Post-synthetic efficient functionalization of polyaniline with phosphorus-containing groups. Effect of phosphorus on electrochemical properties

P-postmodified polyaniline was obtained by reacting phosphorus trichloride (PCl3) and chlorodiphenylphosphine (PPh2Cl) and polyaniline (PANI), under mild conditions. The reaction was found to be very selective, as only the imine groups were involved in the P-functionalization, and efficient as well, affording a P-loading of 3 at.% and 5 at.% for PPh2Cl and PCl3, respectively. All the polymers were characterized by different techniques and the results were endorsed by theoretical calculations. Experimental and Density Functional Theory results proved that the reaction occurs through the imine groups and the phosphorus atoms, generating NP bonds. The electrochemical properties of the NP modified materials were evaluated and the catalytic activity towards oxygen reduction reaction was measured. It was found that a high concentration of phenyl groups from PPh2Cl (about 3 at.%) affected negatively the activity of the catalyst since they prevented the access of the oxygen molecules to the catalytic active sites. However, a lower amount of PPh2 groups (1 at.%) or the use of PCl3 avoided this hindrance and resulted in an improved catalytic activity with respect to pristine PANI. The authors thank MINECO, MICIUNIN, FIS2015-64222-C2-2-P and FEDER (RTI2018-095291-B-I00 and MAT2016-76595-R) for the financial support.