Dynamic Potential-pH Diagrams of Ni-Based Anodes for Durable Oxygen Evolution in the Presence of Cl Impurity.

The corrosion of anode materials caused by dissolved chloride ions (Cl) is considered one of the most significant issues in the long term durability of seawater electrolysis systems. This study examined the corrosion behaviors of Ni-based electrodes based on a dynamic potential-pH (Pourbaix) diagram with various buffered electrolytes (borate, carbonate, and phosphate). It was found that NiFeO/Ni plate electrodes degraded faster in media with mild pH than those with alkaline pH, and the corrosion rate depended on the dissolved ionic species in the presence of Cl, which could be explained in terms of the thermodynamic stability of the formed compounds on the surface. No significant corrosion was observed in phosphate-containing electrolytes, which could be explained by the high formation constant and the low solubility of the Ni-PO product with the formed complex. The density functional theory calculation was used to clarify the preferable phosphate adsorption on the Ni site over Cl, which stabilized Ni.