A green approach for enhancing the electrocatalytic activity and stability of NiFe₂O₄/CB nanospheres towards hydrogen production

Among the exfoliation processes applied on layered materials, it is the first time to explore the ultrasonic exfoliation in water for improving the catalytic properties of NiFe₂O₄/CB (CB = carbon black) nanospheres towards the electrocatalytic hydrogen evolution reaction (HER) in acidic media. It is found that after exfoliation, the overpotential of HER on NiFe₂O₄/CB nanospheres is improved by about 90 mV at a current density of 10 mA cm⁻². Moreover, the exfoliated NiFe₂O₄/CB nanospheres are not only more stable than the commercial Pt/C catalyst, but also they exhibit an overpotential improvement of about 100 mV at 50 mA cm⁻², after 6000 CV cycles. It is also found that the ultrasonic process causes uniformed NiFe₂O₄/CB particles, an increase of the electrochemical active sites, enriched Fe²⁺ ion and Fe³⁺ occupied on tetrahedral sites on the surface layer of the NiFe₂O₄/CB nanospheres, as resulted from the analysis with XPS, FTIR etc., leading to a higher activity and excellent durability. Furthermore, the approach also provides new insights on processing of materials in a green route.