Gul Zeb

Decoration of Graphitic Surfaces with Sn Nanoparticles through Surface Functionalization Using Diazonium Chemistry

Composites of tin nanoparticles (Sn NP) and graphene are candidate materials for high capacity and mechanically stable negative electrodes in rechargeable Li ion batteries. A uniform dispersion of Sn NP with controlled size is necessary to obtain high electrochemical performance. We show that the nucleation of Sn particles on highly ordered pyrolitic graphite (HOPG) from solution can be controlled by functionalizing the HOPG surface by aryl groups prior to Sn deposition. On the contrary, we observe heterogeneous deposition of micrometer sized Sn islands on HOPG subjected to oxidation prior to deposition in the same conditions. We demonstrate that functional groups act as nucleation sites for Sn NP nucleation, and that homogeneous nucleation of small particles can be achieved by combining surface functionalization with diazonium chemistry and appropriate stabilizers in solution.

On the chemical grafting of titanium nitride by diazonium chemistry

Current research directions with the aim of extending the applications of titanium nitride (TiN) in areas of microelectronics, electrocatalysis, biosensors etc. require identifying new and efficient methods to modify this durable material with desired organic functionalities. We have clearly demonstrated in this work that diazonium chemistry can be considered for surface modification of titanium nitride. Indeed, a near-monolayer of aminophenylene has been reported to be spontaneously grafted onto the TiN surface by simple immersion of the substrates into an acidic solution of the corresponding diazonium cations. X-ray photoelectron spectroscopy measurements strongly suggested a covalent coating of aminophenyl groups on titanium nitride. Surface functionalization with aminophenylene layers was also investigated in presence of hypophosphorous acid and iron powder. Effect of these homogeneous and heterogeneous reducing agents with respect to the formation of aryl layers at different thicknesses was discussed in detail on the basis of conventional hemolytic dediazoniation mechanism in combination with the XPS results.

The importance of covalent coupling in the synthesis of high performance composite anodes for lithium ion batteries

We present a direct comparison between identical electrostatically and covalently assembled Si–graphene composites for lithium ion battery anodes. The covalent composite is synthesized via amide bond formation between aminated Si nanoparticles and carboxylated graphene using carbodiimide as coupling agent. The composite exhibits 14 times higher reversible capacity retention after 100 lithiation/delithiation cycles in comparison with electrostatically coupled Si–graphene composites. The results indicate that covalent coupling of Si and graphene improves the nanoscale mechanical stability during cycling and improves electrical contact between graphene and Si, thus resulting in higher capacity retention.

Pulse potential deposition of thick polyvinylpyridine-like film on the surface of titanium nitride

Electrografting based on the reduction of diazonium salts has been conventionally performed at the laboratory scale with cyclic voltammetry using a typical three-electrode electrochemical system. However, this promising coating technique still needs simplification for industrial feasibility. In this work, we report that pulse potential deposition, using an only two-electrode system, is a powerful tool for the grafting through diazonium chemistry. Importantly, this method allows the covalent attachment of a 135 nm thick polyvinylpyridine-like polymeric film on a titanium nitride wafer of industrial dimensions (200 mm diameter) using an acidic solution of 4-nitrobenzenediazonium and vinylpyridine monomer. Success in grafting suitable polymer films with well-controlled thickness on real engineering materials, such as titanium nitride, opens the door for many novel applications in micro-electromechanical systems (MEMS).