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

Abstract

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.