Nikita B. Pavzderin

An oxygen pump is an electrochemical device that extracts oxygen from the air and has the potential to be used in medicine. The development and test results of a microtubular solid oxide oxygen pump with Ce_0.76Gd_0.24O_2−δ (GDC) electrolyte are presented. The supporting components of the oxygen pump are symmetrical dense electrode layers made of the La_0.8Sr_0.2Co_0.2Fe_0.8O_3−δ (LSCF)–GDC composite. Studies carried out by impedance spectroscopy on planar samples showed that the polarization resistance of the dense electrodes was greatly lower (by 2.5–5 times) than that of standard porous LSCF electrodes. Microtubular oxygen pumps were fabricated by the isostatic pressing of a stack of tapes rolled into a tube and subsequent co-sintering. The use of a nanosized GDC powder as the initial material for the tapes allowed their co-sintering at 1200 °C. In such a way, the chemical interaction between GDC and LSCF was prevented. Samples of the prepared cells had an outer diameter of 1.9 and 3.5 mm, and the thickness of the electrolyte and of the dense supporting electrodes was 20 and 130 µm, respectively. The specific oxygen productivity of the cells was 0.29 L∙h⁻¹∙cm⁻² at 800 °C and a current density of 1.26 A·cm⁻² (0.53 V). Thus, the energy consumption with the developed design for the production of 1 L of oxygen was 2.3 W∙h. The microtubular oxygen pumps appeared highly resistant to thermal shock.

Solid oxide fuel cells (SOFC) are promising, environmentally friendly energy sources. Many works are devoted to the study of materials, individual aspects of SOFC operation, and the development of devices based on them. However, there is no work covering the entire spectrum of SOFC concepts and designs. In the present review, an attempt is made to collect and structure all types of SOFC that exist today. Structural features of each type of SOFC have been described, and their advantages and disadvantages have been identified. A comparison of the designs showed that among the well-studied dual-chamber SOFC with oxygen-ion conducting electrolyte, the anode-supported design is the most suitable for operation at temperatures below 800 °C. Other SOFC types that are promising for low-temperature operation are SOFC with proton-conducting electrolyte and electrolyte-free fuel cells. However, these recently developed technologies are still far from commercialization and require further research and development.

Solvent-free aerosol jet printing has been investigated for fabricating metallic and semiconductor (gas-sensitive) microstructures based on copper nanoparticles on alumina, borosilicate glass, and silicon substrates. The synthesis of nanoparticles was carried out using a spark discharge directly in the printing process without the stage of preparing nano-ink. Printed lines with a width of 100–150 µm and a height of 5–7 µm were formed from submicron agglomerates consisting of primary nanoparticles 10.8 ± 4.9 nm in size with an amorphous oxide shell. The electrical resistivity, surface morphology, and shrinkage of printed lines were investigated depending on the reduction sintering temperature. Sintering of copper oxides of nanoparticles began at a temperature of 450 °C in a hydrogen atmosphere with shrinkage at the level of 45–60%. Moreover, aerosol heat treatment was used to obtain highly conductive lines by increasing the packing density of deposited nanoparticles, providing in-situ transformation of submicron agglomerates into spherical nanoparticles with a size of 20–50 nm. Copper lines of spherical nanoparticles demonstrated excellent resistivity at 5 μΩ·cm, about three times higher than that of bulk copper. In turn, semiconductor microstructures based on unsintered agglomerates of oxidized copper have a fairly high sensitivity to NH₃ and CO. Values of response of the sensor based on non-sintered oxidized copper nanoparticles to ammonia and carbon monoxide concentration of 40 ppm were about 20% and 80%, respectively.

Formation of dense La(Sr)Fe(Ga)O_3–δ (LSFG) interlayers on the surface of La_0.88Sr_0.12Ga_0.82Mg_0.18O_3–δ (LSGM) solid electrolyte by magnetron sputtering has been investigated. Their effect on electrode characteristics of the porous La_0.7Sr_0.3Fe_0.95Ga_0.05O_3–δ cathodes has been studied. It is shown that the elemental composition of the interlayers depends mainly on the elemental composition of the target, whereas the conditions of deposition (discharge power, atmosphere, etc.) have an insignificant effect. The synthesized interlayers contain the larger amounts of La and Ga and the smaller amount of Sr and Fe as compared with the target composition. The introduction of the dense interlayer between the porous electrode and the electrolyte improves the electrode characteristics by making easier the transition of O^2– ions across the electrode/electrolyte interface. The dense LSFG interlayers with the thickness of 600 and 800 nm decrease the polarization resistance of the electrode at 850°С by 33 and 43%, respectively.