TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Compound: The transition metal atom of polynuclear complex contains metal such as vanadium, chromium, manganese, iron, cobalt, nickel and/or copper. The coordinating atom of polynuclear complex is nitrogen atom and/or oxygen atom. The transition metal atom of polynuclear complex is cross-linked with an oxygen atom of alkoxide or phenoxide. Preferred Properties: The interatomic distance of transition metal atom is 3.6 Angstrom or less. An oxygen molecule is adsorbed to the mononuclear metal complex. The absolute value of difference of Mulliken electric charge of two oxygen atoms in oxygen molecule is 0.02-0.062, calculated by density functional method. The sum of Mulliken electric charge of two oxygen atoms in oxygen molecule is -0.25 or more, calculated by density functional method. The electrode catalyst is obtained by heating mononuclear metal complex at 250-1500 degrees C.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Compound: The ligand is of formula (I or II). The electrode catalyst contains a mononuclear metal complex containing an organic compound having 2 or more phenol rings and 3 or more aromatic heterocyclic rings as a ligand. The mononuclear metal complex is of formula (III).Q1,Q2=divalent organic group having C=N bondings;T1=monovalent organic group having a C=N bonding;R1,R2,R11=H or substituent;Q11=divalent organic group having aromatic heterocyclic ring;T11=monovalent organic group having an aromatic heterocyclic ring;M=transition metal atom;X=counter ion or neutral molecule;andn= greater than or equal to 0.Two of R1 or R2 are combined. Two or more of adjacent R11 are combined. Two of T11 are combined. Preferred Properties: The electrode catalyst is obtained by heating polynuclear complex at 250-1500 degrees C. The acid dissociation constant (pKa) of conjugated acid of aromatic heterocyclic ring is -2 or more.    TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: The polynuclear complex or mononuclear metal complex contains a carbon support and/or a conductive polymer.