Exceptional Electrocatalytic Hydrogen Evolution—Untapped Potential of Using Cation Distribution in Spinel CoFe₂O₄ Nanosheets as an Activity Descriptor

Exploring cost-effective and efficient electrocatalysts for the hydrogen evolution reaction (HER) is essential for realizing green energy technologies such as water electrolyzers and fuel cells. To this end, identifying descriptors that determine the activity of the employed catalysts would render the process more efficient and help to design selective catalytic materials. Herein, cation distribution (δ) is presented as the activity descriptor for the HER of CoFe₂O₄ spinels. A one-step hydrothermal synthesis method is demonstrated for the fabrication of flower-shaped spinel CoFe₂O₄ nanosheets on Ni foam at various pHs with different cation distribution. The XPS and Raman analyses revealed the cation distribution of Co and Fe as the main factor determining the catalytic activity of the material. This has been confirmed both experimentally and computationally. The catalyst with the largest δ (0.33) showed as low as 66 mV overpotential at -10 mA cm^-2 with exceptional stability for 44 hours of continuous electrolysis in 1 M KOH. Our study demonstrates cation distribution as a catalytic activity descriptor of spinels for HER.