Bimetallic nanoparticles confined in an N-doped graphitic carbon shell: a high-performance trifunctional catalyst for efficient water splitting

Abstract

Understanding the structure–property relationship of materials and identifying the active centers responsible for electrochemical water splitting are essential for designing high-performance electrocatalysts. This study presents the synthesis of nickel-titania (Ni–TiO₂) nanostructures encapsulated in nitrogen-doped graphitic carbon shells, with electrochemical performance tuned by adjusting the pyrolysis temperature. The optimized catalyst, NT@NC-8, features a core–shell design that enhances electroactive sites and stability. NT@NC-8 delivers excellent trifunctional catalytic activity for the oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and oxygen reduction reaction (ORR) in alkaline media. In an alkaline medium, for the OER, NT@NC-8 achieves a current density of 10 mA cm⁻² at a low overpotential of 355 mV and 50 mA cm⁻² at 465 mV, with a low Tafel slope of 63 mV dec⁻¹, whereas for the HER, it requires an overpotential of 326 mV to reach 10 mA cm⁻². The ORR follows a four-electron pathway, showing an onset potential of 0.78 V vs. RHE and a limiting current density of −5.10 mA cm⁻². NT@NC-8 also exhibits a high surface area (4.45 cm²) and a low charge transfer resistance (53.2 Ω).