Anatolii K. Demin

The idea of nuclear-hydrogen energy draws growing interest of power engineering specialists. One of the ways to implement such a direction of development is integration of nuclear power station and high temperature electrochemical devices, namely solid oxide electrolyzers (SOE) and fuel cells (SOFC). This paper reviews the principal features of the devices and their high efficiency of energy transformation. The electrical efficiency of the SOEs can exceed 100 % at the expense of high-grade potential heat energy consumed by the electrolyzer. The efficiency of the SOFCs amounts to 70 %. The state of the art of long-term tests of single cells of SOEs and SOFC stacks are presented.

Hydrogen sensors, especially those operating at high temperatures, are essential tools for the emerging hydrogen economy. Monitoring hydrogen under process conditions to control the reactions for detecting confined species is crucial to the safe, widespread use and public acceptance of hydrogen as fuel. Hydrogen sensors must have a sensitivity ranging from traces of hydrogen (parts per million (ppm)) up to levels near the lower explosive limit (LEL = 4% H₂ in the air) for safety reasons. Furthermore, they need to operate in cryogenic, ambient, and high-temperature environments. Herein, emphasis is given to hydrogen sensors based on solid oxide electrolytes (operating at high temperatures), in particular oxygen ion and proton conductors. The review is devoted to potentiometric, amperometric, and combined amperometric-potentiometric hydrogen sensors. Experimental results already reported in the international literature are presented and analyzed to reveal the configuration, principle of operation, and the applied solid electrolytes and electrodes of the high-temperature hydrogen sensors. Additionally, an amperometric sensor able to detect hydrogen and steam in atmospheric air through a two-stage procedure is presented and thoroughly discussed. The discussion reveals that high-temperature hydrogen sensors face different challenges in terms of the electrodes and solid electrolytes to be used, depending on the operating principle of each sensor type.

The present communication describes the results of the performance and the assessment of a sensor based on a solid oxide electrolyte with a composition of 0.9ZrO₂ + 0.1Y₂O₃ (YSZ), equipped with a ceramic diffusion barrier for measuring the water vapor and hydrogen content in air. The possibility of determining the concentration of water vapor and hydrogen in the air is based on the measurement of the limiting current value. For the calculation of the steam and hydrogen concentration in ambient air, analytical expressions were obtained and applied, using the limiting current values measured in air with a standard oxygen concentration of 20.9 vol.% and in the analyzed air. A two-stage method for the determination of the hydrogen and steam amount in ambient air is proposed. It is stated that the sensor operates successfully at the temperature of 700 °C and can be applied for the continuous determination of steam or hydrogen concentrations in air.

The rapid development of science, technology, and engineering in the 21st century has offered a remarkable rise in our living standards. However, at the same time, serious environmental issues have emerged, such as acid rain and the greenhouse effect, which are associated with the ever-increasing need for energy consumption, 85% of which comes from fossil fuels combustion. From this combustion process, except for energy, the main greenhouse gases-carbon dioxide and steam-are produced. Moreover, during industrial processes, many hazardous gases are emitted. For this reason, gas-detecting devices, such as electrochemical gas sensors able to analyze the composition of a target atmosphere in real time, are important for further improving our living quality. Such devices can help address environmental issues and inform us about the presence of dangerous gases. Furthermore, as non-renewable energy sources run out, there is a need for energy saving. By analyzing the composition of combustion emissions of automobiles or industries, combustion processes can be optimized. This review deals with electrochemical gas sensors based on solid oxide electrolytes, which are employed for the detection of hazardous gasses at high temperatures and aggressive environments. The fundamentals, the principle of operation, and the configuration of potentiometric, amperometric, combined (amperometric-potentiometric), and mixed-potential gas sensors are presented. Moreover, the results of previous studies on carbon oxides (CO_x), nitrogen oxides (NO_x), hydrogen (H₂), oxygen (O₂), ammonia (NH₃), and humidity (steam) electrochemical sensors are reported and discussed. Emphasis is given to sensors based on oxygen ion and proton-conducting electrolytes.

BaCeO3-based materials represent a well-known family of proton-conducting electrolytes, which can be used in different solid oxide electrochemical devices. An effective operation of the latter across an intermediate-temperature range requires improved transport of PCEs, including their grain (G) and grain boundary (GB) components. In the present work, some 3d-elements in a small amount were used as sintering additives to verify the possibility of improving the GB conductivity of BaCe0.9Gd0.1O3–δ. It is shown that copper oxide (CuO) can be considered as one of the most effective sintering agents, since its use enables decreasing the GB density of the BCG ceramic material at the reduced sintering temperatures. The obtained results form a new tactic for designing new protonic electrolytes, whose conductivity might be prevail over ones containing Ni-based modifiers.

Reversible protonic ceramic cells (rPCCs) combine two different operation regimes, fuel cell and electrolysis cell modes, which allow reversible chemical-to-electrical energy conversion at reduced temperatures with high efficiency and performance. Here we present novel technological and materials science approaches, enabling a rPCC with symmetrical functional electrodes to be prepared using a single sintering step. The response of the cell fabricated on the basis of P–N–BCZD|BCZD|PBN–BCZD (where BCZD = BaCe_0.5Zr_0.3Dy_0.2O_3−δ, PBN = Pr_1.9Ba_0.1NiO_4+δ, P = Pr₂O₃, N = Ni) is studied at different temperatures and water vapor partial pressures (pH₂O) by means of volt-ampere measurements, electrochemical impedance spectroscopy and distribution of relaxation times analyses. The obtained results demonstrate that symmetrical electrodes exhibit classical mixed-ionic/electronic conducting behavior with no hydration capability at 750 °C; therefore, increasing the pH₂O values in both reducing and oxidizing atmospheres leads to some deterioration of their electrochemical activity. At the same time, the electrolytic properties of the BCZD membrane are improved, positively affecting the rPCC’s efficiency. The electrolysis cell mode of the rPCC is found to be more appropriate than the fuel cell mode under highly humidified atmospheres, since its improved performance is determined by the ohmic resistance, which decreases with pH₂O increasing.

Slight co-doping of Nd_0.5Ba_0.5FeO_3−δ results in enhancement of both ionic transport and electrochemical behavior, indicating that NBFCo is a promising electrode for proton-conducting electrolytes.