Optimizing preparation of carbon supported cobalt catalyst for hydrogen generation from NaBH4 hydrolysis

Abstract

Modified carbon-supported cobalt catalysts have been synthesized by optimization of the preparation conditions including ball-milling pretreatment of the carbon and screening the solvents used for synthesis of the catalysts. Ball-milling treatment on carbon can not only reduce its particle size but also functionalize the surface with oxygen-containing groups, resulting in good affinity to Co2+ ions. The non-aqueous solvent N,N-dimethylformamide (DMF) is beneficial to improve the immersional wetting and adsorption of the cobalt salt solution on the surface of carbon, leading to uniform deposition of cobalt nanoparticles upon chemical reduction. The carbon-supported cobalt catalyst with the Co loading of 13.20wt% obtained under optimum conditions exhibits excellent catalytic activity toward NaBH4 hydrolysis and the average hydrogen generation rate at 27°C is 10.29LH2min-1g(cobalt)-1 corresponding to a turnover frequency of 1473.4molH2(molcobalt)−1h−1, which is higher than the most reported data. Furthermore, the effects of the cobalt loading, catalyst dosage, concentration of NaOH and NaBH4, and reaction temperature on the hydrogen generation have been investigated by hydrolysis of alkaline NaBH4 solution, and the corresponding rate equation can be described as r=Aexp(-42190/RT)[cobalt]0.16[NaOH]0.23[NaBH4]0.30.