Liquid nitrogen quenching inducing lattice tensile strain to endow nitrogen/fluorine co-doping Fe3O4 nanocubes assembled on porous carbon with optimizing hydrogen evolution reaction

In this work, the lattice tensile strain of nitrogen/fluorine co-doping ferroferric oxide (Fe3O4) nanocubes assembled on chrysanthemum tea-derived porous carbon is induced through a novel liquid nitrogen quenching treatment (named as TS-NF-FO/PCX-Y, TS: Tensile strain, NF: Nitrogen/Fluorine co-doping, FO: Fe3O4, PC: Porous carbon, X: The weight ratio of KOH/carbon, Y: The adding amount of porous car-bon). Besides, the electrocatalytic activity influenced by the adding amount of porous carbon, the type of dopant, and the introduction of lattice tensile strain is systematically studied and explored. The inter-connected porous carbon could improve electrical conductivity and prevent Fe3O4 nanocubes from aggre-gating. The induced nitrogen/fluorine could cause extrinsic defects and tailor the intrinsic electron state of the host materials. Lattice tensile strain could tailor the surface electronic structure of Fe3O4 via chang-ing the dispersion of surface atoms and their bond lengths. Impressively, the designed TS-NF-FO/PC5-0.25 delivers a low overpotential of 207.3 +/- 0.4 mV at 10 mA/cm2 and demonstrates desirable reaction dynam-ics. Density functional theory calculations illustrate that the electron structure and hydrogen adsorption free energy (DG*H) are optimized by the synergistic effect among porous carbon, nitrogen/fluorine co-doping and lattice tensile strain, thus promoting hydrogen evolution reaction (HER) catalytic activity. Overall, this work paves the way to unravel the enhancement mechanism of HER on transition metal oxide-based materials by electronic structure and phase composition modulation strategy.(c) 2023 Elsevier Inc. All rights reserved.