Porous carbon electrode materials are utilized in supercapacitors with very fast charge/discharge and high stability upon cycling thanks to their electrostatic charge storage mechanism. Further enhancement of the performance of such materials can be achieved by doping them with heteroatoms which alter the kinetics of charge/discharge of the adsorbed species and result in pseudocapacitance phenomena. Here, microporous N-doped activated carbons were synthesized by thermochemical activation process. The structure and composition of the final material were adjusted by tuning the synthesis conditions and the choice of precursor molecules. In particular, N-doped activated carbons with a controlled specific surface area in the range of 270–1380 m²/g have been prepared by KOH-activation of sucrose/ammonium citrate mixture. By adjusting the composition of precursors, N-doping was varied from ca. 1.5 to 7.3 at%. The role of the components and synthesis conditions on the composition and structure of final products has been evaluated. The N-doped activated carbon with optimized structure and composition has demonstrated an outstanding performance as electrode material for aqueous electrolyte supercapacitors. The specific capacitance measured in a 3-electrode cell with 0.75 mg/cm² loading of optimized activated carbon in 1M H₂SO₄ changed from 359 F/g at 0.5 A/g charging rate to 243 F/g at 20 A/g. Less than 0.01% of capacitance loss has been detected after 1000 charging/discharging cycles.

Solution combustion synthesis (SCS) is often utilized to prepare crystalline nanoparticles of transition metal oxides, in particular Mn oxides. The structure and composition of the final product depend on the conditions of the synthesis, in particular on the composition of metal precursors, its molar ratio to the fuel component, and the mode of heating. In the present work, the study of chemical phenomena that may occur in the SCS process has been studied for the conventional nitrate–glycine synthesis of Mn oxide, as well as for nitrate–citrate–glycine and nitrate–citrate–urea synthesis. In the case of nitrate–glycine synthesis at a 1:1 fuel-to-salt ratio, the formation of a weak complex of Mn(II) and glycine provides the conditions for an instantaneous SCS reaction upon heating, resulting in slight sintering of final oxide nanoparticles. Partial hydrolysis of the Mn precursor during slow solvent evaporation results in the formation of a mixture of oxides, namely MnO and Mn₃O₄. Formation of MnO is completely suppressed when ammonium citrate is added into the initial mixture. Pure Mn₂O₃ oxide is obtained from nitrate–citrate synthesis, while the pure Mn₃O₄ phase is obtained in the case of nitrate–citrate–glycine and nitrate–citrate–urea synthesis, due to the higher temperature generated in the presence of additional fuel. In the presence of citrate, the SCS reaction is slower, resulting in stronger sintering of the nanoparticles. The study of the electrochemical properties of synthesized oxides demonstrates that SCS with the nitrate–citrate–urea mixture provides the highest charge capacitance in 1 M NaOH: 130 F/g at 2 A/g. The impedance characterization of materials allows us to propose a tentative mechanism of degradation of electrode materials during galvanostatic cycling.

Transition metal oxides (TMOs) occupy an increasing share in the search for new electrode materials for Li-Ion batteries. Despite promising electrochemical performances (up to 1000 mAh g⁻¹ in the case of conversion), these materials have poor cyclability linked primarily to hysteresis phenomena. To improve their electrochemical performance, one strategy consists of reducing the particle size. A second strategy relies on the incorporation of fluorine directly into electrode materials to limit the solid–electrolyte interface (SEI). Our study focuses on the impact of fluorination on the electrochemical performance of manganese oxide obtained by solid combustion synthesis (SCS). Two fluorinating agents were used: pure gaseous molecular fluorine F₂ and radical fluorine F^• through xenon difluoride XeF₂ decomposition. The use of F₂ results in strong fluorination localized primarily at the particle surface while XeF₂ diffuses deeper into the particle, resulting in the removal of residual carbon from the synthesis by combustion. The electrochemical performance of the oxide fluorinated with XeF₂ reaches more than 750 mAh g⁻¹ after 160 cycles, whereas that of the oxide fluorinated by F₂ barely exceeds that of the non-fluorinated oxide, less than 200 mAh g⁻¹ after 200 cycles.

Solution combustion synthesis (SCS) is often utilized to prepare crystalline nanoparticles of transition metal oxides, in particular Mn oxides. The structure and composition of the final product depend on the conditions of the synthesis, in particular on the composition of metal precursors, its molar ratio to the fuel component, and the mode of heating. In the present work the study of chemical phenomena which may occur in the during SCS process has been studied for the conventional nitrate-glycine synthesis of Mn oxide, as well as for nitrate-citrate-glycine and nitrate-citrate-urea synthesis. In the case of nitrate-glycine synthesis, formation of a weak complex of Mn(II) and glycine provides the conditions of instantaneous SCS reaction upon heating, resulting in slight sintering of final oxide nanoparticles. However, partial hydrolysis of Mn precursor during slow solvent evaporation results in formation of mixture of oxides, namely MnO and Mn3O4. Formation of MnO is completely suppressed in the presence of ammonium citrate in the initial mixture, and pure Mn3O4 phase is obtained. SCS reaction in this case is slower, resulting in stronger sintering of the nanoparticles. The study of electrochemical properties of synthesized oxides demonstrated that the SCS with nitrate-citrate-urea mixture provides the highest charge capacitance in 1M NaOH: 130 F/g at 2 A/g. Impedance characterization of materials allowed to propose a tentative mechanism of degradation of electrode materials during the galvanostatic cycling.