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Unusual behavior of dynamic hydrogen generation from sodium borohydride

2014    Sankir, Mehmet; Serin, Ramis Berkay; Semiz, Levent; Sankir, Nurdan Demirci

In this study, for the first time, hydrogen gas generation rate is dynamically measured by transferring required amount of sodium borohydride solution to maintain 1 or 2 normal liters of hydrogen gas generation per minute. Three different catalysts (iron, platinum and ruthenium) are used in order to investigate the critical catalyst concentration, catalyst amount and the rate relation and as well as the influence of the sodium borohydride concentration on the rate equations. It has been demonstrated that the linear approximation from the initial hydrogen gas generation data usually reported in the literature is not valid. Moreover, the actual rates reported here are higher and lower than the linear approximations depending on the type of the catalyst. It is about 60 percent lower than linear approximation when iron catalyst is used. Therefore, calculating hydrogen gas generation rate as NL min(-1) g(catalyst)(-1) is invalid. On the other hand, it has been observed that the rate equation may not be dependent on the amount of the sodium borohydride concentration if the highest catalytic activity is achieved. Hence, most of the rate equations in the literature are only valid for a range, which is limited to the highest catalytic activity. Additionally, it has been concluded that the amount of catalyst and sodium borohydride concentration may be optimized to observe almost 100% efficiencies. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.