Synthesis of the Co-N-C-900C reference. 0.5 mmol Co(OAc)2•4H2O (125 mg) was dissolved in 40 mL ethanol. An ethanol solution (10 mL) of 1,10-phenanthroline (Phen, 1.0 mmol, 180 mg) was added dropwise and the reaction mixture was sonicated for 30 min. 90 mg of Phen and 4 g of Mg(OH)2 were then added and the reaction mixture was further sonicated for 30 min.The mixture was then refluxed at 60 °C for 4 h. The ethanol solvent was removed by rotary evaporation and the remaining solids were dried overnight in air and finely ground. The powder was calcinated at 900 °C for 2 h under a nitrogen atmosphere (ramping rate: 2 °C/min). A black solid was obtained. It was stirred in a 1 M HNO3 solution at room temperature for 2 h to remove the MgO support.