Porous N‑Doped Carbon-Encapsulated CoNi Alloy Nanoparticles Derived from MOFs as Efficient Bifunctional Oxygen Electrocatalysts

A porous N-doped carbon-encapsulated CoNi alloy nanoparticle composite (CoNi@N–C) was prepared using a bimetallic metal–organic framework composite as the precursor. The optimal prepared Co1Ni1@N–C material at 800 °C exhibited well-defined porosities, uniform CoNi alloy nanoparticle dispersion, a high doped-N level, and scattered CoNi–N x active sites, therefore affording excellent oxygen catalytic activities toward the reduction and evolution processes of oxygen. The oxygen reduction (ORR) onset potential (E onset) on Co1Ni1@N–C was 0.91 V and the half-wave potential (E 1/2) was 0.82 V, very close to the parameters recorded on the Pt/C (20 wt Pt%) benchmark. Moreover, it is worth noting that the ORR stability of Co1Ni1@N–C was prominently higher than that of Pt/C. Under the oxygen evolution reaction condition, Co1Ni1@N–C generated the maximum current density at the potential of 1.7 V (8.60 mA cm–2) and the earliest E onset (1.35 V) among all Co x Ni y @N–C hybrids. The Co1Ni1@N–C catalyst exhibited the smallest ΔE value, confirming the superior bifunctional activity. The high surface area and porosity, and CoNi–N x active sites on the carbon surface including the proper interactions between the N-doped C shell and CoNi nanoparticles were attributed as the main contributors to the outstanding oxygen electrocatalytic property and good stability.