Hydrochar-Coated FeCo@Ni ₃ S ₂ –CeO _x Core–Shell Nanorods as Bifunctional Electrocatalysts for Sustainable H ₂ Production via Seawater Splitting

Although transition metal sulfides exhibit active oxygen evolution reaction (OER) activity, they suffer from low durability under seawater electrolysis conditions. This article reports a successful one-pot sequential nanostructure growth strategy to synthesize C H -FeCo@Ni 3 S 2 –CeO x core–shell-type nanorods supported on nickel foam for active and durable OER and hydrogen evolution reaction (HER) activities in seawater electrolytes. The catalyst demonstrates remarkable OER activity in a 1.0 M KOH solution, and a current density ( j ) value of 100 mA/cm 2 is realized at a reasonably low overpotential (η) value of 210 mV. The chronoamperometry data recorded at 100 mA/cm 2 revealed a negligible loss in activity until 225 h of run, supporting adequate stability. The electrode also displayed effective OER activity in alkaline seawater, and a j OER value of 100 mA/cm 2 was realized at a η value of 270 mV with an associated durability above 100 h. The density functional theory analysis further supported that the Co/Fe doping on Ni 3 S 2 promoted the catalytic efficiency, whereas the C H coating and CeO x shell on the active FeCo@Ni 3 S 2 core possibly imparted durability under seawater conditions. This work presents a promising strategy for developing high-performance bifunctional electrocatalysts for industrial-grade water splitting applications, offering potential solutions for sustainable hydrogen production.