Subscriber access provided by UNIVERSITY OF TOLEDO LIBRARIES
Article
CoO/CoP Heterostructured Nanosheets with an O-P Interpenetrated Interface as a Bifunctional Electrocatalyst for Na-O2 Battery Junkai Wang, Rui Gao, Lirong Zheng, Zhongjun Chen, Zhonghua Wu, Limei Sun, Zhongbo Hu, and Xiangfeng Liu ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.8b01023 • Publication Date (Web): 07 Aug 2018 Downloaded from http://pubs.acs.org on August 8, 2018
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
CoO/CoP Heterostructured Nanosheets with an O-P Interpenetrated Interface as a Bifunctional Electrocatalyst for Na-O2 Battery
Junkai Wanga, Rui Gaoa, Lirong Zhengb, Zhongjun Chenb , Zhonghua Wub, Limei Sunc* , Zhongbo Hua and Xiangfeng Liua*
a
College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing 100049, P. R. China b
Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China c
Department of Nuclear Physics, China Institute of Atomic Energy, Beijing 102413, China
*Corresponding author.
E-mail:
[email protected].
E-mail:
[email protected] ACS Paragon Plus Environment
1
ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 2 of 27
ABSTRACT: Rechargeable Na-O2 batteries have attracted great interest because of the high energy density and low cost. But the lack of inexpensive bifunctional efficient electrocatalysts, which can simultaneously boost oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), critically hinders their application. Herein, CoO/CoP heterostructured ultrathin nanosheets with an O-P interpenetrated interface have been synthesized through a controlled phosphatization of Co(CO3)0.5(OH)0.11H2O nanosheets, which combine the advantages of the high OER activity of CoP and the high ORR activity of CoO. ORR and OER activity are simultaneously boosted due to the interpenetration of O-P at the interface of CoO/CoP heterostructure, whose ORR or OER activity even exceeds that of parent CoO or CoP. ORR activity is in this order: CoO/CoP>Co3O4≈CoO>CoP while the order for OER is: CoO/CoP>CoP>Co3O4>CoO. O-P interpenetration improves the conductivity and electron transfer of CoO or CoP owing to the inter-doping effect, which is largely responsible for the simultaneous enhancement of OER and ORR activity. The initial capacity, rate capability and cycle stability of Na-O2 battery using CoO/CoP heterostructured nanosheets as cathode catalysts have been largely improved because of the simultaneous enhancement of OER and ORR activity. Additionally, the phase evolution of the discharged product of Na-O2 battery is also unraveled by in-situ x-ray diffraction and ex-situ scanning electron microscope. This study is also instructive to the design of efficient bifunctional electrocatalysts through constructing a heterostructure with an interpenetrated interface.
KEYWORDS:
Na-O2
battery;
nanosheets;
heterostructure;
electrocatalyst;
interface
interpenetration
ACS Paragon Plus Environment
2
Page 3 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
TOC
ACS Paragon Plus Environment
3
ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 4 of 27
INTRODUCTION
Metal-air batteries have attracted great attention as the promising clean energy storage system. Compared with conventional lithium batteries, metal-air batteries show larger specific capacity and higher energy density.1-3 In recent years, Li-O2, Na-O2, Zn-O2, etc.,
4-7
have attracted
extensive attention. Among of them Na-O2 battery has shown a great potential in the large-scale applications due to the low cost, the abundant Na resource and the higher energy density(~1602Wh kg-1).2-3 But some critical issues such as the slow oxygen reduction reaction (ORR), oxygen evolution reaction (OER), the resultant high overpotential, low rate capability, and poor cycle life all block the practical application of Na-O2 batteries. Similar to the case of Li-O2 batteries, bifunctional catalysts with both high OER and ORR activity are also highly desirable for Na-O2 batteries.3,
8, 9
In addition, the electrochemical reaction and the phase
evolution of the discharged product of Na-O2 battery is also not very clear.10-11 A few kinds of discharge products including NaO2, Na2O2, Na2O2·2H2O and Na2CO3 have been reported, and different electrolytes will also affect the discharge processes.2, 12-14
Some strategies such as catalysts design and electrolytes mediation by additives have been extensively applied to overcome or alleviate these problems in Na-O2 batteries. 11, 15-18 Among of the strategies, the catalysts have a significant effect on the charge/discharge process of Na-O2 batteries. Carbon material has ORR activity that can catalyze and promote the discharge process of the metal air battery.19 Some carbon materials such as carbon nanowires, nanotubes, grapheme and porous carbon have been used as catalysts in lithium air batteries and sodium air batteries. 2021
Noble metal usually have a high catalytic activity, but large-scale applications should be
limited by the high cost.
20
Recently, transition metal oxides based cathode catalysts have
ACS Paragon Plus Environment
4
Page 5 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
aroused great interest to replace precious metals in Na-O2 batteries.
23-25
But the single-
component oxide catalyst is usually very hard to simultaneously meet the catalytic activity requirements for ORR and OER. 26 For example, CoO or Co3O4 has been reported to have good ORR activity in some metal-air batteries but their OER activity is very poor, which influence the whole electrochemical performances of the cells.
27-28
Some reports have shown that CoP has a
good OER activity but its ORR activity is low.
29-30
Therefore, the design and exploration of
bifunctional electrocatalysts with both high ORR and OER activity are highly desirable for NaO2 batteries.
In this work, we have proposed a novel facile strategy to construct heterogeneously structured CoO/CoP nanosheets with an O-P interpenetrated interface through a controlled phosphatization of Co(CO3)0.5(OH)0.11H2O. The as-synthesized CoO/CoP heterostructured nanosheets combine the high OER activity of CoP and the high ORR activity of CoO. 31-33 More importantly, ORR or OER activity of the as-prepared CoO/CoP nanosheets even exceeds that of the parent CoO or CoP due to the interpenetration of O-P on the CoO/CoP interface, which enhances the conductivity and electron transfer. 34-38 The initial capacity, rate performance and cycling life of Na-O2 batteries with the catalysis of CoO/CoP nanosheets have been largely enhanced due to the simultaneous enhancement of OER and ORR activity. In addition, the phase formation and decomposition of the discharged product have also been unraveled by in-situ x-ray diffraction and ex-situ scanning electron microscope (SEM).
ACS Paragon Plus Environment
5
ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 6 of 27
EXPERIMENTAL SECTION
The synthesis of Co(CO3)0.5(OH)0.11H2O precursor
30 ml EG (Ethylene glycol) were mixed with 5.5 ml deionized water to form solution. Then 300 mg Co(acac)3(III) and 1.1 g cetyltrimethyl ammonium bromide (CTAB) were subsequently added into the mixed solution. Then, the suspension was magnetic stirring and ultrasonic, and then transferred into a 50 ml Teflon-lined autoclave. The reaction is kept for 48 h at 180°C. Afterwards, we centrifuged and washed sample at room temperature by water and alcohol 3 times respectively. The sample is used for vacuum drying.
Preparation of CoO/CoP Nanosheets:
Co(CO3)0.5(OH)0.11H2O and NaH2PO3·2H2O were mixed with various mass ratios of 1:1, 1:5, 1:10 and then calcined in N2 at 300°C for 30 min. The obtained samples were named as Co3O4, CoO/CoP and CoP, respectively. The following X-ray diffractions confirm that the three samples correspond to Co3O4, CoO/CoP and CoP, respectively.
ACS Paragon Plus Environment
6
Page 7 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
Scheme 1. Schematic illustration of the synthetic process of Co3O4, CoO/CoP and CoP ultrathin nanosheets.
MATERIALS CHARACTERIZATION
X-ray diffraction (XRD) experiments were performed on a diffractometer (RIGAKU SMARTLAB, Cu-Kα) at a scan rate of 10° min-1. Operando x-ray diffraction data of Na-O2 battery were collected on 4B9A in Beijing Synchrotron Radiation Facility (BSRF).
57-58
The
current density is set as 200mA g-1 and the data was collected every 20 min.59 Scanning electron microscope (SEM, HITACHI SU8010) and transmission electron microscope (TEM, HITACHI HT7700 excellent) were used to observe the microstructures. The thickness of the nanosheets were measured using atomic force microscopy (AFM, Dimension Icon). X-ray photoelectron
ACS Paragon Plus Environment
7
ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 8 of 27
spectroscopy (XPS, Thermo escalab 250Xi) was used to analyze the valence of the elements. Xray absorption spectra were collected on 1W1B at BSRF.
ELECTROCHEMICAL MEASUREMENTS
A 2025-type coin cell was fabricated to test the electrochemical performance of Na–O2 batteries. The catalyst (Co3O4, CoO/CoP or CoP, 40 wt%), polyvinylidene fluoride (PVDF, 20 wt%) and super P carbon (40 wt% ) were mixed in N-methyl-2-pyrrolidone to form a slurry. The slurry was then coated on the carbon paper to make air electrode. Then the air electrode was dried at 120°C under vacuum for 12 h. The total mass of the material on the cathode was about 1.66 mg cm-2. The cells with a lithium metal foil anode, a glass fiber separator and an oxygen cathode were assembled in an Ar-filled glovebox (H2O or O2 content
