Electrospun CoFe2O4 nanofibers as bifunctional nanocatalysts for the oxygen evolution and oxygen reduction reactions in alkaline media

Non-noble metal bifunctional nanocatalysts based on CoFe2O4/C were synthetized by the electrospinning method and evaluated for the Oxygen Evolution Reaction (OER) and the Oxygen Reduction Reaction (ORR). The effect of annealing at different temperatures (T=300, 600 and 900°C) on their morphological and structural features was characterized by XRD, EDS, Raman, FESEM, HRTEM and XPS. The nanofibers annealed at 300 °C (CoFe2O4-300) showed a cubic spinel structure and an average diameter of 42 nm. The CoFe2O4-300/C nanocatalyst demonstrated the highest catalytic activity towards the OER, outperforming the benchmark commercial 20 wt. % Pt/C. Meanwhile all CoFe2O4-based nanocatalysts showed fair catalytic activity for the ORR (Eonset ≈ 0.801 V/RHE, n≈ 3.56, %HO2- ≈ 21-39). In addition, the CoFe2O4/C nanocatalysts demonstrated a higher electrochemical stability than Pt/C for both the ORR and the OER.