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Cite This: ACS Appl. Nano Mater. 2019, 2, 2679−2688
Ag-Modified Cu Foams as Three-Dimensional Anodes for Rechargeable Zinc−Air Batteries Jiayuan Yu,†,‡ Fuyi Chen,*,†,‡ Quan Tang,†,‡ Tesfaye Tadesse Gebremariam,†,‡ Jiali Wang,†,‡ Xiaofang Gong,†,‡ and Xiaolu Wang†,‡ †
State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xian, 710072, China School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an, 710072, China
‡
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S Supporting Information *
ABSTRACT: Rechargeable zinc−air batteries are typical environment-friendly energy storage devices with high energy density and low cost. Nevertheless, dendrite formation and self-corrosion of zinc anode directly reduce battery performance. Herein, we report a novel Cu foam substrate with uniform Ag nanoparticles deposited on the surface as threedimensional (3D) anode in rechargeable zinc-air battery and battery stacks for the first time. Tafel and linear scanning voltammetry measurements exhibit the Ag deposited on Cu foam suppresses hydrogen evolution reaction and reduces corrosion current density on the anode. Ag-modified threedimensional anode is used in a primary zinc-air battery with 200 mAh anode capacity and Ag−Cu catalyzed cathode, which demonstrates a high specific capacity of 676 mAh gZn−1, an energy density of 786 Wh kgZn−1 and a high zinc utilization of 87%. Afterward, Ag-modified three-dimensional anode is used in a rechargeable zinc−air battery, which presents a Coulombic efficiency of 94% after 80 cycles with 2 h cycle period. Besides, Ag-modified three-dimensional anode is free of Zn dendrites at different depth of discharge from 5% to 20%. When two rechargeable zinc−air batteries are connected in both series and parallel, these batteries show a high energy efficiency of 55% and 60%, respectively, and deliver stable cycling over 40 cycles. The stable cycling performance can be attributed to Ag nanoparticles on the substrate surface, which regulate the Zn deposition uniformly in the voids between Cu foam skeleton and prevent dendrite formation by providing continuous uniform electronic transmission channels. KEYWORDS: rechargeable zinc−air battery, Ag nanoparticles, copper foam anode, Zn dendrites
1. INTRODUCTION
complexation Zn 2 + + 4OH− F Zn(OH)4 2 −
As the indispensable need for cost-effective and sustainable energy storage devices in our daily life, more than ever before, it is paramount to develop new energy technologies. Zinc−air battery is a typical high-performance environmentally benign energy storage system in addition to lithium−ion battery, which has been widely used in energy storage,1 consumer electronics,2 and other conversion devices because of its low cost, nontoxicity, relatively high specific capacity, high energy density,3,4 competitive power density, and cycling stability. Rechargeable zinc−air battery is a promising technology because of its high theoretical energy density and the abundant and environmentally benign materials. Alkaline zinc−air batteries (ZABs) discharge via the oxidation of metal Zn coupled with the reduction of O2 according to the anodic (eqs 1−3; Zn) and cathodic (eq 4; O2) reactions:5
dehydration Zn(OH)4 2 − F ZnO + H 2O + 2OH− O2 + 2H 2O + 4e− F 4OH−
(4)
However, the corrosion, dendrite growth and shape change are the most detrimental effects for ZABs, resulting in decreasing the effective surface area and utilization of Zn electrode, which seriously cause capacity loss and limited cycle life or lead to catastrophic failure of the battery directly.6 For ZABs, Zn anodes suffer from self-corrosion caused by hydrogen evolution reaction (HER) as Zn has a more negative reduction potential than H2, resulting in capacity decay. Received: January 25, 2019 Accepted: April 29, 2019 Published: April 29, 2019
(1) © 2019 American Chemical Society
(3)
electroreduction
electrooxidation Zn F Zn 2 + + 2e−
(2)
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DOI: 10.1021/acsanm.9b00156 ACS Appl. Nano Mater. 2019, 2, 2679−2688
Article
ACS Applied Nano Materials
this Ag-modified 3D host material, which effectively impeded Zn dendrite formation and corrosion problems, and improved cycling performance compared to unmodified 3D electrode. Highly conductive Ag NPs provide continuous and smooth electron transfer channels and provide low nuclear overpotential deposition sites for Zn deposition, which constrain Zn deposition process effectively.19 Heterogeneous Ag NPs dispersed on 3D skeleton are expected to guide Zn deposition into the 3D host uniformly during C−D process, which effectively constrain the growth of Zn dendrites. Meanwhile, the interconnected 3D skeleton ensures the mechanical strength and toughness of the entire electrode structure, avoiding anode collapse during C−D process. Moreover, the porous structure can relieve the concentration of zincate in the solution and reduce ZnO layer formation, thus inhibiting Zn dendrite growth. Briefly, Ag-modified 3D host structure improves the kinetics and mass transfer of electrochemical reactions, and efficiently minimizes the energy loss of ZABs.20 In this work, the mechanism of dendrite growth and hydrogen evolution corrosion suppression was further investigated based on theoretical and experimental analysis.
Specifically, this reaction consumes Zn and H2O, producing Zn(OH)2 and H2 on the surface of Zn anodes simultaneously Zn + 2H 2O → Zn(OH)2 + H 2
(5)
Theoretically, the electrochemical potentials of the anode and cathode should be between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) of the electrolyte so that the electrolyte will not decompose. However, the electrochemical potential of Zn is above LUMO of the electrolyte, resulting in Zn-electrolyte corrosion reaction.7 As a matter of fact, broader application of ZABs is hindered by limited rechargeability and low Zn utilization (typically
