Fundamental understanding of Prussian blue and its analogues for superior capacitive deionization: A perspective from nanoarchitectonics

Capacitive deionization (CDI) offers an appealing electrochemical solution for water treatment, where electrode materials play a crucial role in ensuring the efficiency of CDI devices. The quest for novel electrode materials is driven by the need to enhance desalination capacity, cycling stability, ion selectivity, and energy efficiency, given that traditional carbon materials relying on electric double layer electrosorption principle often exhibit subpar desalination capabilities. Among the standout options, Prussian blue (Fe₄[Fe(CN)₆]₃) and its analogs (PB/PBAs) have stood out in CDI systems due to their superior performance and durability as coordination polymers. Nevertheless, challenges persist in leveraging their full potential for CDI, stemming from issues like low desalination capacity, slow kinetics, poor conductivity, structural vulnerability, and limited electrochemical activity. Recent years have witnessed the emergence of innovative strategies aimed at addressing these obstacles, particularly through advancements in structural and compositional manipulation. This review seeks to consolidate the latest advancements in the nanoarchitectonics of PB/PBAs, exploring their classification, and synthesis methodologies, and delving into the fundamental principles governing their utility in CDI applications—anchored in considerations of thermodynamics, kinetics, and mechanisms. Notably, the review underscores the prevailing challenges faced by PB/PBAs in CDI deployment, prompting the discussion of proactive approaches to guide future material innovation and usage. By shedding light on the ongoing efforts to enhance PB/PBAs for CDI, this review anticipates that advancements in nanoarchitectonics will unlock fresh possibilities in the realm of high-performance CDI material design and implementation.