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

Abstract

In this study, iron sulfate heptahydrate (FeSO4.7H2O) and sodium borohydride (NaBH4) were used to synthesize Fe-Fe2B nanocrystals via the solvothermal route. Synthesis of Fe-Fe2B nanocrystals was carried out under Argon (Ar) gas atmosphere with aqueous solutions of FeSO4.7H2O and NaBH4 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-Fe2B 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 m2/g, 5.5 m2/g and 16.5 m2/g, for vacuum dried, Ar-calcined and O2-calcined products respectively. The catalytic effect of those nanocrystals for hydrogen generation were studied by determining reaction rates in aqueous alkaline solutions of NaBH4. Their catalytic activities were investigated by varying the amount of catalysts, and the concentrations of NaBH4 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-Fe2B catalyst in 1 % w/w NaBH4 concentration at 25 °C, the hydrogen production rate was 570 mL of H2.g-1.m-1, which reached to 1230 at 50 °C and 2700 mL at 70 °C.