Fig. 2: In operando O–K SXAS spectra of Li₂Co₂O₄.

a, b O–K SXAS spectra of Li₂Co₂O₄ in operando as a function of the number of scans (2 min for each scan) at applied voltages of 1.4 and 1.6 V, respectively. c Comparison of the spectra during the OER (black circles, in operando) and after the OER (magenta circles, in vacuo). Also included are the spectra of LiCoO₂ (cyan line) with the low-spin Co³⁺ state, mixed-valent Co oxide Li_0.66CoO₂ (orange line, from Ref. ²⁹), and Na_0.5CoO₂ (dark cyan line, from Ref. ³⁰) with the same 90° Co–O–Co bond angle. d Spectra of Li₂Co₂O₄ at different applied voltages. e, f Experimental (black lines) and simulated (magenta lines) spectra of Li₂Co₂O₄ under an applied voltage of 1.4 and 1.6 V, respectively, with the simulations being constructed as weighted sums of the spectra of the as-prepared Li₂Co₂O₄ (blue) representing the low-spin Co³⁺ state and of BaCoO₃ (cyan, from Ref. ²⁷) representing the low-spin Co⁴⁺ configuration.