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Summary Among numerous modern high‐performance energy technologies that allow for conversion of chemical energy into electricity and heat, the most interesting are direct carbon fuel cells (DCFCs). They are the only ones among all types of fuel cells that allow for a direct conversion of chemical energy stored in the solid fuel (carbon) into electricity. Furthermore, they are characterized by high performance, which is not limited due to the Carnot's rule, low emissions of such substances as SO2, NOx, fly ashes and others, and a relatively simple design since there are no moving components. Nowadays, DCFCs have been developed all over the world. These cells differ first and foremost in the electrolyte they use. The type of electrolyte determines both configuration of the device and operating temperature. The paper discusses current state of knowledge concerning DCFC technology with alkaline (hydroxide) electrolyte and presents the results of research and development studies concerning such cells all over the world. Furthermore, main factors and parameters that impact on the operation of individual cells and potential challenges that have to be overcome in order to develop these technologies were characterized and discussed.

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Biochar application has been reported to improve the physical, chemical, and hydrological properties of soil. However, the information about the size fraction composition of the applied biochar as a factor that may have an impact on the properties of soil‑biochar mixtures is often underappreciated. Our research shows how sunflower husk biochar (pyrolyzed at 650 °C) can modify the water retention characteristics of arable sandy soil depending on the biochar dose (up to 9.52 wt.%) and particle size (<50 µm, 50–100 µm, 100–250 µm). For comparison, we used soil samples mixed with biochar passed through 2 mm sieve and an unamended reference. The addition of sieved biochar to the soil caused a 30% increase in the available water content (AWC) in comparing to the soil without biochar. However, the most notable improvement (doubling the reference AWC value from 0.078 m3 m−3 to 0.157 m3 m−3) was observed at the lowest doses of biochar (0.95 and 2.24 wt.%) and for the finest size fractions (below 100 µm). The water retention effects on sandy soil are explained as the interplay between the dose, the size of biochar particles, and the porous properties of biochar fractions.