Porous\nN‑Doped Carbon-Encapsulated CoNi Alloy\nNanoparticles Derived from MOFs as Efficient Bifunctional Oxygen Electrocatalysts

Abstract

A porous\nN-doped carbon-encapsulated CoNi alloy nanoparticle composite\n(CoNi@N–C) was prepared using a bimetallic metal–organic\nframework composite as the precursor. The optimal prepared Co₁Ni₁@N–C material at 800 °C exhibited\nwell-defined porosities, uniform CoNi alloy nanoparticle dispersion,\na high doped-N level, and scattered CoNi–N<i>_x</i> active sites, therefore affording excellent oxygen catalytic\nactivities toward the reduction and evolution processes of oxygen.\nThe oxygen reduction (ORR) onset potential (<i>E</i>_onset) on Co₁Ni₁@N–C was 0.91\nV and the half-wave potential (<i>E</i>_1/2) was\n0.82 V, very close to the parameters recorded on the Pt/C (20 wt Pt%)\nbenchmark. Moreover, it is worth noting that the ORR stability of\nCo₁Ni₁@N–C was prominently higher than\nthat of Pt/C. Under the oxygen evolution reaction condition,\nCo₁Ni₁@N–C generated the maximum current\ndensity at the potential of 1.7 V (8.60 mA cm^–2)\nand the earliest <i>E</i>_onset (1.35 V) among\nall Co<i>_x</i>Ni<i>_y</i>@N–C hybrids. The Co₁Ni₁@N–C\ncatalyst exhibited the smallest Δ<i>E</i> value, confirming\nthe superior bifunctional activity. The high surface area and porosity,\nand CoNi–N<i>_x</i> active sites on the\ncarbon surface including the proper interactions between the N-doped\nC shell and CoNi nanoparticles were attributed as the main contributors\nto the outstanding oxygen electrocatalytic property and good stability.