Vol 60, No 3 (2024)

In this paper, optimization of the manufacturing technology of bilayer supporting anode substrates for planar solid oxide fuel cells using precursors is carried out. The bilayer supporting anode substrates for the second generation planar SOFCs were fabricated by tape casting technique. In order to prepare a composite material for a current-collecting layer containing 60 vol. % NiO and a functional layer containing 40 vol. % NiO (proportions were chosen due to percolation theory), nickel sulfate heptahydrate NiSO₄·7H₂O was used. The composite mixture of 8YSZ/NiSO₄ was calcined at a temperature of 1000°С. Application of NiO precursor led to the obtaining of a strong anode substrate that retains mechanical stability during redox cycling. The fine dispersion of NiO in a thin functional layer led to a high density of three-phase boundaries, which positively affected the electrochemical activity of the anode. Model samples of solid oxide fuel cells were made on the base of the manufactured anode substrates, its electrochemical behavior was investigated using standard electrochemical techniques. The power density at an operating temperature of 750°С was 1 Wt/cm².

The evolution of the microstructure and composition of Ni-Co coatings for the protection of current collectors made of stainless chromium steel Crofer 22 APU from oxidation in the operating mode of the anode chamber of solid oxide electrolysis cells (SOEСs) has been studied. It is shown that due to the diffusion of the components of the steel and the coating, as well as the redox reactions occurring under the coating in the operating mode of the SOEС, the diffusion of chromium to the surface of the current collector is blocked. During operation in the air atmosphere of the anode chamber, the composition of the protective coating changes from metallic Ni-Co to a mixture of highly conductive oxides (Fe,Ni,Co)₃O₄ and (Ni,Co)O, which leads to a change in the type of time dependence of the specific surface resistance of the junction current collector-anode. At the same time, the obtained values of ~17 mOhm cm² during tests of 7000 hours are quite low and these coatings can be used to protect SOEС stack current collectors made of stainless chromium steel from oxidation.

The article explores the features of Pt(0) nanoparticle formation at the interface of nickel-aqueous solution of reagents and a similar interface containing nanoflakes of Co(OH)₂. The synthesis was carried out under Successive Ionic Layers Deposition (SILD) conditions, and solutions of Na₂PtCl₆, CoCl₂, and NaBH₄ were used as the reagents. Pt(0) nanolayers were produced on the nickel surface using Na₂PtCl₆ and NaBH₄ solutions, and for Co(OH)₂ nanolayers CoCl₂ and NaBH₄ solutions were used. Structural chemical studies of the samples synthesized were performed by HRTEM, FESEM, EDX, SAED, XPS, FT-IR, and Raman spectroscopy. It was shown that Pt(0) nanolayers consist of separate nanoparticles, while Co(OH)₂ nanolayers consist of nanoflakes. The main attention in the work is paid to the formation features of Pt(0) nanoparticles on a nickel surface to which a nanolayer of Co(OH)₂ was previously applied. The study of the electrocatalytic properties of such samples in the hydrogen evolution reaction (HER) during water electrolysis in the alkaline medium showed that the best properties are exhibited by nanoparticles synthesized after 20–40 SILD cycles and on nickel substrates with Co(OH)₂ nanolayers applied in advance. Also, it was found that among these samples the best properties are displayed by those containing Co(OH)₂ layers synthesized after 5 SILD cycles. One of the best examples of this series was obtained from 40 SILD cycles and is characterized by the overpotential value at 29 mV of current density at 10 mA/cm², the Tafel slope value at 29.5 mV/dec, and high stability of these values at multiple cycle potential. It is noted that the Pt(0) nanoparticles synthesized after 40 SILD cycles are 4–8 nm in size and are located on the surface of the nanoflakes at a distance of about 10 nm from each other for the nickel foam sample, on the surface of which a Co(OH)₂ nanolayer was synthesized as a result of 5 SILD cycles. These features contribute to the formation of a set of Pt(0) nanoparticle contact points with the surface of Co(OH)₂ nanoflakes, which determines the high electrocatalytic activity and stability of properties of such structures.

The results of the development and study of catalysts for the anode of water decomposition electrolyzers with a proton exchange membrane are presented. To deposit catalytic layers on a titanium carrier, the magnetron method of sputtering composite targets in a vacuum was used. Iridium and ruthenium were used as the main catalyst, and molybdenum, chromium, and titanium were used as functional additives. The electrochemical and structural characteristics of catalytic coatings have been studied. Using voltammetry methods, cyclic current-voltage and anodic characteristics of catalytic compositions were obtained, including at different temperatures of subsequent heat treatment in air, as well as at different measurement temperatures. The Tafel slopes of the current-voltage characteristics of the composite anodes, as well as the currents at a potential of 1.55 V (RHE), were determined. It has been shown that the minimum slopes were obtained for the Ir–Ru–Mo–Ti catalytic composition (b = 40–63 mV/dec), and the maximum currents for the Ir–Mo–Cr catalytic composition (i = 100–110 mA/cm² at E = 1.55 V (RHE)). It has been shown that the magnitude of CV adsorption currents in the anodic potential region correlates with the coefficient b of the Tafel equation E–lgi and determines the number of catalytic centers for the deprotonization stage of the oxygen evolution reaction. However, the activity of the catalyst in the OER is determined not only by the number of such centers, but mainly by the functional features of the catalyst itself, i.e., the composition of the catalyst and the conditions for its preparation (including the temperature of subsequent heat treatment of the catalyst in air). Catalytic compositions based on iridium with additions of molybdenum and chromium have higher activity in OER. Structural studies have shown that during magnetron sputtering of composite targets, even with small catalyst loadings, dispersed structures are formed, which on real porous titanium anodes should form on the front surface with a higher catalyst content.

The paper reports study of the applicability of calcium-borosilicate glass-ceramics with high boron oxide content as a sealant for solid oxide fuel cells. Chemical composition of the studied materials was 33 mol% CaO, 21 mol% B₂O₃, 46 mol% SiO₂. The material was studied as an alternative to existing sealants on the base of calcium and barium aluminosilicates, because of the limited adhesion of the latter to steel interconnects in fuel cells. The study has shown that the studied sealant has a softening point of about 920–930°C, which allows one to use for sealing of fuel cells at 925°C. Use of relatively low sealing temperature allows one to avoid overheating of the cell during sealing and to avoid accompanying degradation of the service properties. The studied sealant has demonstrated excellent adhesion to surface of interconnect materials (Crofer 22 APU steel). Furthermore, the studied sealant was found to be thermomechanically compatible with Crofer 22 APU steel and ZrO₂-based electrolytes.