Exploring the role of solvents in structural regulation during ultrasonic synthesis of Co/Ni-layered double hydroxide for oxygen evolution reaction
Zhaojin Li, Qian Ma, Zezhao Li, Di Zhang, Qujiang Sun, Qiujun Wang, Huilan Sun, Bo Wang
Abstract
Cobalt-based layered double hydroxides (LDHs) are highly sought after by researchers due to their low-cost, high efficiency and stability for oxygen evolution reaction (OER) in water electrolysis. The OER performance of these LDHs is closely related to their morphology and electronic structure. However, there is a lack of theory on how to control reaction conditions to regulate the morphologies. In this paper, the growth mechanism of LDH prepared in different solvents is thoroughly studied. Consequently, the Co/Ni-LDHs exhibiting a 3D hierarchical flower-like structure were synthesized with normal alcohol as a solvent, meanwhile, the thickness of the LDHs can be controlled by the molecular weight of the normal alcohol. By adjusting the suitable Co/Ni ratio and solvent, the Co/Ni0.050-LDH-Me was synthesized and exhibited excellent OER performance. At 10 mA cm −2 , the overpotential of Co/Ni0.050-LDH-Me is 307 mV, and the Tafel slope is 76.5 mV dec −1 . • The Co/Ni-LDH with 3D floral structure can be synthesized with normal alcohol as solvent, while Co/Ni(OH) 2 with hexagonal nanosheet structure was obtained when water is adopted as solvent. • Due to the different O solubility of alcohol and water solvents, the proportion and coordination ability of high valent metal ions in the environment vary, resulting in the differences in the final morphology and structure of the LDH. • The thickness of the LDHs can be controlled by the molecular weight of the normal alcohol. When methanol is used as the solvent, the thickness of the prepared Co/Ni0.050-LDH-Me material reaches the thinnest 10 nm. • Due to the synergistic effect between Co and Ni and its unique morphology, the Co/Ni0.050-LDH-Me material exhibits excellent OER performance in alkaline media. At 10 mA·cm −2 , the overpotential of Co/Ni0.050-LDH-Me is 307 mV, and the Tafel slope is 76.5 mV·dec −1 .