Vacancy engineering of FeP dispersed N, P-doped porous carbon for high-performance capacitive deionization

With high theoretical capacity and a safer voltage platform, Iron phosphide (FeP) as an electrode for capacitive deionization (CDI) has rare reported. In this study, nitrogen (N) and phosphorus (P)-doped polymers were impregnated with Fe(NO₃)₃ as the precursor material. Subsequent pyrolysis resulted in the in-situ formation of FeP nanoparticles within a carbon matrix (FeP@NC-x), characterized by a significant number of P vacancies. The optimized FeP@NC-2 electrode exhibited an exceptional specific adsorption capacity of 332.7 mg/g for Cu²⁺ ions in a 500 mg/L CuCl₂ solution at an applied potential of 1.8 V. These remarkable results can be attributed to the well-dispersed nano-FeP and massive P vacancies within the carbon framework. This configuration expanded the electrode's conductivity and served more active sites for adsorption, reduced the diffusion path length for Cu²⁺ ions, and mitigated volume changes during operation. The adsorption selectivity was further elucidated through Density Functional Theory (DFT) calculations, and the adsorption-desorption mechanisms of Cu²⁺ ions were thoroughly investigated. This strategic approach paves the way for effective improvements in the CDI performance of transition metal phosphides and opens new avenues for advanced water purification technologies.