Robust hydrogen production from NaBH4 hydrolysis using 2D/3D hierarchical hollow-architected cobalt oxide: The relationship between structural properties and catalytic activities

The utilization of cobalt-based catalysts for catalyzing sodium borohydride (NaBH₄) hydrolysis to produce H₂ is still receiving tremendous attention. Herein, in this work, we reported a special strategy to fabricate two peculiar cobalt oxides using Co-MOFs as the initial templates. The manipulation of chemical etching allowed the formation of large internal hollow inside these MOFs whereas their external appearances were retained, followed by the calcination step to transform them into hierarchical hollow-architected cobalt oxides. The optimized 3D-CCO and 2D-SCO showed excellent activities for catalyzing the hydrolysis of NaBH₄, in which 100 % of H₂ volume could be produced with high hydrogen production rates (HPRs) (i.e., 2689.1 mL min^-1 g^-1 and 1874 mL min^-1 g^-1) and comparatively low activation energies than many reported catalysts including precious and non-precious metal-based materials. The slightly higher activity of 3D-CCO over 2D-SCO could be attributed to its larger specific surface area, better reducible capability and abundant enriched surface oxygen vacancies. Both materials could remain their surficial structures and activities excellently over 5 consecutive cycles. The mechanism for H₂ production from NaBH₄ hydrolysis was also proposed based on the Michaelis-Menten mechanism. This work not only provides insightful information about the preparation technique for constructing hierarchical hollow-architected cobalt oxide-derived from Co-MOF but also demonstrates the relationship between the structural properties and their catalytic activities in catalyzing the hydrolysis of NaBH₄ to H₂ production.