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

Abstract

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·g_cat^-1.