Design and synthesis of conductive carbon polyhedrons enriched with
Mn-Oxide active-centres for oxygen reduction reaction
Syed Shoaib Ahmad Shah
1
, Tayyaba Najam
1
, Chao Cheng, Siguo Chen, Rui Xiang,
Lishan Peng, Lijuan Lu, Wei Ding
**
, Zidong Wei
*
The State Key Laboratory of Power Transmission Equipment & System Security and New Technology, Chongqing Key Laboratory of Chemical Process for
Clean Energy and Resource Utilization, School of Chemistry and Chemical Engineering, Chongqing University, Shazhengjie 174, Chongqing 400044, China
article info
Article history:
Received 8 January 2018
Received in revised form
20 March 2018
Accepted 2 April 2018
Available online 4 April 2018
Keywords:
ORR
Fuel cell
Mn-oxides
N-doped carbon
abstract
The development of efficient, low-cost and stable electrocatalysts as the alternative to platinum for the
oxygen reduction reaction (ORR) is of significance for many important electrochemical devices, such as
fuel cells and metaleair batteries. Herein we discuss the design and synthesis of a Mn
x
O
y
/N-C hybrid
catalyst that can address both the activity and durability issues caused by the high productivity of
peroxide (H
2
O
2
) in nitrogen-doped carbon (N-C). The high activity and stability of the Mn
x
O
y
/N-C-3
catalyst is ascribed to its novel hybrid structure, in which Mn
x
O
y
is a good catalyst for decomposition of
peroxide, while N-C not only catalyses the ORR but also prevents Mn
x
O
y
agglomeration. RRDE study
indicates a typical 4-electron ORR pathway with very low peroxide production (~1.9%) and considerable
stability. In light of the low cost and high earth abundance of Mn, the highly active Mn
x
O
y
/N-C is a
promising candidate to be used as a cathode material in metaleair batteries and alkaline fuel cells.
© 2018 Published by Elsevier Ltd.
1. Introduction
The most important issue of the modern energy-related elec-
trochemistry is the use of cheap and eventually eco-friendly ma-
terials for solar cells, batteries, fuel cells and supercapacitors to
replace Pt and other costly components with valid alternative
[1e 7]. As an indispensable component of fuel cells and metal-air
batteries, the electrocatalyst for oxygen reduction reaction (ORR)
plays a dominant role in determining their performances [8].
Currently, the prevailing catalysts are mainly Pt-based materials,
which are costly and unstable [9e12]. Durability improvements
and cost reductions must be achieved to render these electro-
chemical devices commercially competitive with conventional
technologies. As such, intensive efforts to explore platinum-free
catalysts for ORR to replace the precious platinum have been
going on for several decades to bring this efficient technology into
real applications [13e15]. In this respect, nitrogen-doped carbon
(N-C) materials represent important candidates as metal-free
catalysts for ORR because of their unique electronic properties and
structural features [16, 17]. In spite of some significant achieve-
ments, the ORR performance and stability of most reported N-C
catalysts is still much inferior to that of commercial Pt/C catalyst
[18, 19]. As theoretically expected for the complete reduction of O
2
to H
2
O; mechanistic analysis of electrochemical process catalysed
by N-C shows that the number of transferred electrons is not al-
ways four, in some cases; lower, uneven values are calculated
[20e26]. These typical numbers of electron being between two and
four thereby responsible for hydrogen peroxide (H
2
O
2
) formation
through two electron transfer mechanism (Scheme S1)
[20e24,27e30]. The H
2
O
2
can oxidise N-C and makes N-C become
very hydrophilic, and finally causes the porous N-C electrode water-
flooded, thus interrupt oxygen transport to the active sites. Hence,
the presence of hydrogen peroxide in N-C based porous electrodes
not only damages the porous structure but also shortens the life-
time of the electrodes made of the N-C catalysts [19,27 ,28].
Therefore, to design a catalyst that can accelerate O
2
reduction to
H
2
O via the 4e
pathway but inhibit O
2
reduction to H
2
O
2
via the
2e
pathway is highly required to substitute Pt/C.
Herein, we develop a Mn
x
O
y
/N-C hybrid catalyst that can
address both the activity and durability issues caused by the high
productivity of H
2
O
2
in N-C catalysis of ORR. In this perspective,
zeolitic imidazole framework (ZIF-8) polyhedrons were selected as
* Corresponding author.
** Corresponding author.
E-mail addresses: dingwei128@cqu.edu.cn (W. Ding), zdwei@cqu.edu.cn
(Z. Wei).
1
These authors have equal contribution.
Contents lists available at ScienceDirect
Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
https://doi.org/10.1016/j.electacta.2018.04.008
0013-4686/© 2018 Published by Elsevier Ltd.
Electrochimica Acta 272 (2018) 169e175