Heterostructure interface-engineered 3D/2D CoMn₂O₄/CoFe₂O₄/NF core/shell Bi-functional electrocatalytic nanomaterials for efficient overall water splitting application in alkaline media

Developing a high-performance, affordable, reinforced, and stable bi-functional nanocatalyst for a sustainable energy conversion process is highly desirable for large-scale commercialization. Inspired by the benefits of heterostructure engineering, herein, we hierarchically constructed an interface-engineered 3D/2D (CoMn₂O₄/CoFe₂O₄) core/shell bi-functional nanohybrid material on a nickel foam (NF) substrate <i>via</i> a facile two-step solvothermal process. As evidenced by HR-TEM and XPS results, heterostructure interfaces were properly established, and strong electronic coupling was built at the heterostructure interfaces. Moreover, electrochemical studies revealed that the synergistic coupling effect expedites rapid charge transfer at the electrode/electrolyte interfaces, elevating accessible metal active sites and oxygen vacancies over the nanomaterial surface, and affords robust electrochemical stability to an electrode material. This combined effect greatly elevates electrochemical performance and facilitates remarkably low overpotential values of 104 mV and 233 mV and minimal Tafel slope values of 73.6 mV dec^-1 and 53.2 mV dec^-1 for the HER and OER, respectively. Moreover, an assembled two-electrode electrochemical cell setup exhibited a small cell voltage of 1.55 V with stupendous stability over 50 h at a current density of 10 mA cm^-2 in 1 M KOH alkaline media. This rational core/shell heterostructure interface-constructed bi-functional electrode will be a new avenue for scaling up the electrochemical reaction kinetics of new-generation energy-conversion technologies.