ZIF-67-derived Co3O4 rhombic dodecahedron as an efficient non-noble-metal catalyst for hydrogen generation from borohydride hydrolysis

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Abstract As Co3O4 is one of the most attractive catalysts for H2 generation (HG) from NaBH4 hydrolysis, Co3O4 nanoparticle (NP)-immobilized composites are intensively developed for NaBH4 hydrolysis. Nevertheless, these Co3O4 composites involve complicated fabrication procedures and long preparation time. More importantly, these composites typically consist of a large fraction of “dead” weight of inactive substrates, causing these composites unnecessarily effective. Unlike immobilizing Co3O4 NPs on substrates, this study proposes a Co3O4 catalyst completely comprised of Co3O4 NPs which are framed but the entire Co3O4 catalyst can still exhibit porosity. To this end, a cobaltic zeolitic imidazolate framework (ZIF-67) with morphology of rhombic dodecahedron is adopted as a templated precursor, which is converted into Co3O4 rhombic dodecahedral (RD) granule. Because of cobaltic species and hierarchical structures of ZIF-67, the resulting Co3O4 RD granule can consist of densely packed Co3O4 NPs, but remain porous, making it a promising catalyst for NaBH4 hydrolysis. This ZIF-67 derived Co3O4 (ZIFCoO) exhibits a considerably higher catalytic activity than its precursors, ZIF-67 and carbonized ZIF-67, as well as the commercial Co3O4 NPs. While a higher dose of ZIFCoO facilitates NaBH4 hydrolysis to generate more H2, 500 mg/L of ZIFCoO is the optimal catalyst dose to obtain the highest HG rate. ZIFCoO also exhibits a relatively low Ea as 39.4 kJ/mol compared to most of the reported catalysts. ZIFCoO can be also reused for multiple cycles of HG efficiently. These features make ZIFCoO a conveniently-prepared and promising heterogeneous catalyst for H2 generation from NaBH4 hydrolysis.