The Catalyst Review May 2024 - 15

Origin of the Oxygen Reduction Activity on Boron-Doped Fe−N−C Catalysts for Zinc−Air Battery
Applications
Development of highly active and stable carbon-based electrocatalysts for the oxygen reduction reaction (ORR) is an ongoing area of
research. To date, Fe−N−C catalysts have been shown to have the highest activity in acidic and alkaline media and are considered potential
alternatives for precious metal catalysts. The ORR activity of these catalysts can be further improved by doping with electropositive boron,
which has been shown to outperform the benchmark Pt/C catalysts. Herein, the authors examine boron and nitrogen-codoped Fe-containing
carbon materials with respect to their ORR activity.
These catalysts were synthesized from polyaniline (from aniline polymerization using FeCl3
The superior ORR activity of one of
these catalysts, Fe−N&B/C-800S
(Eonset
= 1.01 and E1/2
s−1
= 0.88 V) with
a turnover frequency of 3.86 Fesites−1
at
0.8 V), was then applied
to study the zinc-air battery (ZAB)
performance.
The mechanistic investigation of
oxygen and H2
O2 reduction reaction
on a Fe−N&B/C catalyst using
kinetic analysis demonstrates that
the ORR proceeds via a pseudo-4electron
pathway, wherein the boron
sites catalyze the reduction of an
H2
O2 intermediate (Scheme 1). The
TOF calculation from the kinetic
current density for Fe−N&B/C-800S
shows the highest values among
the literature reported for similar
compounds.
SCN- poisoning experiments
confirm that in addition to the Fe
sites, boron plays a vital role in ORR
activity. The improved stability of the
Fe−N&B/C-800S was proved with
the stability tests, and the loss of
pyridinic and graphitic nitrogens was
found to be the cause of the stability
issues (Figure 1).
Theoretical analysis supports the
O2
adsorption on boron sites with a
relatively smaller activation barrier
than the Fe sites. The Fe−N&B/C
catalyst exhibits a superior power
density (193 mW cm−2
300 cycles, and specific capacity
(932 mA h gZn −1
electrolyte battery. This analysis
indicates that the Fe−N&B/C
materials may be potential
electrocatalytic materials for ORR,
while the solid-state ZAB experiment
provided real-time applications of
the materials in devices. Eledath
AN, Poulose AE, and Muthukrishnan
A, (2024). ACS Appl. Energy
Mater. https://doi.org/10.1021/
acsaem.3c03122.
The Catalyst Review
May 2024
15
, stability over
) in a zinc−air liquid
in boric acid) followed by sequential heat
treatment and then characterized to confirm the presence of iron, boron, and nitrogen. The role of each dopant toward ORR activity
was then investigated using ORR activity, stability, poisoning experiments, kinetic and mechanistic analysis, and theoretical analysis.
Scheme 1. Kinetic model of ORR meveloped by Damjanovic et al.a
a The subscripts ad and b refer to adsorbed and bulk species. The orange and purple highlighted
regions correspond to the ORR mechanism in an acidic and neutral-alkaline medium.
Figure 1. (a) RDE voltammograms of the ORRon Fe−N&B/C-800S before and after the
durability test. The C-1s (b) and N-1s (c) XPS of Fe−N&B/ C-800S after the durability test. (d)
Relative weight percentage comparison of the various carbon and nitrogen species before and
after the durability cycles. (e) Stability test of the Fe−N&B/C-800S-coated GC RDE at constant
potential (0.5 V vs RHE) using the chronoamperometry experiment and constant rotation
speed of 1600 rpm in O2-saturated 0.1 M KOH electrolyte. (f) Linear sweep voltammograms
of ORR on Fe−N&B/C-800S catalysts before and after the chronoamperometry stability test.

The Catalyst Review May 2024

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