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 (NaBH 4 ) is paramount but remains challenging. Here, we reported a facile and efficient approach to tune the catalytic performance for NaBH 4 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 CoSO 4 -doped Co 3 O 4 sample was formed and it exhibited excellent activity with the generation of ∼500 mL of hydrogen gas from NaBH 4 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 Na 2 SO 4 and Na 2 S is beneficial for the in situ transformation of Co 3 O 4 into catalytically active Co−B alloys, accompanying a positive change in surface morphology during the NaBH 4 hydrolysis, thereby inducing an excellent hydrogen generation rate of up to 4425 mL•min −1 •g cat −1

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“…To deal with this self-inhibition of the reaction, catalysts have been developed, usually based on cobalt. [152][153][154] On the side of hydrogen release NaBH 4 has many advantages for hydrogen release, but the reverse reaction is very difficult to perform efficiently. The boron-oxygen bonds are very stable, and thus difficult to rehydrogenate directly.…”

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