材料研究学报, 2024, 38(4): 257-268 DOI: 10.11901/1005.3093.2023.256

研究论文

铝空气电池Al-Zn-In-Mg-Ga-Mn合金阳极的电化学性能

吴厚燃1,2, 段体岗,2, 马力2, 邵刚勤,1, 张恒宇2, 张海兵2

1.武汉理工大学 材料复合新技术国家重点实验室 武汉 430070

2.洛阳船舶材料研究所 海洋腐蚀与防护全国重点实验室 青岛 266237

Electrochemical Performance of Al-Zn-In-Mg-Ga-Mn Alloys as Anodes for Al-Air Batteries

WU Houran1,2, DUAN Tigang,2, MA Li2, SHAO Gangqin,1, ZHANG Hengyu2, ZHANG Haibing2

1.State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China

2.National State Key Laboratory for Marine Corrision and Protection, Luoyang Ship Material Research Institute, Qingdao 266237, China

通讯作者: 段体岗,高级工程师,duantigang@sunrui.net,研究方向为海洋腐蚀与防护、化学能源;邵刚勤,研究员,gqshao@whut.edu.cn,研究方向为新能源材料、无机新材料结构构建与解析

责任编辑: 吴岩

收稿日期: 2023-05-08   修回日期: 2023-07-03  

基金资助: 国家重点研发计划(2022YFB3808800)

Corresponding authors: DUAN Tigang, Tel: 15725237618, E-mail:duantigang@sunrui.net;SHAO Gangqin, Tel: 13808694306, E-mail:gqshao@whut.edu.cn

Received: 2023-05-08   Revised: 2023-07-03  

作者简介 About authors

吴厚燃,男,1999年生,硕士生

摘要

研究了铝空气电池的Al-Zn-In-Mg-Ga-Mn合金阳极在2 mol/L NaCl和4 mol/L KOH电解液中的自腐蚀行为和电化学性能。结果表明,在2 mol/L的NaCl和4 mol/L的KOH溶液中,Al-Zn-In-Mg-Ga-Mn合金阳极比纯Al阳极的腐蚀电位(Ecorr)分别负移了0.041和0.018 V,自腐蚀速率分别降低了0.2146和15.1 mg·cm-2·h-1,使金属阳极的电化学活性得以提高,自腐蚀行为受到了抑制。在2 mol/L的NaCl电解液中,合金阳极的放电容量峰值达到2608.96 Ah·kg-1,比纯Al阳极提高了55.59%;能量密度最高为1742.61 Wh·kg-1,比纯Al阳极提高了274.58%,阳极效率为87.55%。在4 mol/L的KOH电解液中,合金阳极的放电容量最高为1605.15 Ah·kg-1,比纯Al阳极提高了131.27%;能量密度最高为1404.83 Wh·kg-1,比纯Al阳极提高了231.52%,阳极效率为53.86%。

关键词: 金属材料; Al-Zn-In-Mg-Ga-Mn合金; 铝空气电池; 电化学性能; 腐蚀行为

Abstract

The free corrosion behavior and electrochemical properties of Al-Zn-In-Mg-Ga-Mn alloys, as anodes working with 2 mol/L NaCl and 4 mol/L KOH electrolytes were studied. Results revealed that in the two electrolytes, the corrosion potential (Ecorr) of alloy anodes shifted negatively by 0.041 V and 0.018 V, and the free corrosion rates decreased by 0.2146 and 15.1 mg·cm-2·h-1, respectively in the contrast to those of pure Al anode. The electrochemical activity of pure Al anode was improved, while its free corrosion behavior was inhibited. In the 2 mol/L NaCl electrolyte, the discharge capacity peak of the alloy anode reached 2608.96 Ah·kg-1, which was 55.59% higher than that of the pure Al anode. The highest energy density attained 1742.61 Wh·kg-1, being 274.58% superior to that of the pure Al anode. The anode efficiency was 87.55%. In the 4 mol/L KOH electrolyte, the highest discharge capacity of the Al-Zn-In-Mg-Ga-Mn alloy anode was 1605.15 Ah·kg-1, which was 131.27% higher than that of the pure Al anode. The highest energy density was 1404.83 Wh·kg-1, which was 231.52% higher than that of the pure Al anode. The anode efficiency was 53.86%.

Keywords: metallic materials; Al-Zn-In-Mg-Ga-Mn alloy; aluminum-air battery; electrochemical performance; corrosion behavior

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吴厚燃, 段体岗, 马力, 邵刚勤, 张恒宇, 张海兵. 铝空气电池Al-Zn-In-Mg-Ga-Mn合金阳极的电化学性能[J]. 材料研究学报, 2024, 38(4): 257-268 DOI:10.11901/1005.3093.2023.256

WU Houran, DUAN Tigang, MA Li, SHAO Gangqin, ZHANG Hengyu, ZHANG Haibing. Electrochemical Performance of Al-Zn-In-Mg-Ga-Mn Alloys as Anodes for Al-Air Batteries[J]. Chinese Journal of Materials Research, 2024, 38(4): 257-268 DOI:10.11901/1005.3093.2023.256

锂离子电池得到了广泛的应用,但是其成本高、易燃且废弃物污染环境[1, 2]。于是,另一种能量密度高、放电电压平坦、安全系数高和成本低的金属空气燃料电池受到了关注[3~6]

Al空气电池的能量密度(8100 Wh·kg-1)和电化学当量(2980 Ah·kg-1) 都比较高,其电化学当量仅次于Li空气电池(3680 Ah·kg-1)而高于其它金属空气电池[7,8]。纯Al阳极在中性(Al+3OH-Al(OH)3+3e-)和碱性(Al+4OH-Al(OH)4-+3e-)介质中的化学反应不同,其标准电极电位分别为-1.66和-2.35 V,在金属阳极中都比较负。因此,Al在金属空气电池的阳极材料应用中显示出巨大的潜力。但是Al阳极也有其不足之处[2,7,9,10]:(1) Al电极的表面易生成Al2O3和Al(OH)3保护层,使其极化而导致电位下降;(2) Al阳极在电解质中发生严重的自腐蚀反应(析氢反应),在碱性溶液电解质中消耗很快,使其效率大大降低。因此,纯Al不能直接用作金属空气电池的阳极。改进方法有:(1) 对纯Al进行合金化,添加Mg[11~13]、Ga[14~18]、In[9,17,19]、Bi[14,17]、Sn[14]、Zn[20]、Hg[21]等以降低电极电位或生成缺陷将其活化;添加Pb[15]、Zn[22]、Sn[23]、Hg[18]等高析氢过电位金属元素以降低Al的自腐蚀/析氢反应。(2) 对Al合金阳极进行适当的塑性变形或热处理以改善其显微组织、减少合金中的元素偏析和抑制析氢腐蚀[24~27]。(3) 在电解质溶液中添加析氢抑制剂以降低Al阳极的自腐蚀速率[28~30]

Al-Zn-In基合金作为牺牲阳极已应用于海水、深水和碱性电解液中[31,32]。Linjee等[1]研究了Al-Zn-In合金在铝空气电池中的腐蚀行为,发现Zn与Al可生成多孔ZnAl2O4膜使离子溶解的稳定性提高;In能激活离子溶解从而提高Al-Zn-In合金的电化学活性,其放电容量为1368.66 Ah·kg-1,能量密度为1094.93 Wh·kg-1。在Al-Zn-In合金中添加Bi、Sn或Ga等元素,可缓解阳极极化、降低电极表面保护层的电阻和提高阳极的放电活性[14,32]。Zhang等[33]研究了添加Mn元素对Al-1Zn-0.1In-0.1Sn-0.5Mg合金电化学性能的影响,发现掺杂Mn使合金的腐蚀电位负移,提高析氢速率和增大腐蚀电流;Al-1Zn-0.1In-0.1Sn-0.5Mg-0.1Mn在4 mol/L NaOH溶液中的自腐蚀速率较低(0.128 mL·cm-2·min-1)、工作电压(1.630 V)和能量密度(2415 Wh·kg-1) 最高,其容量(1481 Ah·kg-1)和阳极利用率(49.75%)也比较高。这表明,Al-Zn-In合金的电化学性能优良且Mg、Ga和Mn可进一步提高其性能。鉴于此,本文研究Al-Zn-In-Mg-Ga-Mn合金阳极在中性和碱性电解液中的自腐蚀行为和电化学性能。

1 实验方法

1.1 样品的制备

将纯Al (99.9%,质量分数,下同)和Zn(99.95%)、In(99.99%)、Mg(99.99%)、Ga(99.99%)、Mn(99.99%)按照Al-(3.0%~7.0%)Zn-(0.01%~0.05%)In-(0.5%~0.15%)Mg-(0.01%~0.04%)Ga-(0.02%~0.10%)Mn的组成配料,用恒温炉熔炼。将纯铝放入熔炼炉中加热至730℃熔化,然后将铝液倒入保温的熔炼坩埚中,再将称好的合金元素加入熔炼坩埚中搅拌,保温一段时间后再搅拌以保证成分均匀。将熔炼好的合金液体倒入模具中自然冷却至室温,得到成型的铝合金锭。

1.2 样品的形貌和性能表征

从制备出的铝合金锭上截取试样,将其用砂纸(400~2000目)研磨后用蒸馏水和无水乙醇清洗、烘干。

使用X射线衍射(Rigaku Smartlab SE)仪分析试样的相组成。使用电子背散射衍射(EBSD-EDAX)观察试样的晶粒特征。用扫描电镜(SEM,ZEISS ULTRA 55)和能谱仪(EDS,JSM 6700F ESCA)观察试样的腐蚀形貌、表面形态以及相分布。

1.3 自腐蚀速率及腐蚀深度的测试

将样品用环氧树脂包裹,只露出一个平整的工作表面(10 mm × 10 mm),用砂纸研磨后用蒸馏水和乙醇冲洗、烘干。然后将其放入2 mol/L NaCl和4 mol/L KOH溶液中分别浸泡48和2 h,以评估自腐蚀速率。将腐蚀后的样品浸泡在80℃的2%CrO3 + 5% H3PO4(质量分数)溶液中5 min以去除腐蚀产物,然后测量其质量损失。使用腐蚀凹坑深度仪测量样品的腐蚀深度。在2 mol/L NaCl溶液中浸泡的样品,测量其上10个位置;在4 mol/L KOH溶液浸泡的样品,测量其上20个位置。将样品在中性和碱性溶液中浸泡单位时间后其单位面积的重量损失定义为自腐蚀速率

Free corrosion rate=W/At

式中∆W为质量损失;A为反应面积;t为浸泡时间。

1.4 电化学性能的测试

使用配备常规三电极电池的电化学工作站(Biologic-VMP3) 测试所有样品的开路电位(OCP)、线性扫描伏安法(LSV)和电化学阻抗谱(EIS)。除了选定的外露表面10 mm × 10 mm外,将其余的外露表面用环氧树脂密封。使用Ag/AgCl作为参比电极,铂片作为对电极,试样为工作电极。将工作表面用400~2000目的SiC砂纸研磨。测试电化学性能前,需将试样在电解液中浸泡30 min,所有测试在2 mol/L NaCl和4 mol/L KOH溶液中进行。测试LSV的扫描速率为1 mV/s,扫描范围为± 0.4 V (vs OCP)。在100 kHz~0.01 Hz的频率范围内,以OCP进行扰动幅度为5 mV的EIS测试。使用ZSimpWin软件拟合结果。所有的测量都在25 ± 3℃的温度下进行,电化学测量和电池测试都进行三次,以确保良好的重复性。电池的放电特性测试系统如图1所示。该系统由反应腔、空气阴极、阳极和电解液循环单元组成。空气阴极和阳极与电解液的接触面积为4 cm2,使用MnO2作为空气阴极氧还原反应的催化剂。电解液为2 mol/L NaCl或4 mol/L KOH溶液。用电化学测试系统(Biologic-VMP3) 测试铝空气电池的放电性能,电流密度分别为0.1、1、5和10 mA·cm-2。放电腐蚀产物是在80℃的2%CrO3 + 5%H3PO4溶液中浸泡5 min后去除的,然后用蒸馏水和乙醇冲洗和烘干。根据放电过程中质量的变化计算放电容量、阳极效率以及能量密度,其中放电容量(Q)和阳极效率(η)分别为

图1

图1   电池放电特性测试系统示意图

Fig.1   Schematic diagram of the battery discharge test system


Q=IT/ΔW

η=Q/Q0

式中Q为放电容量;I为放电电流;T为放电时间;∆W为质量损失;η为阳极效率;Q为放电容量;Q0为理论容量。

2 结果和讨论

2.1 晶相结构

纯Al和Al-Zn-In-Mg-Ga-Mn合金的XRD谱如图2a所示。可以看出:纯Al和Al-Zn-In-Mg-Ga-Mn合金的主相都是α-Al相,都有微量的Al2O3相,其中Al-Zn-In-Mg-Ga-Mn合金中还出现了ZnAl2O3相。从图2b可见,Al-Zn-In-Mg-Ga-Mn合金的晶粒尺寸范围为400~500 μm。图2c给出了Al-Zn-In-Mg-Ga-Mn合金部分区域的IPF图,颜色较为分散,表明这部分区域的晶粒没有明显的择优取向。

图2

图2   纯Al和Al-Zn-In-Mg-Ga-Mn合金的XRD谱、晶粒尺寸分布和晶粒特征图

Fig.2   XRD patterns of pure Al and Al-Zn-in-Mg-Ga-Mn alloy (a), grain size distribution of Al-Zn-In-Mg-Ga-Mn alloy (b) and inverse polar figure (c) of Al-Zn-In-Mg-Ga-Mn alloy


2.2 自腐蚀速率

图3表1可以看出,这几种合金的自腐蚀速率大小的排序为:纯Al (4 mol/L KOH) > Al-Zn-In-Mg-Ga-Mn合金 (4 mol/L KOH) > 纯Al (2 mol/L NaCl) > Al-Zn-In-Mg-Ga-Mn合金(2 mol/L NaCl);腐蚀深度的排序为:纯Al (4 mol/L KOH) > Al-Zn-In-Mg-Ga-Mn合金 (4 mol/L KOH) > 纯Al (2 mol/L NaCl) > Al-Zn-In-Mg-Ga-Mn合金(2 mol/L NaCl)。在2 mol/L NaCl中性电解液和4 mol/L KOH碱性电解液中,合金阳极的自腐蚀速率和局部腐蚀深度都比纯Al的小。这表明,合金阳极的耐腐蚀性提高,与极化曲线的结果相似。图4给出了纯Al和Al-Zn-In-Mg-Ga-Mn合金阳极在2 mol/L NaCl或4 mol/L KOH溶液中分别浸泡48和2 h后的腐蚀形貌。如图4a~d所示,在2 mol/L NaCl溶液中纯Al阳极的表面光滑,腐蚀坑较少,Al-Zn-In-Mg-Ga-Mn合金阳极表面出现连续且深的腐蚀坑。其主要原因是,在合金阳极中加了Zn、In和Ga等元素。其中的Zn能与Al基体生成多孔ZnAl2O4固溶体使保护层中的缺陷增加,根据溶解再沉积原理In和Ga破坏了保护膜起到活化作用[34]。如图4e~h所示,在4 mol/L KOH溶液中纯Al和Al-Zn-In-Mg-Ga-Mn合金阳极表面都严重腐蚀,因为在碱性溶液中Al和合金表面的保护膜溶解了。很明显,加入析氢过电位电位较高的元素(Zn、In、Ga)使纯Al在4 mol/L KOH溶液中的腐蚀强度高于Al-Zn-In-Mg-Ga-Mn合金,有效抑制了自腐蚀[2]。这个结果,与自腐蚀参数计算值的变化趋势相同。

图3

图3   纯Al及Al-Zn-In-Mg-Ga-Mn合金阳极的自腐蚀速率和平均腐蚀深度柱状图

Fig.3   Bar charts of free corrosion rates (a) and average corrosion depths (b) of pure Al and Al-Zn-In-Mg-Ga-Mn anodes in 2 mol/L NaCl and 4 mol/L KOH solutions


表1   纯Al和Al-Zn-In-Mg-Ga-Mn合金阳极的自腐蚀参数

Table 1  Free corrosion parameters of pure Al and Al-Zn-In-Mg-Ga-Mn anodes in 2 mol/L NaCl and 4 mol/L KOH solutions

SolutionsSamples∆W/ mgFree corrosion rate / mg·cm-2·h-1Average corrosion depth / mmMaximum corrosion depth / mm
2 mol/L NaClPure Al11.70.24380.1230.18
Al-Zn-In-Mg-Ga-Mn1.40.02920.0660.12
4 mol/L KOHPure Al84.042.00.3770.70
Al-Zn-In-Mg-Ga-Mn53.826.90.2390.37

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图4

图4   纯Al及Al-Zn-In-Mg-Ga-Mn合金阳极的自腐蚀产物形貌及表面形貌

Fig.4   Morphology of free corrosion products (a, c, e, g) and surface morphology (b, d, f, h) of pure Al and Al-Zn-in-Mg-Ga-Mn anodes in 2 mol/L NaCl and 4 mol/L KOH solutions: pure Al in 2 mol/L NaCl solution (a, b); Al-Zn-In-Mg-Ga-Mn alloy in 2 mol/L NaCl solution (c, d); pure Al in 4 mol/L KOH solution (e, f); Al-Zn-In-Mg-Ga-Mn alloy in 4 mol/L KOH solution (g, h)


2.3 电化学性能

2.3.1 开路电位(OCP)

图5给出了纯铝和Al-Zn-In-Mg-Ga-Mn合金阳极在2 mol/L NaCl或4 mol/L KOH电解质中的OCP与时间的关系曲线。可看出,所有阳极的OCP在中性溶液中比在碱性溶液中正,因为在中性溶液中铝表面有氧化膜。与纯铝相比,Al-Zn-In-Mg-Ga-Mn合金在2 mol/L NaCl和4 mol/L KOH电解液中的OCPs更负。这表明,这些微量元素的加入能负向增大纯Al的OCP,其原因与合金中偏析相的数量增加有关。Zn、In和Mn偏析相的标准电位比Al基体更正,这些偏析相在微电池中起阴极作用,通过微电池效应使铝基体的溶解加速[2,15]

图5

图5   纯Al及Al-Zn-In-Mg-Ga-Mn合金阳极的开路电位

Fig.5   Open circuit potential of pure Al and Al-Zn-In-Mg-Ga-Mn anodes in 2 mol/L NaCl and 4 mol/L KOH solutions


2.3.2 纯Al和Al-Zn-In-Mg-Ga-Mn合金阳极的动电位极化曲线

图6表2分别给出了纯Al和Al-Zn-In-Mg-Ga-Mn合金阳极在2 mol/L NaCl和4 mol/L KOH溶液中的动电位极化曲线及其腐蚀参数。从图6可看出,在2 mol/L NaCl和4 mol/L KOH溶液中Al-Zn-In-Mg-Ga-Mn合金的腐蚀电位(Ecorr)均比纯Al的Ecorr更负,腐蚀电流(Icorr)均比纯Al的Icorr更大,极化电阻(Rp)均比纯Al的Rp小。这表明,Al-Zn-In-Mg-Ga-Mn合金阳极的活化性能比纯Al阳极的更好。在2 mol/L NaCl溶液中,Al-Zn-In-Mg-Ga-Mn合金阳极和纯Al阳极在极化曲线的阳极分支上出现了钝化行为,与其表面生成了保护层有关。这类保护层提高了阳极中电子转移的难度,进而使其放电性能降低[32]。Al-Zn-In-Mg-Ga-Mn合金阳极的点蚀电位/击穿电位(Ep)比纯Al阳极的负,也表明Al-Zn-In-Mg-Ga-Mn合金阳极的电化学活性较好。在氯化物溶液中,Al(OH)3膜与Cl-离子的相互作用使钝化层击穿,其电化学反应方程式为[35]

图6

图6   纯Al及Al-Zn-In-Mg-Ga-Mn合金阳极的动电位极化曲线

Fig.6   Potentiodynamic polarization curves of pure Al and Al-Zn-In-Mg-Ga-Mn anodes in 2 mol/L NaCl and 4 mol/L KOH solutions


Al(OH)3+Cl-Al(OH)2Cl+OH-
Al(OH)2Cl+Cl-Al(OH)Cl2+OH-
Al(OH)Cl2+Cl-AlCl3+OH-

表2   纯Al和Al-Zn-In-Mg-Ga-Mn合金阳极的腐蚀参数

Table 2  Corrosion parameters of pure Al and Al-Zn-in-Mg-Ga-Mn anodes in 2 mol/L NaCl and 4 mol/L KOH solutions

SolutionsSamplesEcorr / V vs. Ag/AgClIcorr / mA·cm-2-βc / mV·dec-1βa / mV·dec-1Rp / Ω·cm2
2 mol/L NaClPure Al-1.1385.158 × 10-395.082.23709.851
Al-Zn-In-Mg-Ga-Mn-1.1795.978 × 10-388.0116.23637.334
4 mol/L KOHPure Al-1.5683.4375 × 102293.4325.62.641
Al-Zn-In-Mg-Ga-Mn-1.5864.7838 × 102310.8455.00.168

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同时,Al-Zn-In-Mg-Ga-Mn合金阳极和纯Al阳极在4 mol/L KOH溶液中的动电位极化曲线比在2 mol/L NaCl溶液中的更负。其原因是,发生反应

Al(OH)3+OH-Al(OH)4-

此时碱性溶液破坏了合金阳极表面保护层。此外,Al-Zn-In-Mg-Ga-Mn合金阳极和纯Al阳极在碱性溶液中的Icorr较高,是水的还原和水与溶解氧的还原反应

2H2O+2e-H2+2OH-
O2+2H2O+4e-4(OH)-

所致[36]

2.3.3 电化学阻抗谱

图7a~d表3给出了纯铝和Al-Zn-In-Mg-Ga-Mn合金阳极在2 mol/L NaCl和4 mol/L KOH溶液中的Nyquist图、Bode图以及拟合参数。模拟这一过程的等效电路,分别嵌在图7a、c中。纯Al的Nyquist图,其特点是在高频有一个电容环,在低频有一个电容环和一个电感环。Al-Zn-In-Mg-Ga-Mn合金的阳极,其Nyquist图的高频和低频区也分别有一个电容环和一个感应环。等效电路中的各个元件,Rs为溶液电阻,CPE1为金属溶解反应和双电层产生的电容,Rt为电荷转移电阻,LRl为吸附物的电感和电阻,R2和CPE2对应表面薄膜的电阻和电容。高频电容环与氧化还原反应(Al-xe-→Al x+)有关,可用Rt与CPE1并联来描述,与Al的氧化对应;低频区的电容环的出现可归因于互补氧化还原反应(Al x+-(3-x)e-→Al3+),可用R2和CPE2描述,对应氢氧根保护层的生成[37,38]。高频电感环(L1)可能是析氢反应的氢气吸附所致,低频的感应回路(L2)可能与阳极表面覆盖的反应产物解吸[13,39]或晶间腐蚀[17,40]有关。高频线圈的直径对应Al溶解过程中的电荷转移电阻RtRt越大表明腐蚀速率越低[15]

图7

图7   纯Al及Al-Zn-In-Mg-Ga-Mn合金阳极的Nyquist和Bode图

Fig.7   Nyquist and Bode plots of pure Al and Al-Zn-in-Mg-Ga-Mn anodes: in 2 mol/L NaCl solution (a, b); in 4 mol/L KOH solution (c, d)


表3   拟合的EIS参数

Table 3  Fitted EIS parameters

Parameters

Al-Zn-In-Mg-Ga-Mn

(in 2 mol/L NaCl)

Pure Al

(in 2 mol/L NaCl)

Al-Zn-In-Mg-Ga-Mn

(in 4 mol/L KOH)

Pure Al

(in 4 mol/L KOH)

L1 / H·cm2--1.153 × 10-61.134 × 10-6
Rs / Ω·cm22.2052.5670.77061.212
CPE1 / F·cm-21.484 × 10-48.184 × 10-50.301713.33
n1 (0 < n1 < 1)0.82590.87930.58570.6489
Rt / Ω·cm2521.1830.70.020.01285
CPE2 / F·cm-20.052179.455 × 10-70.21641.4 × 10-17
n2 (0 < n2 < 1)1110.4314
R2 / Ω·cm2167.4329.90.36050.5716
L2 / H·cm236.97427.21.1160.9376
Rl / Ω·cm2503.4872.10.230.2867

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在2 mol/L NaCl溶液中Al-Zn-In-Mg-Ga-Mn合金阳极的Rt比纯Al阳极的小,表明加入这些微量元素提高了合金的溶解活性。纯Al阳极的RlR2均比Al-Zn-In-Mg-Ga-Mn合金阳极的高,表明在纯Al阳极表面产生的薄膜和吸附物较多。这类保护层和吸附物,影响电子的传输并造成严重的极化。在4 mol/L KOH溶液中Al-Zn-In-Mg-Ga-Mn合金阳极的Rt略比纯Al阳极的大,表明在Zn、In、Mg、Ga和Mn元素的共同作用抑制了自腐蚀,使合金的耐腐蚀性提高。碱性溶液能溶解合金和纯Al表面的保护层和吸附物,因此在4 mol/L KOH溶液中Al-Zn-In-Mg-Ga-Mn合金阳极和纯Al阳极的RlR2值都比较小且数值接近。

2.3.4 电池的放电特性

图8给出了在2 mol/L NaCl和4 mol/L KOH电解液中,纯Al和Al-Zn-In-Mg-Ga-Mn合金阳极在不同电流密度(0.1、1、5、10 mA·cm-2)下的电压-时间曲线。可看出,Al-Zn-In-Mg-Ga-Mn合金阳极的放电电压比纯Al阳极的高。电流密度较小时纯Al阳极与Al-Zn-In-Mg-Ga-Mn合金阳极的放电电压相差不大,但是随着电流密度的提高电压差越来越大。在2 mol/L NaCl电解液中、电流密度为10 mA·cm-2时的电压差约为0.33 V,在4 mol/L KOH电解液中、电流密度为5 mA·cm-2时的电压差约为0.45 V。随着电流密度的提高,Al-Zn-In-Mg-Ga-Mn合金阳极放电电压的衰减程度远低于纯Al阳极。值得注意的是,在4 mol/L KOH电解液中,以小电流密度(0.1 mA·cm-2)放电时,纯Al阳极和Al-Zn-In-Mg-Ga-Mn合金阳极的电压随时间迅速下降后缓缓下降,在其它电流密度下放电时,电压值随时间迅速下降后快速上升并逐渐平缓。这个结果,与Zhang等[14]研究Al-Zn-In阳极电池的放电结果类似。前期电压的迅速下降是RpRt导致的电池内阻引起的[15,41],电压缓慢上升对应放电过程中的阳极激活过程[42],电压逐渐平缓是因为放电产物的产生和脱落达到了平衡状态[43]。在放电过程中工作电压出现短期波动,是阳极表面放电产物“吸附-脱落”的短期不平衡造成的[44]

图8

图8   纯Al及Al-Zn-In-Mg-Ga-Mn合金阳极的电压-时间曲线

Fig.8   Voltage-time curve of pure Al and Al-Zn-In-Mg-Ga-Mn anodes after discharged at current density of 0.1, 1, 5, 10 mA·cm-2, respectively, in 2 mol/L NaCl and 4 mol/L KOH electrolytes


图9a、b给出了不同电流密度下,纯Al阳极和Al-Zn-In-Mg-Ga-Mn合金阳极在2 mol/L NaCl和4 mol/L KOH电解液中的放电特性和阳极效率。Al-Zn-In-Mg-Ga-Mn合金阳极的放电容量和能量密度都比纯Al阳极高得多。在2 mol/L NaCl电解液中,Al-Zn-In-Mg-Ga-Mn合金阳极的放电容量峰值达到了2608.96 Ah·kg-1(10 mA·cm-2),比纯Al阳极提高了55.59%;能量密度最高为1742.61 Wh·kg-1 (5 mA·cm-2),比纯Al阳极提高了274.58%;阳极效率为87.55%。在4 mol/L KOH电解液中,Al-Zn-In-Mg-Ga-Mn合金阳极的放电容量最高为1605.15 Ah·kg-1(10 mA·cm-2),比纯Al阳极提高了131.27%;能量密度最高为1404.83 Wh·kg-1(10 mA·cm-2),比纯Al阳极提高了231.52%;阳极效率为53.86%。如表4所示,在电流密度(10 mA·cm-2)较小时,本工作制备的Al-Zn-In-Mg-Ga-Mn合金阳极在中性和碱性溶液中的放电比容量比Al-Zn-In和Al-Zn-In基合金阳极高。

图9

图9   纯Al及Al-Zn-In-Mg-Ga-Mn合金阳极放电特性和阳极效率

Fig.9   Discharge characteristics (a) and anode efficiencies (b) of pure Al and Al-Zn-In-Mg-Ga-Mn anodes at 0.1, 1, 5,10 mA·cm-2 discharge in 2 mol/L NaCl and 4 mol/L KOH electrolytes


表4   近年来关于Al-Zn-In及Al-Zn-In基合金阳极的相关铝空气电池性能的研究

Table 4  Recent studies on the performance of Al-Zn-In and Al-Zn-In-based alloys related to aluminum air batteries

SamplesEcorr / VQ / Ah·kg-1η / %Refs.
Al-3Zn-0.02In-1.237 (in 4 mol/L NaOH)--[1]
Al-5Zn-0.03In-0.857 (in 3.5% NaCl, mass fraction)2340 (at 1 mA·cm-2)78.52[48]
Al-4.5Zn-0.05In-1.411 (in 4 mol/L NaOH)1595.20 (at 10 mA·cm-2)53.53[32]
Al-5Zn-0.03In-1Er-0.738 (in 3.5%NaCl, mass fraction)2414 (at 1 mA·cm-2)81[48]
Al-4.5Zn-0.05In-0.05Ga-1.457 (in 4 mol/L NaOH)< 1600 (at 10 mA·cm-2)< 53.69[14]
Al-4.5Zn-0.05In-0.05Sn-1.496 (in 4 mol/L NaOH)< 1600 (at 10 mA·cm-2)< 53.69[14]
Al-4.5Zn-0.05In-0.05Bi-1.474 (in 4 mol/L NaOH)< 1600 (at 10 mA·cm-2)< 53.69[14]
Al-4.5Zn-0.05In-0.05Sn-1.496 (in 4 mol/L NaOH)1548.11 (at 10 mA·cm-2)51.95[32]
Al-5.5Zn-0.02In-0.1Si-0.459 (in sea water)2569 (at 0.4~4.0 mA·cm-2)86.21[31]
Al-6Zn-0.02In-1.6Mg-0.06Ti-0.484 (in sea water)2486 (at 0.4~4.0 mA·cm-2)83.42[31]
Al-1Zn-0.1In-0.1Sn-0.5Mg-0.1Mn-1.535 (in 4 mol/L NaOH)1481 (at 20 mA·cm-2)49.75[33]
This work (Al-Zn-In-Mg-Ga-Mn)-0.98 (in 2 mol/L NaCl)2608.96 (at 10 mA·cm-2, in 2 mol/L NaCl)87.55*
-1.387 (in 4 mol/L KOH)1605.15 (at 10 mA·cm-2, in 4 mol/L KOH)53.86

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图10a、b给出了纯Al阳极和Al-Zn-In-Mg-Ga-Mn合金阳极在2 mol/L NaCl电解液中放电后腐蚀产物的SEM照片,右侧是EDS图像。可以看出,在2 mol/L NaCl电解液中纯Al阳极的腐蚀产物层较厚,成分主要是Al(OH)3以及少量的碳酸化合物;Al-Zn-In-Mg-Ga-Mn合金阳极的主要腐蚀产物除了Al(OH)3、其它氢氧化物和少量的碳酸化合物还有ZnO。纯Al阳极放电时产生较厚的产物层,活性面积的减少产生了严重的钝化行为。在纯Al阳极和Al-Zn-In-Mg-Ga-Mn合金阳极表面产物层的晶界发现了裂纹,因为晶界的势能较高[45]。在Al-Zn-In-Mg-Ga-Mn合金阳极的裂纹处发现了偏析在晶界的Zn。图10c、d给出了纯Al阳极和Al-Zn-In-Mg-Ga-Mn合金阳极在4 mol/L KOH电解液中放电后腐蚀产物的形貌。可以看出,纯Al阳极在4 mol/L KOH电解液中放电后的腐蚀程度比Al-Zn-In-Mg-Ga-Mn合金阳极的高,其腐蚀产物是Al(OH)3和少量的碳酸化合物。Zn-In-Mg-Ga-Mn合金的腐蚀产物主要是Al(OH)3、其它氢氧化物、碳酸化合物和ZnO。

图10

图10   纯Al和Al-Zn-In-Mg-Ga-Mn合金阳极放电3 h后的腐蚀形貌和成分分布图

Fig.10   Corrosion morphology (SEM images, left) and elemental distribution (EDS mappings, right) of pure Al and Al-Zn-In-Mg-Ga-Mn anodes after discharged for 3 h at 10 mA·cm-2 in 2 mol/L NaCl and 4 mol/L KOH electrolytes, respectively: pure Al and Al-Zn-In-Mg-Ga-Mn alloy in 2 mol/L NaCl solution (a, b); pure Al and Al-Zn-In-Mg-Ga-Mn alloy in 4 mol/L KOH solution (c, d)


图11a、b表明,纯铝阳极和Al-Zn-In-Mg-Ga-Mn合金阳极在2 mol/L NaCl电解液中发生了晶间腐蚀,是铝合金在氯化物溶液中的典型腐蚀行为[15]。在合金表面能观察到一些几何面,可能与腐蚀优先沿着强度最低、原子间结合力最差、弹性模数最小的(100)晶面的晶向发展有关[46,47]。在4 mol/L KOH电解液中纯铝阳极和Al-Zn-In-Mg-Ga-Mn合金阳极放电表面形貌如图11c、d所示,由于没有保护层,两者均出现了严重的腐蚀。纯铝阳极的腐蚀坑大(约为400 μm)且深,Al-Zn-In-Mg-Ga-Mn合金阳极表面的腐蚀坑较小且排布均匀。因为加入的Ga改变了纯Al阳极晶粒在溶解过程中的各向异性,使合金阳极的腐蚀较为均匀[18]

图11

图11   纯Al和Al-Zn-In-Mg-Ga-Mn合金阳极放电3 h后的表面形貌

Fig.11   Surface morphology of pure Al and Al-Zn-In-Mg-Ga-Mn anodes after discharged for 3 h at 10 mA·cm-2 in 2 mol/L NaCl and 4 mol/L KOH electrolytes, respectively: pure Al and Al-Zn-In-Mg-Ga-Mn alloy in 2 mol/L NaCl solution (a, b); pure Al and Al-Zn-In-Mg-Ga-Mn alloy in 4 mol/L KOH solution (c, d)


图12给出了自组装铝阳极空气电池的演示照片和阴阳极材料照片。这个电池由空气阴极(工作面积为4 cm2)、阳极(Al-Zn-In-Mg-Ga-Mn合金)、4 mol/L KOH电解质和电解液循环系统组成。

图12

图12   铝空气电池放电示意图

Fig.12   Discharge schematic diagram of aluminum-air battery: aluminum-air battery system (a); Al-Zn-In-Mg-Ga-Mn alloy anode (b); MnO2 air cathode (c)


3 结论

(1) 在中性和碱性溶液中Al-Zn-In-Mg-Ga-Mn合金阳极的开路电位(OCP)和腐蚀电位(Ecorr)相对于纯Al阳极负移,表明加入Mg、Ga和Mn合金元素使纯Al阳极的电化学性能提高。

(2) 在中性和碱性电解液中,Al-Zn-In-Mg-Ga-Mn合金阳极的自腐蚀速率和局部腐蚀深度明显低于纯Al阳极,其原因是加入析氢过电位较高的元素(Zn、In和Ga)抑制了合金的自腐蚀。

(3) 在高电流密度下,Al-Zn-In-Mg-Ga-Mn合金阳极的电压衰减比纯Al阳极有显著的改善,其放电容量和能量密度比纯Al阳极高。

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