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The development of Pt-based electrocatalysts with high Pt utilization efficiency towardt he hydrogen evolution reaction(HER) is of great significance for the future sustainableh ydrogen economy.F or rational design of high-performanceH ER electrocatalyst, the simultaneous consideration of both thermodynamic and kinetic aspects remains greatlyc hallenging. Herein, as imple template-derived strategyi sd emonstrated for the in situ growth of ultrafine Pt nanoparticleso nto Co 3 O 4 nanosheet-assembled microflowers (abbreviated as Pt/Co 3 O 4 microflowers hereafter) by using the prefabricated PtCo-based Hofmann coordination polymer as reactive templates.T he elaborate preparation of such intriguing hierarchical architecture with well-dispersed tiny Pt nanoparticles,a bundant metal/ oxide heterointerfaces and open configuratione ndows the formed Pt/Co 3 O 4 microflowers with high Pt utilization efficiency,r ich active sites, lowerede nergy barrier for water dissociation and expedited reaction kinetics. Consequently,t he Pt/Co 3 O 4 microflowers exhibit superior HER activity with ar elatively low overpotential of 34 mV to deliver ac urrent density of 10 mA cm À2 ,s mall Tafel slope (34 mV dec À1)a nd outstanding electrochemical stability, representing an attractive electrocatalyst for practical water splitting. What's more, our concept of in situ construction of metal/oxide heterointerfaces may provide a new opportunity to design high-performance electrocatalysts for av ariety of applications.

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Based on the coprecipitation of FeSO4(NH4)2SO4 with CuCl2 and ZnSO4, CuFe2O4 and ZnFe2O4 nanocrystals were successfully synthesized. The morphology and the crystal structures of the nanoparticles were studied via SEM, TEM and XRD, which showed that MFe2O4 samples were formed aggregated nanoparticles with crystal sizes of 16~20 nm with a narrow dispersion in size. The samples had the typical spinel structures. Magnetic analyses demonstrated that the CuFe2O4 sample had the saturation magnetization (Ms) of 10.10 emu/g with the coercivity of 3459.39 Oe, while the ZnFe2O4 sample had the Ms of 8.27 emu/g with the coercivity of 25.42 Oe at room temperature, respectively.