Tuning d-band width for superior sodium capture in capacitive deionization
Xuexin Wang1, Baochang Cheng1, Dawei Chu2
1Key Laboratory of Fine Chemicals of College of Heilongjiang Province, College of Chemistry and Chemical Engineering, Qiqihar University, Qiqihar 161006, China.
Abstract:
Herein, a d-band width engineering strategy is proposed for the rational design of superior sodium capture electrodes, demonstrated using a lanthanum-doped carbon-encapsulated cobalt‑iron intermetallic (La-CoFe@C) as a model platform. The large ionic radius of lanthanum induces local lattice distortion that broadens the distribution of metal-metal bond lengths. This bond length heterogeneity perturbs d-orbital overlap between adjacent metal atoms, differentially modulating individual d-suborbital energy levels and ultimately widening the total d-band width. The resulting widened d-band serves as an intrinsic descriptor for metal-Na+ interactions, enhancing CDI performance by thermodynamically optimizing Na+ adsorption energy via improved energy matching and orbital overlap, kinetically accelerating ion diffusion through reduced migration energy barriers, and inducing an electron-rich state at Fe/Co sites for high selectivity toward various cations. Consequently, the La-CoFe@C electrode delivers outstanding desalination performance, achieving a high salt adsorption capacity of 298.9 ± 1.1 mg g-1, a rapid desalination rate of 51.4 ± 0.7 mg g-1 min-1, and exceptional multi-ion uptake capacity. This work establishes the d-band width as a key design principle for CDI electrodes, providing a generalizable framework to engineer ion-adsorption energetics for advanced desalination and beyond.
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