Fig. 3: Electrochemical characterizations of the Al-based symmetric cells.

a Typical stripping/plating voltage profile (pink line) of E-Al₈₂Cu₁₈ symmetric cells in 2 M Al(OTF)₃ aqueous electrolyte with C_O2 = 0.13 mg L⁻¹. Current density: 1 mA cm⁻². Insets: representative SEM images and the corresponding SEM-EDS elemental mappings of Al (in red) and Cu (in green) for the E-Al₈₂Cu₁₈ electrode after Al stripping (left) and then Al plating processes (right). Scale bars, 1 μm. b Comparison of rate performance for symmetric cells of E-Al₈₂Cu₁₈ (pink line), Al₂Cu (blue line), and Al (green line) electrodes in 2 M Al(OTF)₃ aqueous electrolyte with C_O2 = 0.13 mg L⁻¹ at various current densities of 0.5, 1.0, 1.5, 2.5 mA cm⁻². Inset: enlarged voltage-time profiles comparing the stripping/plating behaviors of E-Al₈₂Cu₁₈ (pink line) and Al₂Cu (blue line) electrodes at different current densities. c Long-term cycling stability of Al stripping/plating for symmetric cells based on E-Al₈₂Cu₁₈ (pink line), Al₂Cu (blue line), and Al (green line) electrodes at 0.5 mA cm⁻² in 2 M Al(OTF)₃ aqueous electrolyte with C_O2 = 0.13 mg L⁻¹. Inset: voltage evolutions for Al (left), Al₂Cu (middle), and E-Al₈₂Cu₁₈ (right). d–f EIS spectra of E-Al₈₂Cu₁₈ (d), Al₂Cu (e), and Al (f) symmetric cells before and after the stripping/plating cycling measurements for 240 h, 240 h, and 24 h, respectively, in 2 M Al(OTF)₃ aqueous electrolyte with C_O2 = 0.13 mg L⁻¹. The square and circle symbols are the raw data of E-Al₈₂Cu₁₈ (d), Al₂Cu (e), and Al (f) symmetric cells before and after Al stripping/plating for 240 h, respectively, in which the lines represent their fit data.