Trifunctional catalytic activities of trimetallic FeCoNi alloy nanoparticles embedded in a carbon shell for efficient overall water splitting

Abstract

Exploring low-cost and high-performance electrocatalysts for multifunctional activities is highly desirable but challenging. It is a convenient way to couple late transition metals (Fe, Co, Ni) with carbon nanomaterials, as their proximity not only improves the catalytic performance through their synergistic effect but also provides a cost-effective preparation process compared with precious metals (e.g., Pt, Ru, and Ir). Herein, FeCoNi alloy nanoparticles embedded in a nitrogen-doped carbon shell (NC) were synthesized via a simple one-step chemical reaction of three metal salts (Fe, Co, and Ni) and two organic linkers (2-methylimidazole and 2,6-naphthalene dicarboxylic acid dipotassium) followed by pyrolysis. The as-synthesized catalyst with an optimized composition (Fe_1.0Co_1.1Ni_1.4–NC) required overpotentials of 270 mV and 175 mV for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively, to deliver a current density of 10 mA cm⁻² in 1.0 M KOH electrolyte. Moreover, the catalyst demonstrated ethanol oxidation reaction (EOR) activity by achieving a 9% less positive onset potential than for the OER in 1.0 M KOH + 1.0 M C₂H₅OH electrolyte. The high catalytic activity of Fe_1.0Co_1.1Ni_1.4–NC was intrinsically associated with the presence of Fe⁺³ species as revealed by X-ray photoelectron spectroscopy. When the catalyst Fe_1.0Co_1.1Ni_1.4–NC comprised both the anode and cathode in a prototype electrolytic cell for overall water splitting, it required 1.52 V vs. RHE to reach a 10 mA cm⁻² current density in 1.0 M KOH, outperforming the benchmark IrO₂ (or RuO₂)‖Pt/C coupled cells.