Electrodeposited Prussian Blue analogs on carbon nanofiber for electrochemical cesium removal: Transition-metal-dependent intercalation behavior

Abstract

The development of regenerable electrochemical systems for radioactive cesium removal requires both mechanistic understanding and material optimization. Although Prussian Blue analogs (PBAs) are promising candidates for Cs+ adsorption, the transition-metal-dependent factors governing electrochemical Cs+ intercalation in binder-free electrode architectures remain insufficiently clarified. Herein, binder-free NiFe-, CoFe-, MnFe-, and CuFe-carbon nanofiber (CNF) composites were prepared using metal-specific electrodeposition strategies and subsequently evaluated under the same electrochemical adsorption/desorption conditions to compare their Cs+ uptake and release behavior. Distinct transition-metal-dependent limiting regimes were identified: CoFe-CNF exhibited morphology-limited behavior owing to oversized crystal growth, MnFe-CNF showed a reversibility-limited performance attributed to Jahn-Teller distortion-induced lattice strain, and NiFe-CNF was constrained by achievable deposition loading. CuFe-CNF emerged as a balanced system maintaining controlled morphology, sufficient loading, and stable redox reversibility, delivering maximum Langmuir capacities of 68.6 mu mol center dot cm-2 (electrochemical adsorption, EA) and 85.3 mu mol center dot cm-2 (electrochemical desorption, ED), stable cycling, and favorable separation factors (RL = 0.035-0.423). XPS analysis further revealed an asymmetric redox mechanism, wherein Cu2+/Cu+ reduction drives Cs+ intercalation during adsorption and Fe2+/Fe3+ oxidation governs Cs+ expulsion during desorption, with Fe2+/Fe3+ couple becoming increasingly dominant over repeated cycling. Classification of morphology-, loading-, and reversibility-limited regimes provides a rational design framework, highlighting CuFe-CNF as an optimized platform for sustainable electrochemical cesium remediation.