Aqueous zinc-ion batteries(AZIBs)are promising for large-scale energy storage,but their development is plagued by inadequate cycle life.Here,for the first time,we reveal an unusual phenomenon of cathodic underpotential deposition(UPD)of Zn,which is highly irreversible and considered the origin of the inferior cycling stability of AZIBs.Combining experimental and theoretical simulation approaches,we propose that the UPD process agrees with a two-dimensional nucleation and growth model,following a thermodynamically feasible mechanism.Furthermore,the universality of Zn UPD is identified in systems,including VO_(2)//Zn,TiO_(2)//Zn,and SnO_(2)//Zn.In practice,we propose and successfully implement removing cathodic Zn UPD and substantially mitigate the degradation of the battery by controlling the end-ofdischarge voltage.This work provides new insights into AZIBs degradation and brings the cathodic UPD behavior of rechargeable batteries into the limelight.
以阳极氧化处理的碳布（ACC）为导电基体,利用Cu的欠电位沉积（UPD）和Cu与Pt金属前驱体之间的置换反应制备了Pt/碳布（Pt/ACC）电极材料,对其微观结构进行了表征并考察了其电催化分解水制氢性能。结果表明,通过控制Cu的沉积电位可以有效地控制Pt的负载量和其在ACC表面的分散状态。随着沉积电位在0.32~0.15 V vs.RHE变化,Pt/ACC电极材料中Pt的负载量呈线性增加;在0.5 mol/L H2SO4溶液中的产氢反应结果表明,随着Pt负载量的增加,析氢起始电位逐渐降低,当沉积电位为0.15 V vs.RHE时,Pt在ACC表面的负载量为588μg/cm2,所得Pt/ACC电极材料起始电位为-0.05 V vs.RHE,且达到10 m A/cm2电流密度所需的过电位仅为56 m V,Tafel斜率为34.2 m V/dec,电极的催化产氢活性与块体Pt箔相近。
在843 K LiCl-KCl-CeCl_3熔盐中活性铝电极上,研究了Ce(Ⅲ)离子的电化学行为和欠电位沉积Al-Ce合金。对比循环伏安曲线发现,在Al电极上Ce(Ⅲ)/Ce反应的氧化还原电势比在Mo惰性电极上更正;开路计时电位在金属铝和铈的沉积平台之间出现2个平台,这表明Ce(Ⅲ)在A1活性电极上可以生成两种金属间化合物。以上结果在电化学机理上说明Ce(Ⅲ)离子可以在Al电极上欠电位沉积形成金属间化合物。在该实验条件下通过恒电位电解,在Al电极上得到了Al-Ce合金,验证了电化学分析的结果。经XRD表征,证实形成了AlCe和AlCe_3两种合金,结合Al-Ce合金相图分析了只产生这两种合金的原因;结合开路电位计算了生成这两种合金的标准吉布斯自由能变值。经SEM和EDS表征,证明了铈在Al电极表面分布,并形成厚度均一约28μm的Al-Ce合金镀层。
