High-Density Iron–Nickel Dual Sites in Carbon Aerogels as Effective Alkaline Water/Seawater Oxidation Electrocatalysts

Abstract

Carbon-based nanocomposites with atomically dispersed transition metals have been found to exhibit excellent electrocatalytic activity toward the oxygen evolution reaction (OER). Yet, the low metal loads and severe electrooxidation of carbon greatly limit the activity and stability. Reducing the pyrolysis temperature can weaken the aggregation of metal atoms, and using carbon aerogel as a 3D scaffold can maximize accessible metal sites. Simultaneously, a lower pyrolysis temperature can provide a higher oxygen content for the carbon substrate and enhance resistance against electrooxidation. Herein, carbon aerogels embedded with Fe–Ni dual atom centers (NCA/FeNi-500) are synthesized by controlled pyrolysis at 500 °C of a chitosan hydrogel composite along with FeCl₃ and NiCl₂. With an atomically dispersed metal loading of 4.35 wt %, NCA/FeNi-500 exhibits a remarkable OER catalytic activity in both alkaline water and simulated alkaline seawater, featuring a low overpotential of only +294 and +306 mV to reach the current density of 10 mA cm^–2, respectively, along with excellent long-term stability during overall water splitting, a performance much better than those with commercial RuO₂. First-principles calculations show that adjacent NiN₄ sites effectively promote the OER kinetics at FeN₄ sites by reducing the energy barrier of O–O formation. This is also manifested in alkaline saline water splitting.