CoNi nanoparticles anchored inside carbon nanotube networks by transient heating: Low loading and high activity for oxygen reduction and evolution

Abstract

A low-loading CoNi alloy catalyst film was obtained by the transient Joule heating method, which has excellent bifunctional catalytic performance for oxygen. • Rapid preparation of nano-scale CoNi alloys supported on carbon nanotube networks. • Catalyst film shows excellent bifunctional catalytic performance with low loading. • The synergy between two metals improves the activity and stability of the catalyst. Transitional metal alloy and compounds have been developed as the low cost and efficient bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, a high mass loading of these catalysts is commonly needed to achieve acceptable catalytic performance, which could cause such problems as battery weight gain, mass transport blocking, and catalyst loss. We report herein the preparation of fine CoNi nanoparticles (5–6 nm) anchored inside a nitrogen-doped defective carbon nanotube network (CoNi@N-DCNT) by a transient Joule heating method. When utilized as an electrocatalyst for oxygen reduction and evolution in alkaline media, the CoNi@N-DCNT film catalyst with a very low mass loading of 0.06 mg cm −2 showed excellent bifunctional catalytic performance. For ORR, the onset potential ( E onset ) and the half-wave potential ( E 1/2 ) were 0.92 V versus reversible hydrogen electrode ( vs . RHE) and 0.83 V ( vs . RHE), respectively. For OER, the potential at the current density ( J ) of 10 mA cm −2 ( E 10 ) was 1.53 V, resulting in an overpotential of 300 mV much lower than that of the commercial RuO 2 catalyst (320 mV). The potential gap between E 1/2 and E 10 was as small as 0.7 V. Considering the low mass loading, the mass activity at E 10 reached at 123.2 A g −1 , much larger than that of the RuO 2 catalyst and literature results of transitional metal-based bifunctional catalysts. Moreover, the CoNi@N-DCNT film catalyst showed very good long-term stability during the ORR and OER test. The excellent bifunctional catalytic performance could be attributed to the synergistic effect of the bimetal alloy.