Effects of accelerators, and metal salts on the hydrolysis of sodium tetrahydroborate: A kinetic and mechanistic study for hydrogen generation

Abstract

Sodium tetrahydroborate (NaBH4) was used as a fuel source for hydrogen-oxygen fuel cell. The oxalic acid, Ag+, Cu2+ and Ni2+ accelerates the hydrogen (H2 gas) evolution from the self-hydrolysis of NaBH4 at 30 °C. Kinetics of H2 gas generation was evaluated as a function of catalyst, NaBH4, sodium hydroxide concentrations at different temperatures. Hydrolysis NaBH4 follows first-, and fractional-order kinetics with [BH4-], and [H+] respectively. The hydrolysis of NaBH4 decreases with increasing [NaOH] at 30 °C. The metal ions (Ag+, Cu2+, and Ni2+) catalyzed the evolution of H2 gas and hydrolysis followed zero-order kinetics with respect to the metal ions. Hydrolysis of NaBH4 was catalyzed by metal ions and hydrogen ions simultaneously. The activation parameters were calculated and found to be activation energy = 54.9, 59.7, 62.7 kJ/mol, enthalpy of activation = 52.4, 57.5, 60.2 kJ/mol and entropy of activation = −62.2, −48.2, −49.6 J/K/mol for Ag+, Cu2+ and Ni2+, respectively. The catalytic activity of depends on the reduction potential of metal ions; Ag+ (0.799 V) ˃ Cu2+ (0.341 V) ˃ Ni2+ (−0.257).