Fig. 5: Electrochemical performance of FREB.

a CV curves of FREB at 2 mV s−1. b The rate capability of the FREB at various rates. c Corresponding galvanostatic charge/discharge profiles at various rates. d Long-term cycling performance and the corresponding coulombic efficiency at 25 A g−1. e Reflectance spectrum, and (f) CIE 1931 xy chromaticity coordinate changes at the charge/discharge state. g Optical photo of FREB at various states of charge. h In situ spectral emissivity contour map, (i) emissive power and (j) emissive power contour map of the FREB at the corresponding voltages from 2.5 μm to 25 μm. The electrochemical test temperature is 25 °C ± 1 °C.