Fe-N bonds induced highly efficient Fe3O4/g-C3N4 heterojunction for electrocatalytic hydrogen evolution

Fe-based catalysts with the merits of the most abundant reserves in the crust, cheapest, and low toxicity, show significant superiorities to noble-metal catalysts for electrocatalytic water splitting. Fe3O4 as a member of Febased catalysts has been widely used for oxygen evolution reaction (OER). However, it is rarely applied for Hydrogen evolution reaction (HER) owing to the lack of inherent active sites for hydrogen absorption. Fe -N coordination bonds can act as active sites for electrocatalytic performance. Therefore, we reasonably designed and constructed Fe3O4/g-C3N4 heterojunction, where abundant Fe -N bonds acting as HER active sites were formed with the aid of rich Pyridine N of g-C3N4. Activity characterization result indicates the optimized 50%Fe3O4/g-C3N4 heterojunction exhibits excellent HER performance with a low overpotential of 160 mV at 10 mA cm -2, a low Tafel slope of 77.18 mV dec- 1, and outstanding cycle stability. Density functional theory (DFT) calculation demonstrates that the enhanced electrocatalytic performance stems from the Fe -N bonding interaction, which endows 50%-Fe3O4/g-C3N4 with lower water dissociation barrier and a moderate Gibbs free energy of hydrogen adsorption (Delta GH*) in comparison with pristine Fe3O4 and g-C3N4.