Abstract
Abstract One of the barriers to the use of the silicon-water reaction to generate hydrogen for hydrogen fuel cells in portable devices is the lengthy induction period of the reaction caused by the presence of the native oxide layer on the surface of the silicon. Herein is presented a simple pelleting process which can be used to effectively eliminate the induction period in the reaction of pressed silicon powders with 2 wt% sodium hydroxide solution by means of disrupting the native oxide layer. The activation energy of the reaction was found to be 73 kJ/mol by means of an Arrhenius plot. It was also found that the rate of reaction of hydrogen generation could be enhanced by mixing sodium chloride and sodium polyacrylate with the silicon powder before pressing.
Highlights
In recent years, the field of portable consumer electronics has blossomed [1]
Having in our previous work found that silicon powder required an excess of water in order to generate hydrogen in near-quantitative yields [26], it was our expectation that pressing the silicon into pellets, the most ideal form for use in a portable device, would serve to further reduce the rate of hydrogen generation
Two hypotheses were formulated: 1) as the reaction of silicon to form hydrogen is exothermic, the closer proximity of the reaction sites in a pellet relative to a powder may be leading to local heating effects, assisting in the breakdown of the oxide layer by the hydroxide ions and decreasing the induction period and accelerating the initial rate; and 2) the enhancement could be due to a disruption of the oxide layer on the surface of the silicon engendered when pressing it into a pellet
Summary
The field of portable consumer electronics has blossomed [1]. The rapid rise in the functionality of such devices has put considerable strain on battery technology, which is struggling to keep up with the demand for higher power densities and longer lifetimes [2,3]. The same authors reported that this activation can be enhanced by incorporating additives such as sodium chloride and sodium polyacrylate in the milling process They found that these additives do not become covalently bonded to the silicon; rather, they are intimately mixed with it, and serve to activate the silicon towards hydrogen generation by either protecting it from repassivation (i.e. by inhibiting surface oxide layer growth) or improving its dispersion into solution. In another attempt to overcome the problem of lengthy induction periods of the silicon-water reaction in the presence of hydroxide ions, we investigate the effects of a simple pelletisation method and the incorporation of different types of additive on the reaction of silicon with aqueous sodium hydroxide solutions
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