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Page 2 of 16 Li et al. Energy Mater 2023;3:300021 https://dx.doi.org/10.20517/energymater.2023.09

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based catalysts, with a half-wave potential (E ) of 0.90 V and an overpotential of 10 mA cm (E ) of 320 mV.
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More importantly, chronoamperometry (I-T) and accelerated durability tests (ADT) show the unordinary stability
of the catalyst. Both physical characterization and experimental results verify that the Fe-N moieties and Ni Se
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crystalline phase are the main active sites for ORR and OER activities, respectively. The small potential gap
(ΔE = E - E = 0.622 V) represents superior dual-functional activities of the FePc/Se@NiFe catalyst.
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Subsequently, the ZABs assembled using FePc/Se@NiFe exhibit excellent performances. This study offers a
promising design concept for promoting further development of high-performance ORR and OER electrocatalysts
and their application in ZAB.
Keywords: Multi-component, layered double hydroxide, iron (II) phthalocyanine, dual-functional electrocatalyst,
rechargeable zinc-air battery

INTRODUCTION
The critical energy security and environmental degradation issues caused by the depletion of traditional
[1,2]
fossil fuels have prompted a renewed focus on energy harvesting from renewable sources . Rechargeable
ZABs are considered to be one of the most promising energy storage and conversion devices because of
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their high specific capacity (≈820 mAh g based on Zn metal), inherent safety, economical cost, and zero
[3-6]
pollution . The development of reliable dual-functional air electrode catalysts is one of the major
challenges for ZABs, as it is the key to guarantee high conversion efficiency and long cycle life of batteries.
Specifically, the charge-transfer kinetics of the ORR and OER at the air electrode are intrinsically sluggish
during the discharge and charge processes . Pt/C and IrO (or RuO ) are traditionally used as standard
[7]
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ORR and OER electrocatalysts, while dual-functional activity is achieved by their simple mixing. However,
owning the inherent drawbacks such as particularly poor bifunctional oxygen activity, high prices, and earth
scarcity, these precious metal-based catalysts hinder their long-term industrial application for rechargeable
ZABs. To address these issues, great efforts have been made to develop dual-functional oxygen
electrocatalysts without precious metals as alternatives .
[8]

In recent decades, 3d transition metal-based compounds characterized by earth-abundant resources and
low cost have been developed as noble-metal-free catalysts, including transition metal-based sulfides [9,10] ,
[15]
phosphides [11,12] , carbides [13,14] , and alloys , layer double hydroxides (LDHs) [16,17] , and selenides [18,19] . Among
them, the LDHs catalysts, especially NiFe-LDHs, have received much attention because of their prominent
OER catalytic activity in alkaline solutions . Generally, NiFe-LDHs have a special two-dimensional flake
[20]
crystal structure of brucite, in which the solvent molecules and anionic groups are located between the
[21]
layers of metal cations . Because of the unique layered structure of NiFe-LDH, the performance of NiFe-
LDH can be improved in a wide range by adjusting the types of anions and solvent molecules between wide
[22]
layer spacing. This makes NiFe-LDHs considered to be a suitable material for OER catalytic process .
Although LDH-based catalysts exhibit relatively impressive OER performance, the self-agglomeration of
nanoparticles and insufficient exposure of active sites are important factors limiting the further
improvement of OER intrinsic activity . Therefore, in order to improve the catalytic properties of NiFe-
[23]
LDH to OER, a variety of strategies have been proposed, such as defect engineering , interface
[24]
engineering [25,26] , heteroatom doping [27,28] , crystalline phase engineering [29,30] , and morphology control [31,32] .
Among these strategies, constructing a polycrystalline phase composite catalyst by crystalline phase
engineering is a useful pathway to achieve high-performance OER electrocatalytic activities. Each phase in
the polycrystalline phase is considered as the real catalytic active site. For example, Hong et al. reported a
new and simple strategy, “dual-phase engineering”, in which phase catalysts based on efficient transition
metal hydroxides and high metal transition metal boride phases are used in OER . Lou group synthesized
[33]
two-component Co O /NiCo O nanocages with OER activity beyond that of single-component Co O or
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