氧化石墨烯在氧化锌衬底上的电化学还原及其光电性能

Electrochemical Reduction of Graphene Oxide on ZnO Substrate and Its Photoelectric Properties

采用阳极电泳法,在氧化锌(ZnO)衬底上沉积氧化石墨烯(GO)以形成GO-ZnO双层复合膜;采用阴极恒电位法,对复合膜上的GO进行还原。对不同还原时间的GO,通过X射线光电子能谱(XPS),傅里叶变换红外(FTIR)光谱,场发射扫描电子显微镜(FESEM)等手段对其结构变化进行表征,采用紫外-可见(UV-Vis)分光光度法和电化学测试手段对其能级演变进行考察,并对两者的对应关系进行了讨论。研究发现,当GO膜达到最大还原态后,随还原时间增加还会出现进一步的结构转变,并最终碎裂生成边缘羧基增多的小尺寸GO。GO能隙均减小至可见光范围,其能级位置及半导体极性也产生了不同的改变。由对复合膜的光电化学测试可见,除1800 s GO能级不再与ZnO匹配外,60 s到600 s GO-ZnO复合膜均可作为阳极光电极进行太阳光电转换。对光电性能差异的讨论则可得,GO膜碎裂造成叠层形貌向无序形貌的转变有利于光电转换性能的提升。

In the present work, graphene oxide （GO）-ZnO bilayer composites were fabricated by depositing GO on ZnO by an anodic electrophoretic method. The composite films were then subjected to a cathodic electrochemical treatment with different GO reduction times. The as-prepared films were characterized by X- ray photoelectron spectroscopy （XPS）, Fourier transform infrared （FTIR） spectroscopy and field emission scanning electron microscopy （FESEM） to study changes in the GO structure. The evolution of the material＇s energy levels over time was also determined by ultraviolet-visible （UV-Vis） spectroscopy and electrochemical measurements. A series of structural transformations of GO occurred even after it had reached the maximum degree of reduction. Prolonged treatment saw the GO flakes fracture into smaller GO particles with a sharp increase in the proportion of carboxyl groups. The energy gap of GO varied and extended into the visible range with longer reduction time. The energy levels and charge carrier type also varied. Photoelectrochemical tests on the samples revealed that the 60 to 600-s reduced GO-ZnO composite films showed photoelectric conversion behavior as photoanodes. However, the sample reduced for 1800 s was not effective at light-harvesting owing to lowering of the GO conduction band below that of ZnO. The differences in performance indicated that the transformation of the laminated GO geometry to a more disordered distribution enhanced conversion efficiency.