CoFe nanoalloy particles encapsulated in nitrogen-doped carbon layers as bifunctional oxygen catalyst derived from a Prussian blue analogue

Highly active bifunctional catalysts for oxygen evolution reaction (OER) and oxygen reduction reactions (ORR) have attracted increasing attention in metal-air batteries and fuel cells. CoFe nanoalloy particles encapsulated in nitrogen-doped carbon and nitrogen-doped carbon nanotubes (CoFe@NC-NCNT-H) are synthesized by pyrolyzing a Prussian blue analogue precursor (i.e. Fe₃[Co(CN)₆]₂) as low as 600 °C, and followed by HNO₃ treatment. Such low temperature pyrolysis and HNO₃ treatment affords the hybrid mesoporous material with a high level of nitrogen content (∼10%) and a relatively high specific surface area (∼210.5 m² g⁻¹), capable of providing active sites and mass transport channels. In alkaline solution, CoFe@NC-NCNT-H is highly active towards OER with a low onset potential (∼1.35 V) and a small overpotential (∼380 mV) to reach 10.0 mA cm⁻², comparable to the state-of-the-art RuO₂. CoFe@NC-NCNT-H is also a good ORR catalyst, and more importantly it exhibits an improved stability compared to commercial Pt/C. CoFe@NC-NCNT-H displays promise as a bifunctional catalyst with an extremely low potential difference (∼0.87 V between ORR at −3.0 mA cm⁻² and OER at 10.0 mA cm⁻²), superior to commercial Pt/C and RuO₂. The facilely prepared CoFe@NC-NCNT-H with high bifunctional performance and stability promises great potential for ORR and OER.