Fe7C3 nanoparticles anchored on N-doped biochar as electrocatalyst for highly efficient oxygen evolution reaction

As the crucial step of electrolytic water, oxygen evolution reaction (OER) is urgent to be enhanced by developing the most efficient electrocatalysts to accelerate the sluggish OER kinetics. Herein, nitrogen-doped carbon-based Fe7C3 clusters with hierarchical pore structure (NHAC@Fe7C3) were synthesized via a two-step method of FeCl3 and seaweed liquid-phase impregnation combined with physical activation. The optimum NHAC@Fe7C3 = 3:1 catalyst (with a mass ratio of Sargassum Horneri to FeCl3 of 3:1) demonstrated much better catalytic activity and durability towards OER in alkaline electrolyte than the most noble-metal-free catalysts, of which the overpotential reached 181 mV at 10 mA cm−2. Long-term discharging stability of over 33 h at 10 mA cm−2 current density. The excellent performance is attributed to the synergistic effect of graphitic carbon and Fe7C3 clusters, hierarchical pore structure and good electrical conductivity. Density functional theory calculations confirm that the free energy for the potential-limiting step is reduced by the synergistic effect of N-doped carbon and Fe7C3 substrance. This study employs a simple and effective method to synthesize iron carbide embedded in algae-derived biochar, providing an opportunity for the rational design of robust performance electrocatalysts for oxygen evolution reaction.