Chainmail Structures of CoNi Alloys Encapsulated in Nitrogen‐Doped Carbon Nanotubes Empowered Long‐Term Stable Detection of Sodium Ions

Low potential drift is one of the performance criteria for designing all-solid-state sodium ion selective electrodes (Na⁺-SC-ISEs), which directly affects the stability and reliability of detection results. Currently, most attempts primarily focus on improving the hydrophobicity and capacitance of solid-contact (SC) layers to enhance the stability of Na⁺-SC-ISEs, while neglecting the important impact of the stability and capacitance retention rate of SC materials on the long-term stability of Na⁺-SC-ISEs. Herein, chainmail-structured nanomaterials are elaborately designed, where CoNi alloys are encapsulated in nitrogen-doped carbon nanotubes (NCNTs), as SC layers for the construction of all-solid sodium ion selective electrodes. The Na⁺-SC-ISEs based on CoNi-in-NCNTs (CoNi-in-NCNTs/Na⁺-ISEs) achieve a minimal potential drift of 1.14 µV h^-1 during long-term stable detection for 4 days and a commendable capacitance retention rate of 92%. It is revealed by density functional theory (DFT) calculations and kinetic simulations that CoNi alloys continuously penetrate electrons to NCNTs surface, realizing the rapid ion-electron transduction at the SC interface. Besides, NCNTs both serve as physical barriers to the hydrophobic interface to prevent the water layer formation and provide more support sites to restrain CoNi nanoparticles aggregating. Such barrier protection and electron penetration effect of the CoNi-in-NCNTs significantly enhances the long-term stable detection of Na⁺.