The influence of impurities of the transition metals Fe, Ni, and Co on hydrolysis kinetics of BH₄− ions in alkaline solutions

Abstract

The influence of small amounts of the Fe, Co, and Ni impurities on the spontaneous hydrolytic process of borohydride was studied within a temperature range of 60–100°C. The object under study was a simulated solution containing 9.53 M of OH− ions and 0.14 M of BH4− ions, used as a fuel for borohydride fuel cells. The rate constant k of borohydride hydrolysis for a small amount of impurities at different temperature was estimated. The lowest non-accelerating concentrations of the impurities were established ( ∼ 10 ppm for iron; ∼ 1 ppm for cobalt). The strongest accelerating effect on the hydrolysis of BH4− ions was rendered by nickel impurities: self-hydrolysis was accelerated by 1.2 times for 1 ppm Ni. The ambiguous trend of the kinetic curves does not allow to accurately estimate the activation energy; however, the increased temperature enhances the catalytic effect of hydrolysis acceleration according to Arrhenius’ equation.

Keywords

• borohydride
• hydrolysis reaction
• rate constant
• activation energy