425 Korean Chem. Eng. Res., 57(3), 425-431 (2019) https://doi.org/10.9713/kcer.2019.57.3.425 PISSN 0304-128X, EISSN 2233-9558 Development of Micro-Tubular Perovskite Cathode Catalyst with Bi-Functionality on ORR/OER for Metal-Air Battery Applications Yukwon Jeon* , ** ,† , Ohchan Kwon**, Yunseong Ji**, Ok Sung Jeon**, Chanmin Lee*** and Yong-Gun Shul** ,† *School of chemistry, University of St Andrews, Fife, KY16 9ST, United Kingdom **Department of Chemical and Biomolecular Engineering, Yonsei University, Yonsei-ro 50, Seodaemun-gu, Seoul, 03722, Korea ***Research Institute of Sustainable Manufacturing System, Intelligent Sustainable Materials R&D Group, Korea Institute of Industrial Technology (KITECH), 89 Yangdaegiro-gil, Ipjang-myeon, Seobuk-gu, Cheonan-si, Chungcheongnam-do, 31056, Korea (Received 6 March 2019: accepted 3 April 2019) Abstract - As rechargeable metal-air batteries will be ideal energy storage devices in the future, an active cathode electrocatalyst is required with bi-functionality on both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) during discharge and charge, respectively. Here, a class of perovskite cathode catalyst with a micro-tubular struc- ture has been developed by controlling bi-functionality from different Ru and Ni dopant ratios. A micro-tubular struc- ture is achieved by the activated carbon fiber (ACF) templating method, which provides uniform size and shape. At the perovskite formula of LaCrO 3 , the dual dopant system is successfully synthesized with a perfect incorporation into the single perovskite structure. The chemical oxidation states for each Ni and Ru also confirm the partial substitution to B- site of Cr without any changes in the major perovskite structure. From the electrochemical measurements, the micro- tubular feature reveals much more efficient catalytic activity on ORR and OER, comparing to the grain catalyst with same perovskite composition. By changing the Ru and Ni ratio, the LaCr 0.8 Ru 0.1 Ni 0.1 O 3 micro-tubular catalyst exhibits great bi-functionality, especially on ORR, with low metal loading, which is comparable to the commercial catalyst of Pt and Ir. This advanced catalytic property on the micro-tubular structure and Ru/Ni synergy effect at the perovskite mate- rial may provide a new direction for the next-generation cathode catalyst in metal-air battery system. Key words: Metal-air battery, Cathode catalyst, Perovskite, Micro-tubular, Bi-functionality 1. Introduction Through the continuous battery development, the battery market has been wider throughout our society. In recent years, although the secondary battery, mainly lithium ion battery, has been used as a main power sources for mobile phone, notebook, and automobile, new battery systems have been under study due to the limitations of long-term use and charging depending on locations [1-3]. Among many, metal-air battery technology is considered as a next-genera- tion energy supply. The metal-air battery runs by the oxidation reac- tion at the metal (anode), and by the reduction reaction at the catalyst material (usually, Pt-Ir/C) using air as a reactant (cathode), which is a sort of fuel cell system [4-6]. The most common forms are lithium- air, zinc-air, and aluminum-air, etc., which have different energy density/voltage and operating conditions [7-12]. Metal-air batteries do not discharge environmental pollutants and can be constructed to many types by relatively low cost [13-14]. And the O 2 is constantly supplied from air as an energy source, which provides stable voltage until the metal is oxidized. However, some problems are still remained such as battery stabil- ity and sensitivity to the external environment, limited output charac- teristics, temperature range, metal corrosion, and electrolyte loss etc. [15-18]. Particularly, one of the most problems that hinder its further commercialization into the marketplace is the use of expensive cath- ode catalysts. The metal-air battery operates in aqueous solutions by electrochemical reactions of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) during discharge and charge, respectively. However, most of the metal-air batteries suffer from the sluggish kinetic during the ORR/OER cycling, which causes large voltage gap during the cycles and poor power capability [19-21]. Noble metal catalysts such as Pt, Pd for ORR and Ir for OER, have been considered due to the high reactivity, but the high costs and shortage block their widespread use in large-scale applications [22,23]. Therefore, new approaches such as metal oxides and carbon-based materials, have been investigated and designed to achieve bi-func- tionality on ORR/OER with high activity and stability for the use as a cathode materials in metal-air battery systems. Perovskite structured materials, general formula of ABO 3 , have been known as a good catalyst in such kind of oxygen involved reac- tions (ORR/OER) due to its high oxygen ion mobility and chemical/ structural stability [24,25]. Moreover, the cations in A and B can be selected according to the reaction conditions. Meanwhile, the com- pound of LaCrO 3 has been widely studied as an electrode catalyst material owing to its chemical and structural stability [26]. Gener- † To whom correspondence should be addressed. E-mail: [email protected], [email protected]This article is dedicated to Prof. Yong-Gun Shul on the occasion of his retirement from Yonsei University. This is an Open-Access article distributed under the terms of the Creative Com- mons Attribution Non-Commercial License (http://creativecommons.org/licenses/by- nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduc- tion in any medium, provided the original work is properly cited.
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425
Korean Chem. Eng. Res., 57(3), 425-431 (2019)
https://doi.org/10.9713/kcer.2019.57.3.425
PISSN 0304-128X, EISSN 2233-9558
Development of Micro-Tubular Perovskite Cathode Catalyst with Bi-Functionality
on ORR/OER for Metal-Air Battery Applications
Yukwon Jeon*,**,†, Ohchan Kwon**, Yunseong Ji**, Ok Sung Jeon**, Chanmin Lee*** and Yong-Gun Shul**,†
*School of chemistry, University of St Andrews, Fife, KY16 9ST, United Kingdom
**Department of Chemical and Biomolecular Engineering, Yonsei University, Yonsei-ro 50, Seodaemun-gu, Seoul, 03722, Korea
***Research Institute of Sustainable Manufacturing System, Intelligent Sustainable Materials R&D Group, Korea
Institute of Industrial Technology (KITECH), 89 Yangdaegiro-gil, Ipjang-myeon, Seobuk-gu, Cheonan-si, Chungcheongnam-do, 31056, Korea
(Received 6 March 2019: accepted 3 April 2019)
Abstract − As rechargeable metal-air batteries will be ideal energy storage devices in the future, an active cathode
electrocatalyst is required with bi-functionality on both oxygen reduction reaction (ORR) and oxygen evolution reaction
(OER) during discharge and charge, respectively. Here, a class of perovskite cathode catalyst with a micro-tubular struc-
ture has been developed by controlling bi-functionality from different Ru and Ni dopant ratios. A micro-tubular struc-
ture is achieved by the activated carbon fiber (ACF) templating method, which provides uniform size and shape. At the
perovskite formula of LaCrO3, the dual dopant system is successfully synthesized with a perfect incorporation into the
single perovskite structure. The chemical oxidation states for each Ni and Ru also confirm the partial substitution to B-
site of Cr without any changes in the major perovskite structure. From the electrochemical measurements, the micro-
tubular feature reveals much more efficient catalytic activity on ORR and OER, comparing to the grain catalyst with
same perovskite composition. By changing the Ru and Ni ratio, the LaCr0.8Ru0.1Ni0.1O3 micro-tubular catalyst exhibits
great bi-functionality, especially on ORR, with low metal loading, which is comparable to the commercial catalyst of Pt
and Ir. This advanced catalytic property on the micro-tubular structure and Ru/Ni synergy effect at the perovskite mate-
rial may provide a new direction for the next-generation cathode catalyst in metal-air battery system.
Through the continuous battery development, the battery market
has been wider throughout our society. In recent years, although the
secondary battery, mainly lithium ion battery, has been used as a
main power sources for mobile phone, notebook, and automobile,
new battery systems have been under study due to the limitations of
long-term use and charging depending on locations [1-3]. Among
many, metal-air battery technology is considered as a next-genera-
tion energy supply. The metal-air battery runs by the oxidation reac-
tion at the metal (anode), and by the reduction reaction at the catalyst
material (usually, Pt-Ir/C) using air as a reactant (cathode), which is a
sort of fuel cell system [4-6]. The most common forms are lithium-
air, zinc-air, and aluminum-air, etc., which have different energy
density/voltage and operating conditions [7-12]. Metal-air batteries
do not discharge environmental pollutants and can be constructed to
many types by relatively low cost [13-14]. And the O2 is constantly
supplied from air as an energy source, which provides stable voltage
until the metal is oxidized.
However, some problems are still remained such as battery stabil-
ity and sensitivity to the external environment, limited output charac-
teristics, temperature range, metal corrosion, and electrolyte loss etc.
[15-18]. Particularly, one of the most problems that hinder its further
commercialization into the marketplace is the use of expensive cath-
ode catalysts. The metal-air battery operates in aqueous solutions by
electrochemical reactions of oxygen reduction reaction (ORR) and
oxygen evolution reaction (OER) during discharge and charge,
respectively. However, most of the metal-air batteries suffer from the
sluggish kinetic during the ORR/OER cycling, which causes large
voltage gap during the cycles and poor power capability [19-21].
Noble metal catalysts such as Pt, Pd for ORR and Ir for OER, have
been considered due to the high reactivity, but the high costs and
shortage block their widespread use in large-scale applications [22,23].
Therefore, new approaches such as metal oxides and carbon-based
materials, have been investigated and designed to achieve bi-func-
tionality on ORR/OER with high activity and stability for the use as
a cathode materials in metal-air battery systems.
Perovskite structured materials, general formula of ABO3, have
been known as a good catalyst in such kind of oxygen involved reac-
tions (ORR/OER) due to its high oxygen ion mobility and chemical/
structural stability [24,25]. Moreover, the cations in A and B can be
selected according to the reaction conditions. Meanwhile, the com-
pound of LaCrO3 has been widely studied as an electrode catalyst
material owing to its chemical and structural stability [26]. Gener-
†To whom correspondence should be addressed.E-mail: [email protected], [email protected]‡This article is dedicated to Prof. Yong-Gun Shul on the occasion of his retirement from Yonsei University.This is an Open-Access article distributed under the terms of the Creative Com-mons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduc-tion in any medium, provided the original work is properly cited.
426 Yukwon Jeon, Ohchan Kwon, Yunseong Ji, Ok Sung Jeon, Chanmin Lee and Yong-Gun Shul
Korean Chem. Eng. Res., Vol. 57, No. 3, June, 2019
ally, the B cation is known to be responsible for the catalytic activity,
where partial substitution provides structural changes in the valence
state and non-stoichiometry-related defects to improve the catalytic
activity and conductivity of the catalyst [27-29]. Therefore, the high
oxygen ion transfer property from the rearrangement of the lattice
structure and the catalytic properties of the dopant can make a synergetic
reaction mechanism of the perovskite catalyst for an efficient ORR/
OER with relatively lower cost. Tailoring the morphology and surface
structure of the perovskite have been received a great interest in the
field of catalysis and electrochemistry [30,31]. Especially, unique
properties of the fibrous perovskites are reported, such as high
geometrical surface area to allow for a high dispersion of the active
phase, high volumetric density, short diffusion distance for better
mass/charge transfer and flexibility with endless geometric forms,
which are effective on various applications in catalysis and even
electrochemistry fields [32-34].
In an effort to develop an effective bi-functional electrocatalyst for
rechargeable metal-air battery, we designed micro-tubular perovskite
cathode catalysts based on LaCrO3 with a partial dual substitution in
the lattice. To design a bi-functionality at the perovskite material, Ru
and Ni dopant were applied due to these well-known ORR and OER
activities, respectively. The micro-tubular perovskite materials with
different Ru and Ni compositions were synthesized by the ACF tem-
plate method to produce a micro-tubular feature. The positive effect
on the micro-tubular shape at catalytic reactions was seen from the
ORR and OER activity in comparison with the grain perovskite. By
changing the Ru/Ni ratio, the structural difference of the perovskites
was investigated and their catalytic bi-functional properties toward
ORR and OER were explored in an aqueous alkaline electrolyte.
2. Experimental Section
2-1. Synthesis of perovskite micro-tubular materials
The LaCrO3 based micro-tubular materials were synthesized by
following procedure of the ACF (activated carbon fiber) templating
method from our previous work [31,32]. An aqueous (solution)
impregnation synthesis on ACF were used due to its rapid and convenient
process to produce high surface area oxides. The ACF templates
were treated in acid solutions of H2SO4 (6 M) and HNO3 (6 M) to
remove surface impurities and to functionalize the ACF surface. The
calculated stoichiometric solutions of La(NO3)3·9H2O, Cr(NO3)3·9H2O,
Ni(NO3)3·6H2O, and HN4O10Ru were used in water base. The prepared
ACF was immersed for 24 hours in the solutions of a certain
stoichiometric LaIII, CrIII, NiIII, and RuIII ions to ionically bond the
metal cations to the negatively charged carbon surface. After 24
hours drying, the samples were heat-treated at a mild condition of
1027 K for 6 hours in sufficient air flow for the C content combustion
and formation of crystalline structure at the same time. Finally, the