The 3D architecture of Co(II) oxide (CoO) having oxygen defects has been recognized as a highly functional characteristic towards efficient electrocatalysis of water. Herein, different surface structures of CoO in the form of chemically deposited films were fabricated via AACVD technique, directly over the transparent fluorine-doped tin oxide (FTO) electrodes just by varying the deposition times. The as-prepared films were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). As the deposition time is varied, the surface structure of the CoO changes from nanoparticles that are formed just in 15 min to nanobuds at 30-min deposition, and finally to a homogeneously distributed dense population of nanoflowers in 45 min. The evolution of these structures was also accompanied by a preferential exposure of (111) facets and an increasing number of oxygen defects which resulted in an enhancement of electrocatalytic activity towards water oxidation. The CoO nanoflowers (CoO-NFs) with highest number of these active oxygen vacancies showed the best performance with an overpotential of 325 mV vs RHE for a current density of 10 mA/cm² while having a Taefl slope of 98 mV/dec, a mass activity of 35.2 A/g, and the electrochemically active surface area (ECSA) of 1069 μF. However, more importantly, the current density for CoO-NF jumped sharply to the values above 200 mA/cm² with potential less than 1.8 V vs RHE, thereby meeting the commercialization standards while still providing high stabilities of oxygen generation, current densities, and repeated cycling. Such a performance can be considered remarkable for a material fabricated via a rapid and facile synthetic route and is directly deposited on a low cost and relatively less conductive FTO substrate which can be attributed to the synergistic effect of the larger specific surface area of 3D structure and the high distribution of oxygen defects.

Graphical Abstract

具有氧缺陷的Co（II）氧化物（CoO）的3D结构已被视为对水进行有效电催化的高度功能特性。在此，仅通过改变沉积时间，就通过AACVD技术在透明的掺氟氧化锡（FTO）电极上直接制造了化学沉积膜形式的CoO的不同表面结构。通过扫描电子显微镜（SEM），能量色散X射线（EDX），X射线衍射（XRD）和X射线光电子能谱（XPS）表征所制备的膜。随着沉积时间的变化，CoO的表面结构从仅在15分钟内形成的纳米粒子变为在30分钟沉积时的纳米芽，最后在45分钟内变为均匀分布的密集纳米花。这些结构的演变还伴随着（111）晶面的优先暴露和氧缺陷数量的增加，这导致了对水氧化的电催化活性增强。这些活性氧空位数量最多的CoO纳米花（CoO-NFs）在电流密度为10 mA / cm时相对于RHE的325 mV过电位表现出最佳性能^在图2中，其Taefl斜率为98mV / dec，质量活性为35.2A / g，电化学活性表面积（ECSA）为1069μF。但是，更重要的是，CoO-NF的电流密度急剧上升至200 mA / cm ^2以上，电位相对于RHE小于1.8 V，从而达到了商业化标准，同时仍提供了高的产氧稳定性，电流密度和重复循环。对于通过快速便捷的合成路线制造的材料，这种性能可以认为是非凡的，并且可以直接沉积在低成本且导电性相对较低的FTO基板上，这可以归因于3D结构的较大比表面积和氧缺陷分布高。

图形概要