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

Abstract

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 _xNi _y@N-C hybrids. The Co₁Ni₁@N-C catalyst exhibited the smallest Δ E 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.