Abstract
In this work, WO<sub>3</sub> crystal structure films are deposited on conductive glass substrates by seed layer assisted hydrothermal reaction method. Through controlling the concentration of hydrochloric acid, oxalic acid, and the hydrothermal postprocessing temperature, the micro-peony, micro urchin-like, and porous petal-like WO<sub>3</sub> crystal structures are obtained respectively. Scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and electrochemical characterization are used to study the formation mechanism of different structures and their effects on the electrochromic properties of WO<sub>3</sub> films. The Cl<sup>–</sup> in HCl has a strong promoting role towards the <i>c</i> axis in WO<sub>3</sub> crystal growth and oxalic acid has a promoting effect towards an <i>a</i> axis. In terms of color efficiency, the CE value of micro-urchin is 42.37 cm<sup>2</sup>/C, far greater than those of two other WO<sub>3</sub> structures, 15.21 cm<sup>2</sup>/C and 12.71 cm<sup>2</sup>/C. Owing to the cold-water quenching treatment, the CE value of WO<sub>3</sub> micro-peony with porous surface structure is 56.95 cm<sup>2</sup>/C, quadruple CE value of the smooth surface structure, slightly better than that of the micro-urchin structure.
Highlights
WO3 crystal structure films are deposited on conductive glass substrates by seed layer assisted hydrothermal reaction method
C. Owing to the cold-water quenching treatment
2) (College of Ocean and Earth Sciences, Xiamen University, Xiamen 361005, China) ( Received August 2021; revised manuscript received September 2021 )
Summary
图 1 所示为不同 HCl 浓度下的 WO3 晶体拓 扑结构薄膜的 SEM 照片. 从图 1 可以看出, WO3 晶体分别为不规则多边形结构、叶片结构和花朵 结构. HCl 浓度为零时, 水热反应液的 pH 值约为 2.0, WO3 从种子颗粒生长为不规则多边形或者块 状形态, 平均尺寸为 2.5 μm, 是种子层颗粒尺寸 的 6 倍 (图 1(a)), 即无 Cl–时, 从种子层到不规则 多边形, 晶核颗粒朝各个方向共同生长. 但是加入 HCl 后, 晶核取向生长, 得到 WO3 微米树叶和微 米花结构, 见图 1(b)—(d). 图 1 不同 HCl 浓度下生长的 WO3 晶体拓扑结构的 SEM 照片 (a) 0 mL; (b) 0.25 mL; (c) 0.50 mL; (d) 0.75 mL Fig. 1. SEM images of WO3 crystal topology structures with different concentration of HCl: (a) 0 mL; (b) 0.25 mL; (c) 0.50 mL; (d) 0.75 mL. 图 2 不同草酸浓度下生长的 WO3 晶体拓扑结构的 SEM 照 片 (a) 0 mol/L; (b) 0.05 mol/L; (c) 0.10 mol/L; (d) 0.15 mol/L Fig. 2. SEM images of WO3 crystal topology structures with different concentration of oxalic acid: (a) 0 mol/L; (b) 0.05 mol/L; (c) 0.10 mol/L; (d) 0.15 mol/L. SEM images of WO3 micro-peony crystal structures with the porous structure in different magnification. SEM images of WO3 micro-peony crystal structures with the smooth structure in different magnification. 图 6 WO3 大、小微米花晶体结构的 XRD 图谱 Fig. 6. 基于微米花晶体拓扑结构的生长机理, 图 是 整个微米花的简化图. 假定每个花瓣近似成长方体, 小微米花直径约 7.30 μm, 结合图 测量得到花瓣 的平均长度约 1.50 μm, 平均宽度约 1.10 μm, 厚度约 17.00 nm, 平均一个花瓣厚度上堆叠 1.5 层纳米针. 理论计算得到微米花比表面积约为 16.84 m2/g
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