencias y Nanotecnología)"The MWNTs-CNx exhibit important electronic and mechanical properties, that together with its small diameter, make them attractive for sensors production, substances specific filters and as field electrodes. Due to their structure, the MWNTs-CNx could also play an important role as substrates for the deposition of transition metal nanoparticles that allow to develop new catalysts. Thereby, the possibility of depositing some of this metals on MWNTs-CNx by a simple method, that does not involve oxidizing treatments in the nitrogen-doped carbon nanotubes, would enable to take advantages of their other properties. The results obtained from the use of the MWNTs-CNx as substrates for the transition metal nanoparticles deposits are presented in this work. At first stage, it was achieved an iron (Fe) deposit on the MWNTs-CNx, that by subsequent treatments produced a new type of hybrid structure composed by N-doped and undoped carbon nanotubes. Furthermore, are discussed the platinum (Pt) nanoparticles deposits that were also obtained in surface of MWNTs-CNx. Later, the morphological changes observed in the MWNTs-CNx by their electrochemical treatment or by the adding of titanium (Ti) during their synthesis by chemical vapor deposition (CVD) are explained. Finally, the feasibility of achieving silicon (Si) nanoparticles deposits on the surface of MWNTs-CNx by potentiometric techniques is also depicted.

Elastomeric and dynamic MnO2/CNT core-shell structure coiled yarn supercapacitor

Reversibly deformable and highly performing solid-state yarn supercapacitors are obtained using MnO2-deposited microcoiled yarn electrodes. The core(CNT)-shell(MnO2)-structured coiled electrodes achieve high stretchability (37.5%) without the help of elastomeric substrates, minimizing the size of the supercapacitors. Therefore, high specific capacitances of 34.6 F cm−3, 61.25 mF cm−2, and 2.72 mF cm−1 are achieved for coiled supercapacitors without impairing mechanical stretchability or electrochemical cyclability

Improvement of system capacitance via weavable superelastic biscrolled yarn supercapacitors

Yarn-based supercapacitors having improved performance are needed for existing and emerging wearable applications. Here, we report weavable carbon nanotube yarn supercapacitors having high performance because of high loadings of rapidly accessible charge storage particles (above 90 wt% MnO2). The yarn electrodes are made by a biscrolling process that traps host MnO2 nanoparticles within the galleries of helically scrolled carbon nanotube sheets, which provide strength and electrical conductivity. Despite the high loading of brittle metal oxide particles, the biscrolled solid-state yarn supercapacitors are flexible and can be made elastically stretchable (up to 30% strain) by over-twisting to produce yarn coiling. The maximum areal capacitance of the yarn electrodes were up to 100 times higher than for previously reported fibres or yarn supercapacitors. Similarly, the energy density of complete, solid-state supercapacitors made from biscrolled yarn electrodes with gel electrolyte coating were significantly higher than for previously reported fibre or yarn supercapacitors

Woven-yarn thermoelectric textiles

The fabrication and characterization of highly flexible textiles are reported. These textiles can harvest thermal energy from temperature gradients in the desirable through-thickness direction. The tiger yarns containing n- and p-type segments are woven to provide textiles containing n-p junctions. A high power output of up to 8.6 W m−2 is obtained for a temperature difference of 200 °C

Liquid-free covalent reinforcement of carbon nanotube dry-spun yarns and free-standing sheets

Carbon nanotubes (CNTs) possess exceptional mechanical properties, surpassing stiffness and strength metrics of common materials such as steel alloys by 100× at the nanoscale. However, when myriads of individual CNTs are bundled together into macroscopic ensembles like fibers or sheets, the result is a 100-fold drop in strength compared to its individual components. Here we present a general strategy aimed to close this gap in property scaling. By using vapor-phase polymerization of a crosslinkable polymer, we reinforced the weak interlinkages among individual CNTs within both yarns and sheets to promote a better transference of mechanical load across the structure. After the treatment, dry-spun, low-density 2.3 μm thin yarns increased their elastic moduli by at least 300%, and free-standing CNT sheets exhibited a 10× boost. In-situ synchrotron small-angle X-ray scattering revealed that polymer-reinforced yarns undergo limited CNT bundle rearrangement when subjected to tensile loads compared to pristine yarns. This evidence supports the hypothesis that the polymer hinders CNTs slippage, the root cause of the poor scaling of mechanical properties in these materials. While we demonstrated this reinforcement method for CNT structures, it is not specific to CNTs and could be used in a wide variety of other hierarchical nanostructured ensembles

All-Solid-State Carbon Nanotube Torsional and Tensile Artificial Muscles

We report electrochemically powered, all-solid-state torsional and tensile artificial yarn muscles using a spinnable carbon nanotube (CNT) sheet that provides attractive performance. Large torsional muscle stroke (53°/mm) with minor hysteresis loop was obtained for a low applied voltage (5 V) without the use of a relatively complex three-electrode electromechanical setup, liquid electrolyte, or packaging. Useful tensile muscle strokes were obtained (1.3% at 2.5 V and 0.52% at 1 V) when lifting loads that are 25 times heavier than can be lifted by the same diameter human skeletal muscle. Also, the tensile actuator maintained its contraction following charging and subsequent disconnection from the power supply because of its own supercapacitor property at the same time. Possible eventual applications for the individual tensile and torsional muscles are in micromechanical devices, such as for controlling valves and stirring liquids in microfluidic circuits, and in medical catheters

A new catalyst-embedded hierarchical air electrode for high-performance Li-O-2 batteries

The Li-O-2 battery holds great promise as an ultra-high-energydensity device. However, its limited rechargeability and low energy efficiency remain key barriers to its practical application. Herein, we demonstrate that the ideal electrode morphology design combined with effective catalyst decoration can enhance the rechargeability of the Li-O-2 battery over 100 cycles with full discharge and charge. An aligned carbon structure with a hierarchical micro-nano-mesh ensures facile accessibility of reaction products and provides the optimal catalytic conditions for the Pt catalyst. The new electrode is highly reversible even at the extremely high current rate of 2 A g(-1). Moreover, we observed clearly distinct morphologies of discharge products when the catalyst is used. The effect of catalysts on the cycle stability is discussed