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The interest for carbon nanostructure-based hierarchical materials for electrochemical applications has been growing continuously in the last decade, from both an energy and sensing perspective. The use of carbon nanostructures is permitting to explore new opportunities in these research fields. Graphene, carbon nanotubes (CNTs) and single-walled carbon nanohorns (SWCNHs) can contribute to the design of revolutionary devices thanks to their special electronic and structural properties. This dissertation discusses the opportunity of carbon nanostructures integration into the assembly of hierarchical nanomaterials for electrochemical catalysis and electrochemical sensing applications. In particular, the major efforts have been focused in the use of SWCNHs due to their high purity, high conductivity, morphology and porosity, which can considerably aid to enhance performances. The hybrid materials have been synthetized using a hierarchical approach in order to achieve multicomposite-multifunctional nanomaterials able to orchestrate energy related processes such as O2 reduction reaction (ORR) and CO2 reduction reaction (CO2RR) or allow specific H2O2 sensing. In particular, two catalytic systems named t-Fe@MWCNTs (featuring Fe-filled functionalized multi-walled carbon nanotubes) and g-N-SWCNHs (featuring N-doped graphitized carbon nanohorns) have been employed for the O2 reduction reaction catalysis. On the other hand, ternary systems named Pd/TiO2@ox-SWCNHs (integrating oxidized SWCNHs, Pd and TiO2 in a precise hierarchical order) and NiCyclam@BMIM/p-SWCNHs (based on the heterogenization of molecular NiCyclam by embedding into pristine SWCNHs-supported ionic liquids) have been employed for the CO2 reduction catalysis. Finally, a catalyst based on the coating of oxidized SWCNHs with CeO2 (named ox-SWCNHs/CeO2) has been employed for the catalysis of H2O2 reduction exploited for H2O2 amperometric sensing. In all cases, the nanocarbon scaffold may play a multi-role, facilitating electron transfer steps, bringing up specific textural properties, and contributing to physically adsorb gaseous reactants. The result is an enhancement of the catalytic performance in terms of activity, selectivity and stability, which has been communicated through publication (or in the process of being published) in peer-reviewed journals.

The importance of sensing hydrogen peroxide (H2O2) is due to its ubiquity, being extensively used in industry and also being a biologically relevant side-product of several enzymatic processes. Electrochemical sensing is one of the most robust and simple methods for sensing H2O2 and the discovery of new electroactive materials, particularly at the nanoscale, represents a very hot topic of research. Here, we prove that upon appropriate integration of oxidized single-walled carbon nanohorns (ox-SWCNHs) into a per se moderate H2O2 sensor such as cerium dioxide (CeO2), the sensitivity toward H2O2 is enhanced by almost two orders of magnitude (from 0.4 to 160 μA cm−2 mM−1), on par with that of state-of-the-art metal or metal oxide-based sensors. The modified electrode is also very stable (82% response after 2 weeks of continuous use) and the results highly reproducible. The developed nanohybrid ox-SWCNHs@CeO2, characterized fully and whose average size is about 70 nm as measured by both TEM and AFM, was also tested in real case studies such as washing liquids and milk and was confirmed to be a robust and highly selective material, being not affected neither by the presence of complex matrices, nor by interferents in several organic substrates. The high recovery confirmed the excellent specificity and flexibility of this new electrocatalytic material. Fil: Bracamonte, Maria Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. University of Trieste; Italia Fil: Melchionna, Michele. University of Trieste; Italia Fil: Giuliani, Angela. University of Trieste; Italia Fil: Nasi, Lucía. CNR-IMEM Institute; Italia Fil: Tavagnacco, Claudio. University of Trieste; Italia Fil: Prato, Maurizio. University of Trieste; Italia. Carbon Nanobiotechnology Laboratory; España. BasqueFdnSci; España Fil: Fornasiero, Paolo. University of Trieste; Italia

Summary Electrochemical oxygen reduction (ORR) is a challenging approach for the sustainable production of hydrogen peroxide (H 2 O 2 ) and is also a reaction of relevance in fuel-cell applications. Here, we propose an outstanding metal-free electrocatalyst for the unexpectedly selective ORR to H 2 O 2 , consisting of graphitized N-doped single-wall carbon nanohorns (CNHs). The catalyst can operate at acidic pH to a faradic efficiency as high as 98%, but it also shows excellent performance at either physiological or alkaline pH. Moreover, the very positive onset potentials observed at all pH values investigated (+0.40 V, +0.53 V, and +0.71 V at pH 1.0, 7.4, and 13.0, respectively), good stability, and excellent reproducibility make this material a benchmark catalyst for ORR to H 2 O 2 . The outstanding activity arises from a combination of several factors, such as CNH-dependent facilitation of electron delivery, suitable porosity, and a favorable distribution of the types of N atoms.