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. 2022 Mar 9;8(10):eabl8160. doi: 10.1126/sciadv.abl8160

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Fig. 1. — (A) Design principles of creating bimodal distribution of free volumes. (B) SEM images and in situ EDS mappings of phosphorus on the cross section of the PBI-PPA0.34 films before and after carbonization at 600°C. PPA, pyrophosphoric acid (H₄P₂O₇).