Efficient Hydrogen Generation from the NaBH4 Hydrolysis by Cobalt-Based Catalysts: Positive Roles of Sulfur-Containing Salts.

Development of a simple and efficient strategy for improving the catalytic activity of cobalt-based catalysts toward hydrogen evolution from sodium borohydride (NaBH4) is paramount but remains challenging. Here, we reported a facile and efficient approach to tune the catalytic performance for NaBH4 hydrolysis with Co-based catalysts prepared by using cobalt sulfate as a precursor or a mixture of sulfur-containing sodium salts/cobalt salts as a raw material. With the use of cobalt sulfate as the precursor, the CoSO4-doped Co3O4 sample was formed and it exhibited excellent activity with the generation of ∼500 mL of hydrogen gas from NaBH4 hydrolysis under mild conditions. In terms of sulfur-free cobalt salts (e.g., cobalt chloride, cobalt nitrate, and cobalt acetate) as precursors, the obtained Co-based samples were found to be entirely ineffective for hydrogen production. Interestingly, during the cobalt-based catalyst preparation, the introduction of sodium sulfate or sodium sulfide can considerably accelerate hydrogen production. On the contrary, adding sulfur-bearing salts did not inspire any activity improvement only during the hydrogen generation reaction. Control experiments indicate that during catalyst preparation, the presence of Na2SO4 and Na2S is beneficial for the in situ transformation of Co3O4 into catalytically active Co-B alloys, accompanying a positive change in surface morphology during the NaBH4 hydrolysis, thereby inducing an excellent hydrogen generation rate of up to 4425 mL·min-1·gcat-1.