Aluminum foil

Aluminum foil (Al, product number: 326860-3.6G), glucose (C₆H₁₂O₆, product number: PHR1000-1G), magnesium chloride (MgCl₂, product number 449172-10G), oxalic acid (C₂H₂O₄, product number: 247537-500G), perchloric acid (HClO₄, product number: 311421-250ML), phosphoric acid (H₃PO₄, product number: 695017-500ML), sodium hydroxide (NaOH, product number: 306576-100G), and deionized water (H₂O, product number: W4502-1L with a resistivity of 18 MΩ) were procured from Sigma-Aldrich (St. Louis, MI, USA). These reagents were employed as provided, without any further purification, ensuring the consistency of experimental conditions.

The flexible FeS₂@C/CNT film was fabricated by the vacuum filtration method. Firstly, 15 mg of CNT and 35 mg FeS₂@C were dispersed in 80 mL H₂O using an intensive ultrasonication probe for 30 min. Then, the mixed solution was filtered through a mixed cellulose ester membrane (1.2 µm pore size, Millipore). The obtained filter cake was then vacuum-dried for 24 h to get a freestanding film.
The binder-free and freestanding FeS₂@C/CNT directly utilized as a cathode in the AIBs. To compare with commercial FeS₂, the FeS₂ was firstly mixed with KB carbon with the same carbon content in FeS₂@C/CNT. Then the mixture and polytetrafluoroethylene (PTFE) (weight ratio of 9:1) mixed in deionized water followed by overnight high-vacuum heating under 100 °C. The areal loading of the active materials is around 1.0 mg cm⁻². The 1-ethyl-3-methylimidazolium chloride ([EMIm]Cl, 98%, Sigma) mixed with anhydrous aluminum chloride (99.99%, Sigma-Aldrich) (mole ratio of 1.3) to obtain the ionic liquid (IL) electrolyte (35 μL). A piece of glass fiber was used as the separator (Whatman). The aluminum foil (Sigma, 99.999%, 0.25 mm) is directly treated as the anode electrode. We applied soft package and Swagelok-type cells to assemble the batteries in glove box filled with Ar gas.

For ALP staining, differentiated osteoblasts were washed with PBS and fixed in 10% formalin for 2 min. Cells were rinsed with deionized water and incubated with alkaline dye mixture for 30 min by wrapping with aluminum foil according to the manufacturer’s instruction (Sigma-Aldrich). Cells were then rinsed with deionized water and subjected to a microscopic observation. For alizarin red S staining, cells were washed with distilled water, fixed in ice-cold 70% ethanol for 1 h, and then stained with 2% Alizarin red S stain solution (adjusted to pH 4.2 with 10% ammonium hydroxide) (Sigma-Aldrich) for 30 min. Stained cells were washed and observed using a light microscope. At least 10 cell images were captured under a microscope (Olympus IX51 inverted fluorescent microscope, Olympus Optical, Japan) fitted with a DP70 camera system (Olympus) and used for a quantitative analysis with the Image J software. To determine ALP activity, cells were washed and lysed with Triton X-100 lysis buffer (50 mM Tris, 150 mM NaCl, and 1% Triton X-100, pH 10). Cell supernatants were incubated with an ALP substrate. ALP activity assay was performed in triplicate using the LabAssay ALP Kit (Wako Pure Chemical Industries, Japan). Relative ALP activity was calculated by comparing with standard solution and expressed as units per mg of protein according to the manufacturer’s instructions.