Water-assisted clean electro-preparation of Co3Fe7 in molten salts: its enhanced ferromagnetic properties and hydrogen evolution rate†

A clean and efficient method for synthesizing intermetallic Co₃Fe₇ is reported, based on water-assisted molten salt electrolysis employing the CoFe₂O₄ electrode, fabricated through the thermo-mechanochemical treatment of iron and cobalt oxides. The electrolysis is conducted at a cell voltage of 1.5 V, achieving an energy consumption of 1.47 kW h kg⁻¹. Upon formation, the synthesized Co₃Fe₇ serves as an electrode for catalytic hydrogen production, demonstrating a current density of 91.7 mA cm⁻². These performances are compared with those of electrolytic Fe (1.49 kW h kg⁻¹ and 96.4 mA cm⁻²) and electrolytic Co (1.30 kW h kg⁻¹ and 40.8 mA cm⁻²), both prepared under the same electrolysis potential but with different current–time profiles. The electrolytic Co₃Fe₇ exhibits superior ferromagnetic properties, with saturation magnetization, remanent magnetization and coercivity values of 157.0 emu g⁻¹, 4.3 emu g⁻¹ and 48.9 Oe, respectively, surpassing values reported in the literature for Fe–Co alloys. The findings suggest a sustainable approach for the green synthesis of Co₃Fe₇ with enhanced ferromagnetic properties. Additionally, the electrolytic Fe and Co₃Fe₇ show promise as electrode materials for molten salt hydrogen production.