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Two types of air-cooled modular polymer membrane fuel cells (PEMFC) stacks with full equipment were constructed and investigated as components of hybrid power sources. The first, a 2-kW PEMFC stack, was assembled from two 1-kW PEMFC modules electrically connected in parallel and compared with a commercial PEMFC stack built from one 2-kW PEMFC module. The second, a 500-W PEMFC stack, was assembled with three modules connected in parallel. It was found that the two-module PEMFC stack was capable of operation with nominal power of 2 kW. Analysis of the distribution of the air cooling system in both modules was also conducted. The two-module PEMFC stack reduced hydrogen consumption compared to the reference 2-kW PEMFC stack consisting of only one module. The elaborated two-module PEMFC stack was successfully tested in a propulsion system designed to supply an electrical engine with a propeller. The electrical performance of the three-module PEMFC stack was tested separately as well as in a hybrid system in connection with a 5 s Li-Pol battery. It was found that the elaborated PEMFC stack was capable of operation with nominal power of 500 W and variable rapid dynamic electrical loads. It was also successfully tested as a power source to supply servomechanisms and other auxiliary devices.

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In this paper, the impact of partial substitution of calcium for barium in (Ba1-xCax) (M0.9Y0.1) O3, M = Ce, Zr on physicochemical properties of the powders and sintered samples was investigated. The powders, with various contents of calcium (x = 0, 0.02, 0.05, 0.1), were prepared by means of thermal decomposition of organometallic precursors containing EDTA. All of the BaCeO3-based powders synthesised at 1100 °C were monophasic with a rhombohedral structure, however, completely cubic BaZrO3-based solid solutions were obtained at 1200 °C. A study of the sinterability of BaZr0.9Y0.1O3 and BaCe0.9Y0.1O3-based pellets was performed under non-isothermal conditions within a temperature range of 25 to 1200 °C. The partial substitution of barium for calcium in the (Ba1-xCax) (M0.9Y0.1) O3, M = Ce, Zr solid solution improved the sinterability of the samples in comparison to the initial BaCe0.9Y0.1O3 or BaZr0.9Y0.1O3. The relative density of calcium-modified BaCe0.9Y0.1O3-based samples reached approximately 95 to 97 % after sintering at 1500 °C for 2 h in air. The same level of relative density was achieved after sintering calcium-modified BaZr0.9Y0.1O3 at 1600 °C for 2 h. Analysis of the electrical conductivity from both series of investigated materials showed that the highest ionic conductivity, in air and wet 5 % H2 in Ar, was attained for the compositions of x = 0.02 to 0.05 (Ba1-xCax)(M0.9Y0.1)O3, M = Zr, Ce. The oxygen reduction reaction on the interface Pt│BaM0.9Y0.1O3, M = Ce, Zr was investigated using Pt microelectrodes. Selected samples of (Ba1-xCax) (M0.9Y0.1)O3, M = Zr, Ce were tested as ceramic electrolytes in hydrogen-oxygen solid oxide fuel cells operating at temperatures of 700 to 850 °C.

Two constructions of ~300W PEMFC stacks, cooled by different media, were analysed. An open-cathode ~300W PEMFC stack cooled by air (Horizon, Singapore) and a PEMFC F-42 stack cooled by a liquid medium (Schunk, Germany) were chosen for all of the investigations described in this paper. The potential for the design and construction of power sources involving fuel cells, as well as of a hybrid system (fuel cell-lithium battery) for mobile and stationary applications, is presented and discussed. The impact of certain experimental parameters on PEMFC stack performance is analysed and discussed.

The gelcasting method was used to form gastight Ba 0.95 Ca 0.05 Ce 0.9 Y 0.1 O 3 samples proposed for use as proton-conducting electrolytes in solid oxide fuel cells. Methylcellulose was used as an environmentally friendly shaping agent for Ba 0.95-Ca 0.05 Ce 0.9 Y 0.1 O 3 powder in an ethanol solution. Samples of Ba 0.95 Ca 0.05 Ce 0.9 Y 0.1 O 3 were also prepared from the same powder via traditional isostatic pressing, as a reference for cast samples, and sintered in the same conditions. Comparative studies of the physicochemical properties of Ba 0.95 Ca 0.05 Ce 0.9 Y 0.1 O 3 electrolytes, formed by means of these two methods and then sintered at 1550°C for 2.5 h, were presented and discussed. Using the X-ray diffraction method, only the pure orthorhombic phase of BaCe 0.9 Y 0.1 O 3 was detected in the Ba 0.95 Ca 0.05 Ce 0.9 Y 0.1 O 3 powder, as well as in the Ba 0.95-Ca 0.05 Ce 0.9 Y 0.1 O 3 sintered pellets formed via both gelcasting (A) and isostatic pressing (B). Thermal effects occurring during heating of methylcellulose, as well as ceramic Ba 0.95 Ca 0.05 Ce 0.9 Y 0.1 O 3 powder, dried cast samples obtained from the prepared slurry, and sintered Ba 0.95 Ca 0.05 Ce 0.9 Y 0.1 O 3 samples, were examined by differential scanning calorimetry, differential thermal analysis, thermogravimetric analysis, and evolved gas analysis of volatile products using a quadrupole mass spectrometer. The measurements were performed within the temperature range of 20-1200°C in air. Based on dilatometric tests, it was found that the Ba 0.95 Ca 0.05 Ce 0.9 Y 0.1 O 3 cast samples exhibited slightly higher degree of sinterability than the 5CBCY samples obtained by isostatic pressing. In comparison with pressed pellets, higher values of total electrical conductivity in air or in a gas mixture of 5% H 2 in Ar were also attained for Ba 0.95 Ca 0.05 Ce 0.9 Y 0.1 O 3 cast samples. The Ba 0.95 Ca 0.05 Ce 0.9 Y 0.1 O 3 samples were used to construct oxygen-hydrogen electrolytes for solid oxide fuel cells. The results of the electrochemical performance of solid oxide fuel cells with Ba 0.95 Ca 0.05 Ce 0.9 Y 0.1 O 3 electrolytes were comparable to the data in the literature on BaCe 0.9 Y 0.1 O 3 electrolytes. An electrochemical study of a Ba 0.5 Sr 0.5-Co 0.8 Fe 0.2 O 3-d |Ba 0.95 Ca 0.05 Ce 0.9 Y 0.1 O 3 interface was also performed. Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-d appears to be a suitable cathode material for a Ba 0.95 Ca 0.05 Ce 0.9 Y 0.1 O 3 electrolyte.