Carbon nanotubes have aroused great interest since their discovery in 1991. Because of the vast potential of these materials, researchers from diverse disciplines have come together to further develop our understanding of the fundamental properties governing their electronic structure and susceptibility towards chemical reaction. Carbon nanotubes show extreme sensitivity towards changes in their local chemical environment that stems from the susceptibility of their electronic structure to interacting molecules. This chemical sensitivity has made them ideal candidates for incorporation into the design of chemical sensors. Towards this end, carbon nanotubes have made impressive strides in sensitivity and chemical selectivity to a diverse array of chemical species. Despite the lengthy list of accomplishments, several key challenges must be addressed before carbon nanotubes are capable of competing with state-of-the-art solid-state sensor materials. The development of carbon nanotube based sensors is still in its infancy, but continued progress may lead to their integration into commercially viable sensors of unrivalled sensitivity and vanishingly small dimensions.

Atomically precise, inherently charged Au(25) clusters are an exciting prospect for promoting catalytically challenging reactions, and we have studied the interaction between CO(2) and Au(25). Experimental results indicate a reversible Au(25)-CO(2) interaction that produced spectroscopic and electrochemical changes similar to those seen with cluster oxidation. Density functional theory (DFT) modeling indicates these changes stem from a CO(2)-induced redistribution of charge within the cluster. Identification of this spontaneous coupling led to the application of Au(25) as a catalyst for the electrochemical reduction of CO(2) in aqueous media. Au(25) promoted the CO(2) → CO reaction within 90 mV of the formal potential (thermodynamic limit), representing an approximate 200-300 mV improvement over larger Au nanoparticles and bulk Au. Peak CO(2) conversion occurred at -1 V (vs RHE) with approximately 100% efficiency and a rate 7-700 times higher than that for larger Au catalysts and 10-100 times higher than those for current state-of-the-art processes.

The electrochemical activity of stacked nitrogen-doped carbon nanotube cups (NCNCs) has been explored in comparison to commercial Pt-decorated carbon nanotubes. The nanocup catalyst has demonstrated comparable performance to that of Pt catalyst in oxygen reduction reaction. In addition to effectively catalyzing O(2) reduction, the NCNC electrodes have been used for H(2)O(2) oxidation and consequently for glucose detection when NCNCs were functionalized with glucose oxidase (GOx). Creating the catalysts entirely free of precious metals is of great importance for low-cost fuel cells and biosensors.