D-band center optimization of iron carbide via Cr substitution for enhanced alkaline hydrogen evolution

Abstract

Iron carbide (Fe3C) with metallic properties is a good candidate for water oxidation. However, it exhibits poor performance toward hydrogen evolution reaction (HER) due to weak hydrogen desorption induced by an unfavorable d-band center energy level of the Fe site. In this work, we present a new technique for enhancing alkaline hydrogen evolution through tuning the d-band center energy level. A Cr-doped Fe3C@carbon core–shell structure grown on a N-doped graphitic framework (Cr–Fe3C@C-NGF) is presented, demonstrating high HER activity. Cr–Fe3C@C-NGF with the optimal Cr doping level of 0.81 wt% exhibits an overpotential of 126 mV at 10 mA cm−2, which is substantially lower than that of the pristine Fe3C@C-NGF (257 mV). Experimental results and density functional theory calculations both suggest that Cr doping downshifts the d-band center energy level, which accelerates hydrogen desorption from the Fe sites, thus improving HER performance. This work may open a key avenue for the optimization of Fe3C-based HER electrocatalysts via modulation of the d-band energy level.