Atomically Dispersed Fe–Co Dual Metal Sites as Bifunctional Oxygen Electrocatalysts for Rechargeable and Flexible Zn–Air Batteries

Abstract

Single-metal site catalysts have exhibited highly efficient electrocatalytic properties due to their unique coordination environments and adjustable local structures for reactant adsorption and electron transfer. They have been widely studied for many electrochemical reactions, including oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, it remains a significant challenge to realize high-efficiency bifunctional catalysis (ORR/OER) with single-metal-type active sites. Herein, we report atomically dispersed Fe–Co dual metal sites (FeCo–NC) derived from Fe and Co co-doped zeolitic imidazolate frameworks (ZIF-8s), aiming to build up multiple active sites for bifunctional ORR/OER catalysts. The atomically dispersed FeCo–NC catalyst shows excellent bifunctional catalytic activity in alkaline media for the ORR (E 1/2 = 0.877 V) and the OER (E j=10 = 1.579 V). Moreover, its outstanding stability during the ORR and the OER is comparable to noble-metal catalysts (Pt/C and RuO2). The atomic dispersion state, coordination structure, and the charge density difference of the dual metal site FeCo–NC were characterized and determined using advanced physical characterization and density functional theory (DFT) calculations. The FeCo–N6 moieties are likely the main active sites simultaneously for the ORR and the OER with improved performance relative to the traditional single Fe and Co site catalysts. We further incorporated the FeCo–NC catalyst into an air electrode for fabricating rechargeable and flexible Zn–air batteries, generating a superior power density (372 mW cm–2) and long-cycle (over 190 h) stability. This work would provide a method to design and synthesize atomically dispersed multi-metal site catalysts for advanced electrocatalysis.

Synergetic Dual‐Atom Catalysts: The Next Boom of Atomic Catalysts

“…Because of Fe−Co synergy, the d orbital of metal atoms could interact with the 2p orbital of oxygen atoms, which regulated the adsorption energy of *O. FeCo‐DACs/NC showed an open‐circuit voltage of around 1.50 V, while the Pt/C catalyst showed 1.46 V. Moreover, rechargeable ZABs were made using FeCo‐DACs/NC as the cathode, and two batteries were connected in series could light up a light‐emitting diode, whose voltage was about 2.5 V (Figure 3i). Another synergetic catalyst of Fe and Co for ZABs, FeCo‐NC, has been reported and generated a superior power density of 372 mW cm −2 [57] . Currently, most studies on ZABs are conducted at room temperature.…”

“…Another synergetic catalyst of Fe and Co for ZABs, FeCo-NC, has been reported and generated a superior power density of 372 mW cm À 2 . [57] Currently, most studies on ZABs are conducted at room temperature. Lowering the temperature will weaken the ionic conductivity and slow down the charging and discharging process of the cathode.…”

MOF-Derived Co and Fe Species Loaded on N-Doped Carbon Networks as Efficient Oxygen Electrocatalysts for Zn-Air Batteries

“…Metal elements originate from nodes of MOFs and doping processes could uniformly disperse on carbon skeletons by the calcination of MOF precursors [18,27,28]. Therefore, with the assistance of MOFs as precursors, transition metal/ carbon composite catalysts with tight connection and uniform distribution could be facilely prepared [29][30][31]. Meanwhile, MOF-derived metal/carbon composite catalysts could inherent the morphology and porous structure of MOFs, which are beneficial for the exposure of active sites, electron transfer and mass transportation in electrocatalytic processes [27].…”

Non‐Covalent Interaction of Atomically Dispersed Cu and Zn Pair Sites for Efficient Oxygen Reduction Reaction

“…[ 9 ] Such dual–single‐atom catalysts with synergistic effect between Cu and adjacent atomic metal sites can enhance the overlap effect between the 2p orbital of oxygen molecule and the 3d orbital of metallic atoms, thereby improving the oxygen reduction activity. [ 9,10 ] As a unique metal with strong volatility at about 905 °C, Zn atoms can not only be incorporated into Cu–C x N y ‐containing electrocatalysts as heteronuclear metal sites. [ 11 ] The volatilization of Zn can also generate numerous vacancies with controllable sizes to capture Cu atoms and form Cu and Zn atom pairs.…”