Cobalt Oxides As Co_2b Catalyst Precursors For The Hydrolysis Of Sodium Borohydride Solutions To Generate Hydrogen For Pem Fuel Cells

摘要

Cobalt boride (Co_2B) is an inexpensive catalyst for the hydrolysis of sodium borohydride (NaBH_4) to generate hydrogen (H_2) for PEM fuel cells. Preparation of Co_2B in situ in the H_2 generation vessel as well as in an external reactor was studied using cobalt (III) oxide (CO_3O_4) and lithium cobalt oxide (LiCoO_2) as precursors. The oxide precursors were characterized by XRD and the Co_2B catalysts by XRD and ICP. Co_2B formation from the oxide precursors depends on the crystallinity of the oxides as well as the concentration of NaBH_4 in the solution. During reduction of the oxides to CoB_2, Co(s) metal, Co(BO_2)_2 may also form from competing side reactions, however crystalline oxides react faster leading to higher Co_2B yield and better H_2 generation efficiency. Crystallinity of Co_3O_4 was improved by preparing it at a higher temperature. Co_3O_4 prepared at 600 ℃ reacts faster leading to enhanced Co_2B formation than Co_3O_4 prepared at lower temperatures (200 ℃ and 400 ℃). The activation energy for the hydrolysis of NaBH_4 by Co_2B formed in situ from Co_3O_4 produced at 600 ℃ was calculated to be 77.90 kJ mol~(-1). This activation energy value is found to be slightly higher than that of Pt, Ru-based catalysts.