A method for the chemical synthesis of reduced graphene oxide has been developed. It is based on the chemical oxidation of multiwalled carbon nanotubes by means of heptavalent manganese with subsequent reduction. Sodium hypophosphite and sulfite were used as reductants. It has been confirmed by different methods that reduced graphene oxide is obtained. Current-potential curves for electrodes based on reduced graphene oxide in an oxygen fuel cell mock-up with alkaline electrolyte have been studied. It has been found that the characteristics of the electrode of graphene oxide reduced with sodium hypophosphite in oxygen reduction reaction are three to four times higher than those of the electrode of starting multiwalled carbon nanotubes. The electrodes based on reduced graphene oxide are superior to multiwalled carbon nanotube-MnO2 composite in characteristics. The characteristics of oxygen electrodes based on reduced graphene oxide were stable during 6-month tests. The reduced graphene oxide obtained promises much as a material for the oxygen electrodes of electrochemical power sources.

Photoluminescent graphene quantum dots (GQDs) the one- or two-layer graphene nanoparticles 1.5–3 nm in size with a blue emission have been obtained from electrochemically synthesized partially unzipped multi-walled carbon nanotubes ultrasonically treated for one hour. Various physicochemical methods including photoluminescence spectroscopy, XRD, TEM, and Raman spectroscopy, have been used to characterize the electrochemically synthesized partially unzipped multi-walled carbon nanotubes and GQDs. Two-layer oxygen electrodes were fabricated, where GQDs served as an active layer. The investigations of electrocatalytic characteristics of the oxygen electrodes fabricated of the obtained materials were carried out in a fuel half-cell with an alkaline electrolyte. The fabricated oxygen electrodes were stable for six months at a discharge current density of 200 mA cm ⁻² . The obtained GQDs are promising materials as a new type of catalyst carriers for oxygen electrodes of fuel cells.

In this work, a new photovoltaic device was prepared. The device uses titanium (Ti) foil/TiO₂ nanotubes as the photoanode and multi-walled carbon nanotubes (MWCNTs) as a photosensitizer. Titanium dioxide nanotube arrays (TiO₂-NTs) were prepared by one-step anodic oxidation. Cut-MWCNTs with a length of less than 100 nm were obtained by the mixed-acid oxidation of MWCNTs. The two materials were combined to form a TiO₂-NTs@cut-MWCNT heterostructure by electrophoresis. TiO₂-NTs@cut-MWCNTs were characterized by field-emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD), which showed that the two materials were effectively combined. We fabricated the heterostructure into a photovoltaic device, showing an enhanced photocurrent response and an efficiency of 0.0138%, and explained this phenomenon by performing UV-vis absorption spectroscopy and electrochemical tests. It is hoped that this work can provide a reference value for the application of carbon nanotubes in photovoltaic devices.

A new type of metal-free oxygen electrode has been proposed. Its distinguishing feature is applying as an active layer nanodispersed graphitic carbon nitride with electrocatalytic properties controlled by synthesis conditions. Optimal conditions of thermochemical synthesis of g-C₃N₄ by a heat treatment of a solid mixture of melamine precursor and nitrogen-rich urea additive have been defined. The obtained layered g-C₃N₄ has been characterized by XRD, selected area electron diffraction, TEM and FTIR. An investigation of the electrocatalytic characteristics of oxygen electrodes has been carried out in a fuel half-cell with alkaline electrolyte. The electrochemical characteristics of the obtained g-C₃N₄ material with melamine-to-urea ratio 1:2 have been shown to be close to those of platinum electrodes. Electrochemical studies have shown that the obtained carbon nitride is a promising material as metal-free catalyst for oxygen electrodes of fuel cells The long-term testing of produced materials confirmed that they were stable over six months. Graphical Abstract