All-Solid-State Polymeric Membrane Ion-Selective Electrodes Based on NiCo₂S₄ as a Solid Contact

Abstract

The performance criteria for the design of all-solid-state ion-selective electrodes mainly include high electrode-to-electrode reproducibility and a low potential drift. Here, we introduce nickel cobalt sulfide (NiCo2S4) as a solid contact for ion-to-electron transduction based on multiple redox couples. NiCo2S4 materials with different morphologies can be prepared through a facile hydrothermal/solvothermal method. A NiCo2S4-based solid-contact Ca2+-ISE has been developed, which exhibits a Nernstian slope of 27.5 ± 0.2 mV/dec in the activity range from 1.0 × 10–6 to 2.9 × 10–2 M with a detection limit of 5.0 × 10–7 M. A variation of the standard potential E° for eight individual solid-contact electrodes can be obtained as low as 0.35 mV. Due to the synergistic effect of cobalt and nickel ions in the ternary sulfide, an excellent redox capacitance (565 μF) of the buried solid contact coated with the ion-selective membrane can be achieved and is much larger than those obtained from other redox solid-contact materials reported so far, thus yielding a high potential stability of 2.2 ± 0.4 μV/h. In addition, the NiCo2S4-based solid-contact Ca2+-ISE shows a reduced water layer at the sensing membrane/NiCo2S4 interface and provides an excellent resistance to the interferences from light, O2, and CO2. The proposed strategy utilizing NiCo2S4 as a solid contact is a promising alternative for the fabrication of calibration-free ASS-ISEs.

Ion-Electron Transduction Layer of the SnS2-MoS2 Heterojunction to Elevate Superior Interface Stability for All-Solid Sodium-Ion Selective Electrode

“…In the case of MoS 2 and SnS 2 , 0.5 < b < 1, indicating that the electrochemical process is controlled by diffusion. However, in the SnS 2 -MoS 2 , the electrochemical process is surface-controlled (b ≈ 1) (Figure f), which can be attributed to the rapid electron transfer at the heterogeneous interface, leading to increased material capacitance . Detailed CV curves at different sweep speeds can be seen in Figure S6.…”

“…37 The potential drift value of the GC/SnS 2 -MoS 2 /Na + -ISM electrode is 1.43 μV/s, and those of the GC/MoS 2 /Na + -ISM and GC/SnS 2 /Na + -ISM are 7.05 and 79.15 μV/s, respectively. The capacitance (C) value is determined through the approximate equation ΔE/Δt = i/ C. 36 The findings indicate that the capacitance of GC/SnS 2 -MoS 2 /Na + -ISM is 699 μF, which is significantly higher than those of GC/MoS 2 /Na + -ISM (142 μF) and GC/SnS 2 /Na + -ISM (12 μF). Moreover, it surpasses the capacitance of polymer and nanomaterial transduction layers reported in Table 1, indicating that using heterojunction materials to design high capacity and high hydrophobic ion-electron transduction layer materials is an effective method.…”

“…However, in the SnS 2 -MoS 2 , the electrochemical process is surface-controlled (b ≈ 1) (Figure 2f), which can be attributed to the rapid electron transfer at the heterogeneous interface, leading to increased material capacitance. 36 Detailed CV curves at different sweep speeds can be seen in Figure S6. In summary, the heterostructure formed by Sn-doped MoS 2 exhibits a SnS 2 -MoS 2 heterointerface characterized by a swift electron transfer and storage.…”

Emerging functional materials in solid-contact potentiometric sensing, a field full of vitality

“…Recently, Li, Qin and coworkers utilized nickel cobalt sulfide (NiCo 2 S 4 ) as the solid contact for ion-to-electron transduction to develop an all-solid-state polymeric membrane Ca 2+ -ion selective electrode. 41 The synergistic effect of nickel and cobalt ions contributed to the increased redox capacitances of NiCo 2 S 4 , through the redox reactions of Ni 3+ /Ni 2+ and Co 4+ /Co 3+ /Co 2+ redox couples. Following this work, the same authors reported the in situ preparation of quasi-superhydrophobic porous NiCo 2 S 4 nanosheet arrays via one-step electrodeposition and used the prepared NiCo 2 S 4 nanosheet arrays as the solid contact to construct a Ca 2+ -ion selective electrode.…”

Robust Potentiometric Microelectrodes for In Situ Sensing of Ion Fluxes with High Sensitivity

“…Due to good hydrophobicity, excellent conductivity, and large redox capacitance, NiCo 2 S 4 has been synthesized and used as an ion-to-electron transducer for preparation of all-solid-state potentiometric sensors in our previous research. , The presence of the nanostructured NiCo 2 S 4 solid contact not only effectively suppresses the formation of a water layer at the sensing membrane/NiCo 2 S 4 interface but also largely improves the sensor stability and reproducibility. The in situ formed NiCo 2 S 4 nanowire arrays can act as a “superhighway” for ultrafast ion/electron transport and provide a large surface area, redox capacitance, and abundant availability of electrochemical active sites, − thus yielding a high potential stability.…”