In order to develop highly efficient and stable catalysts for oxygen reduction reaction (ORR) that do not contain precious metals, it is necessary to modify carbon nanotubes (CNT) and define the effect of the modification on their activity in the ORR. In this work, the modification of CNTs included functionalization by treatment in NaOH or HNO₃ (soft and hard conditions, respectively) and subsequent doping with nitrogen (melamine was used as a precursor). The main parameters that determine the efficiency of modified CNT in ORR are composition and surface area (XPS, BET), hydrophilic–hydrophobic surface properties (method of standard contact porosimetry (MSP)) and zeta potential (dynamic light scattering method). The activity of CNT in ORR was assessed following half-wave potential, current density within kinetic potential range and the electrochemically active surface area (S_EAS). The obtained results show that the modification of CNT with oxygen-containing groups leads to an increase in hydrophilicity and, consequently, S_EAS, as well as the total (overall) current. Subsequent doping with nitrogen ensures further increase in S_EAS, higher zeta potential and specific activity in ORR, reflected in the shift of the half-wave potential by 150 mV for CNT_NaOH-N and 110 mV for CNT_HNO3-N relative to CNT_NaOH and CNT_HNO3, respectively. Moreover, the introduction of N into the structure of CNT_HNO3 increases their corrosion stability.

The influence of the types and amounts of oxygen (O), nitrogen (N), and/or phosphorus (P) heteroatoms on the surface of carbon nanotubes (CNTs) on stability and catalytic activity in the oxygen reduction reaction (ORR) was investigated in alkaline media. It is shown that functionalization of CNTs leads to growth of the electrochemically active surface and to an increase in activity in the ORR. At the same time, a decrease in stability is observed after functionalization of CNTs under accelerated corrosion testing in alkaline media. These results are most significant on CNTs after functionalization in HNO₃, due to the formation of a large number of structural defects. However, subsequent doping with N and/or P atoms provides a further activity increase and enhances the corrosion stability of CNTs. Thus, as shown by the studies of characteristic parameters (electrochemical active surface values (S_EAS); E_1/2; corrosion stability), CNTs doped with N and NP are promising catalytic systems that can be recommended for use as fuel cell cathodes. An important condition for effective doping is the synthesis of carboxyl and carbonyl oxygen-containing groups on the surface of CNTs.

Platinum deposited on dispersed materials has so far been the most demanded catalyst for creating cathodes for a wide range of electrochemical power sources. This paper sets out to investigate the effect of carbon nanotube (CNT) modification by O, N, and P atoms on the structural, electrocatalytic, and corrosion properties of the as-synthesized monoplatinum catalysts. The investigated Pt/CNT_mod catalysts showed an increased electrochemically active platinum surface area and electrical conductivity, as well as an increased catalytic activity in the oxygen reduction reaction (ORR) in alkaline electrolytes. The improved characteristics of Pt/CNT catalysts are explained by alterations in the composition and number of groups, which are formed on the CNT surface, and their electronic structure. By the sum of the main characteristics, Pt/CNT_HNO3+N and Pt/CNT_HNO3+NP are the most promising catalysts for use as cathode materials in alkaline media.

Bimetallic catalysts containing platinum and transition metals (PtM, M = Mo, Ni, CoCr) were synthesized on carbon nanotubes (CNTs) functionalized in an alkaline medium. Their platinum content is 10–15% by mass. PtM/CNT_NaOH are active in both the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) in alkaline electrolytes. Although catalysts based on a single transition metal are inactive in the HOR, their activity in the cathode process of ORR increases relative to CNT_NaOH. When using the rotating ring-disk electrode method for ORR, PtM/CNT showed a high selectivity in reducing oxygen directly to water. In HOR, the PtM/CNT catalyst had an activity comparable to that of a commercial monoplatinum catalyst. The results obtained show that it is possible to use the PtM/CNT catalyst in an alkaline fuel cell both as an anode and as a cathode.

The sulfonated polynaphthoyleneimide polymer (co-PNIS70/30) was prepared by copolymerization of 4,4′-diaminodiphenyl ether-2,2′-disulfonic acid (ODAS) and 4,4’-methylenebisanthranilic acid (MDAC) with ODAS/MDAC molar ratio 0.7/0.3. High molecular weight co-PNIS_70/30 polymers were synthesized either in phenol or in DMSO by catalytic polyheterocyclization in the presence of benzoic acid and triethylamine. The titration reveals the ion-exchange capacity of the polymer equal to 2.13 meq/g. The membrane films were prepared by casting polymer solution. Conductivities of the polymer films were determined using both in- and through-plane geometries and reached ~96 and ~60 mS/cm, respectively. The anisotropy of the conductivity is ascribed to high hydration of the surface layer compared to the bulk. SFG NMR diffusometry shows that, in the temperature range from 213 to 353 K, the ¹H self-diffusion coefficient of the co-PNIS_70/30 membrane is about one third of the diffusion coefficient of Nafion^® at the same humidity. However, temperature dependences of proton conductivities of Nafion^® and of co-PNIS_70/30 membranes are nearly identical. Membrane–electrode assemblies (MEAs) based on co-PNIS_70/30 were fabricated by different procedures. The optimal MEAs with co-PNIS_70/30 membranes are characterized by maximum output power of ~370 mW/cm² at 80 °C. It allows considering sulfonated co-PNIS_70/30 polynaphthoyleneimides membrane attractive for practical applications.