Department of Electrical and Computer Engineering, Florida International University, Miami, Florida, USA.
Plasma Forming Laboratory, Department of Mechanical and Materials Engineering, Florida International University, Miami, Florida, USA.
Nanoscale. 2023 Feb 16;15(7):3438-3448. doi: 10.1039/d2nr05558a.
Recently, progress in electrochromic (EC) devices has been made in optimizing electrode and device configurations and performance. However, the ion insertion/de-insertion induced charge transfer (CT) nanomechanical effect has remained unexplored, , repetitive electrode size changes at the nanoscale and stress/strain generated during electrochemical cycling, which is the focus of this work due to its intimate correlation with the elastic and plastic deformation at the interface. Considering the intervalence electrons, excellent electrochemical kinetics, and dramatic color changes, tungsten oxide (WO) and nickel oxide (NiO) films are configured as the EC cathode and anode materials, respectively, within a full device. Upon extended cycles (>10 000), the void generation and delamination that occurred at the interface account for performance decay. Encouraged by the findings, nanoindentation mechanical tests and electrical kelvin probe force microscopy were employed to investigate the CT induced effects at the interface. There is a dramatic increase of up to 45% in the elastic Young's modulus in colored/charged WO at ∼40 mC cm. The correlation between CT and synergistic mechanical effect is interpreted by the Lippman equation. Interestingly, despite the charged state (colored; lithiated) with a relatively flat morphology bringing an ∼3.4 times higher electrostatic surface potential, the electrical work function unexpectedly decreases, arising from the dominant effect of the dipole layer potential over the chemical potential. The interatomic cohesive energy and equilibrium distance increase bury the seeds for mechanical deformation in the long run. This work provides fundamental insights into electro-chemo mechanics and interdisciplinary concerted interfacial effects at the nano/atomic level. The dependence of surface potential, stress, work function, and cohesive energy on electrochemical kinetics has been interpreted.
最近，在优化电极和器件结构以及性能方面，电致变色（EC）器件取得了进展。然而，离子插入/脱插引起的电荷转移（CT）纳米机械效应仍未得到探索，主要是因为它与界面处的弹塑性变形密切相关，涉及到纳米尺度上的电极尺寸重复性变化和电化学循环过程中产生的应力/应变。考虑到价间电子、优异的电化学动力学和显著的颜色变化，氧化钨（WO）和氧化镍（NiO）薄膜分别被配置为全器件的 EC 阴极和阳极材料。经过长时间循环（>10000 次）后，界面处出现的空隙生成和分层现象导致性能下降。受此发现的鼓舞，采用纳米压痕力学测试和电 Kelvin 探针力显微镜研究了界面处的 CT 诱导效应。在着色/带电 WO 中，弹性杨氏模量急剧增加高达 45%，约为 40 mC cm。通过 Lippman 方程解释了 CT 和协同力学效应之间的相关性。有趣的是，尽管带电状态（着色；锂化）具有相对平坦的形貌，可带来约 3.4 倍更高的静电表面势，但出乎意料的是，电功函数降低，这是由于偶极层势对化学势的主导作用所致。原子间结合能和平衡距离的增加，从长远来看为机械变形埋下了种子。这项工作为电-化学-力学提供了基本的见解，并在纳米/原子水平上研究了跨学科的协同界面效应。解释了表面势、应力、功函数和结合能对电化学动力学的依赖性。
