A novel porous and crystalline two-dimensional (2D) electrochemically active covalent organic framework (COF) based on ortho-quinone units has been prepared as an innovative approach towards the development of organic cathode materials with multiple redox sites as an efficient electrocatalyst for the oxygen reduction reaction (ORR). In contrast with most of the previously reported COFs as electrocatalysts for the ORR, the electrocatalytic application of this material towards ORR has been investigated without adding any metal or conductive supporting material and avoiding any additional carbonization step. Additionally, the electrochemical properties of the COF material have been compared with two analogue amorphous frameworks with similar chemical composition, which points out the important role of the enhanced crystallinity and porosity of the COF network in its superior performance as an electrocatalyst towards ORR.

In the present work we develop an electrochemical assisted method to form nanopores on the surface of highly oriented pyrolytic graphite (HOPG), which was accomplished by a simple electrochemical route and a scalable nanomaterial, carbon nanodots, without applying high voltages, high temperatures or toxic reagents. HOPG electrodes are in a solution of N-enrich carbon nanodots in acidic media and the potential scans applied on HOPG lead to the formation of a spatially inhomogeneous porous surface. The diameter of the resulting nanopores can be tuned by controlling the number of electrochemical reduction cycles. The resulting nanoporous surfaces are characterized by atomic force microscopy, Raman spectroscopy, scanning electrochemical microscopy, electrochemical impedance spectroscopy and electrochemistry. These nanoporous HOPG showed high capacitance. Hence the potential of these surfaces to the development of energy storage devices is demonstrated.

Carbon nanodots (CNDs) with enriched periphery carboxylic groups were synthesized using the low-cost starting material glucose. The obtained CNDs were assembled onto Au electrodes following one of two strategies: covalent bonding, using cystamine as a cross-linker, or by drop-casting. The immobilized CNDs were covalently modified with the phenothiazine Azure A via electron transfer chemistry; in particular via reactions with aryl diazonium salts. The reaction mechanism for the diazonium functionalization of CNDs was investigated. Spectroelectrochemistry experiments confirmed that electrografting, rather than adsorption, governs the functionalization of CNDs with Azure A. Finally, the application of these CNDs as electrocatalysts for the oxidation of hydrazine was demonstrated.

Scanning electrochemical microscopy represents a powerful tool for electro(chemical) characterization of surfaces, but its applicability has been limited in most cases at microscale spatial resolution, and the greatest challenge has been the scaling down to the nanoscale for fabrication and the use of nanometer-sized tips. Here, Pt nanoelectrodes with nanometer electroactive area were fabricated and employed for imaging a distribution of gold nanoparticles (AuNPs) and bioelectrocatalytic activity of a redox-active enzyme immobilized on gold surfaces.