Electrochemical Synthesis of Multilayered Graphene and Its Use in Co-N-C Electrocatalysts of Oxygen Reduction and Hydrogen Evolution

It is shown that the use of aqueous electrolytes based on salts of various aromatic carboxylic acids in the course of electrochemical exfoliation of graphite allows producing multilayered graphene (MLG) and protects it from the negative oxidative action of oxygen-containing radicals, in particular, (OH)-O-center dot radicals formed at water electrolysis on the graphite anode. It is shown that the electrochemically synthesized MLG can be used for the formation of noble-metal-free carbonized nanocomposite Co-N-C electrocatalysts of the oxygen reduction reaction (ORR) and the hydrogen evolution reaction (HER). Such poly-2,6-diaminopyridine-based catalysts in aqueous 0.5 \M H2SO4 are shown to surpass their acetylene black-based analogues as regards their functional characteristics in ORR and HER and also are highly tolerant with respect to CO and methanol in the course of oxygen reduction. Based on experimental data, it is concluded that the predominant active centers in Co-N-C electrocatalysts based on MLG and acetylene black are of the different nature and that the same active centers are involved in ORR and HER.