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Li et al. Energy Mater 2023;3:300021 https://dx.doi.org/10.20517/energymater.2023.09 Page 5 of 16

-1
-5
2 -1
-6
where the constants related to O were different in alkaline (C = 1.2 × 10 mol cm ; D = 1.9 × 10 cm s )
2
0
0
conditions. Other constants were fixed, which can refer to our previous work . All potentials used in this
[43]
effort were converted to potentials with respect to the reversible hydrogen electrode (RHE) by using the
Nernst equation:
The n and H O yield were calculated by the rotating ring disk electrode (RRDE) tests with the following
2
2
equation:

where I , I and N are all fixed value constants.
c
r
d
Assembly of rechargeable ZABs
Measurements of rechargeable liquid ZABs with our catalyst were accomplished using home-built
electrochemical cells under atmosphere condition. Polished zinc plates were used as anode, and carbon
cloth coated with homemade or Pt/C (J-M 20%) catalyst mass of 0.75 mg cm was served as air cathode. The
-2
mixture solution of 6.0 M KOH + 0.2 M zinc acetate was used as alkaline electrolyte. The LSV charging/
discharging curves were collected by CHI660E electrochemical workstation, and all other performance tests
were performed using a Neware battery test system.

RESULTS AND DISCUSSION
Synthesis and structural investigations of the electrocatalyst
As illustrated in Scheme 1, the FePc/Se@NiFe sample was synthesized via a two-step hydrothermal process.
Firstly, through a simple hydrothermal method, the NiFe-LDH nanosheet precursor was fabricated in a
mixed solution of Ni and Fe salts. A detailed procedure was shown in the Experimental Section. Then,
3+
2+
the collected NiFe-LDH nanosheet experienced an adequate wet chemical selenization during the secondary
hydrothermal process in the environment of selenium and FePc solution at 100 °C. As the interlayer
hydroxyl or carbanion anion of NiFe-LDH was replaced by Se during this process, the derived poly-
2-
crystals were supported by FePc nanoclusters. The crystalline phase and structure of the FePc, NiFe-LDH,
Se@NiFe, FePc/Se@NiFe, FePc/Se@Ni and FePc/Se@Fe materials were analyzed by XRD analysis. As shown
in Figure 1A, the pattern of FePc/Se@NiFe with peaks located at 30.1°, 35.4°, 56.9°, and 62.5° could be
ascribed to the (220), (311), (511), and (440) crystal planes of Fe O , separately (PDF #19-0629) . Peaks at
[44]
3
4
33.3°, 33.6°, 45.1°, 45.4°, and 50.8° are the (-312), (-402), (-514), (-604), and (-310) characteristic crystalline
planes belonging to Ni Se (PDF #89-2020) , while the peak at 23.5°, 29.7°, and 43.6° can match very well
[45]
4
3
[46]
with the (110), (101), and (012) lattice planes of the Se (PDF #86-2246) , respectively. The above XRD