Effect of Fe content on the hydrogen production kinetics of electroless-deposited Co-Ni-Fex-P catalysts by hydrolysis of chemical borohydrides

Abstract

Chemical hydrides such as LiBH4, NaBH4, ¬and NH3BH3, have been studied as a safe and high-capacity hydrogen storage-production material. Most of the chemical hydrides have higher hydrogen density (LiBH4 (13.9 wt.%) NaBH4 (7.9 wt.%) ¬and NH3BH3, (19.6 wt.%)) than gas tank (2.7 wt.%), and they can directly produce hydrogen by hydrolysis using a cost-effective transition metal-based boride/phosphide catalysts. In particular, to increase the catalytic activity and decrease the cost, researchers added metallic substances as main components and/or additives to the catalysts. In this study, the effect of Fe content in electroless deposited Co-Ni-Fex-P alloy catalysts (x = 0~11.8 at.%) from the hydrolysis of NaBH4 is investigated in alkaline ¬solution. The electroless-deposited Co-Ni-Fe5.5-P and Co-Ni-Fe7.6-P alloy catalysts are composed of flake-like micron particles; however, with an increase in Fe content to 11.8 at.%, the flake-like morphology is changed to a spherical shape and the crystal structure of the electroless-deposited Co-Ni-Fe-P catalyst is transformed from FCC to BCC. Among all the Co-Ni-Fex-P alloy catalysts, the Co-Ni-Fex-P (x = 7.6 at.%) catalyst has the highest hydrogen production rate of 1,128 ml min-1 g-1catalyst in 1 wt.% NaOH +10 wt.% NaBH4 alkaline solution at room temperature. For the optimized catalyst, the activation energy of the hydrolysis of NaBH4 is calculated to be 54.26 kJ mol-1, which is 27% lower than the previously reported Co based catalyst. Additionally, we report hydrolysis of Mg(BH4)2 and Ca(BH4)2 in alkaline solution. The Mg(BH4)2 is stored unstably in alkaline solution, whereas the Ca(BH4)2 is stored stably. Furthermore, the maximum hydrogen production rate from hydrolysis of Ca(BH4)2 in alkaline solution shows 784 ml min-1 g-1catalyst in 1wt.% Ca(BH4)2 + 10 wt.% NaOH solution when the Co-Ni-Fe7.6-P alloy catalyst is used.