Fig. 3: Sequential structure evolution of active sites for TQBQ-COF electrodes during sodiation/desodiation processes.

a Discharge and charge profiles of TQBQ-COF electrode at 0.02 A g−1 in the voltage range of 0.8–3.7 V in the initial two cycles. b In-situ FTIR spectra collected at different states corresponding to a. c The C1s XPS spectra of TQBQ-COF electrodes at different charge/discharge states marked in a.