LaSr_2Mn_2O_7 Ruddlesden-Popper manganites for oxygen reduction and electrochemical capacitors

LaSr_2 Mn_2 O_7,a Ruddlesden-Popper type bilayered perovskite,was investigated as oxygen catalyst for oxygen reduction reaction(ORR) and active electrode material for electrochemical capacitors in KOH solutions.XPS results show that Mn takes a mixed Mn~(2+),Mn~(3+)and Mn~(4+)valence state with an average valence of 3.4.As catalyst towards ORR,LaSr_2 Mn_2 O_7 and LaSr_2 Mn_2 O_7/acetylene black composite favor four electron pathways for ORR.LaSr_2 Mn_2 O_7/C composite shows a comparable onset potential for ORR to that of Pt/C electrode.The improved ORR activity of LaSr_2 Mn_2 O_7/acetylene black composite is attributed to the synergy between catalytic LaSr_2 Mn_2 O_7 and conductive acetylene black.As electrode material for electrochemical capacitors,LaSr_2 Mn_2 O_7 exhibits a maximum specific capacitance of 167.2 F/g with 62%faradic contribution at a scan rate of 1 mV/s in cyclic voltammetry test.