Graphene oxide (GO) is a promising material for H2O vapour sensing. However, H2O sensing mechanisms are still under investigation especially in the case of thermally reduced GO. To this purpose, planar devices were fabricated by spin-coating graphene oxide on glass substrates. Ultra high response to H2O was recorded but poor repeatability and stability over time were also noted. Three different degrees of thermal reduction were applied to improve material stability. An inverse change of resistance was observed for reduced graphene oxide compared to pure graphene oxide upon interaction with H2O. The sensing mechanisms that govern GO and reduced GO behaviour were studied based on DC measurements. In the case of GO, strong ionic conductivity was proposed whereas in the case of reduced GO mixed electronic/ionic with the leading mechanism affected by H2O percentage in air, degree of material reduction and sensor working temperature. Finally, it was found that by promoting one sensing mechanism over the other, improved operating humidity range of the sensor can be achieved.

We demonstrate permanent water trapping in reduced graphene oxide after high relative humidity exposure. For this purpose, we grew graphene oxide films via spin-coating on glass substrates followed by thermal reduction. The electrical resistance of the planar device was then measured. We observed that resistance is significantly increased after water vapor exposure and remains stable even after 250 days in ambient conditions. Various techniques were applied to desorb the water and decrease (recover) the material's resistance, but it was achieved only with low temperature thermal annealing (180 °C) under forming gas (H₂/N₂ mixture). The permanent effect of water absorption was also detected by x-ray photoelectron spectroscopy.

Silicon nanoparticles are used to enhance the anode specific capacity for the lithium-ion cell technology. Due to the mechanical deficiencies of silicon during lithiation and delithiation, one of the many strategies that have been proposed consists of enwrapping the silicon nanoparticles with graphene and creating a void area between them so as to accommodate the large volume changes that occur in the silicon nanoparticle. This work aims to investigate the electrochemical performance and the associated kinetics of the hollow outer shell nanoparticles. To this end, we prepared hollow outer shell silicon nanoparticles (nps) enwrapped with graphene by using thermally grown silicon dioxide as a sacrificial layer, ball milling to enwrap silicon particles with graphene and hydro fluorine (HF) to etch the sacrificial SiO₂ layer. In addition, in order to offer a wider vision on the electrochemical behavior of the hollow outer shell Si nps, we also prepared all the possible in-between process stages of nps and corresponding electrodes (i.e., bare Si nps, bare Si nps enwrapped with graphene, Si/SiO₂ nps and Si/SiO₂ nps enwrapped with graphene). The morphology of all particles revealed the existence of graphene encapsulation, void, and a residual layer of silicon dioxide depending on the process of each nanoparticle. Corresponding electrodes were prepared and studied in half cell configurations by means of galvanostatic cycling, cyclic voltammetry and electrochemical impedance spectroscopy. It was observed that nanoparticles encapsulated with graphene demonstrated high specific capacity but limited cycle life. In contrast, nanoparticles with void and/or SiO₂ were able to deliver improved cycle life. It is suggested that the existence of the void and/or residual SiO₂ layer limits the formation of rich Li_XSi alloys in the core silicon nanoparticle, providing higher mechanical stability during the lithiation and delithiation processes.

For environmental and cost purposes, solvent-free electrode manufacturing techniques are needed for lithium-ion cell technology. In this work, we present a stand-alone lithium-ion anode, containing graphene and Poly-lactic acid (PLA) as active and binding material, respectively, manufactured in a free-solvent process. To this purpose, PLA and graphene were thoroughly mixed and a hot-press was used to form the resulting electrode. At a half-cell configuration, the electrodes exhibited a stable reversible specific capacity of more than 300 mAh g⁻¹ at C/15 for over 450 cycles and a promising C-rate performance of around 90 mAh g⁻¹ at 6 C of constant current mode. After cyclic voltammetry analysis of the electrochemical behavior and the kinetics of the prepared electrodes, the Li atom diffusion coefficient was calculated around 1.2 × 10⁻⁸ cm²/s during lithiation and 0.6 × 10⁻⁸ cm²/s during delithiation. Finally, we show that this electrode manufacturing technique can be upscaled for higher mass loading and corresponding areal capacity at least up to 1 mAh/cm² and thus it can be considered for practical applications.