Facile synthesis of the porous FeCo@nitrogen-doped carbon nanosheets as bifunctional oxygen electrocatalysts

Abstract This work reports the synthesis of novel cross-linked and functional porous carbon nanosheets (CNSs). The polyvinylpyrrolidone/transition metal acetates/N–N-dimethylformamide precursors are first woven into networks by electrospinning. The resultant precursor networks are transformed into the three-dimensional (3D) hierarchically porous material consisting of cross-linked and meso/macroporous CNSs (i.e., FeCo@NCNS) after pyrolysis. Characterization results prove that abundant ultrafine FeCo@NC units, N–C bonds, metal-nitrogen doped carbon (M-N-C) species and oxygen-containing functional groups disperse along the surfaces of the FeCo@NCNS, which act as electrocatalytic active sites for Oxygen reduction reaction (ORR) and Oxygen evolution reaction (OER). Due to the synergistic effect of the hierarchically porous structures and high-density active sites, the optimal FeCo@NCNS exhibits more positive onset potential (0.98 V relative to a reversible hydrogen electrode (vs. RHE)) and half-wave potential (0.827 V vs. RHE) than Pt/C (0.97 V vs. RHE and 0.819 vs. RHE) for ORR. Meanwhile, the OER potential at 10 mA cm−2 of the FeCo@NCNS (1.597 V vs. RHE) is more negative than RuO2 (1.631). Furthermore, the oxygen electrode activity (ΔE = E10,OER - E1/2,ORR) of the FeCo@NCNS is as low as 0.772 V, which surpasses the state-of-the-art Pt/C(ORR)-RuO2(OER) catalyst combination (ΔE = 0.812 V). Experimental results prove that the FeCo@NCNS is among the best non-precious metal based bifunctional electrocatalyst for ORR and OER.