Synthesis of Fe-Fe2B catalysts via solvothermal route for hydrogen generation by hydrolysis of NaBH4

Abstract

In this study, iron sulfate heptahydrate (FeSO 4. 7H 2 O) and sodium borohydride (NaBH 4 ) were used to synthesize Fe-Fe 2 B nanocrystals via the solvothermal route. Synthesis of Fe-Fe 2 B nanocrystals was carried out under Argon (Ar) gas atmosphere with aqueous solutions of FeSO 4 .7H 2 O and NaBH 4 at various concentrations and reaction time. The phases and microstructures of nanocrystals thus formed were characterized by X-Ray diffraction (XRD) spectroscopy and scanning electron microscopy (SEM). Surface areas of nanocrystals were measured by a surface area and pore-size analyzer using nitrogen adsorption-desorption method together with Brunauer-Emmett-Teller (BET) equation. The vacuum dried nanoparticles were calcined under both Ar and air at 500 oC. Nano-cylindrical structures Fe-Fe 2 B were observed while calcinating under Ar atmosphere; whereas more irregular shaped particles were obtained by calcination under air. The surface areas of nanocylinders were determined as 12 m 2 /g, 5.5 m 2 /g and 16.5 m 2 /g, for vacuum dried, Ar-calcined and O 2 -calcined products respectively. The catalytic effect of those nanocrystals for hydrogen generation were studied by determining reaction rates in aqueous alkaline solutions of NaBH 4 . Their catalytic activities were investigated by varying the amount of catalysts, and the concentrations of NaBH 4 and NaOH. The effect of temperature on the catalytic activity was also studied by varying the temperatures from 25-70 °C. It was noticed that the catalytic activity of vacuum dried nanocrystals was the highest, and it decreased with the increase in NaOH concentration. With 0.01 g of Fe-Fe 2 B catalyst in 1 % w/w NaBH 4 concentration at 25 °C, the hydrogen production rate was 570 mL of H 2 .g -1 .m -1 , which reached to 1230 at 50 °C and 2700 mL at 70 °C.