Oleg Vladislavovich Levin

The oxygen reduction reaction (ORR) on metal-free carbon catalysts is relevant both for fuel cells and metal-air batteries, where peroxide suppression is desired, and for decentralized H2O2 electrosynthesis, where partial reduction is beneficial. Here, multiwalled carbon nanotubes (MWCNTs) were modified by N+ ion irradiation at 20 keV for 5, 10, and 15 min, corresponding to fluences of about 1.4 × 1016, 2.8 × 1016, and 4.3 × 1016 cm–2 for samples N1, N2 and N3. The treatment preserved the overall nanotube scaffold while introducing progressively higher defect density and nitrogen content. X-ray diffraction and Raman spectroscopy showed expansion of interlayer spacing from 3.46 to 3.51 Å and an increase of ID/IG from 1.61 to 2.31. X-ray photoelectron spectroscopy revealed growth of total nitrogen from 0.7 to 1.4 atom % and of pyridinic plus pyrrolic nitrogen from 0.61 to 1.17 atom %, while conductivity changed nonmonotonically from 0.32 S ·cm–1 for pristine MWCNTs to 0.45, 0.28, and 0.22 ·S·cm–1 for N1, N2 and N3. Electrochemical measurements in alkaline media showed that ion-beam treatment tunes both ORR activity and selectivity. Sample N2 displayed the most positive onset potential, 0.82 V versus the reversible hydrogen electrode, and a lower peroxide-related response under the tested conditions, whereas N3 gave the highest disk currents and a more pronounced peroxide pathway. These results show that ORR selectivity on a single metal-free carbon scaffold can be adjusted through a balance between nitrogen incorporation, defect accumulation, and charge transport, with the intermediate irradiation regime providing the most favorable compromise for low-peroxide oxygen reduction route.

The electrochemical stability of redox-active polymers based on Ni(II)–Salen complexes is of critical importance for their application as electrode materials for supercapacitors and lithium-ion batteries. This study presents a systematic analysis of the influence of fluoride, chloride, and bromide anions on the redox behavior of two polymeric films: poly[Ni(Salen)] and sterically protected poly[Ni(Saltmen)]. Using cyclic voltammetry (CV), electrochemical quartz crystal microbalance (EQCM), and X-ray photoelectron spectroscopy (XPS), we identify two distinct degradation mechanisms: (1) axial coordination of halide ions to the Ni(II) center followed by demetallation, which disrupts the conjugated system and reduces conductivity, and (2) oxidative halogenation of the ligand. In the presence of chloride ions, both poly[Ni(Salen)] and poly[Ni(Saltmen)] lose approximately 70% of their initial capacity over 50 cycles, indicating progressive electrochemical degradation. In contrast, both polymers demonstrate high electrochemical stability in bromide-containing electrolytes, retaining most of their capacity under identical conditions. Fluoride coordinates without compromising redox performance, serving as a model for electrochemically inert ligands. The results highlight the critical role of both electrolyte composition and ligand design in ensuring the long-term stability of nickel–Salen polymers in energy storage devices.

Polymer films of nickel Schiff-base complexes were investigated to clarify degradation mechanisms induced by coordinating impurities—specifically, the protic solvents methanol and isopropanol. Films of poly[Ni(Salen)] and its sterically protected derivatives were electropolymerized in situ and subjected to cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM) measurements in dry acetonitrile electrolyte with 1% vol. alcohol added. In situ monitoring of redox activity and mass changes revealed something. It was revealed that traces of alcohols act as axial ligands to the Ni center. This disrupts the conjugated π-system and conductivity of the polymer. The rate of electrochemical stability strongly depends on the complex structure. The unsubstituted poly[Ni(Salen)] film showed the fastest loss of capacity in both methanol and isopropanol, whereas complexes with methyl substituents in the diimine bridge (poly[Ni(Salpn-1,2)] and poly[Ni(Saltmen)]) exhibited significantly improved stability. EQCM measurements revealed irreversible changes in the mass of all polymer films upon exposure to alcohol-containing electrolytes. These observations are consistent with the axial coordination of alcohol molecules to the Ni centers and the concomitant ingress of solvent species into the polymer matrix. The results demonstrate that molecular design—specifically, introducing steric hindrance around the metal center—markedly enhances resistance to coordinating impurities.