SIMULATION OF STABLE OPERATION MODE FOR HYDROGEN ENERGY SYSTEM BASED ON POROUS SILICON
A lot of methods of sustainable hydrogen production are based on water dissociation specified with photo, thermal or chemical influence. The produced hydrogen can be used for generation of electrical energy with help of fuel cell. Similar system was created on the basis of porous silicon (PS). The surface of PS is fully hydrogenated. During the interaction of PS with water, molecular H2 is produced. It is explained with water dissociation and destruction of SiHx bonds on PS surface. Kinetics of the chemical reaction is nonlinear. The corresponding energy generation in the fuel cell is also irregular. The produced power cannot be directly used for supply of electronic devices. In this article the method is proposed that will provide stable hydrogen production in the described system.
First, the formula was derived that described the chemical reaction kinetics of PS fixed mass portion with water. It was based on fit of the previously obtained experimental curves of hydrogen release kinetics for PS powders in H2O:C2H5OH:NH3 (10%) solution. Ethanol supported better wettability of the powders. Ammonia was used as catalyst.
The next step was to define the function that described the kinetics of hydrogen release when feeding PS to the reaction chamber at a certain time interval. The calculation was made for the following modes of feeding the powder into the reaction chamber:
- feeding a fixed mass of the powder through the same time intervals;
- feeding a fixed mass of the powder at different time intervals;
- feeding the powder through the same time intervals with a periodic change in the mass of the portion.
The batch feed of PS powder into the reaction chamber makes possible to receive linear kinetics of the hydrogen production, when the time interval is about 1 min or it is growing in time. Connection of the reaction chamber to polymer electrolyte fuel cell will ensure the stable mode of power generation. The produced power reaches 0.15 W for 1 mg in the one portion of PS. Periodic change in the mass of the portion as well as long time intervals result in nonlinear behavior of the kinetics.
The rate of hydrogen production grows with an increase in mass of the portion. The kinetics of the reaction remains linear, providing the amount of water significantly exceeds the amount of reacting silicon and the reagents are well mixed. Under these conditions, a stable level of power at the output of the fuel cell is maintained. It makes possible to use the described hydrogen system for supplying low-power electronic devices
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