Cobalt oxides as Co 2B catalyst precursors for the hydrolysis of sodium borohydride solutions to generate hydrogen for PEM fuel cells

Abstract

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 °C reacts faster leading to enhanced Co 2B formation than Co 3O 4 prepared at lower temperatures (200 °C and 400 °C). The activation energy for the hydrolysis of NaBH 4 by Co 2B formed in situ from Co 3O 4 produced at 600 °C 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.