Hybrid and Flow-Electrode Capacitive Deionization: Materials Design, Multispecies Removal, and Smart Regulation

As an emerging desalination technology, capacitive deionization (CDI) has garnered significant attention due to its superior energy efficiency and performance metrics compared to conventional distillation and reverse osmosis (RO) techniques. Over the past decade, substantial advances have been achieved across multiple technical dimensions of CDI systems. This review focuses on two representative CDI architectures-hybrid capacitive deionization (HCDI) and flow-electrode capacitive deionization (FCDI)-highlighting their core innovation mechanisms: the ion storage behavior in HCDI and the continuous operation characteristics of flow electrodes in FCDI. We systematically examine recent research progress in critical areas including innovative electrode materials, optimized cell configurations, and expanded contaminant removal targets (e.g., heavy metals/organic pollutants), while delving into machine learning (ML)-driven strategies for operational parameter optimization and system performance prediction. Ultimately, by synthesizing these technological breakthroughs and aligning them with current engineering requirements, this review aims to facilitate the scalable implementation and industrial adoption of CDI technology within sustainable water treatment frameworks.