Converting silicon nanoparticles into nickel iron silicide nanocrystals within molten salts for water oxidation electrocatalysis

Abstract

We synthesize metal silicide electrocatalysts for water oxidation, by using the high reactivity of silicon nanoparticles and the unique stability and low vapor pressure of molten salt solvents. We can then perform liquid-phase synthesis under vacuum at 300–400 °C. This strategy yields FeSi, Ni₂Si, and Fe-doped Ni₂Si nanocrystals, which exhibit high electrocatalytic activity for the oxygen evolution reaction with an overpotential of 337 mV at 10 mA cm⁻² in 0.1 M KOH for Ni₂Si doped with optimal iron content. We report high stability over 85 hours. Post mortem studies reveal a core–shell–shell nanostructure, where the core remains crystalline Ni_2−xFe_xSi enabling charge percolation. The outer shell of nanocrystalline Ni_1−xFe_xOOH acts as the electrocatalytic species. The amorphous oxide intermediate layer is specific of silicides and passivates the core against further silicon leaching. These nanostructures produced in situ provide a robust, efficient, and low-cost catalyst for water oxidation.