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

Ni-Co bimetallic nanoparticles (NPs) have been synthesized via reduction of Ni and Co hydroxides by hy-drazine 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 Ni25Co75 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 NaBH4, with the highest rate of hydrogen generation observed for Ni50Co50. 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 NaBH4 concentration in the range 0.1 - 1 mol/L; (b) de-creased 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 NaBH4 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 NaBH4 solution and the so-lution obtained after the hydrolysis, a diffusion-controlled reaction mechanism was proposed. (C) 2022 The Author(s). Published by Elsevier B.V. CC_BY_4.0

Automated summary

In this study, Ni-Co bimetallic nanoparticles were successfully synthesized, and the effects of different Ni contents on particle size and polydispersity were observed. Ni50Co50 showed the highest catalytic activity for the hydrolysis of alkaline NaBH4 solutions. The kinetic studies revealed that the hydrolysis rate increased with higher NaBH4 concentration and decreased with higher pH value of the solution. The activation energy of the reaction decreased with decreasing NaBH4 and catalyst contents.