Constructing atomically-dispersed Mn on ZIF-derived nitrogen-doped carbon for boosting oxygen reduction.

Exploring durable and highly-active non-noble-metal nanomaterials to supersede Pt-based nanomaterials is an effective way, which can reduce the cost and boost the catalytic efficiency of oxygen reduction reaction (ORR). Herein, we constructed atomically-dispersed Mn atoms on the ZIF-derived nitrogen-doped carbon frameworks (Mn-Nx/NC) by stepwise pyrolysis. The Mn-Nx/NC relative to pure nitrogen-doped carbon (NC) exhibited superior electrocatalytic activity with a higher half-wave potential (E 1/2 = 0.88 V) and a modest Tafel slope (90 mV dec-1) toward ORR. The enhanced ORR performance of Mn-Nx/NC may be attributed to the existence of Mn-Nx active sites, which can more easily adsorb intermediates, promoting the efficiency of ORR. This work provides a facile route to synthesize single-atom catalysts for ORR.

Precise constructed atomically dispersed Fe/Ni sites on porous nitrogen-doped carbon for oxygen reduction.

Exploring highly-efficient noble-metal-free electrocatalysts for oxygen reduction reaction (ORR) is crucial for preparation of rechargeable metal-air batteries. Herein, FeNi-mIm (guest) was loaded on the surface of ZIF-8 (host) via a novel host-guest strategy, and the resulting ZIF-8@FeNi(mIm)X precursors can be converted to FeNi SAs/NC catalysts with controllable structures. Robust metal-organic framework (MOF)-derived atomically dispersed Fe/Ni dual single atom electrocatalysts for ORR were developed, followed by pyrolysis of the precursors. Characterizations showed that the atomically-dispersed Fe/Ni active sites were uniformly embedded in the N-doped carbon framework. As a result, the ORR performance was obviously improved with lower half-wave potential (E1/2 = 0.91 V) in alkaline media. Such improvement is mainly attributed to the synergy of fully-exposed bimetallic single atom active sites caused by the interaction of Fe/Ni 3d orbitals. The lower adsorption energy of intermediate hydroxyl groups on the active sites and the smaller ORR energy barrier were calculated by the density functional theory. The novelty FeNi SAs/NC catalysts showed faster ORR dynamics in the rate-determining step of four-electron transfer. The synthesis strategy reported here provides an efficient approach to construct high performance dual single-atom catalysts with fully-exposed active sites on the surface.