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_x/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-PO₄ 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.