Challenges and design strategies of metal sulfides for superior-performance capacitive deionization

Capacitive deionization (CDI) is an environmentally friendly water treatment technology that offers energy-efficient and sustainable deionization. Notably, electrode materials as the core of CDI significantly affect the adsorption performance. While traditional carbon-based materials have been widely used, they face limitations such as low adsorption capacity, weak structural stability, and poor performance in multivalent ion removal, which restrict their practical applications in high-salinity or complex water sources. In contrast, metal sulfides, with their unique structural and electrochemical properties, exhibit higher adsorption performance, stability, and selectivity, especially for heavy metal ions, making them ideal for CDI applications. However, few reviews focused on the adsorption performance, design strategies, and potential challenges of metal sulfides in the CDI field. This paper provides a comprehensive review of the adsorption performance and design strategies for metal sulfides, focusing on interface, defect, surface, and structural engineering to enhance CDI efficiency. It also provides various solutions for addressing critical challenges, including optimizing synthesis, fabricating high-performance materials, understanding ion capture mechanisms, developing versatile ion removing materials, and integrating CDI with complementary technologies. Through these insights, this review aims to guide the development of high-performance metal sulfide-based electrodes, paving the way for more efficient and durable CDI technologies.