Bursting Dynamics in Molecular Hydrogen Generation via Sodium Borohydride Hydrolysis

The hydrolysis of borohydride salts is a promising process for the generation in situ of pure molecular hydrogen that can be used as an alternative fuel. One of the obstacles toward its concrete application in the realm of green energy resides in nonlinear behaviors of H2 delivery during the reaction development. In particular, we have recently shown that this system behaves like a chemical oscillator in a wide range of experimental conditions, exhibiting nondesirable fluctuations in the production of molecular hydrogen. Despite the potential of NaBH4 hydrolysis in applicative terms, a deep understanding of the reaction mechanisms leading to these nonlinear dynamics is still left to a primary stage. Here we show how to control a typical bursting-like oscillatory scenario occurring in the gas development from NaBH4 hydrolysis. Bursting transients are isolated and stabilized by using highly concentrated solutions of dihydrogen-phosphate/hydrogenphosphate buffers with an initial pH value around 7. The length of the bursting transients critically depends upon the initial pH, the buffering strength, and the working temperature. The stirring rate also influences this oscillatory dynamics. On the basis of the experimental evidence and NMR analysis of the reactive mixture, we hypothesize a possible kinetic scheme able to explain the onset of oscillatory instabilities.