Highly porous nitrogen-doped carbon nanomaterials have distinct advantages in energy storage and conversion technologies. In the present work, hydrothermal treatments in water or ammonia solution were used for modification of mesoporous nitrogen-doped graphitic carbon, synthesized by deposition of acetonitrile vapors on the pyrolysis products of calcium tartrate. Morphology, composition, and textural characteristics of the original and activated materials were studied by transmission electron microscopy, X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, infrared spectroscopy, and nitrogen gas adsorption method. Both treatments resulted in a slight increase in specific surface area and volume of micropores and small mesopores due to the etching of carbon surface. Compared to the solely aqueous medium, activation with ammonia led to stronger destruction of the graphitic shells, the formation of larger micropores (1.4 nm vs. 0.6 nm), a higher concentration of carbonyl groups, and the addition of nitrogen-containing groups. The tests of nitrogen-doped carbon materials as electrodes in 1M H₂SO₄ electrolyte and sodium-ion batteries showed improvement of electrochemical performance after hydrothermal treatments especially when ammonia was used. The activation method developed in this work is hopeful to open up a new route of designing porous nitrogen-doped carbon materials for electrochemical applications.

Chemical modification improves the performance of the carbon anode in sodium-ion batteries (SIBs). In this work, porous nitrogen-doped carbon (PNC) was obtained by removing template nanoparticles from the thermal decomposition products of calcium glutarate and acetonitrile vapor. The treatment of PNC with a KOH melt led to the etching of the carbon shells at the nitrogen sites, which caused the replacement of some nitrogen species by hydroxyl groups and the opening of pores. The attached hydroxyl groups interacted with Br₂ molecules, resulting in a higher bromine content in the brominated pre-activated sample (5 at%) than in the brominated PNC (3 at%). Tests of the obtained materials in SIBs showed that KOH activation has little effect on the specific capacity of PNC, while bromination significantly improves the performance. The largest gain was achieved for brominated KOH-activated PNC, which was able to deliver 234 and 151 mAh g⁻¹ at 0.05 and 1 A g⁻¹, respectively, and demonstrated stable long-term operation at 0.25 and 0.5 A g⁻¹. The improvement was related to the separation of graphitic layers due to Br₂ intercalation and polarization of the carbon surface by covalently attached functional groups. Our results suggest a new two-stage modification strategy to improve the storage and high-rate capability of carbon materials in SIBs.

Structural imperfections, heteroatom dopants, and the interconnected pore structure of carbon materials have a huge impact on their electrochemical performance in lithium-ion and sodium-ion batteries due to the specific ion transport and the dominant storage mechanism at surface defect sites. In this work, mesopore-enriched nitrogen-doped carbon (NC) materials were produced with template-assisted chemical vapor deposition using calcium tartrate as the template precursor and acetonitrile as the carbon and nitrogen source. The chemical states of nitrogen, the volume of mesopores, and the specific surface areas of the materials were regulated by adjusting the synthesis temperature. The electrochemical testing of NC materials synthesized at 650, 750, and 850 °C revealed the best performance of the NC-650 sample, which was able to deliver 182 mA·h·g⁻¹ in sodium-ion batteries and 1158 mA·h·g⁻¹ in lithium-ion batteries at a current density of 0.05 A·g⁻¹. Our study shows the role of defect sites, including carbon monovacancies and nitrogen-terminated vacancies, in the binding and accumulation of sodium. The results provide a strategy for managing the carbon structure and nitrogen states to achieve a high alkali-metal-ion storage capacity and long cycling stability, thereby facilitating the electrochemical application of NC materials.

Lithium adsorption on high-surface-area porous carbon (PC) nanomaterials provides superior electrochemical energy storage performance dominated by capacitive behavior. In this study, we demonstrate the influence of structural defects in the graphene lattice on the bonding character of adsorbed lithium. Thermally evaporated lithium was deposited in vacuum on the surface of as-grown graphene-like PC and PC annealed at 400 °C. Changes in the electronic states of carbon were studied experimentally using surface-sensitive X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. NEXAFS data in combination with density functional theory calculations revealed the dative interactions between lithium sp² hybridized states and carbon π*-type orbitals. Corrugated defective layers of graphene provide lithium with new bonding configurations, shorter distances, and stronger orbital overlapping, resulting in significant charge transfer between carbon and lithium. PC annealing heals defects, and as a result, the amount of lithium on the surface decreases. This conclusion was supported by electrochemical studies of as-grown and annealed PC in lithium-ion batteries. The former nanomaterial showed higher capacity values at all applied current densities. The results demonstrate that the lithium storage in carbon-based electrodes can be improved by introducing defects into the graphene layers.

Carbon nanomaterials possessing a high specific surface area, electrical conductivity and chemical stability are promising electrode materials for alkali metal-ion batteries and supercapacitors. In this work, we study nitrogen-doped carbon (NC) obtained by chemical vapor deposition of acetonitrile over the pyrolysis product of calcium tartrate, and activated with a potassium hydroxide melt followed by hydrothermal treatment in an aqueous ammonia solution. Such a two-stage chemical modification leads to an increase in the specific surface area up to 1180 m² g⁻¹, due to the formation of nanopores 0.6–1.5 nm in size. According to a spectroscopic study, the pore edges are decorated with imine, amine, and amide groups. In sodium-ion batteries, the modified material mNC exhibits a stable reversible gravimetric capacity in the range of 252–160 mA h g⁻¹ at current densities of 0.05–1.00 A g⁻¹, which is higher than the corresponding capacity of 142–96 mA h g⁻¹ for the initial NC sample. In supercapacitors, the mNC demonstrates the highest specific capacitance of 172 F g⁻¹ and 151 F g⁻¹ at 2 V s⁻¹ in 1 M H₂SO₄ and 6 M KOH electrolytes, respectively. The improvement in the electrochemical performance of mNC is explained by the cumulative contribution of a developed pore structure, which ensures rapid diffusion of ions, and the presence of imine, amine, and amide groups, which enhance binding with sodium ions and react with protons or hydroxyl ions. These findings indicate that hydrogenated nitrogen functional groups grafted to the edges of graphitic domains are responsible for Na⁺ ion storage sites and surface redox reactions in acidic and alkaline electrolytes, making modified carbon a promising electrode material for electrochemical applications.