Triggering Oxygen Redox Cycles in Nickel Ferrite by Octahedral Geometry Engineering for Enhancing Oxygen Evolution

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Spinel-type nickel ferrite (Ni_xFe_3-xO₄) is a common electrocatalyst for the oxygen evolution reaction (OER).
• The adsorbate evolution mechanism (AEM) limits OER activity due to poor metal-d and oxygen-p orbital hybridization.
• Activating lattice oxygen to promote the lattice-oxygen-mediated mechanism (LOM) can enhance OER performance.

Purpose of the Study:

• To develop a stable and highly active electrocatalyst for OER by triggering the LOM pathway.
• To investigate the effect of geometrical defects and cation ratios on OER activity and mechanism.

Main Methods:

• Synthesis of iron foam (IF)-supported Ni_0.75Fe_2.25O₄ (NiFeO) with octahedral defects and a higher Fe:Ni ratio (d-NiFe^HRO/IF) via ion-exchange and annealing.
• Electrochemical characterization of OER activity, kinetics, and stability.
• Theoretical calculations to elucidate the role of defects and cation ratios in OER mechanism.

Main Results:

• The d-NiFe^HRO/IF catalyst demonstrated excellent OER activity (295 mV overpotential for 100 mA cm^-2), fast kinetics (34.6 mV dec^-1 Tafel slope), and remarkable stability (130 h at 100 mA cm^-2).
• Theoretical calculations confirmed that octahedral defects enhance Fe-d and O-p orbital overlap, activating lattice oxygen.
• Increased Fe:Ni ratio promotes lattice oxygen redox activity, facilitating the LOM pathway for improved OER.

Conclusions:

• The engineered d-NiFe^HRO/IF catalyst effectively triggers the LOM pathway for superior OER performance.
• Defect engineering and controlled cation ratios are crucial strategies for designing advanced OER electrocatalysts.
• This work provides insights into optimizing nickel ferrite catalysts for efficient and stable oxygen evolution.