Bimetallic Ni-Co nanoparticles as an efficient catalyst of hydrogen generation via hydrolysis of NaBH4

Abstract

Ni-Co bimetallic nanoparticles (NPs) have been synthesized via reduction of Ni and Co hydroxides by hydrazine in water / ethylene glycol solutions. It was found that the particle size and polydispersity of the obtained chemically homogeneous NPs decrease with a decreasing to 50 at.% content of Ni in the reaction mixture. A different trend was observed for Ni 25 Co 75 and was related to the formation of Ni- and Co-rich particles. Ni-Co-NPs were tested as catalysts of hydrolysis of alkaline solutions of NaBH 4 , with the highest rate of hydrogen generation observed for Ni 50 Co 50 . Zero-order kinetics of hydrogen evolution process was observed for all studied systems. Based on the data of the kinetic studies, we conclude that the rate of the hydrolysis process (a) increased with increasing NaBH 4 concentration in the range 0.1 – 1 mol/L; (b) decreased by 25% with increasing pH of the solution from 9 to 14. Studies of the temperature dependence of the rates of the hydrolysis process showed that the activation energy of the reaction decreased to 26 kJ/mol with decreasing contents of NaBH 4 and catalysts. Based on a comparison of the values of activation energy of hydrolysis reaction and the enthalpy of activation of viscous flow of initial NaBH 4 solution and the solution obtained after the hydrolysis, a diffusion-controlled reaction mechanism was proposed. • Bimetallic Ni-Co nanoparticles were synthesized and used as catalysts of NaBH 4 hydrolysis. • Ni 50 Co 50 nanoparticles showed the best catalytic activity. • Zero-order kinetics of hydrogen generation was observed. • Hydrolysis of NaBH 4 catalyzed by Ni 50 Co 50 showed a low sensitivity to pH. • Activation energy of NaBH 4 hydrolysis can be decreased to 26 kJ/mol.