The shape effect of manganese(II,III) oxide nanoparticles on the performance of electrochemical capacitors

Abstract Manganese(II,III) oxide (Mn 3 O 4 ) with various shapes including square prisms, polyhedra and tetragonal bipyramids are selectively synthesized with the mediation of fatty acids at nanoscale ( 3 O 4 tetragonal bipyramids show the largest gravimetric capacitance of 304 F g −1 with excellent rate capability and long-term cycling stability. In contrast, Mn 3 O 4 polyhedra show relatively large intercalation capacity and poor stability, which could be related to the abundant low-coordination sites (edges, corners and defects) exposed on the surface. Transmission electron microscopy analysis reveals that the capacitance loss is caused by the dissolution of Mn 3 O 4 . Electrochemical analysis shows that the iR drop increases during cycling, probably due to the deterioration of the electric contact between Mn 3 O 4 nanoparticles and the conductive matrix in the electrode.