Metal-organic complexes, [Co(bpy)<inf>3</inf>](NO<inf>3</inf>)<inf>2</inf> and [Co(bpy)<inf>2</inf>NO<inf>3</inf>]NO<inf>3</inf> · 5H<inf>2</inf>O, for oxygen reduction reaction

Recently, pyrolyzed transition metal-carbon-nitrogen based non-precious metal (NPM) catalysts are envisioned as promising alternatives to metal catalysts. However, the precise active site in these NPM catalysts remains elusive, as their surface composition is heterogeneous in nature. Lack of understanding on the electrocatalytic active site for the oxygen reduction reaction (ORR) is one of the fundamental obstacles in design and synthesis of the catalyst. In this study, carbon supported metal-organic complexes,[Co(bpy)3](NO3)2 and [Co(bpy)2NO3]NO3 · 5H2O (where, bpy is 2,2'-Bipyridine) are shown to perform ORR in 0.1 N KOH. Replacement of one of the bipyridine of [Co(bpy)3]2+ with NO3-, yields a catalyst, [Co(bpy)2N O3]+ with improved ORR kinetics. The N O3- ligand influence on the reduction of the oxygen studied using the linear sweep voltammograms obtained using rotating disc electrode, rotating ring-disc electrode and Tafel analysis. The Tafel slope and exchange current density measured on [Co(bpy)2NO3]NO3 · 5H2O and [Co(bpy)3](N O3)2 are 105 mV dec-1, 2 × 10-4 mA cm-2 and 120 mV dec-1, 4 × 10-4 mA cm-2 respectively. Turn-over frequency (ToF) of these complexes estimated to understand the extent of selectivity of these complexes toward 2- and 4-electron reduction of O2.