Wearable solid-state ZAB properties
Since the sample FeN₄-Ti₃C₂Sₓ exhibited high ORR activity, the article further used the developed FeN₄-Ti₃C₂Sₓ catalysts with alkali-resistant dual-network PANa and cellulose hydrogel (PANa-cellulose ) as stretchable solid electrolytes to jointly construct a stretchable and abrasion-resistant fibrous ZAB.Fig. 4a illustrates that it can be stretched over 1000% strain without any fracture and visible cracks, with excellent tensile properties. The structure of the fibrous ZAB is shown in Fig. 4 b. A hydrogel electrolyte was used to first wrap the Zn spring electrode, then stretch it, and finally wrap the FeN₄-Ti₃C₂Sₓ-loaded carbon paper as the air electrode. The charging and discharging curves and corresponding power densities of the fibrous ZAB in the initial and 800% stretched states are shown in Fig. 4c, d. The maximum power density of the ZAB in the initial state is 133.6 mW-cm-², and that of the ZAB in the stretched state at 800 ℃ is 182.3 mW-cm-². indicating that the cell is stretchable and has good electrochemical performance in the stretched state. In addition, the cell exhibits excellent cycling stability with a stable cycling of 110 h at 2 mA cm-², as shown in Fig. 4e. To demonstrate its wear resistance, two fiber-shaped ZABs with a length of 10 cm and a diameter of 2 mm were woven into a wristband and attached to a glove as shown in Fig. 4f and g. The wristband was made of a fiber-shaped ZAB with a diameter of 2 mm. This wristband can power a set of LEDs on the wearing gloves, demonstrating the feasibility of this highly efficient stretchable and wearable fiber-shaped ZAB based on the prepared FeN₄-Ti₃C₂Sₓ catalyst.
Tensile stress versus strain curves of the prepared PANa-cellulose hydrogel, and the inset shows optical photographs of this hydrogel electrolyte in the initial and stretched states; (b) schematic diagram of the stretchable fibrous ZAB; (c) charge-discharge curves of the fibrous ZAB in the initial and 800% stretched states; (d) discharge and power density curves of the fibrous ZAB in the initial and 800% stretched states ; (e) cycling stability test of fiber-shaped ZABs at 2 mA cm-²; (f) photographs of two fiber-shaped ZABs (length: 10 cm, diameter: 2 mm) woven into a wristband; (g) photographs of this wristband attached to a glove; (h) photographs of this wristband attached to a glove to supply power to a set of LEDs
Source of ORR electrocatalytic activity
In the article, the energy band structures of FeN₄-Ti₃C₂ and FeN₄-Ti₃C₂Sₓ samples were investigated using UPS. As shown in Fig. 5a, the cutoff energy of FeN₄-Ti₃C₂ is 17.1 and that of FeN₄-Ti₃C₂Sₓ is 17.23. Further estimation of the figure of merit function (Φ) and valence band maxima (EV) reveals that, compared with FeN₄- Ti₃C₂ compared to FeN₄-Ti₃C₂Sₓ the reduction of Φ and EV shifts to lower energies, indicating that the addition of the S-terminal to the Ti₃C₂ carrier results in the spatial stabilization of the electrons within the FeN₄ part, and a change of the center of the 3d band of energy of Fe(II) . In addition, the corresponding effective magnetic moments (µ) shown in Fig. 5c indicate that the µ effect for sample FeN₄-Ti₃C₂Sₓ is larger than that for sample FeN₄-Ti₃C₂, and that the large µ effect suggests that the number of unpaired d electrons is greater for Fe(II) in the sample. In addition, DFT calculations show that the introduction of the S-terminus can increase the in situ magnetic moment of the Fe center and modulate the spin state of Fe(II) in the FeN₄ fraction (the intermediate spin state is transformed into the high spin state), resulting in the Fe 3d electron delocalization and upward shifting of the d-band centers thereby optimizing the orbital hybridization of Fe 3d with the p orbitals of oxygen-containing moieties, which can enhance the molecular oxygen adsorption, indicating that the FeN₄-Ti₃C₂Sₓ system has a good catalytic activity for ORR, which is in good agreement with the experimental results.
