“…In addition, the peak positions of P 2p 3/2 , P 2p 1/2 , and oxidized P species displayed in the P 2p ( Figure 3 e) spectrum are 130.05, 130.9, and 133.5 eV, respectively. The P-O peak at 133.5 eV is due to the inevitable surface oxidation of the sample exposed to air, which can be attributed to the high oxidation state of P species (PO x ) [ 32 , 54 , 55 ].…”