Electrochemical performance enhancement by the partial reduction of NiFe2O4@g-C3N4 with core-shell hollow structure

Transition metal oxide NiFe2O4 has many advantages such as abundance in nature, easy availability, low toxicity and being environmentally friendly. However, it suffers from poor electrical conductivity which results in unsatisfactory electrochemical performance. In this work, the construction of NiFe2O4@g-C3N4 core-shell hollow spherical structure and the in-situ formation of Fe–Ni alloy have been achieved by facile hydrothermal method followed by annealing in 5%H2/95%Ar. The electrical conductivity of electrode has been greatly improved leading to a specific capacity of 85.3 mAh g−1 at 1 A g−1 and a 67.2% capacity retention at 20 A g−1. A hybrid device exhibits 19.5 Wh kg−1 in specific energy and 150.1 W kg−1 in specific power, and good cycling stability of 100% capacity retention after 10,000 cycles at 6 A g−1. NiFe2O4@g-C3N4 core-shell hollow spheres are obtained by adding NH4F and the formation of Fe–Ni alloy is achieved by partial reduction. [Display omitted] •NiFe2O4@g-C3N4 core-shell hollow spheres are developed with a soft-template method.•Addition of NH4F avoid fast chemical reaction and slow down the urea decomposition.•Fe–Ni alloy is formed by partial reduction of NiFe2O4 in 5%H2/95%Ar at 400 °C.•Introduction of g-C3N4 and Fe–Ni alloy achieve enhanced electrochemical performance.